JP4744682B2 - Schottky barrier diode - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrode structure of a diode.
[0002]
[Prior art]
Conventionally, a PiN diode mainly composed of silicon (Si) has been used as a free wheeling diode (FWDi). The freewheeling diode FWDi is a circuit such as an inverter having an inductance component in the load, and circulates or dissipates current energy stored in the inductance of the load when a power device connected to the circuit is turned off (opened). It is a diode built into the circuit for the purpose of protecting the whole and is also called a commutation diode. It is also used as a bypass in switching circuits and the like. The reason why the PiN diode is used as the freewheeling diode FWDi is that the PiN diode is a bipolar diode, and when a large current is applied with a forward bias, the voltage drop can be lowered by conductivity modulation. However, when a PiN diode is used, carriers remaining in the PiN diode due to conductivity modulation flow into the circuit as a reverse recovery current in the process from the forward bias state to the steeply reverse bias state. This is because a PiN diode mainly composed of Si has a long remaining carrier life, so that many residual carriers exist.
[0003]
On the other hand, when a Schottky barrier diode (SBD) containing Si as a main material is used as the freewheeling diode (FWDi), there is no problem that a large reverse recovery current flows in the circuit. This is because the Schottky barrier diode (SBD) is a unipolar diode and has almost no carrier due to conductivity modulation. The Schottky barrier diode (SBD) is a diode in which a metal and a semiconductor are joined, and is a diode having a rectifying property using a potential barrier (Schottky barrier) at a Schottky interface that is a junction. is there.
[0004]
[Problems to be solved by the invention]
However, when such a Schottky barrier diode (SBD) is used, a new problem occurs next. First, the configuration of the Schottky barrier diode will be briefly described. FIG. 4 is a cross-sectional view of a conventional Schottky barrier diode 40. The Schottky barrier diode 40 includes a flat first anode electrode 41 connected to an external conductor (not shown), a second anode electrode 43 adjacent to the first anode electrode 41, and a second anode electrode. 43 includes an n-type epitaxial layer 44 of Si (silicon) which is a semiconductor layer bonded to 43, an n-type Si substrate 46, and a cathode electrode 47 connected to an external conductor (not shown). In the Schottky barrier diode 40, a p-type semiconductor layer 45 is further formed under the second anode electrode 43. This is called a so-called junction barrier controlled Schottky structure (JBS (Junction Barrier controlled Schottky) structure).
[0005]
The problem with the Schottky barrier diode (SBD) 40 mainly composed of Si is that the electric field strength causing dielectric breakdown is low. This means that it is difficult to achieve a high breakdown voltage. When a high breakdown voltage Schottky barrier diode (SBD) in which reverse recovery current does not flow in the circuit is produced, a large resistance is generated during energization, and therefore a breakdown voltage of about 200 V is the limit in a practical range.
[0006]
Further, since the conventional Schottky barrier diode (SBD) cannot exhibit desired electrical characteristics, it is difficult to mount it on a semiconductor module that can be used in a circuit. This is due to the fact that the Schottky electrode interface 48, which is a path when current flows in the forward direction, cannot obtain originally intended electrical characteristics. For example, considering the case where dust or the like adheres to an external conductor (not shown) connected to the first anode electrode 41 and has irregularities, the first anode electrode 41 is flat and thus connected to the external conductor. In this case, the convex portion of the first anode electrode 41 locally applies a strong pressure to the Schottky interface 48, thereby degrading the electrical characteristics of the Schottky electrode interface 48. Considering the case where the outer conductor and the first anode electrode 41 are wire-bonded by ultrasonic waves, the ultrasonic wave is directly transmitted to the Schottky interface 48 and the structure of the Schottky interface 48 is changed. There is a case.
[0007]
An object of the present invention is to provide a diode in which the structure of the Schottky interface 48 does not change. As a result, the diode can obtain originally intended electrical characteristics .
[0008]
[Means for Solving the Problems]
Schottky barrier diode according to the invention, are given the irregularities on one surface is flat and the other surface, an anode electrode formed of a metal, which one surface is joined to the other surface of the anode electrode An n-type semiconductor layer, a p-type semiconductor layer formed on the surface layer portion of one surface of the n-type semiconductor layer and bonded to the other surface of the anode electrode, and bonded to the other surface of the n-type semiconductor layer A Schottky barrier diode having a cathode electrode formed thereon, wherein the projecting portion of the anode electrode is disposed on the p-type semiconductor layer. Is achieved.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments 1 and 2 of the present invention will be described below with reference to the accompanying drawings.
[0013]
(Embodiment 1)
FIG. 1 is a sectional view of a Schottky barrier diode (SBD) 10 of the present invention and external conductors 12-1 and 12-2 connected to the Schottky barrier diode (SBD) 10 by pressure contact. The Schottky barrier diode (SBD) 10 is a diode in which a metal and a semiconductor are joined.
[0014]
The Schottky barrier diode (SBD) 10 according to the present embodiment is characterized in that the thickness of the anode electrode 1 connected to the external conductor 12-1 is uneven, and the convex portion 2 of the anode electrode 1 is formed on the p-type semiconductor layer 5. In other words, the concave portion corresponds to the n-type epitaxial layer 4 which is an n-type semiconductor layer (up and down relationship). Here, the unevenness is a surface state that is relatively determined from the undulation state in the surrounding height direction.For example, the median value of the highest position and the lowest position in a certain region is set as a reference value, and the reference value. The higher portion can be defined as the convex portion, and the lower portion than the reference value can be defined as the concave portion. By arranging in this way, even if the outer conductor 12-1 is uneven, the convex portion does not apply strong pressure to the Schottky interface 8, and therefore the original of the Schottky barrier diode (SBD) 10 is not generated. Electrical characteristics can be obtained.
[0015]
The Schottky barrier diode (SBD) 10 according to the present invention will be described in detail. A Schottky barrier diode (SBD) 10 includes at least a first anode electrode 1, a second anode electrode 3, an n-type epitaxial layer 4, a p-type semiconductor layer 5, an n-type semiconductor substrate 6, and a cathode electrode. 7.
[0016]
Explaining each component, the first anode electrode 1 is an electrode for ensuring the connection between the Schottky barrier diode (SBD) 10 and the external conductor 12-1. The first anode electrode 1 is connected to the external conductor 12-1 on one side and is joined to the second anode electrode 3 on the other side. The thickness of the side where the first anode electrode 1 is connected to the external conductor 12-1 is provided with unevenness. The convex portion 2 of the anode electrode 1 is used to ensure electrical connection with the external conductor 12-1. According to FIG. 1, the convex and concave portions 2 and concave portions of the concave and convex portions attached to the first anode electrode 1 are described as having a right-angled outline, but are not necessarily limited to a right angle. The shape is not limited as long as it is uneven.
[0017]
Next, the second anode electrode 3 is a flat plate-like electrode, one surface is bonded to the first anode electrode 1, and the other surface is bonded to the n-type epitaxial layer 4 and the p-type semiconductor layer 5. To do. The other surface can be divided into a region bonded to the n-type epitaxial layer 4 and a region bonded to the p-type semiconductor layer 5. In the present embodiment, when simply referring to the “anode electrode”, it means both the first anode electrode 1 and the second anode electrode 3. Note that the second anode electrode 3 may be omitted, and the other side of the first anode electrode 1 may be joined to the n-type epitaxial layer 4 and the p-type semiconductor layer 5.
[0018]
Subsequently, the n-type epitaxial layer 4 is a low-concentration semiconductor layer formed using, for example, Si or the like as a main material. As described above, the Schottky barrier diode (SBD) 10 is a diode in which a metal and a semiconductor are joined. The anode electrode corresponds to “metal” and the n-type epitaxial layer 4 corresponds to “semiconductor”. The junction surface between the anode electrode and the n-type epitaxial layer 4 is called a Schottky interface 8. The n-type epitaxial layer 4 is joined to the n-type semiconductor substrate 6 on the other side.
[0019]
The p-type semiconductor layer 5 is a p-type semiconductor layer containing, for example, Si as a main material. The p-type semiconductor layer 5 is formed under the second anode electrode 3, and its junction surface is also called a Schottky interface 9. The p-type semiconductor layer 5 is provided to prevent an electric field from increasing at the Schottky interface 8. That is, according to the p-type semiconductor layer 5, at the time of reverse bias, the electric field strength on the n-type epitaxial layer 4 side of the Schottky interface 8 can be reduced and the leakage current can be reduced.
[0020]
The n-type semiconductor substrate 6 is an n-type semiconductor substrate whose main material is a high concentration material, for example, Si. The n-type semiconductor substrate 6 is joined to the n-type epitaxial layer 4 on the one hand and to the cathode electrode 7 on the other hand.
[0021]
The cathode electrode 7 is an electrode for ensuring the connection between the Schottky barrier diode (SBD) 10 and the external conductor 12-2. The cathode electrode 7 is connected to the external conductor 12-2 on one side and is joined to the n-type semiconductor substrate 6 on the other side.
[0022]
The current flowing in the Schottky barrier diode (SBD) 10 configured as described above reaches the cathode electrode 7 from the anode electrode through the Schottky interface 8, the n-type epitaxial layer 4 and the n-type semiconductor substrate 6.
[0023]
As described above, the structure in which the p-type semiconductor layer 5 is formed under the second anode electrode 3 is called a junction barrier controlled Schottky structure (JBS (Junction Barrier controlled Schottky) structure). As mentioned above in the description of the p-type semiconductor layer 5, in the JBS structure, the p-type semiconductor layer 5 is deeply related to the characteristics of the Schottky barrier diode (SBD) 10 at the time of reverse bias. On the other hand, in the Schottky barrier diode (SBD) 10 having the JBS structure, the Schottky interface 8 plays a basic role of current control. This is because current flows through the Schottky interface 8 during forward bias. Electrical characteristics of Schottky barrier diode (SBD) 10 as described in the literature ("Rhoderick, EH And Williams, RH Metal Semiconductor Contacts, 2nd edition, Chap. 1, Oxford University Press (1988)") Depends sharply on the structure of the Schottky interface 8. Therefore, when an electrode is connected to the Schottky barrier diode (SBD) 10, it is necessary to take care not to change the structure of the Schottky interface 8.
[0024]
Therefore, the first anode electrode 1 is disposed so that the convex portion 2 is positioned above the p-type semiconductor layer 5 (in a direction perpendicular to the electrode surface of the first anode electrode 1). In other words, the first anode electrode 1 is disposed so that the concave portion of the first anode electrode 1 is located on the Schottky interface 8 of the n-type epitaxial layer 4 (on the external conductor 12-1 side). At this time, when the upper portion of the convex portion 2 of the anode electrode is flat, the width of the convex portion 2 of the first anode electrode 1 is Wa, and the width of the p-type semiconductor layer 5 is Wp, Wa ≦ Wp. This is because the structure of the Schottky interface 8 is not affected even if pressure due to dust or the like is applied to the convex portion 2 as long as this condition is satisfied. If the upper part of the convex part 2 is not flat, a predetermined reference value is obtained as described above, and a part higher than the reference value is defined as a convex part and a part lower than the reference value is defined as a concave part. The width of the portion 2 and the width of the p-type semiconductor layer 5 may be determined. Since FIG. 1 is a cross-sectional view, the term “width” can be rephrased as “size”. Therefore, it can be said that the size of the convex portion 2 of the first anode electrode 1 is equal to or smaller than the size of the p-type semiconductor layer 5.
[0025]
Such an electrode structure is realized by the following manufacturing process. First, the process up to the formation of the p-type semiconductor layer 5 is performed using a known technique such as vapor deposition, crystal growth, ion implantation, and the detailed description thereof is omitted. FIG. 5 shows a Schottky barrier diode (SBD) 10 (FIG. 1) in the manufacturing process. When the p-type semiconductor layer 5 (FIG. 1) is formed, the alignment marker 56 is formed outside the diode element region 54 on the Si wafer 52 when the second anode electrode 3 (FIG. 1) is formed. The alignment marker 56 is used for alignment of the shape of the p-type semiconductor layer 5 (FIG. 1) and the shape of the first anode electrode 1 (FIG. 1).
[0026]
More specifically, before forming the second anode electrode 3 (FIG. 1), a photoresist is coated on the Si wafer 52 by spin coating, and for the second anode electrode 3 (FIG. 1) using a microscope or the like. The mask is exposed and developed in accordance with the shape of the p-type semiconductor layer 5 (FIG. 1). A pattern for the alignment marker 56 is provided on the mask for the second anode electrode 3 (FIG. 1). When the development is completed, a metal (for example, Al) for the second anode electrode 3 (FIG. 1) is deposited on the patterned photoresist by electron beam evaporation or the like, and then the first anode electrode 1 (FIG. 1) A metal for use (for example, Al) is deposited on the metal for the second anode electrode 3 (FIG. 1). Then, by removing the photoresist with an organic solvent or the like, the second anode electrode 3 (FIG. 1) and the convex portion 2 (FIG. 1) are not yet present on the p-type semiconductor layer 5 (FIG. 1). The anode electrode 1 (FIG. 1) is formed. At this time, the alignment marker 56 is also formed outside the diode element region 54. Since the relative positions of the alignment marker 56 and the shape of the p-type semiconductor layer 5 (FIG. 1) are fixed, a mask pattern for giving the convex portion 2 (FIG. 1) to the first anode electrode 1 (FIG. 1) is provided. It is produced so as to correspond to the relative position. Thereby, the pattern of the convex part 2 (FIG. 1) of the 1st anode electrode 1 and the pattern of the shape of the p-type semiconductor layer 5 (FIG. 1) can be match | combined.
[0027]
The photoresist is again coated on the Si wafer 52 by spin coating, and a mask for applying the convex portion 2 (FIG. 1) to the first anode electrode 1 (FIG. 1) is aligned with the alignment marker 56 and exposed by a microscope or the like. ,develop. Thereafter, a metal for the first anode electrode 1 (FIG. 1) is deposited on the patterned photoresist by electron beam evaporation or the like. If this photoresist is removed, the first anode electrode 1 (FIG. 1) having the convex portion 2 (FIG. 1) is formed. In addition, the height of the convex part 2 (FIG. 1) can be changed by changing vapor deposition time. When the convex portion 2 (FIG. 2) is pressed against the outer conductor 12-1 (FIG. 1), the convex portion 2 (FIG. 2) is slightly deformed by the pressure, but the deformation is small because the degree is small. It can be ignored and the convex part 2 (FIG. 2) has sufficient strength.
[0028]
Referring to FIG. 1 again, according to such a structure, even if dust or the like adheres to the external conductor 12-1 and unevenness occurs, the structure of the Schottky interface 8 is not changed when the external conductor is connected. The reason is that when the convex portion of the outer conductor 12-1 due to dust or the like faces the concave portion of the first anode electrode 1, the convex portion of the outer conductor 12-1 corresponds to the concave portion of the first anode electrode 1. This is because the convex portion of the outer conductor 12-1 does not apply a strong pressure to the Schottky interface 8 because it fits in. At this time, the bottom surface of the external conductor 22-1 is prevented from contacting the concave portion of the first anode electrode 1. When bonding is performed using ultrasonic waves, since the ultrasonic waves are transmitted through the convex portion of the first anode electrode 1, bonding can be performed without applying strong local pressure to the Schottky interface 8. On the other hand, when the convex portion of the outer conductor 12-1 is in contact with the convex portion of the first anode electrode 1, the structure of the Schottky interface 9 does not affect the control of the current, so the outer conductor 12-1 There is no problem even if the convex portion of the portion applies a strong pressure to the Schottky interface 9. In this case, it is only necessary that at least the second anode electrode 3 and the p-type semiconductor layer 5 are electrically connected. Even when Wa ≦ Wp as described above, if the difference between Wa and Wp is sufficiently small, no strong pressure is applied to the Schottky interface 8 as in the prior art, so the structure of the Schottky interface 8 is changed. Therefore, the Schottky barrier diode (SBD) 10 can be manufactured.
[0029]
As described above, in the Schottky barrier diode (SBD) 10 having the JBS structure, the thickness of the portion corresponding to the p-type semiconductor layer 5 of the first anode electrode 1 is set to the thickness of the portion corresponding to the n-type epitaxial layer 4. By making the thickness thicker, the original electrical characteristics of the Schottky barrier diode (SBD) 10 can be obtained even when the Schottky barrier diode (SBD) 10 is connected to the external conductors 12-1 and 12-2. The yield during the manufacturing process can be improved. Since the above description is the first feature regarding the structure of the Schottky barrier diode (SBD) 10, it goes without saying that the p-type semiconductor layer 5, the n-type epitaxial layer 4 and the n-type substrate 6 are made of Si. However, the above-described effects can be obtained even when formed from other known materials.
[0030]
(Embodiment 2)
Next, a second embodiment of the present invention will be described. The feature of the second embodiment is that, in the Schottky barrier diode (SBD) 10 of the first embodiment, the n-type epitaxial layer 4 is an n-type SiC semiconductor layer mainly composed of silicon carbide (SiC). By using SiC, a dielectric breakdown electric field strength about 10 times that of Si can be obtained. At the same time, by using the Schottky barrier diode (SBD) 10 having the structure described in the first embodiment, the Schottky interface 8 can be obtained. It is stable and can be mounted on a semiconductor module to exhibit desired electrical characteristics.
[0031]
An example of a semiconductor module to which the Schottky barrier diode (SBD) 10 is applied will be described. FIG. 2 is a cross-sectional view of the pressure contact type semiconductor module 20 on which the Schottky barrier diode (SBD) 10 is mounted. The pressure contact type semiconductor module 20 includes a Schottky barrier diode (SBD) 10, a switching element 23, external conductors 22-1 and 22-2 that sandwich the Schottky barrier diode (SBD) 10 and the switching element 23, and these Insulating module housings 26-1 and 26-2 that fix and integrate these components.
[0032]
A Schottky barrier diode (SBD) 10 is the Schottky barrier diode of the first embodiment, and includes not only the n-type epitaxial layer 4 (FIG. 1) but also the p-type semiconductor layer 5 (FIG. 1) and the n-type substrate 6 (FIG. 1). 1) is also formed using SiC as a main material. This is because it is easy to manufacture with the current technology, but the p-type semiconductor layer 5 (FIG. 1) and the n-type substrate 6 (FIG. 1) may be formed of different materials by other appropriate methods.
[0033]
The outer conductors 22-1 and 22-2 are in pressure contact with the Schottky barrier diode (SBD) 10, and correspond to the outer conductors 12-1 and 12-2 (FIG. 1). The switching element 23 is a semiconductor switching element that performs circuit switching, such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Although one Schottky barrier diode (SBD) 10 and one switching element 23 are shown in FIG.
[0034]
The pressure contact type semiconductor module 20 will be described with reference to the circuit diagram of FIG. FIG. 3 is a circuit diagram of the pressure contact type semiconductor module 20. The same components as those in FIGS. 1 and 2 are denoted by the same reference numerals. In the press contact type semiconductor module 20, the Schottky barrier diode (SBD) 10 and the switching element 23 are connected in antiparallel. As described with reference to FIG. 1, the current flows in the Schottky barrier diode (SBD) 10 from the first anode electrode 1 on the outer conductor 22-1 side to the cathode electrode 7. On the other hand, when the switching element 23 is an IGBT, for example, the electrode 24-1 is a collector electrode, the electrode 24-2 is an emitter electrode, and the electrode 24-3 is a gate electrode. As described above, the Schottky barrier diode (SBD) 10 and the switching element 23 are connected in antiparallel, so that the Schottky barrier diode (SBD) 10 functions as a free-wheeling diode FWDi.
[0035]
As described above, by forming the n-type epitaxial layer 4 (FIG. 1) mainly composed of SiC, a Schottky barrier diode (SBD) 10 having a high breakdown field strength and a high breakdown voltage, and the same are used. The semiconductor module 20 can be obtained. Further, by incorporating such a Schottky barrier diode (SBD) 10 as a free-wheeling diode FWDi in the circuit, the reverse recovery current and the energy loss caused thereby can be drastically reduced. Further, since the reverse recovery current is not superimposed on the current flowing through the switching element 23 when it is turned on (during switching), the risk of element destruction due to overcurrent can be greatly reduced. Further, since the press contact type semiconductor module 20 incorporates the Schottky barrier diode (SBD) 10, it is naturally possible to obtain the effects based on the first embodiment described above.
[0036]
【The invention's effect】
According to the present invention, an uneven surface is provided on one surface, the other surface is flat, an anode electrode made of metal is provided, the convex portion is on the p-type semiconductor layer, and the concave portion is n-type. It arrange | positioned so that it might be located on an epitaxial layer. As a result, even if the outer conductor is uneven, the convex portion does not apply strong pressure to the Schottky interface 8 (FIG. 1), and therefore the structure of the Schottky interface 8 (FIG. 1) does not change. A Schottky barrier diode (SBD) having the above electrical characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a Schottky barrier diode (SBD) of the present invention and an external conductor connected to the Schottky barrier diode (SBD) by pressure contact.
FIG. 2 is a cross-sectional view of a pressure contact type semiconductor module on which a Schottky barrier diode (SBD) is mounted.
FIG. 3 is a circuit diagram of a pressure contact type semiconductor module.
FIG. 4 is a cross-sectional view of a conventional Schottky barrier diode.
FIG. 5 is a diagram showing a Schottky barrier diode (SBD) in the manufacturing process.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st anode electrode, 2 convex part, 3 2nd anode electrode, 4 n-type epitaxial layer, 5 p-type SiC semiconductor layer, 6 n-type SiC substrate, 7 cathode electrode, 8 Schottky interface, 9 Schottky interface , 10 Schottky barrier diode (SBD), 22-1 and 22-2 outer conductor

Claims (3)

An anode formed with metal on one surface, the other surface is flat, and a metal ;
And n-type semiconductor layer in which one surface is bonded to the other surface of the anode electrode,
A p-type semiconductor layer formed on a surface layer portion of one surface of the n-type semiconductor layer and joined to the other surface of the anode electrode;
A Schottky barrier diode comprising a cathode electrode joined to the other surface of the n-type semiconductor layer ,
A Schottky barrier diode in which a convex portion of the anode electrode is disposed on the p-type semiconductor layer. The convex portion upper flat der of the anode electrode is, the size of the flat convex portion top, the less the size of the p-type semiconductor layer, the Schottky barrier diode of claim 1. The n-type semiconductor layer is formed a silicon carbide as a main material, according to claim 1 or Schottky barrier diode according to claim 2.

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