JPS6251260A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a field effect semiconductor device, which can implement high withstanding voltage even in AC driving, by providing means and resistor components having a rectifying function in the forward direction toward a gate electrode between main electrodes and the gate electrode. CONSTITUTION:Means and resistor components, which have rectifying characteristics in the forward direction toward a gate electrode 7 are provided between main electrodes 5 and 8 and the gate electrode 7. For example, a high concentration (n) layer 103 is formed in a boundary region between an island 101 is semiconductor substrate and an insulating film 102. In this island 101, a PB laye 2 and a PE layer 4 are formed by impurity diffusion. An nE layer 1 is formed in the PB layer 2. A part, in which impurities are not diffused, works as a thyristor nB layer 3. On a substrate 100, a silicon oxide film 104 is provided. Through holes provided in the film 104, the cathode electrode 5, the gate electrode and the MOS electrode 6 and 7, and the anode electrode 8 are provided. Resistors and diodes 10-13, 9 and 12 are connected between the gate electrode 7 and the anode electrode 8 and between the gate electrode 7 and the cathode electrode 5 as shown in the Figure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor device, and particularly to a field effect type high voltage semiconductor device suitable for use in alternating current.・ [Background of the Invention] Generally, when a high voltage is applied to a field effect type high voltage semiconductor device, the gate electrode is charged due to the leakage electric field from the drain, and this charged gate voltage causes a relatively low voltage to be applied between the source and drain. Since the area under the gate electrode is inverted and a channel is formed, there is a problem in that the withstand voltage between the source and drain decreases.

- Regarding conventional MO8 field effect semiconductor devices, etc., as a method to reduce the charge on the gate electrode and achieve high withstand voltage.
A method to thicken the oxide film under the gate electrode near the drain junction is described in Electronics Technology Complete Book Volume 3 M published by Kogyo Kenkyukai.
It is disclosed in OS Device p276. Also, the method of creating an offset gate structure is described in the same document or in IEE Transactions on Electron Devices, Volume E.D. 29, page 1171 (19
82) (IE8tl Transaction on
IELactron Devices VoQ.

ED-29, pH71 (1982)), etc.

However, these are all devices intended to be used with direct current, and when used with alternating current, a high withstand voltage can be achieved with an applied voltage of one polarity, but in the case of the opposite polarity, a voltage of several tens of volts can be achieved.
The breakdown voltage is below, and high breakdown voltage cannot be achieved. Furthermore, there is no mention of methods that can be used for alternating current.

The problems encountered when using the former method in exchange will be detailed below.

FIG. 5 shows a MOS-FETk disclosed in the above-mentioned document. In order to achieve high breakdown voltage, a step is formed in the gate oxide film under the gate electrode 7, and the oxide film 27 near the drain 25 is
It is recommended to make it thicker.

In the case of this device, when applying a so-called forward polarity voltage in which the drain 25 is negative and the source 24 is positive, the drain 25 is It is necessary to make the oxide layer 11127 thicker, and it is necessary to provide a significant step difference between the gate oxide film 28 and the portion away from the drain 25.

Therefore, it is necessary to add a step forming process or a process to prevent the gate electrode from breaking at the step, resulting in a problem that the process becomes extremely complicated.

Furthermore, this method has the essential problem that it cannot be applied to AC-driven field effect type high voltage semiconductor devices.

That is, when trying to realize a high withstand voltage by driving the applied voltage with reverse polarity such that the drain 25 is positive and the source 24 is negative in FIG. 5, the gate electrode 7 near the source junction is biased in the opposite direction. This is because the underlying oxide film 28 also needs to be thick. In this case, even if a predetermined gate voltage is applied during forward operation, a channel can be formed in the part corresponding to the thin gate oxide film 28 away from the source 24, but in the part corresponding to the thick gate oxide film near the source 24. A channel is not formed and the device becomes inoperable.

[Purpose of the invention]

An object of the present invention is to overcome the problems of the prior art and to provide a field effect semiconductor device that can achieve high breakdown voltage even when driven with AC.

[Summary of the invention]

An object of the present invention is to provide a field effect semiconductor device having a pair of main electrodes A and B so that the main electrode A and the gate electrode, which have a high potential when forward biased, have approximately the same potential, and have a high potential when reverse biased. This is achieved by making the main electrode B and the gate electrode have approximately the same potential.

That is, this is achieved by connecting short-circuiting means having rectifying characteristics, such as diodes, between the main electrode A and the gate electrode and between the main electrode B and the gate electrode, respectively, in directions that exhibit the above-mentioned operation.

[Embodiments of the invention]

Hereinafter, the details of the present invention and its effects will be explained based on Examples.

FIG. 1 shows a MOS field effect type lateral thyristor which is a first embodiment of the present invention.

In FIG. 1, 100 is a dielectric insulation isolation substrate;
Reference numeral 1 denotes one n-type semiconductor single crystal island embedded through an insulating film 102. A high concentration n layer 103 is formed in the boundary region between the island 101 serving as a semiconductor substrate and the insulating film 102 . A pa layer 2 and a pE layer 4 are formed on the island 101 by impurity diffusion, and an nE layer 1 is formed on the pa layer 2.
The portion where the impurity is not diffused functions as the thyristor n1 layer 3. A silicon oxide film 104 is provided on the substrate 100, and a quad electrode 5, electrical and MOS gate electrodes 6, 7, and an anode electrode 8 are provided through openings provided in the film 104. Between the gate electrode 7 and the anode electrode 8,
Resistors and diodes 10 to 13, 9 and 12 are connected between the gate electrode 7 and the cathode electrode 5 as shown.

In addition, below, each layer 1-4 is simply nE#Pa*n
It is abbreviated as BIPE.

First, a mechanism for achieving high withstand voltage in the OFF state of this device will be explained. In a so-called forward bias state in which the anode terminal A has a higher potential than the cathode terminal, the pn junction formed by PH2 and nE3 is reverse biased. At this time, since the gate electrode 7 and PE4 are connected through the diode 9 and the resistor 10, the diode 9 is forward biased, while
Gate electrode 7 and pa via diode 12 and resistor 11
2 is connected, the diode 12 is reverse biased. As a result, when the thyristor is forward biased, the potential of the gate electrode 7 becomes approximately equal to the potential of nE3, and charging of the gate electrode due to a leakage electric field is prevented, so that the gate electrode 7
Formation of a channel on the n-base surface below is suppressed and a high forward breakdown voltage can be achieved.

Also, when the thyristor is in a reverse bias state, pI! 4 and na
Although the junction formed with 3 is reverse biased.

In this case, diode 9 is also reverse biased while diode 12 is forward biased. As a result, the potential of the gate electrode 7 is substantially equal to the potential of nu3, suppressing the formation of a channel on the surface of n83, and achieving a high reverse breakdown voltage.

As described above, in this device, a high breakdown voltage can be achieved regardless of the thickness of the silicon oxide film 104 of the gate electrode 7, both in the forward and reverse directions, so the thickness of the silicon oxide film 104 can be freely selected according to the requirements of other characteristics. There are advantages that can be achieved.

Next, the operating mechanism for turning on this device will be explained.

When the thyristor is in a forward bias state and the gate terminal G is changed from an open state to a predetermined potential vO, the anode potential V^
When the gate terminal potential is low compared to , a current flows from the anode terminal A to the gate terminal G via the diode 9 and the resistor 10, and a potential difference of (V^-Vo) is maintained between the anode and the gate terminal.

Vo or V^ changes, and this potential difference (■^-Vo)
When the voltage exceeds the threshold voltage at which the n83 surface is inverted, an inversion layer is formed. Therefore, a current flows along the path from anode terminal A→pg→inversion layer→pa→resistance 13→cathode terminal. As a result, the potential across the resistor 13 is nB ・pa
When the voltage at which the junction builds up (build up) is exceeded, injection occurs from nEl and nE! "pB
・The nB transistor part turns on. Then pE-n
The B-pB transistor section is also turned on, and the positive feedback between both transistors causes the thyristor to fire.

Note that this device cannot be turned on from a reverse bias state. In other words, AC drive is achieved in that high withstand voltage can be achieved in both forward and reverse directions.

In this example, na concentration, pI! The surface concentration of PB, and the surface concentration of nB are each
10 "a++-", I X 10 "am-", pa and pE! When the distance between them was 30 μm, a breakdown voltage of 230 V in the forward and reverse directions could be achieved. In addition, in this embodiment, the thickness of the oxide film under the gate electrode 7 is approximately 0.4 μm.
When the resistor 13 was set to approximately 6 Ω, the thyristor could be ignited by forming a potential difference (■^-Vo) of approximately 3.5 V between the terminals G and A.

FIG. 2 shows an M, O8 field effect lateral thyristor according to a second embodiment of the present invention. Components equivalent to those shown in FIG. 1 are given the same reference numerals.

This embodiment has the advantage that the same functions as those of the first embodiment can be realized with a smaller number of element configurations, that is, when integrated into an IC, the same functions can be realized with a smaller occupied area.

In this embodiment, the high voltage diode 9 of the first embodiment has a pH value of
4 and no. 3, the high voltage diode 12 is shared by the junction formed by pa. 2 and nB3, and the resistors 10 and 11 are used as the resistor 14. This embodiment has exactly the same configuration and the same operating mechanism as the embodiment. Therefore, three elements can be reduced, and the number of IC
If it becomes

The occupied area can be reduced to about 60% of that of the first embodiment.

The characteristics of the device of this example are the same as those of the first example, with a forward and reverse breakdown voltage of approximately 230V and a gate duty for firing the thyristor of approximately 3.5V.

FIG. 3 shows a complementary gate MO8 field effect lateral thyristor according to a third embodiment of the present invention.

In this device, the MOS gate electrode 7 is provided on noa as in the first embodiment, and the MOS gate electrode 19 is also provided on pH2, so that the gate potential can be high or low with respect to the anode or cathode potential. The thyristor should be able to fire even if the

In addition, a diode 29 is provided between GK- in order to prevent the MOS gate electrode 19 from being charged when the thyristor is forward biased, a channel is formed on p-16 and pal, and the withstand voltage is lowered. When turning on the electrode 19
A resistor 30 is provided below to obtain a potential to form a channel. Also, by providing p layer 17.18, pl!・MOS-FE composed of nB-pB
While the T has an offset structure, the P layer 16 is provided to relax the electric field of the PA junction under the gate electrode 19, thereby realizing a higher withstand voltage.

The p layer 16.17 is an integrated layer surrounding pH2, and the G
Both terminals K and G^ are connected externally.

First, the operating mechanism that achieves high breakdown voltage in the off state will be explained.

In the first embodiment, for example, when the thyristor is forward biased, the potential of the gate voltage wA7 is fixed to approximately the anode potential, so depletion of the n8 surface under the gate electrode 7 near the pB"nB junction is suppressed, and the depletion layer does not spread sufficiently to the nu side, the electric field becomes concentrated, and a breakdown phenomenon occurs at low voltages, resulting in a relatively low forward breakdown voltage.Also, when the thyristor is reverse biased, a similar phenomenon occurs under the gate electrode 7. PE of
- Occurs near the nB junction and has a relatively low reverse breakdown voltage.

However, in the case of this embodiment, a higher breakdown voltage can be achieved by setting the p layer to a predetermined concentration of 17.18. For example, if the thyristor is forward biased, p below the gate electrode 7
The expansion of the depletion layer near the B'nB junction toward the nts 3 side is approximately the same as in the first embodiment, but the P layer 17
By setting the surface concentration of P to about 5.times.1.0 "an-", the depletion layer can be extended to the P layer 17 side, and electric field concentration can be significantly alleviated. Similarly, when the thyristor is reverse biased, the depletion layer near the PE'nB junction is
It can also be extended to the sides, significantly reducing electric field concentration.

In this case, in the vicinity of the PE4 not facing pa2, the electric field concentration near the junction can be alleviated due to the so-called field plate effect brought about by the anode electrode 8 extending beyond the PE'nB junction to the nu side. As a result, each layer was made to have the same impurity concentration as in the first embodiment, and P layer 1
．． 6,17゜18 each length is 15 μm, p layer 17
．． The ignition mechanism of the sixth-order thyristor that can achieve a high forward and reverse breakdown voltage of about 450 V when the interval between the electrodes 18 and 18 is 25 μm and the length of the electrode protruding toward the nu side from pE is 25 μm will be described.

As mentioned earlier, this device operates at a predetermined potential V while the thyristor is in a forward bias state and the gate terminal G^ is open.
When set to o, the thyristor can be fired regardless of the level relationship between the anode potential V^ and cathode potential VK of the thyristor and the gate potential Va. Hereinafter, three types of potential relationships will be classified and explained. Note that the MOS gate electrode 7 of nu 3J- and its terminal G^ will be collectively described as Op, and the MOS gate electrode 19 on pB4 and its terminal GK will be collectively described as Gn.

(1) When v^ is a lower potential than Vo, the MOS transistor pp ns pa portion is not driven because the accumulation of nu3 under the MOS gate voltage 1mGp is promoted. On the other hand, vertical MOS transistor n[! PBn
In the B portion, when the difference between Va and PR potential is larger than the threshold voltage, an upper n lower channel of the MOS gate electrode is formed.

As a result, a current flows through the path from the anode terminal A-) pE4 → ne → n channel → npl → cathode terminal, and this current serves as a trigger to fire the thyristor using the so-called known thyristor anode gate drive mechanism. .

(2) When v is higher potential than Vo, vertical MO8) - transistor nE pa n8 part is MO
Accumulation of pa2 and p-16 under the S gate electrode Gn is promoted and is not driven. On the other hand, in the lateral MOS transistor pE nu p8 portion, when the difference between the Vo and nB potentials is larger than the threshold voltage, a p channel is formed under the MOS gate electrode GP.

As a result, anode terminal A → ps4 → P channel → pB
A current flows through the path from →resistor 12 →cathode terminal, and this current serves as a trigger to fire the thyristor using a so-called known thyristor cathode gate drive mechanism.

(3) In cases other than (1) and (2), that is, when Vo is at a lower potential than VA and higher than vK, the thyristor is fired by either mechanism (1) or (2).

In the case of this example, the oxide film thickness under the gate electrode 7 is set to 0.4 μm.
By setting the oxide film thickness under the gate electrode 19 to 0.3 μm and setting the resistor 12 to about 6 to Ω, potential differences (-VA - Va ) of about 3.5 V and 4.5 V (7) are formed, respectively. As a result, the thyristor could be fired regardless of the relationship between the thyristor's anode/power sword terminal potential and the gate potential. The on-voltage of the thyristor is 1.2 when 100mA is applied.
v, on-resistance is 8Ω, which poses no practical problem.

FIG. 4 shows an MO8 field effect lateral thyristor according to a fourth embodiment of the present invention.

The device configuration is the same as that of the first embodiment except that the high breakdown voltage diode 9.12 in the first embodiment is replaced with a high breakdown voltage n-channel MO8-FET 20.23. The mechanism for achieving high withstand voltage in the OFF state of this device is as follows. n channel MO8-F when thyristor is forward biased
The source and gate of the ET 20 are short-circuited, and a higher potential than the potential of the p-layer is applied to the gate electrode, so a channel is formed and turned on. On the other hand, n-type MO8-F
Although the source and gate of ET23 are short-circuited, a potential approximately equal to the potential of the p-layer is applied to the gate electrode, so it remains off. As a result, a high potential equivalent to that of the anode appears on the gate electrode 7 and becomes approximately equal to nB3, so that the generation of a channel to na3 is suppressed, and a high forward breakdown voltage can be realized. Next, when the thyristor is reverse biased, n
The source and gate of the channel MO5-FET23 are short-circuited, and a potential higher than the potential of the p-layer is applied to the gate electrode, so that a channel is formed and turned on. On the other hand, although the source and gate of the n-channel MO8-FET 20 are short-circuited, a potential approximately equal to the potential of the p-layer is applied to the gate electrode, so it remains off. As a result, a high potential equivalent to that of the cathode appears on the gate electrode 7, which becomes a potential substantially equal to na3, so that the generation of a channel to nfl is suppressed and a high reverse breakdown voltage can be realized.

Next, the ignition mechanism of this device will be explained. When the thyristor section is forward biased and a potential lower than the anode potential is applied to the gate terminal G, the n-channel MO8/FET 20 is turned on, so a current flows through the path of the anode -> MO8/FET 20 -> resistor 21 -> gate terminal. n-channel MO8-FE
If the on-resistance of T20 and the value of the resistor 21 are sufficiently high, the threshold voltage of the p-channel MOS-FET consisting of pHnB can be increased simply by passing a small current, and a p-channel can be formed on the surface of n8, so that the anode terminal A →pE4
A current flows along the path →P channel →pn 2 →resistance 13 →cathode terminal, and the thyristor is fired by a so-called known cathode gate drive mechanism.

In the case of this embodiment, compared to the diode of the first embodiment, M
Since the on-resistance of OS-FETs 20 and 23 can be easily increased □, even if the resistance values of resistors 21 and 22 are reduced, minute currents such as □ anode, - gate terminals A, G
The thyristor can be adjusted to 7. □5 Say □ Ah. −
□. :,,1. Since the device occupies a larger area compared to an 8-FET to achieve the same resistance value, if this device is integrated into an IC, the overall area it occupies will be 11'' smaller than that of the first embodiment.

Although the effects and details of the present invention have been described above based on four embodiments, the present invention is not limited to these one embodiment, and various modifications and applications are possible.

For example, the thyristor serving as the main switch may be a p-channel lateral MO8 FET that requires voltage resistance in both forward and reverse directions. Also, the n-channel MO8-FET in the fourth embodiment
may be an element having another rectifying function such as a p-channel MO8-FET or a bipolar transistor, and the first . The resistor 11 of the third embodiment and the resistor 22 of the fourth embodiment may be deleted. In addition, in the embodiment of section 4, MOS-FET20,2
By using an element with a sufficiently large on-resistance □ as the resistor 21.2'*, it is possible to eliminate the resistor 21.2'*. Furthermore, let's talk about an embodiment in which the main switch has a lateral structure! However, it may also be a vertical structure such as a power thyristor. □ □ Also, when each device is converted into an I'C, it can be realized using various isolation substrates or plates such as a pn junction isolation substrate instead of a dielectric insulation isolation substrate.

[Effects of the Invention] 5. As described above, according to the present invention, since charging of the gate electrode in a field effect semiconductor device can be suppressed, the withstand voltage in both forward and reverse directions can be improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an MO5 field-effect lateral thyristor according to a first embodiment of the present invention, and FIG. 3 and 4 are cross-sectional views of an MO8 field-effect lateral thyristor, which are embodiments of 2.3.4 of the present invention, and FIG. 5 is a cross-sectional view of a lateral MO8-FET, which is a known example. be. 1.2, 3.4-... Thyristor nl! *PB+
rlB. pE layer, 5, 6.8... Thyristor cathode, gate, anode electrode, 7... MOS gate electrode, 9°1
2...Diode, 10, 11. ．． 13...Resistance. 104...Silicon oxide film.

Claims (1)

[Claims] 1. In a semiconductor device in which a semiconductor substrate has at least three semiconductor layers having sequentially different conductivity types, each main electrode is provided in each of the outermost layers, and a gate electrode is provided in an intermediate layer with an insulating film interposed therebetween. 1. A semiconductor device comprising: a means having a rectifying function in a forward direction toward the gate electrode; and a resistive component provided between the gate electrode and the gate electrode.