JP2576758B2 - Semiconductor element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar type diode, and more particularly to a diode which can be used as a diode for protecting an input / output signal of an IC.

[0002]

2. Description of the Related Art An example of a conventional diode is shown in a sectional view of FIG. As shown in FIGS. 10 (a) and 10 (b), windows are selectively formed in the oxide films provided on the surfaces of the N-type semiconductor substrates 20a and 20b, and P-type impurities are introduced through these windows to form P-type guard rings. Forming mold regions 22a and 22b are formed. After forming an oxide film on the N-type semiconductor substrates 20a and 20b again, FIG.
As shown in (a), a high concentration P-type impurity is introduced into a region surrounded by a P-type region 22a to form a P ⁺ region having a required breakdown voltage.
Form 23. Alternatively, as shown in FIG. 10B, a polycrystalline semiconductor (P ⁺ region) 24 containing a high concentration of a P-type impurity to a required breakdown voltage is formed. And the anode electrode
25a and 25b and cathode electrodes 26a and 26b are formed. The diode configured as described above includes anode electrodes 25a and 25a.
b and the cathode electrodes 26a and 26b are connected to an external circuit via leads or the like, and required sealing is performed.

[0003] When an electrostatic protection diode for an input / output signal terminal of an IC is manufactured, the following electrical characteristics are required. (1) The breakdown voltage of the diode is lower than the breakdown voltage of the IC so that the IC is not destroyed by static electricity. (2) Since the input / output signal waveform is not disturbed, the capacitance between the terminals of the diode is small, and the breakdown voltage of the diode is higher than the input / output signal voltage. (3) To reduce power consumption, reduce diode leakage current at input / output signal voltages.

When the breakdown voltage of a diode is 5 V or less,
In the diode shown in FIG. 10, the Zener breakdown becomes dominant, the leakage current increases, and the operating resistance increases. For example, when an electrostatic protection diode of a 3V signal IC is to be manufactured with a conventional structure, when a diode having a breakdown voltage of 4V is manufactured, a leakage current at 3V is several mA.
About. Therefore, an electrostatic protection diode of an IC having an input / output signal voltage of less than 5 V has a problem that it cannot be manufactured with a conventional structure due to a problem of leakage current.

[0005] Alternatively, a diode as shown in FIG. 11 is known. A window is opened in the silicon oxide film 28 on the N-type semiconductor substrate 27 with a photoresist, and a P-type impurity is diffused to form a P-type region 29. Similarly, diffuse N-type impurities,
An N-type region 30 is formed. Then, electrodes 31 and 32 are deposited on the N-type region 30 side and the N-type semiconductor substrate 27 side to produce a pellet.

[0006] breakdown voltage of the constant voltage diode of the prior art pellet structure as shown in FIG. 11, although the operation resistance is reduced as compared with the structure of FIG. 10 in order determined by the punch-through breakdown voltage,
There is a problem in mass production that it is difficult to control the breakdown voltage and the variation in the breakdown voltage in the wafer surface increases.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art and to provide a diode having a small operating resistance. It is another object of the present invention to provide an electrostatic protection diode having a small leakage current and a high electrostatic capacity.

[0008]

According to the present invention, a semiconductor device according to the present invention includes an insulated gate field effect transistor (hereinafter referred to as a MOS transistor) for determining a breakdown voltage and a bipolar transistor for amplifying a drain current. Part.

More specifically, the semiconductor device according to the first aspect of the present invention comprises a P-channel MOS transistor having a source and a drain on one main surface side of a semiconductor substrate, a collector, an emitter and a base. Having an NPN-type bipolar transistor portion, connecting the source and the collector, and connecting the gate, the drain, and the base of the insulated gate field-effect transistor portion,
The characteristics between the collector and the emitter are utilized as a constant voltage diode.

More specifically, a semiconductor device according to a second aspect of the present invention comprises an N-channel MOS transistor portion having a source and a drain on one main surface side of a semiconductor substrate, a collector, an emitter and a base. Having a PNP-type bipolar transistor portion, connecting the source and the collector, and connecting the gate, the drain, and the base of the insulated gate field-effect transistor portion,
The characteristics between the collector and the emitter are utilized as a constant voltage diode.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments and reference examples of the present invention will be described with reference to the drawings. FIG. 1 shows a vertical sectional view (a) of a pellet and an equivalent circuit diagram (b) showing a constant voltage diode according to a first reference example of the present invention. Incidentally, in FIGS. 1A and 1B,
C, B and E in the white circle indicate the collector, base and emitter of the bipolar transistor, respectively.
S, D and G indicate the source, drain and gate of the MOS transistor section, respectively.

As shown in FIG. 1A, a window is opened in the oxide film on the N-type semiconductor substrate 1 with a photoresist, and P-type impurities are diffused to form P-type regions 3 and 4. The P-type region 3 becomes the base B of the bipolar transistor portion and the drain D of the MOS transistor portion, and the P-type region 4 becomes the source S of the MOS transistor portion. Similarly, the N ⁺ type region 5,
6 is formed. The N ⁺ type region 5 becomes the emitter E of the bipolar transistor portion, and the N ⁺ type region 6 becomes the collector extraction portion connected to the collector C of the bipolar transistor portion. Then, the oxide film used for forming these regions is removed, and an oxide film 2 serving as a gate oxide film is newly formed.

Next, immediately below the gate G of the MOS transistor portion
Of an impurity ions are implanted into the channel region, controls the turn-on voltage V _T of the MOS transistor portion,
Electrodes 7, 8, and 9 are deposited to form a pellet. Electrode 7
Are the electrode of the emitter E of the bipolar transistor and M
The electrode 8 is a common electrode of the collector C of the bipolar transistor portion and the source S of the MOS transistor portion, and the electrode 9 is a substrate electrode.

Next, the operation of the first embodiment will be described with reference to FIG. Negative electrode 7, a positive voltage is applied to the electrode 9, the drain current flows when the voltage exceeds V _T, current is injected into the base of the bipolar transistor part, the bipolar transistor portion is turned on. Since the bipolar transistor section amplifies the current, the operating resistance is reduced.

A constant voltage diode having a withstand voltage of 1 V was manufactured, and the results shown in the following Table 1 were obtained.

[0016]

[Table 1] Relative comparison (value when the value of conventional structure is set to 100)

As compared with the conventional structure shown in FIG. 11, the operating resistance and the breakdown voltage within the wafer surface are about 1/3 to 1/4. The operating resistance of the constant voltage diode of the conventional structure (FIG. 10) having a withstand voltage of 5 V or less increases as the withstand voltage decreases. Therefore, when the first reference example of the present invention is applied to a low voltage constant voltage diode, the effect of improving the operating resistance is increased.

FIG. 2 is a vertical sectional view (a) of a pellet and an equivalent circuit diagram (b) showing a constant voltage diode according to a first embodiment of the present invention. In addition, like FIG. 1, (a) of FIG.
In (b), C, B and E in the white circle indicate the collector, base and emitter of the bipolar transistor, respectively, and S, D and G indicate the source, drain and gate of the MOS transistor, respectively.

As shown in FIG. 2A, a window is opened in the oxide film on the N-type semiconductor substrate 10 with a photoresist, and P-type impurities are diffused to form P-type regions 11 and 12. Similarly, N
⁺ -Type regions 13 and 14 are formed. Then, the oxide films used in these regions are selectively removed to newly form oxide films 15 and 16 including a gate oxide film. The impurity ions are implanted into the channel region directly below the gate G of the MOS transistor portion, controls the turn-on voltage V _T. Electrodes 17, 18, 19,
20 is deposited to produce a pellet.

Here, the P-type region 11 is the base B of the bipolar transistor portion and the drain D of the MOS transistor portion, the P-type region 12 is the source S of the MOS transistor portion, and the N ⁺ type region 14 is the collector C of the bipolar transistor portion. And the N ⁺ region 13 is the emitter E of the bipolar transistor portion. An electrode 18 is a base electrode of the bipolar transistor portion and a gate electrode of the MOS transistor portion, an electrode 19 is an emitter electrode of the bipolar transistor portion, and an electrode 17 is a collector electrode of the bipolar transistor portion and a source S electrode of the MOS transistor portion. Yes, electrode 20 is a substrate electrode.

Next, the operation of the first embodiment of the present invention will be described with reference to FIG. A negative voltage is applied to the electrode 19 and a positive voltage is applied to the electrode 20. When the voltage exceeds _VT + _VBE (forward voltage between the base and the emitter), a drain current flows, and a current is injected into the base of the bipolar transistor portion. The bipolar transistor turns on. Since the bipolar transistor section amplifies the current, the operating resistance is reduced. The breakdown voltage of the pellet becomes V _T + V _BE. Since V _T has a temperature coefficient of about 2 mV / ° C. and V _BE has a temperature coefficient of about −2 mV / ° C., the temperature coefficient of the withstand voltage of the pellet becomes very small.
The operating resistance of a constant voltage diode having a conventional structure ( FIG. 10 ) having a withstand voltage of 5 V or less increases as the withstand voltage decreases. Therefore, when the present invention is applied to a low voltage constant voltage diode,
The effect of improving the operating resistance increases.

The semiconductor element of the first embodiment has a parasitic thyristor 100 as shown by a dotted line in FIG. 3A, and a thyristor action (negative resistance) occurs when a certain current value is exceeded. This is the same for the semiconductor device of the first embodiment of the present invention . That is, as shown in FIG. 3A, during operation, almost no current flows to the source, so that point B and the back electrode have substantially the same potential, but point A is
Due to the voltage drop of the N-type semiconductor substrate, the potential drops below the back electrode. Therefore, when a current is applied to some extent, (potential at point A) <(potential at point B) + (diffusion potential of the PN junction formed by the N-type region at point A and the P-type region at point B ) As shown in FIG. 3C showing the characteristics of the thyristor, the parasitic thyristor turns on.

[0023]Here, the parasitic thyristor will be described. Rhinoceros
The lister is composed of a PNPN junction as shown in FIG.
When viewed from a different point of view, as shown in FIG.
Has an NPN transistor and a PNP transistor
You. Circuit composed of two transistors shown in FIG.
FIG. 12 (c) shows the equivalent circuit of FIG. FIG.
Referring to the equivalent circuit shown in (c), the operation of the thyristor
explain. Current I from the gate to the cathode _B1 Shed
And I _B1 Collector current I _C1 (= I _B1 × h
_FE1 ) (Where h _FE1 Is the current of the NPN transistor
Amplification factor) flows through the NPN transistor. This collector
Current I _C1 Is the base current I of the PNP transistor _B2 Same as
I _B2 Collector current I
_C2 (= I _B2 × h _FE2 = I _B1 × h _FE1 × h _FE2 )(here
And h _FE2 Is the current amplification factor of the PNP transistor)
It flows to the NP transistor. This collector current I _C2 Is
Base current I of NPN transistor _B1 So
Current I _B1 Is larger than the current initially passed. G
The current gain of the transistor becomes a current value that drops to "1"
Until this operation (NPN transistor and PNP transistor)
The current amplification is alternately performed by the
Anti (thyristor action) appears. Therefore, two
If the transistor does not work, the thyristor action is
Does not wake up.

FIG . 3A shows a parasitic thyristor.
The two transistors of the above equivalent circuit are shown, and so on.
The value circuit is shown in FIG. In FIG. 3A, a square
C, B, and E surrounded by PNP transistor collector
C, B, and E, which are shown by white circles,
Are the collector, base and emitter of the NPN transistor
Is shown. PNP transistor base (enclosed in a square
B) and the emitter (E in a box)
It is connected to the electrode 9 via. Therefore, NPN
When the collector current of the transistor flows, the voltage drop of the substrate resistance
The bottom occurs and the emitter of the PNP transistor (square
Encircled E) and the base (B enclosed in a square)
It is iased. This voltage drop causes the PNP transistor
Emitter (boxed E) and base (boxed)
When the voltage exceeds the forward voltage (diffusion potential) of B), the PNP
The base current flows through the transistor and the PNP transistor operates.
Make, thyristor action occurs.

The current value at which this thyristor action occurs is given by the following equation. _{I thyrister ≒ (V d × A} p) / [ρ × (t _p -d _p)] where _I thyrister: current thyristor action occurs V _d: if the diffusion voltage of the PN junction (semiconductor substrate is Si General
Specific value of about 0.6V) A _p: area pellets [rho: resistivity of the semiconductor substrate t _p: pellet thickness d _p: depth of the P-type region

When this semiconductor element is used as a constant voltage diode, if a current value at which a thyristor action occurs is within the operating current range of the semiconductor element, a malfunction or the like of a circuit in which the semiconductor element is used becomes a problem. . In such a case, instead of the N-type semiconductor substrate of FIGS. 1 and 2, as shown in FIGS. 4 and 5, the same as the N-type semiconductor substrate 1 to the low-resistivity N ⁺ type semiconductor substrate 1A The problem can be solved by using an N-type region layer 1B having a resistivity formed by epitaxial growth or the like.

FIGS. 4 and 5 are modifications of the embodiment of FIG. 1 and the embodiment of FIG. 2. Corresponding portions are allotted with the same reference numerals, and description thereof is not repeated. However,
Satisfy the following equation. V _d > (I _MAX / A _p ) × [(ρ _N · t _N ) − (ρ _n · t _p )
+ (Ρ _n · t _n )] where I _MAX : maximum operating current value of the semiconductor element ρ _N : resistivity of the N ⁺ type semiconductor substrate t _N : thickness of the N ⁺ type semiconductor substrate ρ _n : N type region layer _Tp : depth of P-type region _tn : thickness of N-type region layer

In the structure of FIG. 1 and FIG.
In the case of 40 mm square, the pellet thickness of 230 μm, the resistivity of the N-type semiconductor substrate of 5 Ωcm, and the depth of the P-type region of 4 μm, a thyristor action occurs around 8 mA. However, in the structure of FIGS. 4 and 5, the pellet size is 0.40 mm square, the thickness of the N type region layer is 7 μm, the thickness of the N ⁺ type semiconductor substrate is 223 μm, the resistivity of the N type region layer is 5 Ωcm, and the size of the N ⁺ type semiconductor substrate is Resistivity 8mΩc
When the depth of the m and P-type regions is 4 μm, a thyristor action occurs at around 600 mA. Thus, the current value at which the thyristor action occurs can be increased.

It is conceivable to positively use the thyristor described above. FIG. 6A shows a diode according to such a second characteristic. An oxide film is provided on the surface of the N-type semiconductor substrate 1 shown in FIG. 1, a window is selectively opened, and P-type impurities are introduced through the window to form P-type regions 3 and 4. Similarly, N ⁺ regions 5 and 6 are formed by introducing N-type impurities.

An oxide film is selectively removed and formed, and a gate oxide film 2 is formed. MOS transistor gate direct
An impurity is implanted into the lower channel region , and the turn-on voltage V
Control _T. The electrode 7, the electrode 8, and the electrode 9 are deposited to form a pellet. Thus, a thyristor is formed by the P-type region 4, the N-type semiconductor substrate 1, the P-type region 3, and the N ⁺ -type region 5. Fig. 6 shows an equivalent circuit of this pellet.
(B). Positive to the electrode 9, a negative voltage is applied to the electrode 7, when the voltage exceeds V _T, 7 the drain current flows as (a), current is injected into the gate of the base and the thyristor portion of the bipolar transistor part As a result, the bipolar transistor section turns on. Therefore, the current rapidly when the voltage exceeds V _T begins to flow. Conversely, when the voltage does not exceed the V _T, almost no current flows. That is, the leakage current is small. Here, in FIG.
3 and the P-type region 4 are connected to each other. This is
Display the state where the MOSFET is operating pressure beyond the V _T
doing. The P-type region between oxide film 2 and point B is
Represents the channel [inversion layer] of the section. Therefore, the voltage
When not exceed V _T is, P-type region 3 and the P-type region 4
Is not connected.

[0031] In FIG. 7 (a), when the collector current I ₂ is small, points A and B are the same potential, the thyristor is not turned on. The collector current I ₂ increases,
The potential at point B drops by the voltage drop, and the thyristor turns on. The voltage-current characteristics are as shown in FIG. 8B, and the leakage current is small.

FIG. 8 shows an equivalent circuit of static electricity. Since the voltage of the static electricity is sufficiently higher than the withstand voltage of the diode, the current i _(t) flowing through the diode due to the static electricity is hardly affected by the withstand voltage of the diode. i _(t) = [(voltage of capacitor C) − (withstand voltage of diode)] / (resistance R) Therefore, the power consumption of the diode due to static electricity becomes ₍ withstand voltage of diode) × i _(t) . The lower the power, the lower the power consumption. Since i _(t) is as shown in FIG. 8B, the power consumption of the diode decreases as the current value causing the thyristor action decreases.
For this reason, the electrostatic withstand capability increases as the current value causing the thyristor action decreases.

In order to reduce the current value causing the thyristor action, the DC current amplification factor of the bipolar transistor portion (the surface portion of the semiconductor substrate) shown in FIG. by increasing the resistance value, it is necessary to increase the voltage drop at the point B in FIG. 7 (a). The gate oxide film 2 is made as thick as possible in order to obtain a low inter-terminal capacitance and a high electrostatic capacity. As shown in FIG.
When the OS transistor portion is formed in a ring shape, the gate electrode portion of the anode electrode 7 may be partially formed in order to suppress the inter-terminal capacitance.

In the case of manufacturing an electrostatic protection diode for an IC in which the voltage of an input / output signal is smaller than 5 V, the resistance of the N-type semiconductor substrate 1 is about 5 Ωcm or more and the gate oxide film 2 is
When the thickness is about Å or more, the resistance to static electricity is improved. Also, adjust the junction area and gate electrode size so that
When it is less than pF, the signal waveform is not disturbed with respect to the input / output signal of a practical level. The leakage current of the diode manufactured in this manner is about several nA or less. This structure has a structure in which a breakdown voltage is determined by a MOS transistor having a small leakage current, and a MOS transistor having a low electrostatic capacity is protected by a thyristor.

FIG. 9 is a reference example of a diode according to the second feature described above. An oxide film is provided on the surface of the N-type semiconductor substrate 40 shown in FIG. 1, a window is selectively opened, and P-type impurities are introduced through the window to form P-type regions 41, 42, and 50. Similarly, N ⁺ regions 43 and 44 are formed by introducing N-type impurities. An oxide film is selectively removed and formed, and a gate oxide film 45 is formed.
And an oxide film 46 is formed. MOS transistor gate
Impurities are implanted into the channel region directly below, to control the turn-on voltage V _T. An anode electrode 47, an electrode 48, and a cathode electrode 49 are deposited to produce a pellet. FIG. 9B shows an equivalent circuit of the pellet.

Since the diode portion is formed as compared with the reference example of FIG. 6, when static electricity is applied in the forward direction of the diode, the diode portion absorbs the static electricity.
When the voltage is applied in the opposite direction, the static electricity is absorbed by the thyristor, as in the reference example of FIG. As described above, the present invention has been described with respect to an example in which the MOS transistor section is configured by a P-channel insulated gate field effect transistor and the bipolar transistor is configured by an NPN bipolar transistor. However, the MOS transistor section is configured by an N-channel insulated gate field effect transistor. However, it will be apparent to those skilled in the art that the present invention can be similarly implemented even if the bipolar transistor is formed of a PNP bipolar transistor.

[0037]

As described above, according to the present invention, since the MOS transistor portion and the bipolar transistor portion are formed on the semiconductor substrate, there is an effect that the operating resistance is reduced.
The operating resistance of a constant voltage diode having a withstand voltage of 5 V or less in the conventional structure is particularly large. Therefore, when the present invention is applied to a low voltage withstand voltage constant voltage diode, the effect of improving the operating resistance is large. As described above, according to the present invention, since the MOS transistor portion, the bipolar transistor portion, and the thyristor portion are formed on the semiconductor substrate, there is a result that a diode for static electricity protection having a small leakage current and a high electrostatic capacity can be manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a constant voltage diode according to a first reference example of the present invention.

FIG. 2 is a diagram showing a constant voltage diode according to a first embodiment of the present invention.

FIG. 3 is a diagram illustrating the influence of a parasitic thyristor according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a constant voltage diode according to a second reference example of the present invention.

FIG. 5 is a diagram showing a constant voltage diode according to a second embodiment of the present invention.

FIG. 6 is a diagram showing a constant voltage diode according to a third reference example of the present invention.

FIG. 7 is a diagram illustrating an operation of a third reference example of the present invention.

FIG. 8 is an equivalent circuit illustrating the effect of static electricity.

FIG. 9 is a diagram showing a constant voltage diode according to a fourth reference example of the present invention.

FIG. 10 is a diagram showing a conventional constant voltage diode.

FIG. 11 is a diagram showing a conventional constant voltage diode.

FIG. 12 shows the structure of a thyristor and its equivalent circuit.
FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 N-type semiconductor substrate 2 P-type region 3 P-type region 4 N ⁺ region 5 N ⁺ region 6 Gate oxide film 7 Electrode 8 Electrode 9 Substrate electrode 10 N-type semiconductor substrate 11 P-type region 12 P-type region 13 N ⁺ region 14 N ⁺ region 15 Gate oxide film 16 Oxide film 17 Electrode 18 Electrode 19 Electrode 20 Electrode 20 Substrate electrode 20a, 20b N-type semiconductor substrate 21a, 21b Oxide film 22a, 22b P-type region (guard ring) 23 P ⁺ region 24 Polycrystalline semiconductor ( P ⁺ region) 25a, 25b Anode electrode 26a, 26b Cathode electrode 50 P-type region

Claims (2)

(57) [Claims] 1. A semiconductor device comprising: a P-channel insulated gate field effect transistor having a source and a drain on one main surface side of a semiconductor substrate; and an NPN bipolar transistor having a collector, an emitter and a base. A source and the collector are connected, and a gate of the insulated gate field effect transistor section is connected to the drain and the base, and characteristics between the collector and the emitter are used as a constant voltage diode. Semiconductor element. 2. An N-channel insulated gate field effect transistor portion having a source and a drain on one main surface side of a semiconductor substrate and a PNP type bipolar transistor portion having a collector, an emitter and a base are formed. A source and the collector are connected, and a gate of the insulated gate field effect transistor section is connected to the drain and the base, and characteristics between the collector and the emitter are used as a constant voltage diode. Semiconductor element.