JPS5857747A - Semiconductor device - Google Patents

Abstract

PURPOSE:To improve a critical OFF voltage increase rate of a vertical type photo silicon controlled rectifier (SCR) by making large hFE of pnp element and photo sensitivity by thermal treatment, while making small a gate resistance and by integrating elements in the same chip. CONSTITUTION:Response of pnp element of photo SCR delays when hFE is made large, while gate resistance RG and gate voltage VG are in the relation VG CRGXdv/dt, and when RG is made small, a critical off voltage increase rate becomes large. Meanwhile, a displacement current by dv/dt is a transient phenomenon and therefore (dv/dt)M can be improved fantastically by making large hFE and small RG by a mutual reinforcing effect by these two effects. When hFE is increased by making longer the life time of base layer, a photo sensitivity is generally enhanced, while the minimum trigger current reduces a little and the (dv/dt)M is as much improved. Such photo sensitivity is improved by about 30% through annealing under the N2 atmosphere at 900 deg.C. When the RG 9 (P layer) is provided in the substrate 1 and the one end is connected to the gate 4, while the other end to the cathode 8 through the electrode 10, the (dv/dt)M can be improved by 2-3 times as compared with that when a resistor is provided externally.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photothyristor, and more particularly to a semiconductor device that can be used as an optically coupled semiconductor device in combination with a light emitting diode.

Conventionally, as shown in FIG. 1, a photothyristor coupler that uses a light emitting diode GL on the input side and a photothyristor PT on the output side in a single package has been put into practical use. Compared to electromagnetic relays, this type of photosilic coupler has the following characteristics: ■Extremely good insulation between input and output, ■Fast operating speed, ■Long life, ■Less noise generation, and ■No influence from external magnetic fields. ,■ They have advantages such as their small size, and as the use of electronic circuits in various devices progresses, they are used in a wide range of fields such as isolation of signal transmission systems and AC controllers.

However, when a steep voltage is applied between the anode A and the cathode of the photothyristor, the photothyristor turns on at a voltage lower than the original breakover voltage of the photothyristor. This phenomenon is caused by a steep rising voltage r:F:, (”/,, )
is applied, a displacement current ID expressed by the following equation flows through the capacitor CO (junction capacitor, etc.) as shown in the photothyristor equivalent circuit diagram of FIG.

; D−dZ, =4(CoZ,'==codZ,
10vdcH, (1) Here, assuming that Co is constant (
1) Equation further becomes as follows.

1=Codv/d, (2) D As a result, if the value of s"At is large, the photothyristor will be in the on state. Find the value of the maximum rising voltage (d'i/dt)M that does not cause this phenomenon. This is called the critical off-voltage rise rate.

Therefore, when actually using the photothyristor coupler, as shown in Figure 3, the photothyristor gate PG
A resistor R6 and a capacitor CG are connected between the terminal and the cathode to prevent malfunction when a steep voltage is applied. However, when designing the actual circuit, it is necessary to connect the resistor and capacitor externally. This is extremely inconvenient due to the installation location and increased cost.

The present invention has been made in view of the problems with the conventional photothyristor couplers described above, and relates to a photothyristor coupler that does not require external components.

Various reports have been published regarding the improvement of malfunction caused by the steep rise voltage d-1 of photothyristors.
The following methods are mainly known for increasing (d'/'at)M[.

(1) PNP) Reduce the hFE of the run lister.

(2) Reduce gate resistance R6.

However, when (d%t)M is increased by the method described above, the minimum Triuer current 'FT becomes large, which is a practical problem. Therefore, “” )M (!: IFT
In order to solve all problems simultaneously, the following two methods (3) and (4) have been proposed.

(3) Method of controlling gate resistance with transistors FIG. 4 shows an example of a circuit in which gate resistance R6 is controlled with transistors Q and Q2. When a steep voltage is applied in this circuit, part of the displacement current is ) -y n) Star Q
1 is applied to the current level, turns on the transistor Q1, and increases the M value by (dV/dt). When light is irradiated, phototransistor Q2' is turned on, Ql is turned off, and IFT can be kept small.

However, there is a problem in that dielectric isolation technology is required to make the circuit shown in FIG. 4 into one chip, which complicates the process.

(4) A method of controlling gate resistance with MOS FET.

An example of a circuit using this method is shown in FIG. However, in the photothyristor, two sets of Ql, Qs and Q2-Ql are connected in antiparallel. The operating principle is as follows.

Now consider a photothyristor represented by transistors Q+ and Qs. MO5FETQ6 is connected in parallel to the gate resistance R61 of photothyristor Q+, Qs, and M-O
The gate potential of S F E T Qs is the transistor Q3
connected to the base of. For this reason, photothyristor Q1. The anode potential of Q3 is the threshold voltage V of MO5FETQa. When the value exceeds 0, MO5FETQ is turned on and the gate resistance of the photothyristor is reduced. It has a so-called zero-crossing function, and when the anode potential exceeds vl, the photothyristor turns on, and in effect the dVdt
becomes higher.

In this method, a high voltage of several hundred V is applied to the gate of the MOSFET, so the MOSFET can withstand high voltage.
is required and requires a special process during creation.

Therefore, the present invention does not use the above-mentioned complicated steps (d
Provided is a photothyristor which has improved V/dt)M and prevents malfunctions due to steeply applied voltages.

To summarize the present invention, in a vertical photothyristor, contrary to the conventional method (1) described above, the hFE and photosensitivity of the PNP (PNP) run thyristor are increased, the gate resistance is decreased, and the resistance is reduced by photothyristor. This can be achieved by incorporating the thyristor into the same chip.

The present invention will be described in detail below with reference to Examples.

FIG. 6 shows the structure of a vertical photothyristor according to the present invention.

In the figure, 1 is an N-type semiconductor substrate, usually 20 to 50
Silicon having a specific resistance of Ω·G and a thickness of about 200 μm is used. 2, Porons diffuses about 100μ of P-type impurities such as gallium from both sides of the N-type semiconductor substrate 1, and
This anode was created by separating the type substrate 1 through and through it, and further diffusing P-type impurities over the entire back surface. 3 is a gate formed by diffusing 5 to 60μ of P-type impurity poron into the substrate 1 from the main surface of the substrate, and is generally an anode.
It is created at the same time as the diffusion on the entire back surface of the board (diffusion resistance pressure, which may vary depending on hFE). Reference numeral 4 denotes a cathode formed by diffusing N-type impurity phosphorus into the gate 3. The depth is generally about 2 to 20 microns. The main surface of the semiconductor substrate on which the above regions are formed by diffusion is covered with an insulating film 5, and 5i02 is generally used as the insulating film 5.

Each of the above regions has an anode electrode 6. Gate electrode 7
, the cathode electrode 8 is made of metal such as A4.

As mentioned above, the cross-sectional structure is the same as that of the conventional vertical photothyristor, but in order to increase (dVdt)M, the photothyristor according to this embodiment has a large hFE of the PNP) run risk included in the photothyristor. The gate resistance is reduced.

That is, such hFE and gate resistance characteristics are usually obtained by increasing the lifetime of the base region of the transistor, and are obtained by performing heat treatment.

As an example, after the diffusion of the cathode region 4 is completed, the temperature is 900°C N2.
When heat-treated inside, the hFE of PNP) run risk is 1
．． Improved by 5-3 times. In this case, the surface of a general photothyristor is protected with 5i02, and when it is heat-treated in an oxygen atmosphere, the hFE of the NPN l-run risk is significantly degraded. Therefore, it is necessary to add another process such as once removing the SO2 film. Other methods such as dislocation-free diffusion technology and optimization of impurity concentration may also be used.

In the structure of the vertical photothyristor described above, when the hFE of the PNP l-lancistor is changed by heat treatment etc., the order of light emitting diodes required to shift the photothyristor from OFF to ON state in the photothyristor coupler shown in Fig. 1 is changed. Minimum value of directional current (minimum trigger current:
Figure 7 shows the relationship between I,,) and the critical off-voltage rise rate "/a t." The peak value of hFE is shown.

Straight line A in Figure 7 shows the gate resistance R6 fixed at 20Ω (N
PN l-ranjis! hFE is also fixed), P
NP) Run risk hFE of 0.5. 1. Q.

IFT and (dot) when sequentially changed to 2.5.5
, shows the relationship with . Straight line A has a relatively gentle slope, indicating that the change in (dVdt)M with respect to IFT is small.

Next, the relationship between IF□ and (dv/dt)M when the bFE of the PNP) run risk is constant (the value of the NPN transistor is also constant) and the gate resistance R6 is changed is expressed by the straight line B5.
Shown below. Straight line B5 is PNP) run risk hFE”5
Therefore, the straight line passes through the point hFEw5 on the straight line A. IIFEt 2.5.1.0゜0.5
, the change is represented by a straight line that passes through each bFEQ point on the straight line A and is almost parallel to the straight line B5.

As can be seen from straight line B5, when the gate resistance is changed,
The change in (d'/Jt) with respect to TPT is very large.

Now, assuming that the photocylinuta's PNP) run risk is set to hFE=5, the minimum trigger current of the light emitting diode is 1. is 5 mA, in the conventional device (d″V
dt) M is 7v/l1sec, but according to the present invention, it becomes 44"/&sec from the straight line B5, which is an improvement of 63 times. Also, if IFT is selected as IOmA, it is 300 times (dt)
v/dt)M can be increased.

The effect becomes even more pronounced as the hFE of the PNP) run risk becomes even larger.

In the conventional photothyristor beam, =O, 1~0.1°R
Although it is used at approximately 6=2 OKΩ, in the present invention, as mentioned above, it is desirable that h is large and R6 is small.

The significant improvement in dVdt values according to the present invention is explained as follows.

First, consider the response of the PNP l-run risk part in the photothyristor. The response of the transistor is expressed by the following equation.

tPNP = 11pHX tD(3)tDUPNP)
This value is determined depending on the structure of run risk. Generally, when hFE is increased, the response becomes slower and it becomes impossible to follow steep signals.

Next, consider the effect of gate resistance. Consider the case where a gate resistor R6 is connected between the gate LPG and the cathode of the photothyristor in the photothyristor equivalent circuit shown in FIG. The displacement current based on equations (1) and (2) first flows through the gate resistor R6, and the gate potential is expressed by the following equation (%) (4) above V. When the value becomes equal to or higher than the activation voltage V6B of the thyristor, the thyristor is turned on. Therefore, if the gate resistance is decreased, the rate of increase in the critical off-voltage increases.

By the way, the displacement current due to ~t is a transient phenomenon. Therefore, the above two effects can be expected to have a synergistic effect. In this way, by increasing the hFE of the PNP run risk and decreasing the gate resistance, the M value (dVdt) can be significantly improved.

Furthermore, the method of increasing hFE of PNP) run risk is generally accompanied by the effect of increasing photosensitivity. For this reason, IFT
This has the effect of reducing the (dVdt)M value and further enhances the effect of improving the (dVdt)M value. Generally, N2 at 900°C as mentioned above.
When annealing inside the film, the photosensitivity is improved by about 20-30%.

Furthermore, the gate resistor R6 can be easily integrated into a single chip with the photothyristor main body. An example is shown in FIG. Reference numeral 9 denotes a resistor made by diffusing P-type impurity poron into the substrate 1. One end of the resistor is made to overlap the gate part 4, and the other end is connected to the cathode electrode 8 by an electrode 10.

When comparing a structure with an external resistor and a structure with a built-in resistor using the same resistance value, the M value (dVdt) of the built-in resistor is two to three times larger. This means that the transient phenomenon of '%t needs to be considered as a distribution function, and that the gate resistance needs to be installed close to the photothyristor. This effect allows further improvement of the present invention.

By the way, when a chip is formed, electron holes are generated in the semiconductor by light irradiation from a light emitting diode, and the gate resistance value changes due to conductivity modulation. As an example R6=2
In the case of 0 KΩ, when 10 mA is applied to the light emitting diode, the resistance value decreases by 20% and the IFT increases, but according to the present invention, the gate resistance value can be significantly reduced by 11\, and the resistance change can be virtually ignored.

Furthermore, since the resistance value can be reduced, the chip area can also be reduced.

In addition, in FIG. 9, as shown by 11, the resistance portion 9 is
If the gate resistance is covered by 1, the change in gate resistance due to light becomes even smaller.

As described above, according to the present invention, the dVdt value can be made very large in a vertical photothyristor, and a photothyristor coupler that does not require external components can be manufactured.

Although the present invention has been described with respect to a photothyristor coupler, it is an advantage of the photothyristor itself. The present invention is not limited to the structures shown in FIGS. 6 and 9, but can also be applied to amplification gate type photothyristors and general thyristors.

[Brief explanation of drawings]

Fig. 1 shows an optically coupled photothyristor, Fig. 2 shows an equivalent circuit diagram of the photothyristor, Fig. 3 shows a conventional improved optically coupled photothyristor, and Figs. 4 and 5 show the conventional photothyristor. An equivalent circuit diagram of another improved photothyristor, FIG. 6 is a sectional view of a vertical photothyristor according to the present invention, and FIG. 7 is a diagram (d
v/di)-I. FIG. 8 is an equivalent circuit diagram for explaining the operation of the photosylisk according to the present invention, and FIG. 9 is a sectional view of another embodiment according to the present invention. GL2 full light emitting diode PT: Photosilifter R6:
Gate resistance agent Patent attorney Aihiko Fukushi Figure 1 A Figure 2 Figure 3 Figure 7 ITT (mA) Figure 8 Figure 9

Claims (1)

[Claims] 1. In a vertical photothyristor having a PNPN stacked structure, the hFE of the PNPI-run risk included in the photothyristor is increased, and the resistance connected to the gate is reduced. 1. A semiconductor device characterized by improved critical off-voltage rise rate. 2. The semiconductor device according to claim 1, wherein the resistor connected to the gate is formed integrally with the photothyristor in the same chip.