JP5487645B2 - Semiconductor device and power conversion device - Google Patents

Description

  The present invention relates to a semiconductor device having a freewheeling diode and a power conversion device.

In order to suppress the oscillation phenomenon (ringing) of the freewheeling diode that occurs at the time of reverse bias, a semiconductor device in which a capacitor having a predetermined capacitance value is connected in parallel with the freewheeling diode has been proposed (see, for example, Patent Document 1).

JP 2004-281462 A

  Although the amplitude of the vibration phenomenon can be suppressed by the semiconductor device proposed above, the convergence time of the vibration phenomenon cannot be shortened. For this reason, it is not possible to suppress adverse effects on peripheral circuits caused by noise generated in the voltage / current due to the oscillation phenomenon of the freewheeling diode. In addition, since the capacitance value and resistance value of the snubber circuit are fixed, it is necessary to prepare a plurality of snubber circuits with different capacitance and resistance values according to the specifications of the freewheeling diode connected in parallel with the snubber circuit. is there.

  In view of the above problems, an object of the present invention is to provide a semiconductor device that does not require the preparation of a plurality of snubber circuits having different capacitances and resistance values, and can shorten the convergence time of a vibration phenomenon that occurs in a freewheeling diode during reverse biasing And providing a power converter.

The present invention relates to a pair of connection terminals, a freewheeling diode connected between the pair of connection terminals , a resistor formed of a semiconductor substrate, a capacitor disposed on one main surface of the semiconductor substrate, and the other of the semiconductor substrate A semiconductor substrate having a back electrode connected to one of the pair of connection terminals and a plurality of surface electrodes which are spaced apart from each other and connectable to the other of the pair of connection terminals. The free- wheeling diode and the semiconductor snubber circuit are connected in parallel between the pair of connection terminals by selecting one or more surface electrodes selected from the plurality of surface electrodes and connected to the other terminal. The values of the capacitor and resistance of the semiconductor snubber circuit are variable according to the total area of the surface electrode .

  According to the present invention, since the capacitance and resistance values of the semiconductor snubber circuit are variable, it is not necessary to prepare a plurality of snubber circuits having different capacitance and resistance values. It is possible to provide a semiconductor device and a power conversion device that can shorten the convergence time of a vibration phenomenon that occurs.

1 is a schematic circuit diagram showing a configuration of a semiconductor device according to a first embodiment of the present invention. It is a schematic diagram which shows the mounting example of the semiconductor device which concerns on the 1st Embodiment of this invention. FIG. 5 is a schematic circuit diagram showing another configuration of the semiconductor device according to the first embodiment of the present invention. It is sectional drawing which shows the structure of the free-wheeling diode which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. 1 is a circuit diagram of a power conversion device using a semiconductor device according to a first embodiment of the present invention. It is a circuit diagram of other power converters using the semiconductor device concerning a 1st embodiment of the present invention. It is a schematic diagram which shows the other mounting example of the semiconductor device which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is a top view which shows the structural example of the coupling | bonding surface electrode of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is a top view which shows the other structural example of the coupling | bonding surface electrode of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is a schematic diagram which shows the example of a method of forming the coupling | bonding surface electrode of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor snubber circuit which concerns on the 1st Embodiment of this invention. It is a graph which shows the simulation result of the attenuation waveform of a vibration phenomenon. It is a graph which shows the relationship between an electrostatic capacitance ratio, a vibration phenomenon convergence time ratio, and the increase margin of a transient loss. It is a typical circuit diagram which shows the structure of the semiconductor device which concerns on the 2nd Embodiment of this invention. It is a schematic diagram which shows the example of the mounting form of the semiconductor device which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the structure of the switching element which concerns on the 2nd Embodiment of this invention. It is a circuit diagram of the power converter device using the semiconductor device which concerns on the 2nd Embodiment of this invention. It is a circuit diagram of other power converters using the semiconductor device concerning a 2nd embodiment of the present invention. It is sectional drawing which shows the structure of the free-wheeling diode which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the structure of the switching element which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the other structure of the switching element which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the other structure of the switching element which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the other structure of the free-wheeling diode which concerns on the 3rd Embodiment of this invention. It is a schematic diagram which shows the example of the mounting form of the semiconductor device which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the structure of the semiconductor chip which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 4th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 4th Embodiment of this invention. It is a schematic diagram which shows the example of the mounting form of the semiconductor device which concerns on the 5th Embodiment of this invention. It is sectional drawing which shows the structure of the semiconductor chip which concerns on the 5th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 5th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 5th Embodiment of this invention. It is sectional drawing which shows the other structure of the semiconductor chip which concerns on the 5th Embodiment of this invention.

  Next, first to fifth embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the following first to fifth embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the embodiments of the present invention include the materials of components, The shape, structure, arrangement, etc. are not specified below. The embodiment of the present invention can be variously modified within the scope of the claims.

(First embodiment)
As shown in FIG. 1, the semiconductor device 10 according to the first embodiment of the present invention includes a pair of connection terminals including an anode terminal 300 and a cathode terminal 400, and a unipolar connected between the anode terminal 300 and the cathode terminal 400. The semiconductor device 10 includes an operating free-wheeling diode 100 and a semiconductor snubber circuit 200 that is connected in parallel with the free-wheeling diode 100 between an anode terminal 300 and a cathode terminal 400 and includes at least a capacitor 210 and a resistor 220. As will be described later, the values of the capacitor 210 and the resistor 220 of the semiconductor snubber circuit 200 are variable.

  Note that the freewheeling diode 100 is equivalent to a unipolar operation by controlling the lifetime of minority carriers that are the main components of excess carriers injected from the P-type region when conducting, for example, even in the structure of a PN junction diode. Therefore, the diode having the same characteristics as the unipolar operation is also included in the diode that performs the unipolar operation described in the present invention.

  In the first embodiment, as an example, a case where the freewheeling diode 100 and the semiconductor snubber circuit 200 are formed as different semiconductor chips will be described. The freewheeling diode 100 includes a freewheeling diode that operates in the same manner as the unipolar operation.

  FIG. 1 shows an example in which the semiconductor snubber circuit 200 is configured as a so-called RC snubber circuit in which a capacitor 210 and a resistor 220 are connected in series. However, if the capacitor 210 and the resistor 220 are at least connected in series, a plurality of parts It may be divided and formed, for example, alternately.

  FIG. 2 is an example of a specific mounting form of the semiconductor device 10 including the freewheeling diode 100 (for example, silicon carbide Schottky barrier diode) and the semiconductor snubber circuit 200 (for example, silicon semiconductor RC snubber circuit). In FIG. 2, as an example of a semiconductor package on which the semiconductor device 10 is mounted, an anode-side metal film 310 and a cathode-side metal film 410 made of a metal material such as copper or aluminum are formed on an insulating substrate 500, for example. The case where a ceramic substrate is used is shown. The insulating substrate 500 is an insulating substrate formed of, for example, ceramic and has a function as a support.

  On the ceramic substrate, a semiconductor chip (indicated by reference numeral 100 in the figure) on which the free-wheeling diode 100 is arranged and a semiconductor chip (indicated by reference numeral 200 in the figure) on which the semiconductor snubber circuit 200 is arranged are arranged. . Here, the terminal connected to the cathode terminal of the freewheeling diode 100 and the cathode terminal 400 of the semiconductor snubber circuit 200 is disposed in contact with the metal film 410 via a bonding material such as solder or brazing material. The surface electrode 13 connected to the anode terminal of the freewheeling diode 100 and the anode terminal 300 of the semiconductor snubber circuit 200 is connected to the metal film 310 via metal wirings 320 and 330 such as aluminum wires and aluminum ribbons. As shown in FIG. 2, the metal film 410 is connected to the cathode terminal 400, and the metal film 310 is connected to the anode terminal 300.

  In the mounting example of the semiconductor device 10 shown in FIG. 2, three surface electrodes 13 that can be connected to the anode terminal 300 are formed in advance in the semiconductor snubber circuit 200, and two of the surface electrodes 13 are connected via the metal wiring 330. An example of connection to the metal film 310 is shown. However, the number of surface electrodes 13 may be plural, and at least one of them may be connected to the metal film 310.

  1 shows an example in which the capacitor 210 is connected to the anode terminal 300 to which the anode terminal of the freewheeling diode 100 is connected, and the resistor 220 is connected to the cathode terminal 400 to which the cathode terminal of the freewheeling diode 100 is connected. As shown in FIG. 3, the resistor 220 may be connected to the anode terminal 300 and the capacitor 210 may be connected to the cathode terminal 400.

  In the first embodiment, the semiconductor snubber circuit 200 is formed of, for example, silicon as a semiconductor base material, and is formed so that an electrode connected to the anode terminal 300 and an electrode connected to the cathode terminal 400 face each other. The case of a vertical semiconductor chip will be described. The case where the freewheeling diode 100 is a Schottky barrier diode using, for example, silicon carbide as a semiconductor substrate material will be described. As for this Schottky barrier diode, a so-called vertical Schottky barrier diode formed so that an electrode connected to the anode terminal 300 and an electrode connected to the cathode terminal 400 face each other will be described as an example.

  FIG. 4 and FIG. 5 show examples of cross-sectional structure diagrams of semiconductor chips constituting the freewheeling diode 100 and the semiconductor snubber circuit 200, respectively.

As shown in FIG. 4, the free-wheeling diode 100 is made of a substrate material in which an N ⁻ type drift region 2 is formed on an N ⁺ type substrate region 1 of, for example, silicon carbide polytype 4H type. . For the substrate region 1, for example, a general low resistance substrate having a resistivity of about several mΩcm to several tens of mΩcm and a thickness of about several tens of μm to several hundreds of μm can be used. Note that the resistivity and thickness may be outside the above ranges depending on the element structure and the required breakdown voltage, but in general, the smaller the resistivity and thickness, the more the loss during conduction can be reduced. The drift region 2 has, for example, an N-type impurity density of 10 ¹⁵ to 10 ¹⁸ cm ⁻³ and a thickness of 0.1 μm to several tens of μm. Note that the impurity density and thickness of the drift region 2 may be out of the above range depending on the element structure and required breakdown voltage.

In the first embodiment, for example, a case will be described in which the drift region 2 having an impurity density of 10 ¹⁶ cm ⁻³ , a thickness of 5 μm, and a breakdown voltage of 600 V class is employed. However, the withstand voltage is not limited to the 600V class. In the first embodiment, the case where the semiconductor substrate is a substrate composed of two layers of the substrate region 1 and the drift region 2 will be described. However, the resistivity is formed only by the substrate region 1 that does not depend on the above example. A laminated substrate may be used, or a multilayer substrate may be used. In the first embodiment, the substrate material is a silicon carbide material, but other semiconductor materials such as silicon may be used.

  As shown in FIG. 4, the surface electrode 3 is formed on the main surface of the drift region 2 facing the bonding surface with the substrate region 1, the surface electrode 3 is opposed to the surface region 3, and the back electrode 4 is in contact with the substrate region 1. Is formed. The surface electrode 3 is composed of a single-layer or multi-layer metal material including at least a metal material that forms a Schottky barrier with the drift region 2. Examples of the metal material that forms the Schottky barrier include titanium, nickel, molybdenum, gold, and platinum. Further, since the surface electrode 3 is connected to an external electrode as the anode terminal 300, a multilayer structure using a metal material such as aluminum, copper, gold, nickel, silver or the like on the outermost surface of the surface electrode 3 may be used. On the other hand, the back electrode 4 is made of an electrode material that is in ohmic contact with the substrate region 1. Examples of the electrode material to be ohmic-connected include nickel silicide and titanium material, and the back electrode 4 is connected to an external electrode as a cathode terminal 400. 4 functions as a diode in which the front electrode 3 is an anode terminal and the back electrode 4 is a cathode terminal.

FIG. 5 is an example of a cross-sectional structure diagram of the semiconductor snubber circuit 200. For example, a dielectric region 12 made of a dielectric material such as a silicon oxide film is formed on a substrate region 11 of, for example, silicon N ⁻ type. In the configuration shown in FIG. 5, the substrate region 11 functions as a resistor 220, and the dielectric region 12 functions as a capacitor 210. The resistivity and thickness of the substrate region 11 are set according to the magnitude of the resistance value required for the resistor 220. For example, a substrate having a resistivity of several mΩcm to several hundreds Ωcm and a thickness of several tens to several hundreds μm is used. For example, a substrate having a resistivity of 100 Ωcm and a thickness of 300 μm is used so as to be at least larger than the resistance value included in the freewheeling diode 100. 5 illustrates the case where the substrate region 11 is formed so as to have a single resistivity, the substrate region 11 may be composed of a plurality of portions having different resistivity. In FIG. 5, the conductivity type of the substrate region 11 is N-type, but it may of course be P-type.

  The thickness and area of the dielectric region 12 are determined according to the withstand voltage required for the capacitor 210 and the required capacitance. The breakdown voltage is preferably higher than that of the freewheeling diode 100 in order to prevent the dielectric region 12 from being broken. The capacitance can be selected in the range of about 1/100 to about 100 times the capacitance of the depletion layer generated when the freewheeling diode 100 is cut off (when a high voltage is applied). In consideration of the chip area necessary for exhibiting a sufficient snubber function and suppressing the increase in loss as much as possible, it is preferably about 1/10 to about 10 times as shown in the calculation results described later.

  In the first embodiment, the dielectric region 12 has a thickness of, for example, 1 μm so that the breakdown voltage is higher than that of the freewheeling diode 100, for example, and the capacitance of the capacitor 210 is formed when the freewheeling diode 100 is cut off. The case of the same level as will be described. The dielectric region 12 may be any material other than a silicon oxide film as long as it has a predetermined withstand voltage and functions as the capacitor 210. However, the dielectric region 12 has a dielectric breakdown electric field and a relative dielectric constant. A material having a product value larger than that of the silicon oxide film is even better.

When such a material is used, a necessary capacitance can be obtained with a small area while maintaining the withstand voltage of the dielectric region 12. For example, when the physical property value of a general silicon oxide film is a dielectric breakdown electric field of 1 × 10 ⁹ V / m and a relative dielectric constant of 3.9, the thickness per 1 cm ² when the thickness of the silicon oxide film is 1 μm. The capacitance is about 3.4 nF. On the other hand, when a silicon nitride (Si ₃ N ₄ ) film is used instead of the silicon oxide film, the thickness is 1 μm when the dielectric breakdown electric field is 1 × 10 ⁹ V / m and the relative dielectric constant is 7.5. Therefore, the equivalent breakdown voltage can be secured. At this time, the electrostatic capacity per 1 cm ² when the Si ₃ N ₄ film is used is about 6.6 nF.

As described above, when the Si ₃ N ₄ film is used for the dielectric region 12, the capacitance is about twice as large as when a silicon oxide film is used, and the dielectric strength of the dielectric region 12 is maintained. However, a larger capacitance can be obtained. Accordingly, the area efficiency is improved and the wafer cost can be reduced. This effect can be compared by the product of the dielectric breakdown electric field and the relative dielectric constant of the dielectric material, and the value of the Si ₃ N ₄ film is about twice that of the silicon oxide film. Further, if the material of the dielectric region 12 is a ferroelectric such as BaTiO ₃ , this value is about 13 times that of the silicon oxide film, and the area of the dielectric region 12 can be further reduced. In addition, the dielectric region 12 is not limited to a single dielectric material, and a laminate of a plurality of dielectric materials may be used. For example, in the ONO structure sandwiching the Si ₃ N ₄ film with the silicon oxide film as shown in FIG. 6, the leakage current in the Si ₃ N ₄ film can be minimized with a silicon oxide film.

  In the first embodiment, as will be described later, when, for example, a Schottky barrier diode is used as the freewheeling diode 100, the capacitance is reduced against the current / voltage oscillation phenomenon that is essentially generated by the unipolar operation. By connecting the semiconductor snubber circuit 200 having the small and small size capacitor 210 and the resistor 220 in parallel, the vibration phenomenon can be easily and effectively suppressed. That is, it is not necessary to use a technique of wiring an external discrete component such as a film capacitor or a metal clad resistor in a path through which a main current flows, which is conventionally used as a snubber circuit for reducing the vibration of a diode operating in bipolar operation. Further, as a design formula that effectively exhibits the snubber function, a relational expression of C = 1 / (2πfR) where C is the capacitance value of the capacitor 210, R is the resistance value of the resistor 220, and f is the frequency of the vibration phenomenon. Is generally known. In the first embodiment, the capacitor 210 and the resistor 220 can be easily set by using the semiconductor snubber circuit 200 having a small capacitance so as to satisfy the above relational expression.

  As shown in FIGS. 5 and 6, a plurality of front surface electrodes 13 are formed on the dielectric region 12, a back surface electrode 14 is formed so as to face the front surface electrode 13 and contact the substrate region 11. The surface electrode 13 is formed of, for example, a metal material so as to be connected to an external electrode as the anode terminal 300, and has a single layer structure or a multilayer structure using a metal material such as aluminum, copper, gold, nickel, silver, or the like on the outermost surface. is there. Similarly, the back electrode 14 is also formed of, for example, a metal material so as to be connected to an external electrode as the cathode terminal 400, and a single layer structure using a metal material such as aluminum, copper, gold, nickel, silver or the like on the outermost surface. Or it is a multilayer structure. As described above, in the semiconductor snubber circuit 200 shown in FIGS. 5 and 6, the front electrode 13 is connected to the anode terminal of the freewheeling diode 100 shown in FIG. 4, and the back electrode 14 is connected to the cathode terminal of the freewheeling diode 100 shown in FIG. Connected to function as a semiconductor RC snubber circuit.

  In the semiconductor snubber circuit 200, a plurality of surface electrodes 13 are formed in advance, and wiring is performed according to the capacitance value of the capacitor 210 and the resistance value of the resistor 220 necessary for suppressing the oscillation phenomenon of current and voltage. The number of surface electrodes 13 connected to the anode terminal 300 is determined in the process step. 5 and 6 show a case where two of the three surface electrodes 13 formed on the center and the right side are connected to the anode terminal 300.

  As described above, by providing a plurality of surface electrodes 13 that can be connected to the anode terminal 300, a capacitance value or resistance can be obtained using a semiconductor chip (snubber chip) on which one kind of semiconductor snubber circuit 200 is arranged. A semiconductor snubber circuit 200 having a variable value can be realized. That is, the semiconductor snubber circuit 200 that can be applied to the freewheeling diode 100 having various characteristics can be provided by one type of snubber chip. In addition, by using a configuration including a plurality of surface electrodes 13, a part of a mask or a process for manufacturing the semiconductor snubber circuit 200 is shared by the semiconductor snubber circuits 200 having different capacitance values and resistance values. Manufacturing costs can be reduced. Further, even when the circuit configuration is changed, the vibration phenomenon of current / voltage can be stably suppressed only by changing the wiring.

  Next, the operation of the semiconductor device 10 according to the first embodiment will be described. The semiconductor device 10 is a power conversion device such as a converter (FIG. 7) or an inverter (FIG. 8) generally used as one of the power energy conversion means shown in FIGS. It is connected so as to have a reverse bias connection with respect to the voltage (+ V), and is used as a passive element that circulates current. The operation mode of the semiconductor device 10 changes from a cut-off state in which current is cut off to a conductive state in which current is circulated and from a conductive state to a cut-off state in conjunction with the switching operation of a switching element such as a MOSFET or IGBT. In a power conversion device, a stable operation that is low loss and is unlikely to cause malfunctions is required for a passive element that circulates current as well as a switching element. In the first embodiment, the operation will be described by taking the converter circuit of FIG. 7 as an example. In addition, the switching element S in FIG. 7 is comprised, for example by IGBT.

  In a state where the switching element S is turned on and a current flows through the switching element S, the semiconductor device 10 which is a passive element is in a reverse bias state and is in a cut-off state. In the freewheeling diode 100 (here, the Schottky barrier diode) shown in FIG. 4, since a reverse bias voltage is applied between the anode terminal 300 and the cathode terminal 400, the depletion extended from the Schottky junction with the surface electrode 3. A layer is created in the drift region 2 and the interrupted state is maintained. In the semiconductor snubber circuit 200 shown in FIG. 5, the dielectric region 12 functioning as the capacitor 210 is charged with a high voltage, and the cut-off state is maintained. Thus, in the cut-off state, the operation is performed in the same manner as when the passive element is composed of only the Schottky barrier diode.

  Next, when the switching element S is turned off, the semiconductor device 10 enters a forward bias state and shifts to a conductive state in conjunction with the switching element S shifting to the off state. The depletion layer extending in the drift region 2 of the free-wheeling diode 100 shown in FIG. 4 recedes, and the Schottky junction formed between the surface electrode 3 and the drift region 2 corresponds to the Schottky barrier height. When the forward bias voltage is applied, the freewheeling diode 100 becomes conductive. At this time, the current flowing through the freewheeling diode 100 is substantially constituted only by the electron current from the electrons supplied from the back electrode 4 side into the drift region 2 and performs a unipolar operation. Further, in the semiconductor snubber circuit 200 shown in FIG. 5, since the high voltage reverse bias state shifts to the low voltage forward bias state, the electric charge charged in the dielectric region 12 is discharged, and a transient current flows.

  However, in the semiconductor device 10 according to the first embodiment, the capacitance of the dielectric region 12 is almost the same as the depletion capacitance formed when the free-wheeling diode 100 is cut off, and is very small. For this reason, the magnitude of the transient current that flows due to the discharge is much smaller than the forward bias current that flows through the freewheeling diode 100 connected in parallel with the semiconductor snubber circuit 200, and has little effect on the operation. The semiconductor snubber circuit 200 becomes a forward bias state after the transient current accompanying the change of the bias voltage flows, and enters a steady state, so that the semiconductor snubber circuit 200 is cut off and only the freewheeling diode 100 is turned on.

  When the freewheeling diode 100 is formed of a Schottky barrier diode made of a silicon carbide material semiconductor substrate, the resistance of the drift region 2 can be made lower than that of a general PN junction diode made of silicon material. , Conduction loss can be reduced. As described above, in the first embodiment, the same effect as in the case where the passive element is configured only by the Schottky barrier diode is obtained even in the conductive state.

  Next, when the switching element S is turned on, in conjunction with the switching element S shifting to the on state, the semiconductor device 10 enters the reverse bias state and shifts to the cutoff state. In the freewheeling diode 100 which is a Schottky barrier diode, the electron current due to the electrons supplied from the back electrode 4 side into the drift region 2 decreases as the forward bias voltage decreases. When the forward bias voltage becomes equal to or lower than the voltage corresponding to the Schottky barrier height of the Schottky junction, and when the reverse bias voltage starts to be applied to the Schottky junction, The depletion layer extending from the Schottky junction spreads and the free-wheeling diode 100 shifts to a cut-off state.

  When transitioning from the conductive state to the cut-off state, a current that is transiently generated in the process in which excess carriers accumulated in the freewheeling diode 100 disappear is the reverse recovery current. This reverse recovery current flows as a transient current in the semiconductor device 10 and the switching element S, and a loss (herein referred to as reverse recovery loss) occurs in each of the semiconductor device 10 and the switching element S. For this reason, the reverse recovery current generated in the freewheeling diode 100 should be as small as possible.

  When the freewheeling diode 100 is formed of a unipolar Schottky barrier diode formed of a semiconductor material made of silicon carbide, the reverse recovery current is much smaller than that of a general PN junction diode formed of silicon. That is, reverse recovery loss can be greatly reduced.

  This difference in reverse recovery loss can be explained by the difference in the shutoff / conduction mechanism between them as follows.

A PN junction diode formed of general silicon has a drift region conductivity modulation effect by minority carrier injection during forward bias conduction. For this reason, in order to ensure a breakdown voltage while reducing conduction loss as much as possible, it is common to form the drift region with a small thickness and a low impurity concentration. For example, if a PN junction diode with a breakdown voltage of 600 V class is to be realized, the thickness is about 50 μm when the impurity density in the drift region is set to about 10 ¹⁴ cm ⁻³ due to the limitation of feasibility of low impurity concentration. It is necessary to use a substrate having a relatively thick drift region. When conducting, due to the conductivity modulation effect of bipolar operation, minority carriers and majority carriers are injected into the drift region in accordance with the magnitude of the flowing current, so that a low resistance can be obtained. For example, when a forward bias current of about several hundred A / cm ² flows, carriers are injected to the extent that the concentration of majority carriers (electrons) and minority carriers (holes) are both 10 ¹⁷ cm ⁻³ , and they are excessive. Operates as a carrier.

On the other hand, in a Schottky barrier diode, the current that flows during conduction is composed of electrons that are majority carriers. For this reason, the amount of excess carriers generated when shifting to the cut-off state is almost the amount of only carriers discharged from the depletion layer when the depletion layer is formed in the return diode 100. In other words, for example, even when the drift region having a breakdown voltage of 600 V class, an impurity density of 10 ¹⁶ cm ⁻³ , and a thickness of 5 μm is depleted, the carrier density is 1/10 compared to the PN junction diode. The thickness of the drift region in which carriers are distributed becomes 1/10, and only about 1 / 100th of excess carriers are generated in total. From this, by forming the freewheeling diode 100 with an element that operates unipolarly, the reverse recovery current is greatly reduced, and as a result, the reverse recovery loss can be greatly reduced. As described above, the effect of reducing the reverse recovery loss is the same as that in the case where the passive element is composed only of the Schottky barrier diode.

  Furthermore, the semiconductor device 10 according to the first embodiment has a reverse recovery operation that occurs when the passive element performs a unipolar operation, which cannot be essentially solved when the passive element is composed of only a Schottky barrier diode. It has a function to suppress current / voltage oscillation phenomenon.

  This vibration phenomenon itself is caused by a parasitic inductance Ls generated in a circuit of a power converter such as an inverter incorporating a freewheeling diode, and a cutoff speed (dIr / dt) of a reverse recovery current Ir generated in the freewheeling diode during reverse recovery operation. It is generally known that a surge voltage is generated by the interaction, and that the surge voltage is generated as a starting point. This vibration phenomenon of current and voltage causes damage to the element due to surge voltage, increase of loss during vibration operation, malfunction of surrounding circuits, etc. . In order to reduce the vibration phenomenon, it is necessary to alleviate the current interruption speed (dIr / dt) during the reverse recovery operation, and further to have a mechanism that quickly attenuates the oscillating current and converges the vibration.

  However, with only a Schottky barrier diode that performs unipolar operation, the component of the reverse recovery current Ir is composed of majority carriers. Therefore, although the reverse recovery current Ir due to excess carriers is greatly reduced, the reverse is almost determined by the formation rate of the depletion layer. The recovery time t can hardly be controlled. For this reason, a vibration phenomenon is likely to occur in the current / voltage, and the vibration is not easily attenuated. There are two main reasons.

  One reason is that, in the Schottky barrier diode, the excess carriers injected from the cut-off state to the conductive state are composed only of majority carriers that supplement the depletion region formed in the drift region at the time of cut-off. . That is, the reverse recovery current cutoff speed (dI / dt) of the Schottky barrier diode almost depends only on the formation speed of the depletion region, and there are almost no minority carriers. Cannot be used as is. For this reason, when only the Schottky barrier diode is used, if the switching speed of the switching element is improved to reduce the transient loss, a more severe vibration phenomenon occurs. In other words, there is a trade-off relationship between reducing transient loss and suppressing vibration phenomena.

  Another reason is that since the Schottky barrier diode operates with almost majority carriers only when conducting, the resistance inside the Schottky barrier diode is a resistance according to the thickness of the drift region and the impurity concentration, both when conducting and immediately before interruption. This is the same point. As described above, the PN junction diode has a low resistance due to the conductivity modulation effect when conducting, but the drift region has a high resistance during the reverse recovery operation in which the conductivity modulation is canceled, and the reverse recovery current Ir is limited in resistance. It has a mechanism. On the other hand, the Schottky barrier diode has its own resistance component having a low resistance both during conduction and immediately before interruption, and does not have a mechanism for limiting the reverse recovery current Ir. Therefore, a vibration phenomenon is likely to occur in the current / voltage, and the vibration is not easily attenuated. Furthermore, by using a wide gap semiconductor such as silicon carbide as the semiconductor material, the resistance of the element itself is small, so that the conduction loss can be reduced, but the vibration phenomenon is more likely to occur. For this reason, when only the Schottky barrier diode is used, there is a trade-off relationship between the loss during conduction and the suppression mechanism of the vibration phenomenon.

  On the other hand, in the semiconductor device 10 according to the first embodiment, a simple configuration in which the freewheeling diode 100 and the semiconductor snubber circuit 200 are connected in parallel suppresses the vibration phenomenon while reducing the transient loss and the conduction loss. be able to.

  That is, in the semiconductor device 10, when the forward bias current decreases to zero in the freewheeling diode 100, a depletion layer due to the reverse bias voltage is formed in the drift region 2, and a reverse recovery current composed of excess carriers starts to flow. . Almost simultaneously with the application of the reverse bias voltage, an equivalent reverse bias voltage is also applied to the capacitor 210 formed of the dielectric region 12 in the semiconductor snubber circuit 200, and a corresponding transient current flows in the semiconductor snubber circuit 200. start. The transient current flowing through the semiconductor snubber circuit 200 is determined by the size of the capacitor 210 formed of the dielectric region 12 and the size of the resistance component of the substrate region 11, and can be designed freely. The semiconductor snubber circuit 200 connected in parallel has three effects.

  The first effect is that the semiconductor snubber circuit 200 does not operate unless there is a transient voltage fluctuation, and therefore, the switching speed of the switching element S is not affected, and the loss depending on the switching speed is kept low as in the conventional case. This is a possible point. That is, since the cutoff speed of the forward bias current flowing through the freewheeling diode 100 can be set at a high speed, the loss accompanying the cutoff of the main current can be reduced. The second effect is that when the freewheeling diode 100 enters the reverse recovery operation, the capacitor component and the resistance component of the semiconductor snubber circuit 200 connected in parallel to the freewheeling diode 100 act, and the reverse recovery current cutoff speed (dIr / dt) can be relaxed, and the surge voltage itself can be reduced. The third effect is that since the current flowing through the semiconductor snubber circuit 200 is consumed by the resistance component of the substrate region 11, the energy generated by the parasitic inductance Ls is absorbed and the vibration phenomenon is quickly converged.

As described above, the semiconductor device 10 according to the first embodiment has the performance of reducing the transient loss and the conduction loss of the freewheeling diode 100, and at the same time, using the semiconductor snubber circuit 200, the vibration inherent in the unipolar operation. The phenomenon can be solved.
The RC snubber configuration is a generally known circuit, but a semiconductor snubber circuit 200 in which a snubber circuit is formed on a semiconductor substrate is the first to be combined with a freewheeling diode 100 having an operation equivalent to a unipolar operation or a unipolar operation. A sufficient function can be achieved as a snubber circuit.

  Conventionally, it is practically difficult to form a snubber circuit on a semiconductor chip for a PN junction diode made of silicon, which has been generally used in power conversion devices such as inverters. It has been necessary to arrange a capacitor composed of a film capacitor or the like, which is a discrete component, and a resistor composed of a metal clad resistor or the like in a path through which a main current flows inside or outside the semiconductor package of the power converter. The reason for this is that in order for the snubber circuit to function sufficiently, the capacitance through which a transient current comparable to the reverse recovery current flowing in the freewheeling diode flows in order to reduce the reverse recovery current cutoff speed (dIr / dt). And a resistor having a power capacity capable of consuming the current flowing through the capacitor is required to attenuate the vibration phenomenon.

  As described above, in the PN junction diode, the magnitude of the reverse recovery current varies depending on the magnitude of the circulating current. In the above example, the reverse recovery current is 100 times that of the unipolar Schottky barrier diode. As the current density flowing through the freewheeling diode further increases or the withstand voltage class increases, the excess carriers injected during conduction increase and the reverse recovery current also increases. Therefore, when the free-wheeling diode is a PN junction diode, the thickness of the capacitor is limited by the required breakdown voltage when the capacitor is formed on the semiconductor chip. Therefore, the area of the capacitor is simply calculated as compared with the free-wheeling diode that operates unipolarly. Needs to be multiplied by 100. Moreover, since the electric power to be consumed for the resistance is 100 times, the volume needs to be 100 times, and as a result, a chip size of 100 times is required. For this reason, it has been practically difficult to form a snubber circuit in a power converter using a semiconductor chip.

  In the first embodiment, paying attention to the fact that the transient current flowing through the freewheeling diode 100 is a transient current consisting only of carriers generated when a depletion layer is formed in the drift region 2 at most, the snubber circuit is configured with a capacitance. The semiconductor snubber circuit 200 having a small size is different from the prior art. Furthermore, the configuration described in the first embodiment provides the following new effects not found in the prior art in terms of the function of reducing transient loss and conduction loss and the function of suppressing vibration phenomena.

  One effect is that when a semiconductor snubber circuit 200 having a predetermined capacitance value and resistance value is connected in parallel to the freewheeling diode 100 that performs unipolar operation, the snubber is applied in the entire current range and the entire temperature range in which the freewheeling diode 100 operates. The function works effectively. As described above, the reverse recovery current of the Schottky barrier diode is composed only of excess carriers generated when a depletion layer is generated by the reverse bias voltage. For this reason, a substantially constant reverse recovery current flows every time regardless of the magnitude of the current flowing during the reflux operation. For the same reason, an almost constant reverse recovery current flows with little influence on the temperature of the freewheeling diode. For this reason, it is possible to reduce the transient loss and suppress the vibration phenomenon in the entire current range and temperature range. These are effects that cannot be obtained in combination with a general PN junction diode.

  Another effect is that by forming the snubber circuit with the semiconductor snubber circuit 200, the semiconductor snubber circuit 200 can be mounted with a low inductance in the immediate vicinity of the freewheeling diode 100 as shown in FIG. It is a point which can reduce and suppress a vibration phenomenon. This is because the smaller the parasitic inductance generated when the semiconductor snubber circuit 200 is connected in parallel to the freewheeling diode 100, the easier the transient current flows through the semiconductor snubber circuit 200. Therefore, the blocking speed of the reverse recovery current flowing through the freewheeling diode 100 (dIr / Dt) and the back electromotive force generated by the parasitic inductance superimposed on the voltage applied to the capacitor 210 in the semiconductor snubber circuit 200 is reduced, and the switching time is reduced within the breakdown voltage range of the capacitor 210. It depends on what you can do fast. For this reason, in the first embodiment, the parasitic inductance is reduced as compared with the case of the snubber circuit using a capacitor or resistor of discrete components, thereby shortening the switching time and reducing the transient loss and reverse recovery. It is possible to moderate the current interruption speed and suppress the vibration phenomenon.

  Further, mounting the semiconductor snubber circuit 200 in the immediate vicinity of the freewheeling diode 100 also reduces unnecessary noise emission. For example, in the case of a snubber circuit using capacitors and resistors of discrete components, the oscillating current generated in the freewheeling diode 100 passes through a path returning to the freewheeling diode 100 via these discrete components. At that time, the oscillating current is suppressed by the resistance, but until then, the surface formed by this current path works as a kind of loop antenna and radiates noise. In the case where the snubber circuit is formed by the semiconductor snubber circuit 200, the size of the surface formed by the current path of the oscillating current is reduced by mounting the semiconductor snubber circuit 200 in the immediate vicinity of the freewheeling diode 100 as compared with the case where discrete components are used. The noise emission due to the oscillating current is reduced significantly. Thereby, it is possible to prevent malfunction of the control circuit and the like due to noise.

  Furthermore, by forming the snubber circuit with the semiconductor snubber circuit 200, the power conversion device can be configured using the same mounting process as that of the freewheeling diode 100. Therefore, the vibration phenomenon can be easily and easily suppressed, and the required volume can be greatly reduced as compared with a snubber circuit using discrete components.

  Further, since the resistance component of the semiconductor snubber circuit 200 can be formed of a semiconductor substrate and directly mounted on a semiconductor package as shown in FIG. 2, high heat dissipation can be obtained. Therefore, it is possible to design a resistor with a higher density than an external resistor. That is, it has high resistance to destruction and can be further downsized.

  When a predetermined breakdown voltage is obtained, the resistance of the free-wheeling diode 100 itself is reduced and the low conduction loss can be reduced as the wide band gap semiconductor element is adopted for the free-wheeling diode 100 to reduce the thickness of the depletion layer. On the other hand, the reverse recovery current cut-off speed (dIr / dt) increases and vibration energy is not consumed, so that the vibration phenomenon becomes more prominent. For example, when a Schottky barrier diode made of silicon is used as the freewheeling diode 100, a certain level of effect can be obtained as an effect of the present invention. However, due to restrictions on the impurity concentration and thickness of the drift region 2, the silicon carbide material In comparison, the freewheeling diode 100 itself has a large resistance component, and the freewheeling diode 100 itself consumes vibration energy and is easily attenuated. On the other hand, when the free-wheeling diode 100 is made of a wide band gap semiconductor such as silicon carbide, it is possible to more remarkably reduce both the conduction loss and the vibration phenomenon. That is, as exemplified in the first embodiment, the effect of the present invention can be maximized by configuring the freewheeling diode 100 with a Schottky barrier diode made of silicon carbide.

  In addition to the case where the semiconductor material of the free-wheeling diode 100 is silicon carbide, the same effect can be obtained even if a wide-gap semiconductor such as gallium nitride or diamond is used for the free-wheeling diode 100.

  In addition to the semiconductor package using the ceramic substrate shown in FIG. 2 as an example of the mounting form, for example, as shown in FIG. 9, a metal base material 420 covered with a mold resin 510 is used as a support base material and a cathode terminal. A so-called mold package type mounting form having the anode terminal 300 and the cathode terminal 400 may be used, or another mounting form may be used. In the example shown in FIG. 9, three surface electrodes 13 are formed in advance in the semiconductor snubber circuit 200, and two of them are connected to the metal film 340 on the anode side via the metal wiring 330.

  In the first embodiment, the case where each of the freewheeling diode 100 and the semiconductor snubber circuit 200 is one chip is shown. However, one or both of the freewheeling diode 100 and the semiconductor snubber circuit 200 are composed of a plurality of chips. Also good. 2 and 9, the back electrode 4 and the back electrode 14 on the cathode terminal side are mounted by solder or the like, and the anode terminal side is wired with the metal wirings 320 and 330. However, the cathode terminal and the anode terminal are shown. Both of them may be mounted by solder or the like. The cooling performance is improved by mounting both the cathode terminal and the anode terminal with solder or the like. For this reason, the heat dissipation of the freewheeling diode 100 and the heat dissipation of the resistor 220 of the semiconductor snubber circuit 200 are increased, and mounting can be performed at a higher density.

  Although the semiconductor snubber circuit 200 has been described above with reference to FIG. 5 as an example of the structure of the semiconductor snubber circuit 200, the semiconductor snubber circuit 200 having the configuration shown in FIGS. 10 to 21 can also be used.

  In the configuration example shown in FIG. 10, a plurality of surface electrodes 13 having different areas are formed in advance, and the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon at the stage of the wiring process. Depending on the value, the number and location of the surface electrodes 13 connected to the anode terminal 300 are determined. The configuration example shown in FIG. 10 shows a case where two of the three surface electrodes 13 formed on the left side and the right side of the drawing are connected to the anode terminal 300. With the configuration shown in FIG. 10, the total area of the surface electrode 13 connected to the anode terminal 300 can be set finer than in the configuration example shown in FIG. 4. Other configurations are the same as the configuration example shown in FIG.

  In the configuration example shown in FIG. 11, the plurality of surface electrodes 13 are formed in advance, and the plurality of surface electrodes 13 are formed according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon. At least some of these are connected by a combined surface electrode 1001 disposed on the surface electrode 13. The combined surface electrode 1001 is connected to the anode terminal 300. FIG. 11 shows a case where two of the three surface electrodes 13 formed on the center and the right side are connected by the combined surface electrode 1001. With the configuration shown in FIG. 11, the region between the surface electrodes 13 can also be used as part of the capacitor 210, so that the total area of the surface electrode 13 connected to the anode terminal 300 and the combined surface electrode 1001 can be reduced. Can be set finely. Other configurations are the same as the configuration example shown in FIG.

  FIG. 12 is a top view of the semiconductor snubber circuit 200 and shows a configuration example of the coupling surface electrode 1001. In the example shown in FIG. 12, a total of nine surface electrodes 13 of 3 × 3 are formed, and 8 of them are connected by the combined surface electrode 1001. In the configuration example shown in FIG. 12, for example, a bonding surface electrode 1001 and a photoresist film are formed on the entire surface of the semiconductor snubber circuit 200, and a photoresist film patterned into a desired shape using a photolithography technique is used as a mask material. It is obtained by patterning the bonding surface electrode 1001 by etching. Therefore, the values of the capacitor 210 and the resistor 220 can be arbitrarily set within a predetermined range simply by changing the mask pattern of the photoresist film.

  FIG. 13 is a top view of the semiconductor snubber circuit 200 and shows another example of forming the coupling surface electrode 1001. In the example shown in FIG. 13, a total of nine surface electrodes 13 of 3 × 3 are formed in the same manner as in FIG. 12, and eight of the surface electrodes 13 are connected by three coupled surface electrodes 1001. . The difference from FIG. 12 is that the surface electrodes 13 are connected using a plurality of coupled surface electrodes 1001 having the same shape. In the configuration example shown in FIG. 13, if one mask pattern of a photoresist film is prepared, the number of surface electrodes 13 to be connected can be arbitrarily selected only by changing the exposure program of an exposure apparatus such as a stepper. . Therefore, versatility can be improved without increasing the mask cost as compared to the configuration example shown in FIG.

  FIG. 14 shows another method for forming the bonded surface electrode 1001. In FIG. 14, when the bonding surface electrode 1001 is formed, the bonding surface electrode 1001 is patterned using an evaporation metal mask 1002. By using such a process, the process cost can be reduced without using a photolithography technique.

  The configuration example shown in FIG. 15 is an example in which the dielectric region 12 is formed by a plurality of dielectric regions having different film thickness disposed along the surface electrode 13, and the surface electrode 13 is formed on each dielectric region. . As shown in FIG. 15, the film thickness of the dielectric region 12 varies along the surface electrode 13. In the wiring process stage, the number and location of the surface electrodes 13 connected to the anode terminal 300 are determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon. FIG. 15 shows an example in which two of the three surface electrodes 13 formed on the center and the right side are connected to the anode terminal 300. With the configuration shown in FIG. 15, the capacitance of the capacitor 210 can be set in a wider range than the configuration example shown in FIG. 5. Other configurations are the same as the configuration example shown in FIG.

The configuration example illustrated in FIG. 16 illustrates an example in which the dielectric region 12 includes a plurality of dielectric regions 121 to 123 made of a plurality of dielectrics having different dielectric constants arranged along the surface electrode 13. Surface electrodes 13 are formed on the dielectric regions 121 to 123, respectively. In the example shown in FIG. 16, the dielectric region 121 under the left surface electrode 13 is made of a TiBaO ₃ film, the dielectric region 122 under the center surface electrode 13 is made of a SiO ₂ film, and the dielectric under the right surface electrode 13 is made. The region 123 is made of a Si ₃ N ₄ film. In the wiring process stage, the number and location of the surface electrodes 13 connected to the anode terminal 300 are determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon. FIG. 16 shows an example in which two of the three surface electrodes 13 on the center and the right side are connected to the anode terminal 300. With the configuration shown in FIG. 16, the capacitance of the capacitor 210 can be set in a wider range than in the configuration example shown in FIG. Other configurations are the same as the configuration example shown in FIG.

  In the configuration example shown in FIG. 17, the substrate region 11 is formed by a plurality of substrate regions having different film thicknesses arranged along the surface electrode 13, and the surface electrode 13 is formed above each substrate region. As shown in FIG. 17, the film thickness of the substrate region 11 varies along the surface electrode 13. In the wiring process stage, the number and location of the surface electrodes 13 connected to the anode terminal 300 are determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon. In the configuration example shown in FIG. 17, the substrate region 11 is thickest under the surface electrode 13 on the right side of the drawing, and the value of the resistor 220 is large. The substrate region 11 is the thinnest below the left surface electrode 13 and the value of the resistor 220 is small. FIG. 17 shows an example in which two of the three surface electrodes 13, the center and the right side, are connected to the anode terminal 300. With the configuration shown in FIG. 17, the value of the resistor 220 can be set in a wider range than the configuration example shown in FIG. Other configurations are the same as the configuration example shown in FIG.

  The configuration example illustrated in FIG. 18 illustrates an example in which the substrate region 11 includes a plurality of substrate regions 111 to 113 having different impurity concentrations and different resistivities. As shown in FIG. 18, the substrate region 111 to the substrate region 113 are arranged along the surface electrode 13. For example, in the substrate region 11, the resistivity of the substrate region 111 on the left side of the drawing is 0.1 Ωcm, the resistivity of the central substrate region 112 is 0.2 Ωcm, the resistivity of the right substrate region 113 is 0.3 Ωcm, and the like. Surface electrodes 13 are formed above the substrate region 111 to the substrate region 113, respectively. In the wiring process stage, the number and location of the surface electrodes 13 connected to the anode terminal 300 are determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon. FIG. 18 shows an example in which two of the three surface electrodes 13, the center and the right side, are connected to the anode terminal 300. With the configuration shown in FIG. 18, the value of the resistor 220 can be set in a wider range than the configuration example shown in FIG. Other configurations are the same as the configuration example shown in FIG.

  In the description of the first embodiment, as an example of the structure of the semiconductor snubber circuit 200, the capacitor 210 is formed of a dielectric and the resistor 220 is formed of a substrate region. However, the capacitor 210 and the resistor 220 are described. Of course, may be formed by other methods.

  FIG. 19 shows a case where a conductive type region 15 having a conductivity type different from that of the substrate region 11, that is, a P-type opposite conductivity type region 15 is formed as the dielectric region 12 made of the silicon oxide film shown in FIG. In the case of the configuration shown in FIG. 5, the oscillation phenomenon is suppressed by charging the capacitor 210 by the dielectric region 12 with the voltage applied when the freewheeling diode 100 performs the reverse recovery operation. On the other hand, in the configuration shown in FIG. 19, an N-type substrate region 11 having a plurality of substrate regions 111 to 113 having different impurity concentrations and a P-type opposite conductivity type region 15 are formed. The depletion layer is used as the capacitor 210.

  In the configuration example illustrated in FIG. 19, the substrate region 11 includes substrate regions 111 to 113 having different impurity concentrations, and the thicknesses of the depletion layers formed in the substrate regions 111 to 113 are different. For this reason, the capacitance of the capacitor 210 is also different in the substrate region 111 to the substrate region 113. An advantage of using the depletion layer as the capacitor 210 is that deterioration due to a transient current is relatively small as compared to the dielectric region 12 such as a silicon oxide film. That is, it is advantageous in terms of long-term reliability.

  As another configuration for forming a depletion layer in the substrate region 11, for example, as shown in FIG. 20, the substrate region 11 and the Schottky junction are formed on the substrate region 11 having the substrate regions 111 to 113 having different impurity concentrations. It is also possible to employ a method of forming the surface electrode 13 made of a metal material that forms the surface. Since the thicknesses of the depletion layers formed between the surface electrode 13 and the substrate regions 111 to 113 are different from each other, the capacitances due to the depletion layers are also different. In addition to the Schottky junction, the same effect can be obtained with any configuration as long as a depletion layer is formed when a reverse bias voltage such as a heterojunction is applied.

  In the configurations shown in FIGS. 19 and 20, there is a concern that forward current flows during forward bias. However, since the resistance value of the substrate region 11 shown in FIGS. 19 and 20 is larger than the resistance of the drift region 2 of the freewheeling diode 100, most of the current flows through the low resistance freewheeling diode 100. For this reason, there is almost no effect on conduction loss during forward bias.

  As shown in FIGS. 21 and 22, the capacitor 210 may be configured by forming a plurality of regions in series or in parallel. FIG. 21 is a circuit diagram in which a capacitor using the dielectric region 12 shown in FIG. 5 and a capacitor using a depletion layer obtained by forming the opposite conductivity type region 15 shown in FIG. A configured example is shown. FIG. 22 shows an example in which the capacitor 210 is configured by connecting the capacitor formed by the dielectric region 12 and the capacitor formed by the depletion layer shown in FIG. 20 in parallel. In any case, as long as the capacitor 210 and the resistor 220 are formed to be connected in series, the capacitor 210 may be configured in any region.

FIG. 23 shows an example in which the resistor 220 composed of the substrate region 11 is formed outside the substrate region 11 in the configuration shown in FIG. In the configuration example shown in FIG. 23, instead of the substrate region 11 used in FIG. 5, a low resistance substrate region 16 formed of an N ⁺ type low resistance substrate is formed. Then, as the resistor 220, a plurality of resistance regions 17 made of, for example, polycrystalline silicon and having different resistivities are formed on the dielectric region 12. An advantage of the resistance region 17 made of polycrystalline silicon is that the resistance value can be freely set by changing the thickness and impurity concentration. That is, the semiconductor snubber circuit 200 according to the first embodiment can be formed no matter what substrate is selected when selecting the substrate region as the support base. For this reason, it becomes possible to raise the freedom degree, such as material selection.

  Furthermore, by setting the resistivity of the three resistance regions 17 shown in FIG. 23 to different resistivity, the value of the resistor 220 can be arbitrarily set in a wide range. The resistance region 17 may be made of any material other than polycrystalline silicon, but the resistance region 17 is preferably made of a material having a higher dielectric breakdown electric field than silicon, and the manufacturing process of the resistance region 17 is further improved. More easily. For example, when 100 V is applied as a surge voltage to both ends of the freewheeling diode 100 during reverse recovery, a transient current flows through the capacitor 210 in the semiconductor snubber circuit 200. Applied. At this time, the resistance 220 is required to have a breakdown voltage equal to or higher than the breakdown voltage determined from the breakdown field and thickness according to the material. In the case of silicon, in order to have a breakdown voltage of 100 V, since the dielectric breakdown electric field of silicon is about 0.3 MV / cm, a thickness of about 3 μm is required. When poly silicon carbide having a higher breakdown electric field than silicon is used in the resistance region, the breakdown electric field of poly silicon carbide is about 3.6 MV / cm, so the thickness is reduced to about 1/10 of that of silicon. be able to. Therefore, it is possible to shorten the deposition time when manufacturing the resistance region, and to facilitate the process. In addition, since silicon carbide has a thermal conductivity approximately three times better than that of silicon, there is an effect of improving the heat dissipation of the resistance region 17.

  24 shows an example in which the resistor 220 is configured by connecting a plurality of resistor regions 17 having different resistivities shown in FIG. 23 and the substrate region 11 shown in FIG. 5 in series. As described above, the resistor 220 may be configured in any region as long as it is formed so as to be connected in series with the capacitor 210.

  As described above, in the configuration examples shown in FIGS. 10 to 24, by forming the plurality of surface electrodes 13 in advance, depending on the required values of the capacitor 210 and the resistor 220, during the wiring process. The number and arrangement of the surface electrodes 13 connected to the anode terminal of the reflux diode 100 can be selected. Thereby, it is possible to provide the semiconductor snubber circuit 200 that can be applied to the freewheeling diode 100 of various specifications. Further, by forming the plurality of surface electrodes 13, a part of a mask and a process for manufacturing the semiconductor snubber circuit 200 can be shared by the semiconductor snubber circuits 200 having different capacitance values and resistance values. Reduce costs. Furthermore, even when the circuit configuration is changed, the vibration phenomenon of current / voltage can be stably suppressed only by changing the wiring.

  In the configuration example shown in FIG. 5, a case where a plurality of surface electrodes 13 are formed and the number of the surface electrodes 13 connected to the anode terminal of the reflux diode 100 is selected at the time of wiring is shown. On the other hand, in the configuration example shown in FIG. 25, the values of the capacitor 210 and the resistor 220 can be changed by changing the area of the surface electrode 13. Therefore, if the substrate region 11 and the dielectric region 12 having a certain area are prepared in advance, the semiconductor snubber circuit 200 that can be applied to the freewheeling diode 100 of various specifications can be provided only by changing the area of the surface electrode 13. can do. With the structure shown in FIG. 25, a common mask and a common process can be used in the process of forming the substrate region 11 and the dielectric region 12, and the cost can be reduced. In the configuration shown in FIG. 25, the surface electrode 13 is formed only on part of the dielectric region 12. That is, it is shown that the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon are formed according to the free-wheeling diodes 100 connected in parallel.

  In the configuration example shown in FIG. 25, as a method of patterning the surface electrode 13, a method using a dedicated photolithography mask, a predetermined pattern, as in the case where the combined surface electrode 1001 is formed in FIGS. A method of forming an arbitrary pattern by changing the program of the exposure apparatus using the photolithographic mask, a method of patterning using the metal mask for vapor deposition, and the like can be used.

  26 and 27 use a circuit simulator for the relationship between the capacitance C of the capacitor used in the snubber circuit and the suppression effect of the vibration phenomenon and the increase in the loss due to the transient current flowing in the capacitor. This is an example calculated. The vibration reduction of the snubber circuit is composed of the parasitic inductance Ls in the circuit, the capacitance component C0 of the freewheeling diode, and the capacitance C of the snubber circuit capacitor connected in parallel to the freewheeling diode and the resistance value R of the resistor. It can be calculated with a simple circuit. In this calculation, as an example, the parasitic inductance Ls in the effect circuit is fixed to 99 nH and the resistance value R is 40 Ω, and the decay time of the vibration phenomenon and the transient loss generated in the snubber circuit depending on the size of the capacitance ratio C / C0. The change in the increase of the cost was calculated. The electrostatic capacitance component C0 of the reflux diode was set to 150 pF.

  FIG. 26 shows a waveform of a vibration phenomenon when the capacity ratio C / C0 is 0.004 times to 40 times. As shown in FIG. 26, as the capacitance ratio C / C0 increases, the decay time of the vibration phenomenon decreases. In particular, the damping effect of the vibration phenomenon becomes remarkable from the capacity ratio C / C0 of about 0.1 times. On the other hand, when the capacity ratio C / C0 exceeds 10, the convergence time ratio value of the vibration phenomenon tends to be saturated.

  In the left axis of FIG. 27, the time until the voltage or current vibration is attenuated to 1/10 in the absence of the snubber circuit is t0, and when the snubber circuit is added, the vibration is equivalent to that in the case where the snubber circuit is not present. The vibration phenomenon convergence time ratio t / t0 when the time until is t is shown. The axis on the right side of FIG. 27 shows the increase amount of excess loss E / E0 where E0 is the loss caused by the excessive current flowing in the freewheeling diode and E is the loss caused by the excessive current flowing in the capacitor of the snubber circuit. . Since a loss E due to a transient current proportional to the magnitude of the capacitance C of the capacitor occurs during transient operation, the capacitance C of the capacitor is preferably as small as possible. As described above, the capacitance of the capacitor 210 included in the semiconductor snubber circuit 200 is 1/10 times or more and 10 times larger than the capacitance of the capacitor component in the cutoff state of the freewheeling diode 100. By selecting in the following range, it is possible to reduce the vibration phenomenon more remarkably while suppressing an increase in loss.

  From the above, the capacitance value of the capacitor 210 of the semiconductor snubber circuit 200 is selected in the range of 1/10 to 10 times the capacitance of the capacitor component in the cutoff state of the freewheeling diode 100. It is preferable. As a result, the vibration phenomenon can be reduced more significantly while suppressing an increase in loss. This effect can be obtained in any of the configuration examples described in the first embodiment.

  As described above, in the semiconductor device 10 according to the first embodiment, the semiconductor snubber circuit 200 includes a plurality of surface electrodes 13 that can be connected to the anode terminal 300. Alternatively, the area of the surface electrode 13 of the semiconductor snubber circuit 200 connected to the anode terminal 300 can be made variable. As a result, the capacitance value of the capacitor 210 and the resistance value of the resistor 220 can be set to desired values. That is, by making the capacitance value and resistance value of the semiconductor snubber circuit 200 variable, it is not necessary to prepare a plurality of snubber circuits having different values of the capacitor 210 and the resistor 220 according to the specifications of the freewheeling diode 100, and It is possible to provide a semiconductor device capable of shortening the convergence time of the oscillation phenomenon that occurs in the free-wheeling diode during reverse bias.

  Further, in the above description, an example in which there are a plurality of surface electrodes connected to the anode terminal 300 of the capacitor 210 or the area is made variable is shown. Of course, it may be variable. Further, the plurality of surface electrodes and the surface electrode whose area is variable may be the electrode of the capacitor 210 or the electrode of the resistor 220.

(Second Embodiment)
The semiconductor device according to the second embodiment of the present invention will be described below, but the description of the same parts as in the first embodiment will be omitted, and different features will be described.

  As shown in FIG. 28, the semiconductor device 10A according to the second embodiment includes a free-wheeling diode 100 that performs the unipolar operation described in the first embodiment or an operation equivalent to the unipolar operation, at least a capacitor 210, and a resistor 220. In addition to the semiconductor snubber circuit 200 including the switching diode 600, the switching diode 600 connected in parallel to the freewheeling diode 100 and the semiconductor snubber circuit 200 is further provided. In the example shown in FIG. 28, the semiconductor snubber circuit 200 is an RC snubber circuit in which a capacitor 210 and a resistor 220 are connected in series. As shown in FIG. 28, the emitter terminal 301 is connected to the emitter terminal of the switching element 600, the anode terminal of the freewheeling diode 100, and the resistor 220 of the semiconductor snubber circuit 200. The collector terminal 401 is connected to the collector terminal of the switching element 600, the cathode terminal of the freewheeling diode 100, and the capacitor 210 of the semiconductor snubber circuit 200.

  In the second embodiment, as an example, a case where the freewheeling diode 100, the semiconductor snubber circuit 200, and the switching element 600 are formed in different semiconductor chips will be described. A case where the configuration of the semiconductor snubber circuit 200 and the configuration of the freewheeling diode 100 are the same as those described in the first embodiment will be described. For the switching element 600, for example, when an IGBT using silicon as a semiconductor base material is used, the switching element 600 is a so-called vertical IGBT in which the emitter terminal and the collector terminal are formed of electrodes facing each other. An example will be described.

  29 shows a semiconductor device 10A including the freewheeling diode 100 (for example, silicon carbide Schottky barrier diode), the semiconductor snubber circuit 200 (for example, silicon semiconductor RC snubber), and the switching element 600 (for example, silicon IGBT) shown in FIG. It is the figure which showed the specific mounting example. As shown in FIG. 29, the semiconductor device 10A can be mounted on a semiconductor package using a ceramic substrate as in the example shown in FIG.

  As shown in FIG. 29, a semiconductor chip in which a freewheeling diode 100 is disposed on a metal film 410 on the cathode side (freewheeling diode chip, indicated by reference numeral 100 in the figure), and a semiconductor chip in which a semiconductor snubber circuit 200 is disposed. (Snubber chip, indicated by reference numeral 200 in the figure) and a semiconductor chip in which the switching element 600 is arranged (switching element chip, indicated by reference numeral 600 in the figure) are arranged. The terminals connected to the collector terminals 401 of the freewheeling diode chip, the snubber chip, and the switching element chip are arranged so as to be in contact with the metal film 410 via a bonding material such as solder or brazing material. The terminals connected to the emitter terminals 301 of the free-wheeling diode chip, the snubber chip, and the switching element chip are connected to the metal film 310 on the anode side through metal wirings 320, 330, and 350 such as aluminum wires and aluminum ribbons, for example. Is done. The gate terminal of the switching element 600 is connected to the metal film 700 on the gate side through the metal wiring 710.

  FIG. 29 shows an example in which three surface electrodes 13 are formed in advance in the semiconductor snubber circuit 200, and two of them are connected to the metal film 340 on the anode side through the metal wiring 330. However, the number of surface electrodes 13 is not limited to three but may be plural, and at least one of them may be connected to the metal film 340 on the anode side.

  Examples of the cross-sectional structures of the switching element chip, the free wheel diode chip, and the snubber chip constituting the switching element 600, the free wheel diode 100, and the semiconductor snubber circuit 200, respectively, are shown in FIG. 30, FIG. 4, and FIG. It is.

FIG. 30 shows a case where the switching element 600 is a general IGBT. For example, a case will be described where a substrate material in which an N-type buffer region 22 and an N ⁻ -type drift region 23 are stacked on a P ⁺ -type substrate region 21 made of silicon is used. The substrate region 21 has, for example, a resistivity of several mΩcm to several tens of mΩcm and a thickness of about several to several hundreds μm. For example, the drift region 23 has an N-type impurity density of 10 ¹³ cm ⁻³ to 10 ¹⁶ cm ⁻³ and a thickness of several tens to several hundreds of μm.

Note that the resistivity, impurity density, and thickness may be outside the above ranges depending on the element structure and required breakdown voltage, but in general, the smaller the resistivity and thickness, the lower the conduction loss, so that the resistance is as much as possible. It is preferable to reduce the rate and thickness. In the second embodiment, a case will be described where a drift region 23 having an impurity density of 10 ¹⁴ cm ⁻³ , a thickness of 50 μm, and a withstand voltage of 600 V class is used, for example.

  The buffer region 22 is formed to prevent punch-through with the substrate region 21 when a high electric field is applied to the drift region 23. FIG. 30 shows an example in which the substrate region 21 is a support base material, but the buffer region 22 and the drift region 23 may be a support base material. The buffer region 22 may be omitted as long as the substrate region 21 and the drift region 23 do not punch through.

As shown in FIG. 30, a P-type well region 24 is formed in a part of the surface layer portion in the drift region 23, and an N ⁺ -type emitter region 25 is formed in a part of the surface layer portion in the well region 24. . A gate insulating film 26 made of, for example, a silicon oxide film is formed on the surface layer portions of the drift region 23, well region 24, and emitter region 25, and a gate electrode made of, for example, N-type polycrystalline silicon is formed on the gate insulating film 26. 27 is disposed. Further, an emitter electrode 28 made of, for example, an aluminum material is formed in contact with the emitter region 25 and the well region 24 in the opening formed in the gate insulating film 26. An interlayer insulating film 29 made of, for example, a silicon oxide film is formed between the emitter electrode 28 and the gate electrode 27 so that the emitter electrode 28 and the gate electrode 27 do not contact each other. A collector electrode 30 is formed so as to be in ohmic contact with the substrate region 21. The IGBT used in the switching element 600 shown in FIG. 30 is a so-called planar type in which the gate electrode 27 is formed on the semiconductor substrate plane.

  The configuration of the free-wheeling diode (here, the Schottky barrier diode) illustrated in FIG. 4 as the cross-sectional structure diagram of the free-wheeling diode chip shown in FIG. 29 is the same as that described in the first embodiment, and thus a duplicate description. Is omitted.

  Although the basic configuration of the semiconductor snubber circuit 200 illustrated in FIG. 5 as the cross-sectional structure diagram of the snubber chip shown in FIG. 29 is the same as that of the first embodiment, in order to effectively exert the snubber function. The structures of the capacitor 210 and the resistor 220 are preferably determined in consideration of the switching element 600 newly connected in parallel. However, as will be described later, when a reverse recovery current flows through the freewheeling diode 100, the switching element 600 is always in a cut-off state. For this reason, the capacitor 210 and the resistor 220 of the semiconductor snubber circuit 200 can be set according to the depletion capacity when the free wheel diode 100 and the switching element are cut off, as in the case described in the first embodiment.

  For the substrate region 11, the resistivity and thickness of the substrate are set according to the magnitude of the resistance value necessary for the resistor 220. For example, the substrate region 11 is set using a substrate having a resistivity of several mΩcm to several hundreds Ωcm and a thickness of about several tens of μm to several hundreds of μm. Also, regarding the capacitance of the capacitor 210, the thickness and area of the dielectric region 12 are set so that the required withstand voltage is satisfied at a minimum and the necessary capacitance is obtained. The capacitance of the capacitor 210 is selected in the range of about 1/100 to 100 times the sum of the depletion capacities in which the free-wheeling diode 100 and the switching element 600 are charged in the cutoff state (when a high voltage is applied). be able to. However, when a sufficient snubber function is exhibited, the increase in loss is suppressed as much as possible, and the required chip area is taken into consideration, the capacitor is approximately in the range of about 1/10 to about 10 times as shown in the calculation results described later. It is preferable to select a capacitance of 210. In the description of the second embodiment, for example, the thickness of the capacitor 210 is set to 1 μm so that the withstand voltage of the freewheeling diode 100 and the switching element 600 is higher, for example, and the capacitance of the capacitor 210 is equal to the freewheeling diode 100 and the switching element 600. It is assumed that it is about the same as the sum of depletion capacities formed in the cutoff state.

  Also in the second embodiment in which the switching elements 600 are connected in parallel, as will be described later, when, for example, a Schottky barrier diode is used as the freewheeling diode 100, current / voltage oscillations that are essentially generated by unipolar operation. In response to the phenomenon, the oscillation phenomenon can be easily and effectively suppressed by connecting in parallel the semiconductor snubber circuit 200 having the small capacitance 210 and the capacitor 220 having a small capacitance. That is, it is not necessary to use a technique of wiring an external discrete component such as a film capacitor or a metal clad resistor in a path through which a main current flows, which is conventionally used as a snubber circuit for reducing vibration of a diode that operates in bipolar. Further, as already described, C = 1 / (2πfR) is generally known as a design formula that effectively exhibits the snubber function, but the second embodiment also satisfies the design formula. In addition, the capacitor 210 and the resistor 220 using the semiconductor snubber circuit 200 having a small electrostatic capacity can be easily set.

  Next, the operation of the semiconductor device 10A according to the second embodiment will be described.

  The semiconductor device 10A is used for a power converter such as a so-called inverter that moves a three-phase AC motor as shown in FIG. 31 or a so-called H bridge as shown in FIG. Can do. For example, in the inverter shown in FIG. 31, for example, a lower arm is formed with a semiconductor device 10A composed of a switching element E and a passive element B connected in parallel to form an upper arm for a power supply voltage (+ V) of 400V. A switching element G and a semiconductor device 10A composed of passive elements F connected in parallel are connected in series so as to be connected in reverse bias. This connection is connected for three phases to form a three-phase inverter.

  In the semiconductor device 10A shown in FIG. 31, when the switching element of either the upper arm or the lower arm performs the switching operation, the switching element and the passive element of the arm that is not performing the switching operation interlock to cut off the current. It operates from a state to a conductive state that circulates current, and from a conductive state to a cut-off state. Here, the operation of the semiconductor device 10A will be described with reference to the operation of one of the three phases shown in FIG. 31, and in particular, the switching element G of the lower arm performs the switching operation, and the switching of the upper arm is performed. A case where the element E and the passive element B perform a reflux operation will be described.

  In a state where the switching element G is turned on and a current flows through the switching element G, the switching element E and the passive element B of the upper arm are in a reverse bias state and are in a cutoff state. In addition, in the passive element F connected in parallel to the switching element G in the conductive state, the free wheeling diode 100 and the semiconductor snubber circuit 200 maintain the cutoff state.

That is, although the reverse bias voltage is applied to both ends of the Schottky barrier diode (FIG. 4) that is the freewheeling diode 100, which is as low as the ON voltage of the switching element G, the freewheeling diode 100 is in the cut-off state. Since the semiconductor snubber circuit 200 shown in FIG. 5 operates only when the voltage changes in the dielectric region 12 functioning as the capacitor 210, the semiconductor snubber circuit 200 is cut off in a state where a voltage of about the ON voltage of the switching element G is applied in a steady state. State.
Further, the switching element E and the passive element B in the upper arm are also maintained in the cut-off state because the reverse bias voltage of about the power supply voltage is applied together. This is because the depletion layer extending from the PN junction with the well region 24 drifts because the reverse bias voltage is applied between the emitter terminal 301 and the collector terminal 401 for the IGBT which is the switching element 600 shown in FIG. This is because it is formed in the region 23 and the cut-off state is maintained. Further, in the Schottky barrier diode which is the freewheeling diode 100 shown in FIG. 4, since a reverse bias voltage is applied between the front surface electrode 3 and the back surface electrode 4, the depletion extended from the Schottky junction with the front surface electrode 3. A layer is created in the drift region 2 and the interrupted state is maintained. Also in the semiconductor snubber circuit 200 shown in FIG. 5, the dielectric region 12 functioning as the capacitor 210 is charged with a high voltage and maintains the cutoff state.

As described above, when the switching element G of the lower arm is in the conductive state, the upper and lower arms operate in the same manner as in the prior art in which the passive element is composed of only the Schottky barrier diode.
Next, the case where the switching element G of the lower arm is turned off and shifts to the cutoff state will be described.

  In the motor inverter circuit (L load circuit) as shown in FIG. 31, when the switching element G is turned off, the phase of voltage rise and current interruption is shifted. For this reason, the voltage rise of the switching element G first occurs in a state where the current during conduction is substantially maintained.

  On the other hand, the voltage applied to the passive element F connected in parallel to the switching element G to be turned off is changed from a reverse bias voltage as low as the ON voltage to a high voltage as high as the power supply voltage as the voltage of the switching element G increases. Changes to reverse bias voltage. For this reason, a transient current corresponding to the speed of the voltage change flows through the freewheeling diode 100 and the semiconductor snubber circuit 200. That is, in the free-wheeling diode 100 shown in FIG. 4, when a depletion layer spreads from the surface electrode 3 side into the drift region 2 as the voltage rises, electrons flow as a transient current to the back electrode 4 side. In the semiconductor snubber circuit 200 shown in FIG. 5, since the dielectric region 12 serving as the capacitor 210 is charged according to the applied voltage, a transient current flows. At this time, the charging action of the capacitor in the dielectric region 12 of the semiconductor snubber circuit 200 mitigates the transient voltage rise that occurs between the collector and the emitter of the switching element G, and the generation of a surge voltage due to the parasitic inductance included in the circuit. It is suppressed. In other words, in the motor inverter circuit shown in FIG. 31, by connecting the switching element 600 in parallel with the free wheeling diode 100 and the semiconductor snubber circuit 200, even when the switching element 600 performs the turn-off operation, Surge voltage causing malfunction to the peripheral circuit is reduced, and more stable operation can be realized.

  After the voltage increase of the switching element 600, the current is cut off at a predetermined speed. At this time, in the IGBT described as an example in the second embodiment, although the current interruption speed is limited and a loss occurs due to the influence of the hole current injected from the substrate region 21 during conduction, the vibration phenomenon due to the current interruption is unlikely to occur. As a result, it operates stably. After the current of the switching element 600 is cut off, the lower arm switching element G and the passive element F are in a steady off state and maintain the cut-off state.

  On the other hand, the passive element B of the upper arm enters a forward bias state and shifts to a conductive state in conjunction with the turn-off operation of the switching element G of the lower arm. That is, the depletion layer extending in the drift region 2 of the free-wheeling diode 100 shown in FIG. 4 recedes, and the Schottky barrier height formed at the Schottky junction formed between the surface electrode 3 and the drift region 2 is increased. When a forward bias voltage corresponding to is applied, the freewheeling diode 100 becomes conductive. At this time, the current flowing through the free-wheeling diode 100 is substantially constituted only by the electron current supplied from the back electrode 4 side into the drift region 2, and the free-wheeling diode 100 performs a unipolar operation.

  Also, in the semiconductor snubber circuit 200 shown in FIG. 5, similarly to the freewheeling diode 100, the charge charged in the dielectric region 12 is discharged because the high voltage reverse bias state shifts to the low voltage forward bias state. , Transient current flows. However, in the second embodiment, the capacitance of the dielectric region 12 is almost the same as the depletion capacitance formed when the free wheel diode 100 and the switching element 600 are cut off, and is very small. For this reason, the magnitude of the transient current that flows due to the discharge is much smaller than the forward bias current that flows through the parallel free-wheeling diodes 100 and has little effect on the operation.

  In addition, for the switching element E, the collector-emitter voltage shifts from the reverse bias voltage state to the forward bias state, but the gate signal is controlled to maintain the off state, and further, between the substrate region 21 and the buffer region 22. Since the PN junction is in a reverse bias state, the OFF state is maintained. However, since the voltage state between the collector and the emitter is displaced, a transient current due to the discharge of the capacitor accompanying the capacitance change of the depletion layer that has occurred in the drift region 23 in the switching element 600 flows. However, similar to the semiconductor snubber circuit 200, this transient current is very small compared to the forward bias current flowing through the freewheeling diode 100 connected in parallel to the switching element E, and hardly affects the operation. Then, the semiconductor snubber circuit 200 and the switching element 600 are cut off because a transition is made between the forward bias state and the steady state after the transient current accompanying the change in the bias voltage flows, and only the freewheeling diode 100 is turned on.

  In the second embodiment, when the freewheeling diode 100 is formed of a Schottky barrier diode made of a silicon carbide semiconductor substrate, the resistance of the drift region 2 is lower than that of a PN junction diode made of a general silicon material. It can be formed low. For this reason, conduction loss during forward bias conduction can be reduced. Thus, even in the conductive state, the same effect as in the conventional technique in which the passive element is configured only by the Schottky barrier diode is obtained.

  Next, an operation in which the switching element G of the lower arm is turned on and the switching element G is turned on again will be described. In the motor inverter circuit (L load circuit) shown in FIG. 31, when the switching element G is turned on, the phases of current increase and voltage decrease are shifted. For this reason, a current starts to flow through the switching element G in a state where a relatively high voltage is applied.

  At this time, a transient current flows through the passive element F connected in parallel to the switching element G. This is because as the current flows through the switching element G and the voltage between the collector and the emitter decreases, the voltage applied to the passive element F decreases from a high reverse bias voltage such as a power supply voltage to a low ON voltage. This is because the current changes to a reverse bias voltage, and a transient current corresponding to the speed of the voltage change flows to the freewheeling diode 100 and the semiconductor snubber circuit 200. At this time, in the free-wheeling diode 100 shown in FIG. 4, the depletion layer that has spread in the drift region 2 as the voltage decreases gradually narrows to the front electrode 3 side, and electrons flow from the back electrode 4 side to the drift region 2. Flows as a transient current. Further, in the semiconductor snubber circuit 200 shown in FIG. 5, since the dielectric region 12 serving as a capacitor capacitance is discharged with a decrease in applied voltage, a transient current flows.

  The transient current flowing through the semiconductor snubber circuit 200 has a magnitude that hardly affects the operation as compared with the turn-on current flowing through the switching element 600 connected in parallel. Since the semiconductor snubber circuit 200 and the freewheeling diode 100 in the lower arm transition to a steady state after the transient current flows and the current is cut off, only the switching element 600 is in a conductive state.

  On the other hand, the passive element B connected in parallel with the switching element E of the upper arm enters a reverse bias state in conjunction with the turn-on operation of the switching element G of the lower arm and shifts to the cutoff state. In the Schottky barrier diode shown in FIG. 4, the electron current due to the electrons supplied from the back electrode 4 side into the drift region 2 decreases as the forward bias voltage decreases. When the forward bias voltage becomes equal to or lower than the voltage corresponding to the Schottky barrier height of the Schottky junction, and when the reverse bias voltage starts to be applied to the Schottky junction, The depletion layer extending from the Schottky junction spreads and shifts to the cutoff state.

  When transitioning from the conductive state to the cut-off state, a transiently generated current is a reverse recovery current in the process in which excess carriers accumulated in the element of the freewheeling diode 100 disappear. This reverse recovery current flows as a transient current through the passive element B and the switching element G of the lower arm, and a loss (herein referred to as reverse recovery loss) occurs in each element. For this reason, it is better that the reverse recovery current generated in the freewheeling diode is as small as possible.

  In the semiconductor device 10A according to the second embodiment, when a unipolar Schottky barrier diode formed of a semiconductor material made of silicon carbide is used as the free wheeling diode 100, it is compared with a PN junction diode formed of general silicon. This reverse recovery current is much smaller. That is, reverse recovery loss can be greatly reduced.

  Furthermore, the semiconductor device 10A exhibits a current / voltage oscillation phenomenon during a reverse recovery operation caused by a unipolar operation that cannot be essentially solved when the passive element of the prior art is composed of only a Schottky barrier diode. It has a function to suppress. That is, in the semiconductor device 10A, when the forward bias current of the freewheeling diode 100 decreases to zero, a depletion layer is formed in the drift region 2 due to the reverse bias voltage, and a reverse recovery current composed of excess carriers starts to flow. Almost simultaneously with the application of the reverse bias voltage, an equivalent reverse bias voltage is applied to the switching element 600 and the capacitor 210 formed of the dielectric region 12 in the semiconductor snubber circuit 200, so that the switching element 600 and the semiconductor snubber circuit 200 are applied. Appropriate transient current begins to flow inside. The transient current flowing through the semiconductor snubber circuit 200 is determined by the size of the capacitor 210 formed of the dielectric region 12 and the size of the resistance component of the substrate region 11, and can be designed freely.

  There are three effects of the semiconductor snubber circuit 200 as described in the first embodiment. That is, (1) since the cutoff speed of the forward bias current flowing through the freewheeling diode 100 can be set to a high speed, the loss accompanying the interruption of the main current can be reduced; (2) the freewheeling diode 100 has entered reverse recovery operation. Sometimes the surge voltage itself can be reduced; (3) The energy generated by the parasitic inductance Ls is absorbed and the vibration phenomenon can be quickly converged.

As described above, the semiconductor device 10A according to the second embodiment has the performance of reducing the transient loss and conduction loss of the freewheeling diode 100, and at the same time, using the semiconductor snubber circuit 200, the vibration peculiar to the unipolar operation. The phenomenon can be solved.
In the second embodiment of the present invention, the transient current flowing through the freewheeling diode 100 and the switching element 600 is a transient current consisting only of carriers generated when a depletion layer is formed in the drift regions 2 and 23 at most. Focusing on the above, the point where the snubber circuit is formed by the semiconductor snubber circuit 200 having a small electrostatic capacity is different from the prior art.

  Further, even with the configuration described in the second embodiment, as in the first embodiment, the following new features not found in the prior art are suppressed in suppressing the performance and vibration phenomenon of reducing transient loss and conduction loss. There is an effect.

  One effect is that a semiconductor snubber circuit 200 having a predetermined capacitance and resistance is connected in parallel to the free-wheeling diode 100 and the switching element 600 that perform unipolar operation, so that the full-current range and the full-temperature range in which the free-wheeling diode 100 operates. This means that the snubber function works effectively. As described above, the reverse recovery current generated at the time of reverse recovery of the Schottky barrier diode is composed only of excess carriers generated when a depletion layer is generated in the freewheeling diode 100 and the switching element 600 by the reverse bias voltage. Regardless of the magnitude of the current flowing during the reflux operation, a substantially constant reverse recovery current flows every time. For the same reason, the freewheeling diode 100 is hardly affected by temperature, and a substantially constant reverse recovery current flows. For this reason, it is possible to reduce the transient loss and suppress the vibration phenomenon in the entire current range and temperature range. These are effects that cannot be obtained in combination with a general PN junction diode.

  Another effect is that by forming the snubber circuit with the semiconductor snubber circuit 200, the semiconductor snubber circuit 200 can be mounted with low inductance in the immediate vicinity of the free wheeling diode 100 and the switching element 600 as shown in FIG. Transient loss can be reduced and vibration phenomena can be suppressed. As described above, the smaller the parasitic inductance, the easier the transient current that flows in the snubber circuit flows, the easier it is to relax the reverse recovery current cutoff speed that flows in the freewheeling diode, and the switching time within the withstand voltage range of the capacitor. It depends on what you can do fast. Therefore, also in the second embodiment, by reducing the parasitic inductance, the switching time can be shortened and the transient loss can be reduced by reducing the parasitic inductance as compared with the case of the conventional snubber circuit using the capacitor and the resistor. The breaking speed of the recovery current can be appropriately relaxed to suppress the vibration phenomenon.

  Further, as already described, unnecessary noise emission is reduced by mounting the snubber circuit in the immediate vicinity of the freewheeling diode. Thereby, it is possible to prevent malfunction of the control circuit and the like due to noise.

  Furthermore, by forming the snubber circuit with the semiconductor snubber circuit 200, it is possible to configure the power conversion device using the same mounting process as the free wheel diode 100 and the switching element 600. Therefore, the vibration phenomenon can be easily and easily suppressed, and the required volume can be significantly reduced as compared with the conventional snubber circuit.

  Further, similarly to the first embodiment, the resistance component of the semiconductor snubber circuit 200 can be formed by a semiconductor substrate and directly mounted on a semiconductor package as shown in FIG. For this reason, high heat dissipation can be obtained. As a result, it is possible to design a resistor with a higher density than when an external resistor or the like is used. That is, the resistance to destruction is high and further downsizing can be realized.

  Furthermore, as exemplified in the first embodiment, the effect of the present invention can be maximized by configuring the freewheeling diode 100 with a Schottky barrier diode made of silicon carbide. As already described, by configuring the free-wheeling diode 100 with a wide band gap semiconductor such as silicon carbide, it is possible to more remarkably reduce both the conduction loss and the vibration phenomenon. Even when a wide gap semiconductor such as gallium nitride or diamond other than silicon carbide is used as the semiconductor material of the freewheeling diode 100, the same effect can be obtained.

  As for the mounting form, as in the first embodiment, a mold package type mounting form corresponding to FIG. 8 or another mounting form may be used. In the second embodiment, the case where each of the free-wheeling diode chip, the snubber chip, and the switching element chip is one chip is illustrated, but any one chip or all of the chips may be provided. Further, as described in the first embodiment, a method of mounting both surfaces of the collector terminal and the emitter terminal with solder or the like may be employed.

  Further, although an example of the structure of the semiconductor snubber circuit 200 has been described with reference to FIG. 5, as in the first embodiment, the capacitor 210 and the resistor 220 are formed by various configurations shown in FIGS. 10 to 25. May be.

  As described above, according to the semiconductor device 10 </ b> A according to the second embodiment, the number and area of the surface electrodes 13 of the semiconductor snubber circuit 200 connected to the anode terminal 300 can be made variable. In addition to the effect that the capacitance value and the resistance value of the resistor 220 can be set to desired values, various effects can be obtained by connecting the switching element 600 to the free-wheeling diode 100 and the semiconductor snubber circuit 200 in parallel. Others are substantially the same as those in the first embodiment, and redundant description is omitted.

  As described with reference to FIGS. 20 and 21 in the first embodiment, the capacitance C of the capacitor used in the snubber circuit and the sum C0 of the capacitor capacitance components of the free-wheeling diode and the switching element in the cut-off state When the capacitance ratio C / C0 is around 0.1, the damping effect of the vibration phenomenon becomes remarkable, and the value of the convergence time ratio of the vibration phenomenon tends to be saturated when the capacitance ratio C / C0 exceeds 10. Further, during a transient operation, a loss E occurs due to a transient current proportional to the capacitance of the capacitor formed in the snubber circuit. For this reason, it is preferable that the capacitance of the capacitor 210 be as small as possible.

  From this, the capacitance C of the capacitor 210 of the snubber circuit used in the second embodiment is 10 times smaller than the sum of the capacitances of the capacitor components in the cutoff state of the free-wheeling diode 100 and the switching element 600. By selecting in the range of not less than 10 times and not more than 10 times, it is possible to more significantly reduce the vibration phenomenon while suppressing an increase in loss. This effect can be obtained in any configuration example described in the second embodiment.

(Third embodiment)
In the third embodiment, in the configuration in which the freewheeling diode 100, the semiconductor snubber circuit 200, and the switching element 600 described in the second embodiment are connected in parallel, the freewheeling diode 100 and the switching element 600 are respectively other than the Schottky barrier diode and The case where it comprises with elements other than IGBT is demonstrated. 33 shows an example of a cross-sectional structure of the freewheeling diode 100 corresponding to FIG. 4, and FIG. 34 shows an example of a cross-sectional structure of the switching element 600 corresponding to FIG. Below, the description of the same part as 1st Embodiment or 2nd Embodiment is abbreviate | omitted, and a different characteristic is demonstrated.

The freewheeling diode 100 shown in FIG. 33 is made of a substrate material in which an N ⁻ type drift region 42 is formed on an N ⁺ type substrate region 41 of, for example, a silicon carbide polytype 4H type. The substrate region 41 has, for example, a resistivity of several mΩcm to several tens of mΩcm and a thickness of about several tens of μm to several hundreds of μm.

The drift region 42 has, for example, an N-type impurity density of 10 ¹⁵ to 10 ¹⁸ cm ⁻³ and a thickness of several to several tens of μm. Of course, the resistivity, impurity density, and thickness may be out of the above range depending on the element structure and required breakdown voltage, but in general, the smaller the resistivity and thickness, the lower the conduction loss. It is preferable to do. In the third embodiment, a case will be described in which a drift region 42 having an impurity density of 10 ¹⁶ cm ⁻³ , a thickness of 5 μm, and a breakdown voltage of 600 V class is used.

  In the configuration example shown in FIG. 33, the semiconductor substrate is a two-layer substrate including the substrate region 41 and the drift region 42. However, the resistivity is not limited to the above example, but only the substrate region 41 is formed. A laminated substrate may be used, or a multilayer substrate may be used. Moreover, although the case where a proof pressure is a 600V class is demonstrated as an example, a proof pressure class is not limited to this.

As shown in FIG. 33, hetero semiconductor region 43 made of polycrystalline silicon having a band gap smaller than that of silicon carbide is deposited on the main surface of drift region 42 facing the bonding surface with substrate region 41. A heterojunction diode made of silicon carbide and polycrystalline silicon, which are materials having different band gaps, is formed at the junction between the drift region 42 and the hetero semiconductor region 43, and an energy barrier exists at the junction interface. In the heterojunction diode, the height of the energy barrier of the heterojunction can be controlled by changing the impurity density of the hetero semiconductor region 43. For this reason, the optimum barrier height can be set according to the required breakdown voltage. Here, as an example, it is assumed that the hetero semiconductor region 43 has a P-type impurity density of 10 ¹⁹ cm ⁻³ and a thickness of 0.5 μm.

  A surface electrode 44 is formed on the hetero semiconductor region 43. The surface electrode 44 is connected to an external electrode as the anode terminal 302. Further, a back electrode 45 that is in ohmic contact with the substrate region 41 is formed. The back electrode 45 is connected to an external electrode as a cathode terminal 402.

  As described above, the free-wheeling diode 100 shown in FIG. 33 functions as a vertical heterojunction diode having the front electrode 44 as an anode terminal and the back electrode 45 as a cathode terminal.

On the other hand, FIG. 34 shows an example in which switching element 600 is a MOSFET made of silicon carbide. In FIG. 34, for example, a substrate material in which an N ⁻ type drift region 52 is formed on an N ⁺ type substrate region 51 whose polytype of silicon carbide is 4H type is used. For example, the substrate region 51 has a resistivity of several mΩcm to several tens of mΩcm and a thickness of about several μm to several hundred μm.

The drift region 52 has, for example, an N-type impurity density of 10 ¹⁴ cm ⁻³ to 10 ¹⁷ cm ⁻³ and a thickness of several μm to several tens of μm. In general, a smaller resistivity and thickness can reduce loss during conduction, and therefore it is preferable that the resistivity and thickness be as small as possible. For example, a drift region 52 having an impurity density of 2 × 10 ¹⁶ cm ⁻³ , a thickness of 5 μm, and a breakdown voltage of 600 V class is used. In the third embodiment, a case where the substrate region 51 is used as a support base material will be described as an example, but the drift region 52 may be used as a support base material.

A P type well region 53 is formed in a part of the surface layer portion in the drift region 52, and an N ⁺ type source region 54 is formed in a part of the surface layer portion in the well region 53. A gate insulating film 55 made of, for example, a silicon oxide film is formed in contact with the surface layer portions of the drift region 52, well region 53, and source region 54, and a gate electrode 56 made of, for example, N-type polycrystalline silicon is formed on the gate insulating film 55. It is arranged.

  Further, a source electrode 57 made of, for example, an aluminum material is formed in contact with the source region 54 and the well region 53 in the opening formed in the gate insulating film 55. An interlayer insulating film 58 made of, for example, a silicon oxide film is formed between the source electrode 57 and the gate electrode 56 so that the source electrode 57 and the gate electrode 56 are not in contact with each other. A drain electrode 59 is formed so as to be in ohmic contact with the substrate region 51. As described above, the MOSFET shown in FIG. 34 is a so-called planar type in which the gate electrode 56 is formed on the plane of the semiconductor substrate.

  In the description of the third embodiment, the case where the free wheel diode 100 shown in FIG. 33 and the switching element 600 shown in FIG. 34 are used in parallel with the semiconductor snubber circuit 200 shown in FIG. explain. At this time, in order to effectively exhibit the snubber function, it is preferable to set the capacitor by the dielectric region 12 and the resistance by the substrate region 11 in consideration of the capacitor capacitance in the cutoff state of the freewheeling diode 100 and the switching element 600. . Similar to the first and second embodiments, in the third embodiment, for example, the thickness of the capacitor 210 is set to 1 μm so as to be higher than the breakdown voltage of the freewheeling diode 100 and the switching element 600, for example. Assume that the capacitance of the capacitor 210 is approximately the same as the sum of the depletion capacitances formed when the free-wheeling diode 100 and the switching element 600 are in the cut-off state.

The operation of the third embodiment will be described below in correspondence with the operation of the inverter shown in FIG. 31 as in the second embodiment.
In a state where the switching element G in FIG. 31 is turned on and a current flows through the switching element G, the switching element E and the passive element B of the upper arm are in the reverse bias state and are in the cutoff state.

  Since the switching element G in the conductive state is composed of a MOSFET made of a silicon carbide material, it is conductive with a lower on-resistance than the IGBT described in the second embodiment. This is because the band gap of the silicon carbide material is about three times larger than that of the silicon material and the maximum insulating electric field is about one digit larger, so that the thickness of the drift region 52 can be reduced and the impurity concentration can be increased. For this reason, the resistance of the drift region 52 can be lowered even when the bipolar operation like the IGBT is not performed.

  In addition, in the passive element F connected in parallel with the switching element G in the conductive state, the free wheeling diode 100 and the semiconductor snubber circuit 200 maintain the cutoff state. The reason why the heterojunction diode which is the freewheeling diode 100 is maintained in the cut-off state is that a reverse bias voltage is applied to both ends of the freewheeling diode 100 although it is as low as the ON voltage of the switching element G. In addition, the semiconductor snubber circuit 200 is maintained in the cut-off state because the dielectric region 12 functioning as the capacitor 210 operates only when the voltage changes, so that a voltage on the order of the ON voltage of the switching element G is applied in a steady state. It is because it will be in the interruption | blocking state in a state.

  On the other hand, the switching element E and the passive element B of the upper arm are also maintained in the cut-off state because a reverse bias voltage of about the power supply voltage is applied. The MOSFET which is the switching element 600 maintains the cutoff state because a reverse bias voltage is applied between the source terminal 302 and the drain terminal 402, so that the depletion layer extending from the PN junction with the well region 53 is drift region 52. This is because it is formed inside and the cut-off state is maintained. The reason why the heterojunction diode which is the freewheeling diode 100 is maintained in the cut-off state is that a depletion extending from the heterojunction with the hetero semiconductor region 43 is applied because a reverse bias voltage is applied between the front electrode 44 and the back electrode 45. This is because a layer is formed in the drift region 42. Also in the semiconductor snubber circuit 200, the dielectric region 12 functioning as the capacitor 210 is charged by a high voltage, and maintains the cutoff state.

  As described above, when the switching element G of the lower arm is in the conductive state, the passive elements of the upper and lower arms operate in the same manner as the conventional technique configured in the second embodiment.

  Next, the case where the switching element G of the lower arm is turned off and shifts to the cutoff state will be described. In the motor inverter circuit (L load circuit) as shown in FIG. 31, when the switching element G is turned off, the phase of voltage increase and current interruption is shifted. For this reason, the voltage rise of the switching element G first occurs in a state where the current during conduction is substantially maintained.

  For the passive element F connected in parallel to the switching element G, a transient current flows through each of the freewheeling diode 100 and the semiconductor snubber circuit 200. This is because, as the voltage of the switching element G increases, the reverse bias voltage as low as the ON voltage changes from the reverse bias voltage as high as the power supply voltage, so that a transient current corresponding to the speed of the voltage change flows. Because. That is, in the freewheeling diode 100, when a depletion layer spreads from the hetero semiconductor region 43 side in the drift region 42 as the voltage increases, electrons flow as a transient current to the back electrode 45 side. The semiconductor snubber circuit 200 is charged with the dielectric region 12 serving as the capacitance of the capacitor 210 in accordance with the applied voltage, so that a transient current flows.

  As described above, the charging action of the capacitor capacitance in the dielectric region 12 of the semiconductor snubber circuit 200 alleviates the transient voltage rise generated between the collector and the emitter of the switching element G, and the surge voltage due to the parasitic inductance included in the circuit. Is suppressed. In other words, by connecting the freewheeling diode 100 and the semiconductor snubber circuit 200 in parallel with the switching element 600, even when the switching element 600 itself is turned off, the surge voltage that causes element breakdown or malfunction to other peripheral circuits is reduced. can do.

  In the MOSFET made of silicon carbide cited as an example in the third embodiment, the current is sharply interrupted after the voltage rises. This is different from the IGBT described in the second embodiment, because the MOSFET performs a unipolar operation when conducting, and the electron current discharged from the depletion layer due to the voltage rise depends on the speed of the depletion layer extension. This is because it is blocked. That is, since the switching element 600 is a MOSFET made of silicon carbide, a low on-resistance can be realized when conducting, but the switching element 600 itself is easily turned off due to the speed of the cutoff performance of the switching element. . Furthermore, since the on-resistance is small, there arises a problem that the vibration phenomenon is not easily attenuated. However, in the third embodiment, since the semiconductor snubber circuit 200 is disposed in parallel with the switching element 600, the vibration phenomenon can be effectively reduced.

  That is, when the current of the switching element 600 is interrupted, the current and voltage start to vibrate due to resonance with the parasitic inductance in the circuit, but the capacitor 210 including the dielectric region 12 of the semiconductor snubber circuit 200 has an equivalent voltage. Is applied and a corresponding transient current begins to flow. Then, the inclination of current vibration (dI / dt) is relaxed by the capacitor 210 and the resistor 220, and energy generated in the parasitic inductance Ls due to the resistance component of the substrate region 11 is consumed, so that the vibration phenomenon can be quickly converged. Therefore, as in the third embodiment, the vibration phenomenon can be suppressed even when the switching element 600 is a unipolar type and has a high-speed cutoff performance.

  Further, even if the switching element 600 is made of a wide gap semiconductor having a smaller conduction loss and the vibration phenomenon is difficult to attenuate, the vibration phenomenon can be easily attenuated without deteriorating the conduction loss. As described above, in the third embodiment, the switching element 600 also has a configuration in which conduction loss and transient loss can be achieved at a high level, that is, the switching element 600 is a unipolar switching element capable of high-speed operation. In the case where the semiconductor device is a wide band gap semiconductor that can realize a low on-resistance, a higher effect can be obtained.

  After the current of the switching element 600 is cut off, the switching element G and the passive element F in the lower arm are in a steady off state and maintain the cut-off state.

  On the other hand, the passive element B connected in parallel with the switching element E of the upper arm enters a forward bias state and shifts to a conductive state in conjunction with the turn-off operation of the switching element G of the lower arm. That is, the depletion layer extending in the drift region 42 of the free-wheeling diode 100 shown in FIG. 33 recedes, and the heterojunction formed between the hetero semiconductor region 43 and the drift region 42 has a hetero barrier height. A corresponding forward bias voltage is applied, and the freewheeling diode 100 becomes conductive.

  In the heterojunction diode, although a forward current flows with a voltage drop determined by the sum of the built-in potentials spreading from the heterojunction to the drift region 42 side and the hetero semiconductor region 43 side, there is a heterobarrier against holes on the valence band side. Since it is large, the current is almost constituted only by the electron current supplied from the back electrode 45 side in the drift region 42, and performs a unipolar operation. At this time, in the Schottky barrier diode described in the second embodiment, since the Schottky barrier height is uniquely determined by the work function difference inherent to the Schottky metal of the surface electrode 13, in order to obtain a predetermined breakdown voltage, The impurity concentration and thickness of the drift region 42 are limited. On the other hand, in the third embodiment, since the height of the hetero barrier of the heterojunction diode can be changed by controlling the impurity concentration of the hetero semiconductor region 43, the resistance of the drift region 42 is made lower. can do. That is, loss during conduction can be further reduced.

  Further, in the semiconductor snubber circuit 200 shown in FIG. 5, when the freewheeling diode 100 shifts from the reverse bias state to the forward bias state, the charge charged in the dielectric region 12 is discharged as a transient current. In the third embodiment, the capacitance of the dielectric region 12 as the capacitor 210 is as small as the depletion capacitance formed in the freewheeling diode 100 and the switching element 600. For this reason, although a transient current flows due to discharge, the transient current has a magnitude that hardly affects the operation as compared with the forward bias current flowing in the free-wheeling diode 100 connected in parallel. The semiconductor snubber circuit 200 shifts to a steady state after the transient current flows, and the current is cut off.

  As for the switching element E connected in parallel to the passive element B, the gate signal is controlled to be maintained in the OFF state, although the drain-source voltage shifts from the reverse bias voltage state to the forward bias state. Although the PN junction between the well region 53 and the drift region 52 is in a forward bias state, the off state is maintained because the built-in potential is as large as 2 to 3V. However, since the voltage state between the drain and the source changes, a transient current due to the discharge accompanying the capacitance change of the depletion layer generated in the drift region 52 in the switching element 600 flows. However, like the semiconductor snubber circuit 200, this transient current has a magnitude that hardly affects the operation compared to the forward bias current flowing through the free-wheeling diode 100 connected in parallel. The semiconductor snubber circuit 200 and the switching element 600 in the upper arm shift to a steady state after a transient current flows, the current is cut off, and only the freewheeling diode 100 becomes conductive.

  Next, an operation in which the switching element G of the lower arm is turned on and the switching element G is turned on again will be described. As described above, in the motor inverter circuit (L load circuit) shown in FIG. 31, when the switching element G is turned on, a current starts to flow through the switching element G with a relatively high voltage applied. .

  As the current flows through the switching element G and the drain-source voltage decreases, the voltage applied to the passive element F changes from a high reverse bias voltage such as a power supply voltage to a low reverse bias voltage such as an on voltage. To change. A transient current corresponding to the speed of the voltage change flows through the free wheel diode 100 and the semiconductor snubber circuit 200 of the passive element F. In other words, in the freewheeling diode 100, the depletion layer that has spread in the drift region 42 gradually decreases toward the hetero semiconductor region 43 as the voltage decreases, and electrons flow from the back electrode 45 side into the drift region 42 as a transient current. Flowing. In the semiconductor snubber circuit 200, the dielectric region 12 serving as the capacitor 210 is discharged as the applied voltage decreases, and a transient current flows. This transient current has a magnitude that hardly affects the operation as compared with the turn-on current flowing through the switching elements 600 connected in parallel. The semiconductor snubber circuit 200 and the freewheeling diode 100 in the lower arm shift to a steady state after the transient current flows, the current is cut off, and only the switching element 600 is turned on.

  On the other hand, the passive element B of the upper arm enters a reverse bias state in conjunction with the turn-on operation of the switching element G of the lower arm, and shifts to the cutoff state. That is, in the free-wheeling diode 100 that is a heterojunction diode, the electron current supplied from the back electrode 45 side into the drift region 42 decreases as the forward bias voltage decreases. When the forward bias voltage becomes equal to or lower than the voltage corresponding to the hetero barrier height of the heterojunction, and when the reverse bias voltage is further applied to the heterojunction, the depletion layer extends from the heterojunction with the hetero semiconductor region 43. Is generated in the drift region 42, and the freewheeling diode 100 shifts to a cut-off state.

  The heterojunction diode used in the third embodiment performs a unipolar operation similarly to the Schottky barrier diode described in the first embodiment and the second embodiment. For this reason, the reverse recovery current is much smaller than that of a PN junction diode formed of general silicon. That is, reverse recovery loss can be greatly reduced.

  Furthermore, in the third embodiment, by combining a heterojunction diode capable of reducing conduction loss as compared with a Schottky barrier diode and the semiconductor snubber circuit 200, both conduction loss and transient loss can be achieved at a high level. . That is, in the third embodiment, when the freewheeling diode 100 performs the reverse recovery operation, the reverse bias voltage is applied in the drift region 42 and the reverse recovery current composed of excess carriers starts to flow almost simultaneously. The equivalent reverse bias voltage is also applied to the capacitor composed of the dielectric region 12 in the switching element 600 and the semiconductor snubber circuit 200, and a corresponding transient current starts to flow in the switching element 600 and the semiconductor snubber circuit 200. The size of the capacitor 210 is set so that the transient current due to the discharge is substantially equal to the transient current flowing through the freewheeling diode 100 and the switching element 600. For this reason, the reverse recovery current cutoff speed (dI / dt) can be relaxed without substantially changing the switching speed of the switching element G of the lower arm. Furthermore, since the current flowing through the semiconductor snubber circuit 200 is consumed by the resistance component of the substrate region 11, the energy generated by the parasitic inductance Ls can be absorbed and the vibration phenomenon can be quickly converged. That is, even if the freewheeling diode 100 is made a heterojunction diode and the conduction loss is reduced, the oscillation phenomenon caused by the unipolar operation is caused to occur in the semiconductor snubber circuit as in the case where the Schottky barrier diode described in the second embodiment is used. 200.

  As described above, by using a heterojunction diode capable of realizing a low on-resistance as the freewheeling diode 100, a higher effect can be obtained.

  Further, since the switching element 600 is also a unipolar type, the snubber function is effective in the entire current range and the entire temperature range when the switching element 600 is turned off in addition to the reverse recovery operation of the freewheeling diode 100. work.

  The same effect can be obtained by using other unipolar elements as shown in FIG. 35 and FIG.

In the switching element shown in FIG. 35, for example, an N ⁻ type drift region 62 is formed on an N ⁺ type substrate region 61 of a silicon carbide polytype of 4H type, and the drift region 62 is joined to the substrate region 61. In this structure, a hetero semiconductor region 63 made of, for example, N-type polycrystalline silicon is formed on the main surface facing the surface. That is, the junction between the drift region 62 and the hetero semiconductor region 63 is a hetero junction formed of silicon carbide and polycrystalline silicon, which are materials having different band gaps, and an energy barrier exists at the junction interface. A gate insulating film 64 made of, for example, a silicon oxide film is formed on the hetero semiconductor region 63 and the drift region 62. A gate electrode 65 is formed on the gate insulating film 64, and a source electrode 66 in contact with the hetero semiconductor region 63 is formed above the gate electrode 65. An interlayer insulating film 67 made of, for example, a silicon oxide film is formed between the gate electrode 65 and the source electrode 66. A drain electrode 68 is formed in contact with the substrate region 61.

  An operation of switching element 600 shown in FIG. 35 will be described. The switching element 600 shown in FIG. 35 is also used by grounding the source electrode 66 and applying a positive potential to the drain electrode 68, like the MOSFET.

  When the gate electrode 65 is set to the ground potential or the negative potential, the switching element 600 maintains the cutoff state. This is because an energy barrier against conduction electrons is formed at the heterojunction interface between the hetero semiconductor region 63 and the drift region 62.

  When a positive potential is applied to the gate electrode 65 in order to shift from the cutoff state to the conduction state, an electron accumulation layer is formed on the surface layer portions of the hetero semiconductor region 63 and the drift region 62 to which the gate electric field extends through the gate insulating film 64. It is formed. For this reason, the surface layer portions of the hetero semiconductor region 63 and the drift region 62 have potentials where free electrons can exist, the energy barrier extending toward the drift region 62 becomes steep, and the energy barrier thickness is reduced. As a result, an electronic current flows through the switching element 600. At this time, the length of the so-called channel portion for controlling the conduction / cutoff of the switching element 600 shown in FIG. 35 is about the thickness of the energy barrier formed by the hetero barrier, and the channel length necessary for holding the withstand voltage in the MOSFET. Since it is smaller than that, it conducts with lower resistance. For this reason, the semiconductor snubber circuit 200 can achieve both a conduction loss and a transient loss at a higher level.

  In the switching element 600 shown in FIG. 35, when the gate electrode 65 is grounded again to shift from the conductive state to the cut-off state, accumulation of conduction electrons formed at the heterojunction interface between the hetero semiconductor region 63 and the drift region 62 is accumulated. The state is released and tunneling in the energy barrier stops. When the flow of conduction electrons from the hetero semiconductor region 63 to the drift region 62 stops and the conduction electrons in the drift region 62 flow to the substrate region 61 and are depleted, a depletion layer spreads from the hetero junction to the drift region 62 side. The switching element is cut off.

In the switching element 600 shown in FIG. 35, reverse conduction (reflux operation) in which the source electrode 66 is grounded and a negative potential is applied to the drain electrode 67 is also possible. For example, when the source electrode 66 and the gate electrode 65 are grounded and a predetermined positive potential is applied to the drain electrode 67, the energy barrier to the conduction electrons disappears, and conduction electrons flow from the drift region 62 side to the hetero semiconductor region 63 side, and vice versa. It becomes a conductive state. At this time, since there is no injection of holes and conduction is made only with conduction electrons, loss due to reverse recovery current when shifting from the reverse conduction state to the cutoff state is small. It is also possible to use the gate electrode 65 as a control electrode without grounding.
The configuration of the switching element 600 shown in FIG. 35 can also be applied as a unipolar freewheeling diode, and thus, for example, the freewheeling diode 100 can be realized with the same configuration as that shown in FIG. That is, when the switching element shown in FIG. 35 is used as the switching element 600, in addition to forming the switching element 600 and the free wheeling diode 100 as separate chips, the free wheeling diode 100 and the switching element 600 are integrated into a single chip, and the semiconductor package. Can be miniaturized. Thereby, the parasitic inductance generated in the wiring or the like is reduced, and the vibration phenomenon can be further reduced. Shortening the wiring length also has an effect of reducing radiation noise generated from the wiring by the oscillating current. Further, the manufacturing cost is reduced by reducing the chip size, and the sum of the capacitor capacities of the freewheeling diode 100 and the switching element 600 is reduced, so that the capacitance of the capacitor 210 necessary for the semiconductor snubber circuit 200 can also be reduced. it can. That is, the small semiconductor snubber circuit 200 can suppress the vibration phenomenon at low cost.

  As described above, in FIG. 35, the example in which polycrystalline silicon is used as the material used for the hetero semiconductor region 63 has been described. However, other silicon materials such as single crystal silicon and amorphous silicon can be used as long as the material forms a heterojunction with silicon carbide. Or any other semiconductor material such as germanium or silicon germanium, or other polytypes of silicon carbide such as 6H or 3C. In addition, as an example, the description has been given using N-type silicon carbide as the drift region 62 and P-type polycrystalline silicon as the hetero semiconductor region 63. However, the drift region 62 and the hetero semiconductor region 63 are replaced with N-type silicon carbide. Any combination may be employed, such as P-type polycrystalline silicon, P-type silicon carbide and P-type polycrystalline silicon, or P-type silicon carbide and N-type polycrystalline silicon.

Next, a junction type FET called a junction type FET (JFET) shown in FIG. 36 will be described. Switching element shown in FIG. 36, for example polytype of silicon carbide N on the substrate region 71 is a N ⁺ -type 4H types ^- type drift region 72 is formed, P-type gate in the drift region 72 In this structure, a region 73 and an N ⁺ -type source region 74 are formed. An interlayer insulating film 77 is formed on the drift region 72, the gate region 73 and the source region 74. In the opening of the interlayer insulating film 77, the gate region 73 is connected to the gate electrode 75, and the source region 74 is connected to the source electrode 76. The substrate region 71 is in contact with the drain electrode 78.

  Since the JFET shown in FIG. 36 operates in a unipolar manner like the MOSFET, it is possible to obtain the same effect as that obtained by the MOSFET. Furthermore, since a gate insulating film that is essential for a MOSFET is not necessary for a JFET, operation at a high temperature exceeding, for example, 200 ° C. is relatively easy, which is advantageous in terms of ensuring reliability. For this reason, by using JFET for the switching element 600, the advantage that the vibration phenomenon can be suppressed irrespective of the operating temperature range, which is the effect of the present invention, can be utilized as a strength. In high temperature applications, for example, as shown in FIGS. 19 and 20, the configuration using a depletion capacitor that does not use a silicon oxide film as the capacitor 210 is more effective while ensuring the reliability of the semiconductor snubber circuit 200. It can be demonstrated.

  As described above, the case where the switching element other than the MOSFET is used as the switching element 600 has been described. However, the free-wheeling diode 100 has been described so far as long as it is a diode that operates in a unipolar operation or a unipolar operation. The same effect as that of the present invention can be obtained.

  For example, even in the structure of a PN junction diode as shown in FIG. 37, when conducting, by measures such as heavy metal diffusion using gold or platinum, electron beam irradiation using electron beams, ion irradiation using protons, etc. By controlling the lifetime of minority carriers, which are the main components of excess carriers injected from the P-type region, an operation equivalent to the unipolar operation is performed. In this case, the effect of the present invention can be obtained even if the freewheeling diode 100 has a PN junction diode structure.

For example, the case where the PN junction diode shown in FIG. 37 is configured by a soft recovery diode will be described. The freewheeling diode 100 shown in FIG. 37 is made of a substrate material in which an N ⁻ type drift region 82 is formed on an N ⁺ type substrate region 81 made of, for example, silicon. The substrate region 81 has, for example, a resistivity of several mΩcm to several tens of mΩcm and a thickness of about several tens of μm to several hundreds of μm. The drift region 82 has, for example, an N-type impurity density of 10 ¹³ cm ⁻³ to 10 ¹⁷ cm ⁻³ and a thickness of several μm to several hundred μm. Here, it is assumed that the drift region 82 has an impurity density of 10 ¹⁴ cm ⁻³ , a thickness of 50 μm, and a breakdown voltage of 600 V class. FIG. 37 shows a case where the semiconductor substrate is a substrate composed of two layers of a substrate region 81 and a drift region 82, but the resistivity is a substrate formed only of the substrate region 81 not according to the above example. It may be used, or a multilayer substrate may be used. Moreover, although the case where a proof pressure is a 600V class is demonstrated as an example, a proof pressure class is not limited to this.

  As shown in FIG. 37, a P-type opposite conductivity type region 83 and a surface electrode 84 are laminated on the main surface of the drift region 82 facing the bonding surface with the substrate region 81, and the back surface electrode 85 is in contact with the substrate region 81. Is formed. Note that the free wheeling diode shown in FIG. 37 is formed of only a PN junction, but for example, a part thereof may be configured to function as a Schottky diode, or may include other configurations.

  One method for allowing the PN junction diode shown in FIG. 37 to function as a soft recovery diode is to control the lifetime of minority carriers injected into the drift region 82 during conduction. For example, the lifetime of minority carriers in the drift region 82 is controlled to be different between the region near the opposite conductivity type region 83 and the region near the substrate region 81 by irradiating the drift region 82 with ions. As a result, the transient current due to the minority carriers flowing during reverse recovery is reduced, while the reduction time of the minority carriers staying on the substrate region 81 side is alleviated, so that the vibration phenomenon does not occur in the reverse recovery operation at the time of large current. Can be.

  However, in a PN junction diode in which the minority carrier lifetime is controlled, the minority carrier lifetime is shortened regardless of the magnitude of the current. For this reason, when the current is small, minority carriers disappear instantaneously at the time of reverse recovery, and the PN junction diode operates almost the same as the unipolar operation. In this case, the transient current flowing in the diode shown in FIG. 37 is a current due to the movement of majority carriers when the depletion layer spreads as in the unipolar diode described with reference to FIG. For this reason, a vibration phenomenon occurs when the semiconductor snubber circuit 200 is not present. However, by connecting the semiconductor snubber circuit 200 in parallel with the freewheeling diode 100, the vibration phenomenon at the time of low current can be reduced.

  Therefore, the combination of the freewheeling diode 100, which is a soft recovery diode, and the semiconductor snubber circuit 200 can alleviate the vibration phenomenon at both a large current and a small current. Here, the effect of the third embodiment has been described by taking the soft recovery diode as an example. However, even when a fast recovery diode whose reverse recovery characteristic is not softened at the time of a large current is used, the operation is equivalent to the unipolar operation. If there is a current region for performing the above, an effect of suppressing at least a vibration phenomenon at a low current can be obtained. In addition, in materials such as PN junction diodes made of silicon carbide that are less likely to recover crystals due to heat treatment than silicon materials, the lifetime of minority carriers, such as when a P-type region is formed by ion implantation, is not sufficient. Even in the originally small diode, as described above, the effect of suppressing the vibration phenomenon can be obtained. In any structure, the effect of the present invention can be obtained when the PN junction diode is operated for reverse recovery under the condition that at least current does not flow and minority carriers are not injected.

  As described above, if the freewheeling diode 100 performs at least a part of the operation equivalent to the unipolar operation, the effect of the present invention can be obtained that the vibration phenomenon is reduced during the reverse recovery operation.

  Note that the freewheeling diode 100 shown in FIG. 37 exhibits the same effect even when the switching element 600 described in the first embodiment is not connected in parallel to the freewheeling diode 100. For this reason, only the freewheeling diode 100 and the semiconductor snubber circuit 200 may be connected in parallel.

  Furthermore, in the third embodiment, the case where the combination of the elements of the free wheel diode 100 and the switching element 600 is different from the combination described in the second embodiment has been described. You may combine using any element demonstrated by the 1st-3rd embodiment. That is, for example, a combination using the Schottky barrier diode described in the second embodiment for the freewheeling diode 100 and the MOSFET described in the third embodiment for the switching element 600 may be used. Further, the reflux diode 100 and the switching element 600 may be formed on the same chip.

  As described above, also in the third embodiment, attention is paid to the fact that the transient current flowing through the freewheeling diode 100 and the switching element 600 is only the carriers generated when the depletion layer is formed at most in the drift region. The point that the snubber circuit is formed by the semiconductor snubber circuit 200 is different from the prior art. Others are substantially the same as those in the first and second embodiments, and redundant description is omitted.

  Further, as described with reference to FIGS. 26 and 27 in the first embodiment, the capacitance C of the capacitor used in the snubber circuit and the capacitor capacitance component of the free-wheeling diode and the switching element in the cut-off state When the sum is C0, the damping effect of the vibration phenomenon becomes remarkable when the capacity ratio C / C0 is around 0.1, and the convergence time ratio value of the vibration phenomenon tends to be saturated when the capacity ratio C / C0 exceeds 10. Become. Further, since a loss E occurs due to a transient current proportional to the capacitance of the capacitor formed in the snubber circuit during the transient operation, the capacitance C of the capacitor is preferably as small as possible.

  Therefore, the capacitance of the capacitor 210 of the semiconductor snubber circuit 200 used in the third embodiment is 1/10 times or more and 10 times the total capacitance of the capacitor components in the cutoff state of the free-wheeling diode 100 and the switching element 600. Select from the following ranges. As a result, the vibration phenomenon can be reduced more significantly while suppressing an increase in loss. This effect can be obtained in any configuration example described in the third embodiment.

(Fourth embodiment)
The fourth embodiment exemplifies a case where the free wheeling diode 100 and the semiconductor snubber circuit 200 are formed on the same chip.

  FIG. 38 is an example of a semiconductor chip mounting diagram corresponding to FIG. FIG. 39 is an example of a cross-sectional structure diagram of the semiconductor chip used in the mounting diagram of FIG. 38, and shows a cross-sectional structure of the semiconductor chip in which the free-wheeling diode 100 and the semiconductor snubber circuit 200 are formed. Below, the description of the same part as 1st Embodiment is abbreviate | omitted, and a different characteristic is demonstrated in detail.

  As shown in FIG. 38, a chip (a snubber built-in freewheeling diode chip, indicated by reference numeral 800 in the figure) on which a freewheel diode 100 including a freewheeling diode 100 and a semiconductor snubber circuit 200 is arranged is a metal on an insulating substrate 500. It is disposed on the membrane 410. The cathode terminal of the snubber built-in reflux diode chip is in contact with the metal film 410 on the cathode side through a bonding material such as solder or brazing material. The anode terminal of the snubber built-in reflux diode chip is connected to the metal film 310 on the anode side through a metal wiring 320 such as an aluminum wire or an aluminum ribbon. Although not shown in FIG. 38, a plurality of surface electrodes 13 of the semiconductor snubber circuit 200 are formed, and at least a part of the plurality of surface electrodes 13 is connected to the metal film 310 via the metal wiring 320.

  FIG. 39 shows a cross-sectional structure of a snubber built-in reflux diode chip. As shown in FIG. 39, the snubber built-in freewheeling diode 800 includes a portion of the freewheeling diode 100 formed on the right side of the right broken line in FIG. 39 and a semiconductor snubber circuit 200 formed on the left side of the left broken line in FIG. It is composed of parts.

The part of the free-wheeling diode 100 is made of, for example, a substrate material in which an N ⁻ type drift region 2 is formed on a substrate region 1 of a silicon carbide polytype 4H type N ⁺ type. The substrate region 1 has a resistivity of, for example, several mΩcm to several tens of mΩcm and a thickness of about several tens to several hundreds of μm. The drift region 2 has, for example, an N-type impurity density of 10 ¹⁵ cm ⁻³ to 10 ¹⁸ cm ⁻³ and a thickness of several μm to several tens of μm. In the configuration example shown in FIG. 39, the drift region 2 having an impurity density of 10 ¹⁶ cm ⁻³ , a thickness of 5 μm, and a breakdown voltage of 600 V class can be used. However, the breakdown voltage class is not limited to the 600V class. In the fourth embodiment, the case where the semiconductor substrate is a substrate composed of two layers of the substrate region 1 and the drift region 2 will be described, but only the substrate region 1 whose magnitude of resistivity does not depend on the above example. The substrate formed in (1) may be used, or a multilayer substrate may be used.

  In the part of the free-wheeling diode 100 formed on the right side of the right broken line in FIG. 39, the surface electrode 3 is formed on the main surface of the drift region 2 facing the junction surface with the substrate region 1, and is opposed to the surface electrode 3. In addition, a back electrode 4 is formed in contact with the substrate region 1. The surface electrode 3 is made of a single-layer or multi-layer metal material including at least a metal material that forms a Schottky barrier with the drift region 2. The surface electrode 3 is connected to an external electrode as an anode terminal 300. On the other hand, the back electrode 4 is made of an electrode material that is in ohmic contact with the substrate region 1. The back electrode 4 is connected to an external electrode as a cathode terminal 400. As described above, the free-wheeling diode 100 shown in FIG. 39 functions as a diode having the front electrode 3 as an anode terminal and the back electrode 4 as a cathode terminal.

  Further, as shown in FIG. 39, a field insulating film 5 made of, for example, a silicon oxide film is formed between the drift region 2 and the surface electrode 3 except for the region where the freewheeling diode 100 is formed. The field insulating film 5 is a field insulating film that is generally used for relaxing the electric field concentration at, for example, a Schottky junction on the outer periphery of the chip when the freewheeling diode 100 is manufactured as a semiconductor chip. In FIG. 39, as an example of the end shape of the field insulating film 5, a case where the portion in contact with the surface electrode 3 is a right angle is shown, but the end portion may be an acute angle shape.

  Further, as a configuration of the outer peripheral end where the field insulating film 5 is formed, for example, as shown in FIG. 40, a P-type electric field is formed in the drift region 2 immediately below the portion where the surface electrode 3 and the field insulating film 5 are in contact. Relaxation region 7 may be formed. Furthermore, in addition to the configuration shown in FIG. 40, one or a plurality of guard rings may be formed so as to surround the outer periphery of the electric field relaxation region 7.

  Next, the semiconductor snubber circuit 200 formed on the left side of the left broken line in FIG. 39 will be described. A plurality of resistance regions 6 made of, for example, polycrystalline silicon are formed on a predetermined region of the field insulating film 5 used for electric field relaxation at the outer peripheral end of the free-wheeling diode 100. Then, the surface electrode 13 is formed on each resistance region 6. At least a part of the plurality of surface electrodes 13 is connected to an anode terminal 300 to which the anode terminal of the reflux diode 100 is connected. The number of surface electrodes 13 connected to the anode terminal 300 is determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon.

  In the semiconductor snubber circuit 200 according to the fourth embodiment, the resistance region 6 functions as the resistor 220, and the field insulating film 5 functions as the capacitor 210. The impurity concentration and thickness of the resistance region 6 can be set according to the required resistance value. Also, the thickness and area of the field insulating film 5 can be set according to the required breakdown voltage and the required capacitance of the capacitor 210.

  With respect to the breakdown voltage, not only as a function of the semiconductor snubber circuit 200 but also from a Schottky barrier diode formed by the freewheeling diode 100 in order to satisfy the function of electric field relaxation of the freewheeling diode 100 to prevent the field insulating film 5 from being broken. It is preferable that the pressure resistance is high. The capacitance of the capacitor 210 can be selected in the range of about 1/100 to about 100 times the depletion capacity charged when the free-wheeling diode 100 is cut off (when a high voltage is applied). However, when a sufficient snubber function is exhibited and an increase in loss is suppressed as much as possible, and a necessary chip area is taken into consideration, a range of about 1/10 to about 10 times is preferable as shown in the calculation results described later. .

  In the fourth embodiment, for example, the thickness is 1 μm so that the breakdown voltage of the free-wheeling diode 100 is higher than that of the Schottky barrier diode, and the capacitance of the capacitor 210 is the depletion capacity formed when the free-wheeling diode 100 is cut off. A case where the same level is set will be described. The field insulating film 5 may be any material other than a silicon oxide film as long as it is a dielectric material having a predetermined withstand voltage and functioning as an electric field relaxation function and a capacitor 210. It is even better if the value of the product with the dielectric constant is larger than that of the silicon oxide film. When such a material is used for the field insulating film 5, it is possible to obtain a necessary capacitance with a small area while maintaining the dielectric strength of the dielectric region 12.

For example, as described in the first embodiment, when the thickness is 1 μm, Si ₃ N ₄ instead of the silicon oxide film is used instead of the silicon oxide film in which the capacitance per cm ² is about 3.4 nF. When the film is used, an equivalent breakdown voltage can be secured with a thickness of 1 μm, and the capacitance per cm ² when the Si ₃ N ₄ film is used is about 6.6 nF. In other words, when a Si ₃ N ₄ film is used for the field insulating film 5, the electrostatic capacity is increased about twice, and a larger electrostatic capacity can be obtained while maintaining the withstand voltage of the dielectric region. Therefore, the area efficiency can be improved and the wafer cost can be reduced.

  Further, as described above, the resistance size of the resistance region is preferably set so as to satisfy a general design formula C = 1 / (2πfR) that effectively exhibits a snubber function.

  As described above, even when the free-wheeling diode 100 and the semiconductor snubber circuit 200 are formed on the same chip, the operations and effects described in the first embodiment can be obtained.

  In the fourth embodiment shown in FIG. 39, the freewheeling diode 100 and the semiconductor snubber circuit 200 share the substrate region 1 and the drift region 2 as the supporting base, and share the back electrode 4 as the electrode material. The same material can be used for the surface electrode 3 and the surface electrode 13. Further, the field insulating film 5 that functions as an electrolytic relaxation function of the freewheeling diode 100 functions as a capacitor 210. Since these shared portions can be formed by the same process, the manufacturing process can be simplified. Further, by mounting the free wheel diode 100 and the semiconductor snubber circuit 200 on one chip, the mounting area (site area) can be reduced, so that the semiconductor package can be reduced in size.

  Furthermore, when the fourth embodiment is used for an L load circuit, a new effect is achieved by integrating the freewheeling diode 100 and the semiconductor snubber circuit 200 into one chip. As already described, the semiconductor snubber circuit 200 does not operate when the free-wheeling diode 100 is cut off and is conducting, and operates only during a transient state. The resistor 220 generates heat to consume the transient current. On the other hand, the freewheeling diode 100 does not generate much heat due to the influence of the phase shift between the current and voltage during the turn-on and turn-off transient operations. Therefore, the freewheeling diode 100 generates the most heat during steady conduction. That is, the timing of generating heat during a series of operations differs between the free wheeling diode 100 and the semiconductor snubber circuit 200. For example, when the portion of the freewheeling diode 100 is generating heat when conducting, the portion of the semiconductor snubber circuit 200 is in a cut-off state and does not generate heat. For this reason, when it is made into one chip, the temperature rise of the whole chip can be suppressed as compared with the case of another chip. In other words, the conduction performance of the free-wheeling diode 100 can be improved by using one chip.

  As described above, in the fourth embodiment, both the effect of suppressing the vibration phenomenon and improving the transient performance and the conduction performance can be improved, and at the same time, miniaturization and cost reduction can be realized.

  In FIGS. 39 and 40, the case where the freewheeling diode 100 is a Schottky barrier diode has been described. However, for example, the heterojunction diode described in the third embodiment can be easily realized. FIG. 41 shows a cross-sectional view corresponding to FIG. 39 when the freewheeling diode 100 is a heterojunction diode.

  As shown in FIG. 41, a field insulating film 46 is formed in addition to a heterojunction diode composed of a substrate region 41, a drift region 42, a hetero semiconductor region 43, a front surface electrode 44, and a back surface electrode 45. The field insulating film 46 is formed between the drift region 42 and the hetero semiconductor region 43 except for the region where the freewheeling diode 100 is formed. A plurality of resistance regions 47 made of, for example, polycrystalline silicon are formed on a predetermined region of the field insulating film 46. Then, the surface electrode 13 is formed on the resistance region 47, and a part of the plurality of surface electrodes 13 is connected to the anode terminal 300. As shown in FIG. 40, a P-type electric field relaxation region may be formed, or a guard ring may be formed so as to surround the outer periphery of the electric field relaxation region.

  The snubber circuit and the free-wheeling diode described in the fourth embodiment as well as the effect that the free-wheeling diode 100 and the switching element 600 described in the third embodiment can be realized by various elements by the free-wheeling diode 800 with the snubber shown in FIG. It is possible to realize the effect by making the chip into one chip. Furthermore, a feature of the snubber built-in free wheeling diode 800 shown in FIG. 41 is that the resistance region 47 is formed of the same material as the hetero semiconductor region 43 of the free wheeling diode 100. With this configuration, in addition to the effect of using a heterojunction diode as the freewheeling diode 100, the manufacturing process can be further simplified and realized at low cost.

  In addition, the freewheeling diode 100 and the semiconductor snubber circuit 200 can be integrated into one chip with the configuration shown in FIGS.

  The configuration shown in FIG. 42 is different from the configuration shown in FIG. 39 in that the resistor 220 of the semiconductor snubber circuit 200 is configured by the low concentration drift region 8. The configuration shown in FIG. 42 can be easily realized by forming the drift region 2 by introducing impurities and activating the impurities using, for example, a semiconductor material in which the substrate region 1 and the low concentration drift region 8 are stacked. With the configuration shown in FIG. 42, even when the freewheeling diode 100 and the semiconductor snubber circuit 200 are made into one chip, the semiconductor substrate can be used as a resistance component, and the thermal energy generated by the vibration phenomenon passes through the semiconductor substrate. Since the heat is dissipated, the resistance portion can be densified.

  The configuration shown in FIG. 43 is different from the configuration shown in FIG. 39 in that a PN junction diode having an operation equivalent to the unipolar operation shown in FIG. 37 is configured as the freewheeling diode 100 instead of the Schottky barrier diode. Even if the configuration shown in FIG. 43 is adopted, a single chip can be easily realized, and the effect of further suppressing the vibration phenomenon and improving the transient performance and the conduction performance are improved, and at the same time, miniaturization and cost reduction are realized. it can.

  The configuration shown in FIG. 44 is different from the configuration shown in FIG. 43 in that the resistor 220 of the semiconductor snubber circuit 200 is configured by the low concentration drift region 88. The configuration shown in FIG. 44 can be easily realized by forming the drift region 82 by introducing impurities and activating the impurities using, for example, a semiconductor material in which the substrate region 81 and the low concentration drift region 88 are stacked. With the configuration shown in FIG. 44, even when the freewheeling diode 100 and the semiconductor snubber circuit 200 are made into one chip, the semiconductor substrate can be used as a resistance component, and the thermal energy generated by the vibration phenomenon passes through the semiconductor substrate. Since the heat is dissipated, the resistance portion can be densified.

  The configuration shown in FIG. 45 is that a part of the capacitor 210 of the semiconductor snubber circuit 200 is configured by a PN junction formed between the opposite conductivity type region 89 and the low concentration drift region 88. FIG. Different from the configuration shown. The structure shown in FIG. 45 uses, for example, a semiconductor material in which a substrate region 81 and a low-concentration drift region 88 are stacked to form a drift region 82 by impurity introduction and impurity activation, and by impurity introduction and impurity activation. This can be easily realized by simultaneously forming the opposite conductivity type region 83 functioning as the freewheeling diode 100 and the opposite conductivity type region 89 functioning as the semiconductor snubber circuit 200. With the configuration shown in FIG. 45, since the freewheeling diode 100 and the semiconductor snubber circuit 200 can be formed by the same process, the manufacturing process can be simplified and the manufacturing cost can be reduced.

  Also in the configuration shown in FIG. 45, the semiconductor substrate can be used as a resistance component, and heat energy generated by the vibration phenomenon is radiated through the semiconductor substrate, so that the resistance portion can be densified. 45, the capacitor 210 of the semiconductor snubber circuit 200 has a PN junction depletion capacitance formed between the opposite conductivity type region 89 and the low-concentration drift region 88, and a capacitance due to the field insulating film 86. Is a capacitor connected in series, but a configuration having only a PN junction capacitor may be used.

  In the above, a plurality of configurations in which the freewheeling diode 100 and the semiconductor snubber circuit 200 are integrated into one chip have been exemplified. However, in addition to the above examples, the combination of the elements of the freewheeling diode 100 and the semiconductor snubber circuit 200 is changed to 1 Of course, it may be a chip.

  In the fourth embodiment, the case where only the freewheeling diode 100 and the semiconductor snubber circuit 200 corresponding to the first embodiment are connected in parallel is illustrated, but the second embodiment and the third embodiment are exemplified. The effect of the present invention can also be obtained in a circuit in which the switching elements 600 are connected in parallel as shown in FIG. In any case, at least the free-wheeling diode 100 and the semiconductor snubber circuit 200 are integrated into one chip, so that both the effect of suppressing the vibration phenomenon and improving the transient performance and the conduction performance are improved, and at the same time, it is small and low-cost. can do.

  In addition, as described with reference to FIGS. 26 and 27 in the first embodiment, the damping effect of the vibration phenomenon becomes significant when the capacitance ratio C / C0 is around 0.1, and the capacitance ratio C / C0. The value of the convergence time ratio of the vibration phenomenon tends to saturate from around 10 above. In consideration of the generation of the loss E due to the transient current, the capacitance of the capacitor is preferably as small as possible. That is, the capacitor 210 of the semiconductor snubber circuit 200 used in the fourth embodiment is in the range of 1/10 to 10 times the total sum of the capacitances of the capacitor components in the cutoff state of the free-wheeling diode 100 and the switching element 600. By selecting, the vibration phenomenon can be reduced more significantly while suppressing an increase in loss. This effect can be obtained in any of the configuration examples described in the fourth embodiment.

  As described above, in the fourth embodiment, the number and area of the surface electrodes 13 of the semiconductor snubber circuit 200 that is integrated with the free-wheeling diode 100 can be varied, so that the capacitance of the capacitor 210 can be increased during the wiring process. The resistance value of the value and resistor 220 can be set to a desired value. Thereby, the semiconductor snubber circuit 200 applicable to various free-wheeling diodes 100 can be provided. By adopting such a configuration, even when the circuit configuration is changed, the current / voltage oscillation phenomenon can be stably suppressed only by changing the wiring.

(Fifth embodiment)
In the fifth embodiment, the case where the switching element 600 and the semiconductor snubber circuit 200 are formed on the same chip in the circuit of the second embodiment shown in FIG. 28 will be exemplified.

  FIG. 46 is an example of a semiconductor chip mounting diagram corresponding to FIG. FIG. 47 is an example of a cross-sectional structure diagram of the semiconductor chip used in the mounting diagram of FIG. 46, and shows a cross-sectional structure of the switching element 600 and the semiconductor snubber circuit 200. In the following, description of the same parts as in the second embodiment will be omitted, and different features will be described in detail.

  As shown in FIG. 46, a chip on which a snubber built-in switching element 900 including the switching element 600 and the semiconductor snubber circuit 200 is formed (a snubber built-in switching element chip, indicated by reference numeral 900 in the figure) is formed on the insulating substrate 500. It is disposed on the metal film 410. The collector terminal of the snubber built-in switching element chip and the cathode terminal of the reflux diode 100 are in contact with the metal film 410 on the cathode side through a bonding material such as solder or brazing material. The emitter terminal of the snubber built-in switching element chip and the anode terminal of the freewheeling diode 100 are connected to the metal film 310 on the anode side through a metal wiring 350 such as an aluminum wire or an aluminum ribbon. Although not shown in FIG. 46, a plurality of surface electrodes 13 of the semiconductor snubber circuit 200 are formed, and at least a part of the plurality of surface electrodes 13 is connected to the metal film 310 through the metal wiring 350.

  FIG. 47 shows a cross-sectional structure of the snubber built-in switching element chip. As shown in FIG. 47, the snubber built-in switching element 900 includes a portion of the switching element 600 formed on the right side of the right broken line in FIG. 47 and a semiconductor snubber circuit 200 formed on the left side of the left broken line in FIG. It consists of parts.

The part of the switching element 600 shown in FIG. 47 is configured by a general IGBT as an example. For example, the switching element 600 is made of a substrate material in which an N-type buffer region 22 and an N ⁻ -type drift region 23 are stacked on a P ⁺ -type substrate region 21 made of silicon. A P-type well region 24 is formed in a part of the surface layer portion in the drift region 23, and an N ⁺ -type emitter region 25 is formed in a part of the surface layer portion in the well region 24. A gate insulating film 26 made of, for example, a silicon oxide film is disposed on the surface layer portions of the drift region 23, the well region 24, and the emitter region 25, and a gate electrode 27 made of, for example, N-type polycrystalline silicon is formed on the gate insulating film 26. It is arranged. An emitter electrode 28 made of, for example, aluminum is formed in contact with the emitter region 25 and the well region 24 in the opening formed in the gate insulating film 26. A collector electrode 30 is formed in ohmic contact with the substrate region 21. Thus, the IGBT shown in FIG. 47 is a so-called planar type in which the gate electrode 27 is formed on the semiconductor substrate plane.

  Further, as shown in FIG. 47, a field insulating film 31 made of, for example, a silicon oxide film is formed on the drift region 23 and the well region 24 in the outer periphery of the region where the switching element 600 is formed. As already described, the field insulating film 31 is used to alleviate electric field concentration at the PN junction at the outer periphery of the chip. Further, as a configuration of the outer peripheral end portion where the field insulating film 31 is formed, a guard ring may be formed so as to surround the outer periphery of the well region 24.

  Next, the semiconductor snubber circuit 200 formed on the left side of the left broken line in FIG. 47 will be described. Formed, for example, when a gate insulating film 26, an interlayer insulating film (not shown), or the like of the switching element 600 is formed on a predetermined region of the field insulating film 31 used for electric field relaxation at the outer peripheral edge of the switching element 600. A plurality of resistance regions 33 made of polycrystalline silicon are formed through the insulating film 32 to be formed. 47 illustrates the case where the insulating film 32 is formed, but the resistance region 33 may be formed on the field insulating film 31 without the insulating film 32 interposed therebetween. A surface electrode 13 is formed on each of the plurality of resistance regions 33. At least some of the plurality of surface electrodes 13 are connected to the emitter terminal 301 to which the emitter terminal of the switching element 600 is connected. The number of surface electrodes 13 connected to the emitter terminal 301 is determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon.

  In the semiconductor snubber circuit 200 shown in FIG. 47, the resistance region 33 functions as the resistor 220, and the field insulating film 31 and the insulating film 32 function as the capacitor 210. The impurity concentration and thickness of the resistance region 33 can be set according to the magnitude of the resistance value required for the resistor 220. The thickness and area of the field insulating film 31 can also be set according to the breakdown voltage required for the capacitor 210 and the required capacitance. The withstand voltage is set not only as a function of the semiconductor snubber circuit 200 but also higher than the withstand voltage of the switching element 600 in order to prevent the field insulating film 31 functioning as an electric field relaxation of the switching element 600 from being destroyed. preferable.

  The capacitance of the capacitor 210 is about 1/100 of the depletion capacity charged when the freewheeling diode 100 connected in parallel with the semiconductor snubber circuit 200 is cut off (when a high voltage is applied). It can be selected in the range of about 100 times. However, as already described, when the sufficient snubber function is exhibited and the increase in loss is suppressed as much as possible and the necessary chip area is taken into consideration, the capacitance of the capacitor 210 is equal to the depletion capacitance charged in the freewheeling diode 100. A range of about 1/10 to about 10 times is preferable.

  In the semiconductor snubber circuit 200 shown in FIG. 47, the thickness of the capacitor 210 is set to about 1 μm so as to be higher than the withstand voltage of the switching element 600, and the capacitance of the capacitor 210 is formed when the switching element 600 and the free wheeling diode 100 are cut off. It is formed to be approximately the same as the sum of the depletion capacities. The field insulating film 31 may be any material other than a silicon oxide film as long as it has a predetermined breakdown voltage and functions as an electric field relaxation function and a capacitor 210. Moreover, it is preferable to set the magnitude | size of the resistance of the resistance area | region 33 so that the general design formula C = 1 / (2 (pi) fR) which exhibits a snubber function effectively may be satisfy | filled.

  As described above, even when the switching element 600 and the semiconductor snubber circuit 200 are formed on one chip, the operations and effects described in the first embodiment can be realized.

  In the configuration shown in FIG. 47, the switching element 600 and the semiconductor snubber circuit 200 share the substrate region 21, the buffer region 22, and the drift region 23 as the support base, and share the collector electrode 30. The same material can be used for the emitter electrode 28 and the surface electrode 13. The field insulating film 31 that functions as an electric field relaxation function of the switching element 600 also functions as the capacitor 210. Furthermore, a polycrystalline silicon film serving as the gate electrode 27 of the switching element 600 can be formed in the same manner as the resistance region 33 that is the resistor 220. That is, these portions can be formed by the same process, and the manufacturing process can be simplified.

  Further, by mounting the semiconductor snubber circuit 200 and the switching element 600 on one chip, the mounting area (site area) can be reduced, so that the semiconductor package can be reduced in size.

  Further, when the configuration shown in FIG. 47 is applied to the inverter circuit shown in FIG. 31, for example, a new effect can be produced in which the switching element 600 and the semiconductor snubber circuit 200 are integrated into one chip. That is, as described in the second embodiment and the third embodiment, when the freewheeling diode 100 performs a reverse recovery operation, the semiconductor snubber circuit 200 has the freewheeling diode 100 and the switching element to alleviate the oscillation phenomenon. The transient current generated due to the 600 depletion capacity and the capacitor 210 of the semiconductor snubber circuit 200 is consumed, and the resistor 220 generates heat. On the other hand, when the freewheeling diode 100 performs reverse recovery operation, the switching element 600 connected in parallel to the freewheeling diode 100 is not in a conductive state, and therefore hardly generates heat. As described above, when the semiconductor snubber circuit 200 generates heat during reverse recovery, the switching element 600 is in a cut-off state and does not generate heat. For this reason, by making the switching element 600 and the semiconductor snubber circuit 200 into one chip, the temperature rise of the entire chip can be suppressed to be lower than in the case of another chip. That is, by integrating the switching element 600 and the semiconductor snubber circuit 200 into one chip, high integration of the resistance region 33 due to heat generation can be expected.

  As described above, according to the fifth embodiment, both the effect of further suppressing the vibration phenomenon and improving the transient performance and the conduction performance can be improved, and at the same time, the size and cost can be reduced.

  In the configuration example shown in FIG. 47, the case where the switching element 600 is an IGBT has been described. For example, the various switching elements 600 described in the second embodiment and the third embodiment are integrated into one chip with the semiconductor snubber circuit 200. This can be easily realized as in the case where the switching element 600 is an IGBT. An example is shown in FIGS.

FIG. 48 shows a case where a MOSFET is used as the switching element 600 instead of using the IGBT shown in FIG. Note that the MOSFET shown in FIG. 48 is made of, for example, a silicon carbide semiconductor substrate. For example, a substrate material in which an N ⁻ type drift region 52 is formed on an N ⁺ type substrate region 51 is used. A P type well region 53 is formed in a part of the surface layer portion in the drift region 52, and an N ⁺ type source region 54 is formed in a part of the surface layer portion in the well region 53. A gate insulating film 55 made of, for example, a silicon oxide film is formed in contact with the surface layer portions of the drift region 52, well region 53, and source region 54, and a gate electrode 56 made of, for example, N-type polycrystalline silicon is formed on the gate insulating film 55. Is arranged. Further, a source electrode 57 in contact with the source region 54 and the well region 53 is formed in the opening formed in the gate insulating film 55. A drain electrode 59 is formed in ohmic contact with the substrate region 51.

  Further, as shown in FIG. 48, a field insulating film 31 made of, for example, a silicon oxide film is formed on the outer peripheral portion of the region where the switching element 600 is formed in contact with the surface layer portions of the drift region 52 and the well region 53. Yes.

  Next, the semiconductor snubber circuit 200 formed on the left side of the left broken line in FIG. 48 will be described. For example, an insulating film 32 or an interlayer insulating film (for example, formed when the gate insulating film 55 of the switching element 600 is formed on a predetermined region of the field insulating film 31 used for electric field relaxation at the outer peripheral edge of the switching element 600. A plurality of resistance regions 33 made of polycrystalline silicon are formed via a not-shown). 48 illustrates the case where the insulating film 32 is formed, but the resistance region 33 may be formed on the field insulating film 31 without the insulating film 32 interposed therebetween.

  A surface electrode 13 is formed on each of the plurality of resistance regions 33. At least some of the plurality of surface electrodes 13 are connected to the source terminal 302 to which the source terminal of the switching element 600 is connected. The number of surface electrodes 13 connected to the source terminal 302 is determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon.

  In the semiconductor snubber circuit 200 shown in FIG. 48, the resistance region 33 functions as the resistor 220, and the field insulating film 31 and the insulating film 32 function as the capacitor 210. The impurity concentration and thickness of the resistance region 33 can be set according to the magnitude of the resistance value required for the resistor 220.

The configuration shown in FIG. 48 has the effect that the free wheel diode 100 and the switching element 600 described in the third embodiment can be realized by various elements, and the semiconductor snubber circuit 200 and the switching element 600 described in the fifth embodiment. The effect can be realized by using one chip. Further, the feature of the configuration shown in FIG. 48 is that the resistance region 33 is formed of the same material as the gate electrode 56 of the switching element 600. With the configuration shown in FIG. 48, in addition to the effect of using a MOSFET as the switching element 600, the manufacturing process can be further simplified and the cost can be reduced.
FIG. 49 shows a case where a transistor for driving the heterojunction portion shown in FIG. 35 with an insulated gate electrode is used as the switching element 600 instead of using the IGBT shown in FIG.

First, the switching element 600 formed on the right side of the right broken line in FIG. 49 will be described. For example, an N ⁻ type drift region 62 is formed on a substrate region 61 of silicon carbide polytype 4H type N ⁺ type, and on the main surface of the drift region 62 facing the junction surface with substrate region 61, For example, a hetero semiconductor region 63 made of N-type polycrystalline silicon is formed. A gate insulating film 64 made of, for example, a silicon oxide film is formed on the hetero semiconductor region 63 in contact with the drift region 62 at the opening of the hetero semiconductor region 63. A gate electrode 65 is formed on the gate insulating film 64, and a source electrode 66 is disposed in contact with the hetero semiconductor region 63. A drain electrode 68 is connected to the substrate region 1. Further, a field insulating film 31 made of a silicon oxide film or the like is formed in contact with the surface layer portion of the drift region 62 in the peripheral portion of the region where the switching element 600 is formed.

  Next, the semiconductor snubber circuit 200 formed on the left side of the left broken line in FIG. 49 will be described. A plurality of resistance regions 33 made of polycrystalline silicon are formed on a predetermined region of the field insulating film 31 used for electric field relaxation at the outer peripheral edge of the switching element 600. A surface electrode 13 is formed on each of the plurality of resistance regions 33. At least some of the plurality of surface electrodes 13 are connected to the source terminal 302 to which the source terminal of the switching element 600 is connected. The number of surface electrodes 13 connected to the source terminal 302 is determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon.

  In the semiconductor snubber circuit 200 illustrated in FIG. 49, the resistance region 33 functions as the resistor 220, and the field insulating film 31 and the insulating film 32 function as the capacitor 210. The impurity concentration and thickness of the resistance region 33 can be set according to the magnitude of the resistance value required for the resistor 220.

  Even with the configuration shown in FIG. 49, the effect that the free wheel diode 100 and the switching element 600 described in the third embodiment can be realized by various elements, and the semiconductor snubber circuit 200 and the switching element 600 described in the fifth embodiment. It is possible to realize the effect of having been integrated into one chip. Further, as a feature of the configuration shown in FIG. 49, the resistance region 33 is formed of the same material as the hetero semiconductor region 63 of the switching element 600. Further, as in the case of the switching element 600 shown in FIGS. 47 and 48, the resistance region 33 can be formed of the same material as the gate electrode 65 of the switching element 600.

FIG. 50 shows a case where the JFET shown in FIG. 36 is used as the switching element 600 instead of using the IGBT shown in FIG. In switching element 600 shown in FIG. 50, for example, an N ⁻ type drift region 72 is formed on an N ⁺ type substrate region 71 whose polytype of silicon carbide is 4H type. An N ⁺ type source region 73 and a P type gate region 74 are formed in the surface layer portion in the drift region 72. The gate region 74 is connected to the gate electrode 75, and the source region 73 is connected to the source electrode 76. The substrate region 71 is connected to the drain electrode 78. Further, a field insulating film 31 made of, for example, a silicon oxide film is formed on the outer peripheral portion of the switching element 600 in contact with the surface layer portion of the drift region 72.

  Next, the semiconductor snubber circuit 200 formed on the left side of the left broken line in FIG. 50 will be described. For example, an insulating film 32 or an interlayer insulating film formed when forming an insulating film 77 of the switching element 600 on a predetermined region of the field insulating film 31 used for electric field relaxation at the outer peripheral edge of the switching element 600 (see FIG. A plurality of resistance regions 33 made of polycrystalline silicon are formed via a not-shown). 50 illustrates the case where the insulating film 32 is formed, but a plurality of resistance regions 33 may be formed on the field insulating film 31 without the insulating film 32 interposed therebetween.

  A surface electrode 13 is formed on each of the plurality of resistance regions 33. At least some of the plurality of surface electrodes 13 are connected to the source terminal 302 to which the source terminal of the switching element 600 is connected. The number of surface electrodes 13 connected to the source terminal 302 is determined according to the values of the capacitor 210 and the resistor 220 necessary for suppressing the current / voltage oscillation phenomenon.

  In the semiconductor snubber circuit 200 illustrated in FIG. 50, the resistance region 33 functions as the resistor 220, and the field insulating film 31 and the insulating film 32 function as the capacitor 210. The impurity concentration and thickness of the resistance region 33 can be changed according to the magnitude of the resistance value required for the resistor 220.

  With the configuration shown in FIG. 50, the effect that the free wheel diode 100 and the switching element 600 described in the third embodiment can be realized by various elements, and the semiconductor snubber circuit 200 and the switching element 600 described in the fifth embodiment are achieved. The effect can be realized by using one chip. With such a configuration, the manufacturing process can be further simplified and realized at low cost.

  Further, in the fifth embodiment, as described in the third embodiment, when the configuration employed in the switching element 600 can be used as a unipolar freewheeling diode, the freewheeling diode 100 is mounted on a separate chip. In addition to the formation, the free-wheeling diode 100, the switching element 600, and the semiconductor snubber circuit 200 can be made into one chip, and the semiconductor package can be downsized. Thereby, the parasitic inductance generated in the wiring or the like can be further reduced, and the vibration phenomenon can be further reduced by the semiconductor snubber circuit 200.

  Further, by forming the freewheeling diode 100, the switching element 600 and the semiconductor snubber circuit 200 in one chip, the wiring length is further shortened, and there is an effect of further reducing radiation noise generated from the wiring due to the oscillating current. Further, the manufacturing cost is reduced by reducing the chip size. Further, since the sum of the capacitor capacities of the freewheeling diode 100 and the switching element 600 is reduced, the capacitance required for the capacitor 210 of the semiconductor snubber circuit 200 can also be reduced. That is, the vibration phenomenon can be suppressed with a small size and low cost.

  The example in which the switching element 600 and the semiconductor snubber circuit 200 are made into one chip has been described above. However, when the chip is made into one chip, the resistance 220 of the semiconductor snubber circuit 200 is not limited to the resistance region 33 made of, for example, polycrystalline silicon. A substrate region or drift region in the semiconductor substrate may be used. Further, as the capacitor 210 of the semiconductor snubber circuit 200, in addition to the field insulating film 31 made of, for example, a silicon oxide film, a configuration in which a depletion layer is formed at the time of reverse bias such as a PN junction or a heterojunction is adopted. The capacitor 210 may be used. Further, for example, a freewheeling diode 100 may be built in the switching element 600 such as a MOSFET having a Schottky barrier diode, and the semiconductor snubber circuit 200 may be integrated into one chip. In any configuration, the vibration phenomenon, which is a feature of the present invention, can be further suppressed, and both the transient performance and the conduction performance can be improved.

  As described with reference to FIGS. 20 and 21 in the first embodiment, the capacitance C of the capacitor used in the snubber circuit and the sum C0 of the capacitor capacitance components of the free-wheeling diode and the switching element in the cut-off state When the capacitance ratio C / C0 is around 0.1, the damping effect of the vibration phenomenon becomes remarkable, and the value of the convergence time ratio of the vibration phenomenon tends to be saturated when the capacitance ratio C / C0 exceeds 10. Further, during a transient operation, a loss E occurs due to a transient current proportional to the capacitance of the capacitor formed in the snubber circuit. For this reason, it is preferable that the capacitance of the capacitor 210 be as small as possible.

  From this, the electrostatic capacitance C of the capacitor 210 of the snubber circuit used in the fifth embodiment is more than 1/10 times the total sum of the capacitances of the capacitor components in the cutoff state of the freewheeling diode 100 and the switching element 600. By selecting within a range of 10 times or less, the vibration phenomenon can be reduced more significantly while suppressing an increase in loss. This effect can be obtained in any configuration example described in the fifth embodiment.

  As described above, in the fifth embodiment, the number and area of the surface electrodes 13 of the semiconductor snubber circuit 200 that is integrated with the switching element 600 can be made variable. The resistance value of the value and resistor 220 can be set to a desired value. Thereby, the semiconductor snubber circuit 200 applicable to various switching elements 600 can be provided. By adopting such a configuration, even when the circuit configuration is changed, the current / voltage oscillation phenomenon can be stably suppressed only by changing the wiring.

(Other embodiments)
As described above, the present invention has been described according to the first to fifth embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  If the semiconductor snubber circuit 200 is connected in parallel with at least the freewheeling diode 100, the effect of reducing the oscillation phenomenon can be obtained even if it is not mounted on the same mounting board.

  In the first to fifth embodiments, the materials of the free wheeling diode 100, the switching element 600, and the semiconductor snubber circuit 200 have been described using silicon materials, silicon carbide materials, and the like as examples. However, the effect of reducing the vibration phenomenon is obtained. If possible, the substrate material may be other semiconductor materials such as silicon germane, gallium nitride, and diamond. Moreover, although 4H type was demonstrated as a polytype of silicon carbide, other polytypes, such as 6H and 3C, may be sufficient. Further, the drift region of the switching element 600 and the freewheeling diode 100 has been described in the case of the N type, but may of course be configured of the P type.

  In addition, as a power conversion device to which the semiconductor device according to the first to fifth embodiments can be applied, a DC / DC converter, a three-phase AC inverter, and the like have been described as an example. You may use for the power converter called. In any case, all types of power conversion, such as inverters that convert DC voltage to AC voltage, rectifiers that convert AC voltage to DC voltage, and DC / DC converters that change and output DC voltage voltage It can be applied to the device. And if it is a power converter device using the semiconductor device which concerns on 1st thru | or 5th embodiment, in any area | region of a large electric current area | region and a zero electric power area | region, and also in both the low temperature and high temperature vibration The phenomenon can be reduced. For this reason, the conduction loss and the transient loss can be reduced and the density can be increased, and the vibration phenomenon can be reduced and the operation can be stably performed, so that the basic performance of the apparatus can be improved at the same time.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

  The semiconductor device of the present invention can be used in the electronic equipment industry including a manufacturing industry for manufacturing a semiconductor device having a freewheeling diode and a power converter.

DESCRIPTION OF SYMBOLS 1, 11, 21, 41, 51, 61, 71, 81 ... Substrate area | region 2, 23, 42, 52, 62, 72, 82 ... Drift area | region 3, 13, 44, 84 ... Surface electrode 4, 14, 45, 85 ... Back electrode 5, 31, 46, 86 ... Field insulating film 6, 17, 33, 47 ... Resistance region 7 ... Electric field relaxation region 8, 88 ... Low concentration drift region 10, 10A ... Semiconductor device 12 ... Dielectric region 15, 83, 89 ... opposite conductivity type region 16 ... low resistance substrate region 22 ... buffer region 24 ... well region 43, 63 ... hetero semiconductor region 100 ... freewheeling diode 200 ... semiconductor snubber circuit 210 ... capacitor 220 ... resistor 500 ... insulating substrate 600 ... Switching element 800 ... Snubber built-in reflux diode 900 ... Snubber built-in switching element 1001 ... Coupling surface electrode

Claims (13)

A pair of connection terminals;
A unipolar freewheeling diode connected between the pair of connection terminals;
A resistor formed of a semiconductor substrate, a capacitor disposed on one main surface of the semiconductor substrate, a back electrode disposed on the other main surface of the semiconductor substrate and connected to one of the pair of connection terminals, and the capacitor A semiconductor snubber circuit having a plurality of surface electrodes that are spaced apart from each other and connectable to the other of the pair of connection terminals, respectively .
The one or more surface electrodes selected from the plurality of surface electrodes are connected to the other terminal, whereby the free wheel diode and the semiconductor snubber circuit are connected in parallel between the pair of connection terminals, and are selected. The semiconductor device is characterized in that the values of the capacitor and the resistance of the semiconductor snubber circuit are variable in accordance with the total area of the surface electrode . The semiconductor device according to claim 1 , further comprising a combined surface electrode disposed on the plurality of surface electrodes so as to connect two or more of the plurality of surface electrodes. Claim 1, characterized in that said capacitor comprises a plurality of dielectric regions of different thickness which are arranged along the surface electrodes, the plurality of surface electrodes are respectively disposed above the plurality of dielectric regions Or the semiconductor device of 2 . The capacitor includes a plurality of dielectric regions made of dielectrics having different dielectric constants disposed along the surface electrode, and the plurality of surface electrodes are respectively disposed above the plurality of dielectric regions. The semiconductor device according to claim 1 . Claim 1, wherein the resistor comprises a plurality of substrate regions of different thickness which are arranged along the surface electrodes, the plurality of surface electrodes, characterized in that it is arranged above the plurality of substrate regions 5. The semiconductor device according to any one of items 1 to 4 . Claim 1, wherein the resistor comprises a plurality of substrate regions having different resistivities which are disposed along the surface electrodes, the plurality of surface electrodes, characterized in that it is arranged above the plurality of substrate regions The semiconductor device according to any one of 1 to 5 . A semiconductor region having a different conductivity type from the plurality of substrate regions is disposed on the plurality of substrate regions, the plurality of surface electrodes are respectively disposed above the semiconductor regions, and the capacitor includes the plurality of substrate regions and the plurality of substrate regions. The semiconductor device according to claim 6 , further comprising a capacitance due to a depletion layer formed between the semiconductor regions. The semiconductor device according to claim 6 , wherein the capacitor includes a capacitance due to a depletion layer formed between the plurality of substrate regions and the plurality of surface electrodes. The semiconductor device according to any one of claims 1 to 8, further comprising a parallel-connected switching element to the return diode. The semiconductor snubber circuit, the semiconductor device according to any one of claims 1 to 9, characterized in that it is arranged in the return diode on the same chip. 11. The semiconductor device according to claim 9 , wherein the semiconductor snubber circuit is disposed on the same chip as the switching element. The snubber circuit, the semiconductor device according to any one of claims 1 to 11, characterized in that a resistor and a capacitor is a configuration connected in series. Power conversion apparatus comprising the semiconductor device according to any one of claims 1 to 12.

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