JPS58140160A - Semiconductor device - Google Patents

Abstract

PURPOSE:To omit the complicated process of a semiconductor device by a method wherein base width of the P-N-P transistor is made to be the most suitable, the current amplification factor and photosensitivity are enlarged, moreover gate resistance is reduced, and the transistor is formed in a chip the same with a photo thyristor. CONSTITUTION:Boron of P type impurity is diffused to 5-60mum at the prescribed places of an N type substrate 1 to form an anode 2, a gate 3. Then phos phorus of N type impurity is diffused in the gate 3 to form a cathode 4. An anode electrode 6, a gate electrode 7 and a cathode electrode 8 of Al respectively are provided in the regions 2, 3, 4 thereof. By making base width of the P-N- P transistor to be contained in the photo thyristor to be the most suitable, while by providing a phosphorus diffusion region S at the circumference of the chip surrounding the element region provided with the anode 2 and the cathode 4, the current amplification factor is enlarged, nd moreover gate resistance is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photothyristor, and more particularly to a photothyristor that is used as an optically coupled semiconductor device in combination with a light emitting diode.As shown in FIG. Photothyristor P on the output side
A photothyristor coupler in one package using T has been put into practical use. Compared to electromagnetic relays, this type of photothyristor coupler has the following features: ■Extremely good insulation between input and output, ■Fast operating speed, ■Long life, ■Less noise generation, and ■No influence from external magnetic fields. , ■ Due to its advantages such as small size, as electronic circuits of various devices progress, it is used in a wide range of fields such as isolation of signal transmission systems and AC control.

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 its original breakover voltage. This phenomenon occurs when a steep rising voltage (dv/dt) is applied, and as shown in the photothyristor equivalent circuit diagram in Figure 2, a displacement current flows through the capacitor C8 (junction capacitance, etc.) as shown in the following equation. It depends.

1dQ7 = d(C,V)/dt=(, d'7dt+y
dco/dt, -(1)D dt Here, assuming that C0 is constant, equation (1) becomes further as follows.

1D=Cod'/dt・・・・・・・・・・・・・・・
(2) As a result, when the value of dru is large, the thyristor is turned on. The maximum rising voltage (d'
/, t)M(7) value is called critical off-voltage rise rate.

When actually using a photothyristor coupler, the third
As shown in the figure, a resistor R6 and a capacitor CG are connected between the photothyristor gate PG and the cathode to prevent malfunction when a steep voltage is applied. However, in actual use, externally attaching resistors and capacitors is very inconvenient in terms of installation location and increased cost.

The following method has been reported to improve the prevention of malfunction caused by the steep rising voltage of the photothyristor as described above.

(1) PNP) To reduce the hFE of the transistor Ω(2
) Reduce gate resistance R6.

(3) 0(4) whose gate resistance is controlled by a transistor
) Control the gate resistance with a MOS FET.

However, in both methods, even if it is possible to increase the voltage (dVdt), there are disadvantages such as the minimum trigger current IF becoming large and the circuit manufacturing requiring a complicated or special process. There was a problem with the conversion.

The present invention provides a semiconductor device that improves (dv/dt)M without requiring external parts or using complicated processes unlike conventional devices.

The above objective is to optimize the base width of the PNP transistor in a lateral photothyristor, and to improve the PNP transistor by heat treatment, back surface treatment, etc. - This can be achieved by increasing the hFK and photosensitivity of the transistor, reducing the gate resistance, and further fabricating the gate resistance on the same chip as the photothyristor.

The present invention will be explained below using examples.

FIG. 4 shows the structure of a lateral type photothyristor according to the present invention. Reference numeral 1 denotes an N-type semiconductor substrate, which is usually made of silicon having a specific resistance of 20 to 50 Ωα and a thickness of 200 to 400 μ. 2 and 3 are those in which 5 to 60 μm of boron, which is a P-type impurity, is diffused into a predetermined location of the N-type substrate 1, and the diffusion depth is changed depending on the breakdown voltage of 1 hFE or the like. 2 is formed as an anode, 3 is formed as a gate, and the base width d is formed between the two head regions.
is set as . Next, 4 diffuses N-type impurity phosphorus into the gate 3 to form a cathode. The diffusion depth varies depending on the diffusion depth of the gate 3, and is approximately 2 to 20 microns. 5 on the semiconductor substrate 1 is an insulating film, generally 5i02
is used. The electrodes 6 and 7.8 provided in each of the regions 2.3.4 are an anode electrode, a gate electrode, and a cathode electrode, and generally At is used.

As mentioned above, the cross-sectional structure is the same as that of the conventional horizontal photothyristor, but in order to increase (dv7. In addition, the hFE is increased and the gate resistance is decreased.

Among the above conditions, desired characteristics of hFE and gate resistance can be obtained by, for example, performing the following heat treatment, providing a diffusion region, or using both together.

As an example, after the completion of diffusion of the cathode electrode 4, 900°C N2
When heat treated inside, hF of PNP transistor becomes 1
．． Improved by 5-2 times. In this case, the surface of the general photothyristor is protected with SiO□, and when it is heat-treated in an oxygen atmosphere, the hFF of the other NPN transistor is significantly deteriorated. Therefore, it is necessary to add another process such as once removing the 5102 film. Dislocation-free diffusion technology to increase hFF.

Any method such as optimizing the impurity concentration may be used.Also, if the back side of the sea urchin is treated with phosphorus, as is applied to light-receiving elements, the hFE of the PNP transistor will be 1.
．． It becomes 5 to 2.5 times larger. Furthermore, this treatment can increase photosensitivity by 20 to 30%.

Further, by providing a phosphorus diffusion region S at the periphery of the chip, surrounding the element region where the anode 2 and cathode 8 are provided, hFE can be increased and gate resistance can be decreased. That is, the holes injected from the anode 3 are reflected by the phosphorus diffusion region S, and hFE becomes larger by about 1.5 to 2.0 times. If the phosphorus diffusion region S is deep and penetrates the wafer, the effect will be even greater.

In the above lateral photothyristor structure, t-j'
FIG. 5 shows the measured values of the hFE of the PNP) transistor which was manufactured to have a constant base width of, for example, 100 μm by the heat treatment, back surface treatment, etc. described above. The figure shows how photothyristors are optically coupled in the relationship shown in Figure 1, and the collector current is changed in each element to minimize the forward current of the light emitting diode required to transition the photothyristor from off to on state. The peak value of hFE is shown.

Straight line A in Figure 5 indicates that the gate resistance R6 is fixed at 51Ω (N
(PN) transistor hFE is also fixed), PNP
) hFE of transistor 0-2.0.5.1.0.2
This shows the relationship between IFE and (''/, , >M when the values are sequentially changed. Line A has a relatively gentle gradient, indicating that the change in (dv/dt)M with respect to ■ is small. .

Next, set hFE of the PNP transistor to a constant value (hFF of the NPN transistor is also constant), and gate resistance R, (1
: IFT and (dV
dt) The relationship with M is shown in straight line B. Straight line B is PNP)
This is a case where hFE of the transistor is set to 1. Therefore, the straight line passes through the point hF=1 on straight line A.

When hFE is changed to 2.0.0.5.0.2, the change is represented by a straight line that passes through each hFEO point on straight line A and is almost parallel to straight line B. As can be seen from the straight line B, when the gate resistance is changed, the change in (dVdt)M is very large for the IFT.

Now PNP of photothyristor) transistor is hFE=1
If the minimum trigger current IFT of the light emitting diode is 5 mA, then the conventional device
v/dt) Mha 12V/1t88゜TearukaAccording to the present invention, direct #! 130V/It8e from B. next 10.8
For IFT = 10 mA, an improvement of 34 times (dv/dt) Mtl can be obtained. The effect becomes even more pronounced as the hFE of the PNP transistor becomes even larger.

In the conventional lateral type photothyristor, hFF, = 0.0
3-0.3. It is used with Ro=about 50 to IOOKΩ, but in the present invention, as mentioned above, it is desirable that hFE is large and Ro is small.

The above-mentioned improvement in dv/d- becomes more remarkable by selecting the base width d of the PNP transistor of the photothyristor shown in FIG. That is, the base width d is selected so that the dv/dt value is the largest.

Figure 6 shows the photothyristor fabricated under the same manufacturing conditions as those in Figure 5 above when measurements were taken with F = 1.0, but when the base width d was sequentially changed to 50, 100, 150° and 300μ. , shows the relationship between IFT obtained from each photothyristor and (d'7d,)M.

The numbers in parentheses in the figure indicate gate resistance. By increasing the base width d as can be read from the figure, the same IFT
(dv/d,)M changes significantly for the base width d
As (d7dt) increases, it becomes larger. The above effect becomes more pronounced as the value of IFT increases.

In Fig. 6 above, hFK of the PNP transistor
The value of corresponds to 1.5.1.0.0.75.0.48 for pace widths of 50, 100, 150, and 300μ. The above effect becomes more noticeable when the hFE of the PNP transistor is further increased.

By improving the structure of the package when a photothyristor and a light emitting diode are integrated as an optical coupling device! 'Even if IFT is reduced, (dv/dt) M can be increased. - For example, a structure in which light-emitting and light-receiving elements are installed on both sides of a glass film to reduce the distance between pixel elements, or a structure in which the outside of an element optically coupled with transparent resin is surrounded by black resin when molded. The IFT can be made smaller by using a structure in which a white resin is used to utilize reflected light.

The significant improvement in the dv/d value by increasing the hFE, decreasing the gate resistance, and selecting the largest base width is explained as follows. First, in the photothyristor, the PNP transistor part Consider the response of The response of a transistor is expressed by the following equation.

j PNP owe=h F E X j D...
・・Scream・・Decoy・・・(3) tD is PNP)
This value is determined by the structure of the transistor, etc. Generally, when h 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 PG and cathode of the photothyristor in the equivalent circuit of FIG. 7. The above formula f+),
The displacement current based on +2) first flows through the gate resistor R6, and the potential of the gate is expressed by the following equation.

Vo” l DRG ”; CRG dv/dt...”
...""" (4) When the value of V. above becomes equal to or higher than the activation voltage V.B of the thyristor, the thyristor is turned on.

Therefore, if the gate resistance R6 is made smaller, the rate of increase in the critical off-voltage increases.

Furthermore, tD in equation (3) is given by the following equation: tD@
Cd” ・・・・・・・・・・・・・・・・・・
...Scream...Mountain...(5) d is PNP
) indicates the base width of the transistor. In this way, the base width d
The larger the value, the slower the response will be.

By the way, the displacement current due to 1 is a transient phenomenon. Therefore, the above effects can be expected to act synergistically.

In this way, by increasing the base width of the PNP transistor, increasing hFE, and decreasing the gate resistance, the dVdt value can be significantly improved.

Furthermore, the method of increasing hFE of a PNP transistor generally has the effect of increasing photosensitivity. Therefore, the effect of reducing the IFT is lost, and the effect of improving the dv/dt value is further enhanced. Generally, as mentioned above, annealing at 900° C. in N 2 improves photosensitivity by about 20 to 80%.

Furthermore, the gate resistor PG can be easily formed into a photothyristor and an l-chip. An example is shown in FIG. 9 is a semiconductor substrate 1
The resistor is made by diffusing P-type impurity boron into the resistor, and one end of the resistor is made to overlap the gate part 3, and the other end is connected to the cando electrode 8 by an electrode 10. When comparing the case where an external resistor and a built-in resistor are used with the same resistance value, the dv/d value is 2 to 3 times larger with the built-in resistor.

This means that the transient phenomenon of dv/dt needs to be considered as a distribution function, and it is necessary to install the gate resistor close to the photothyristor. This effect allows the present invention to be further improved.

By the way, when integrated into a single chip, electrons and holes are generated in the semiconductor by light irradiation from a light emitting diode, and the gate resistance value changes due to conductivity modulation.

- For example, if the gate resistance R6 is 50Ω and 10mA is applied to the light emitting diode, the resistance value changes to about I/2. Therefore, IFT becomes large. However, according to the present invention, the gate resistance can be significantly reduced and changes in resistance can be virtually ignored. Furthermore, since the resistance value can be reduced, the chip area can also be reduced.

In addition, in FIG. 8, as shown in 11, the resistance portion 9 is
When covered by t, the change in gate resistance due to light becomes even smaller.

As described above, according to the present invention, by selecting the base width to an optimum value, increasing hFE and decreasing the gate resistance to configure a lateral type photothyristor, dv/d can be achieved.

The value can be made very large, making it possible to create photothyristor couplers that do not require external parts. Furthermore, the manufacturing process of the device does not involve any complicated steps, so it has great practical value.

Although the embodiment has been described with respect to one photothyristor, it can also be applied to one chip connected in antiparallel. Moreover, it is applicable not only to photothyristors but also to general thyristors.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an optically coupled photothyristor, Fig. 2 is an equivalent circuit diagram of the photothyristor, Fig. 3 is a diagram showing a conventional improved optically coupled photothyristor, and Fig. 4 is a horizontal type according to the present invention. 5 and 6 are cross-sectional views of the photothyristor (d) for explaining the operation of the photothyristor according to the present invention.
v/dt)M-IFT, FIG. 7 is an equivalent circuit diagram for explaining the operation of the photothyristor according to the present invention, and FIG. 8 is a sectional view of another embodiment according to the present invention. . GL: Light emitting diode, PT: Photothyristor, Ro
: Gate resistance, d: Base width. Agent Patent Attorney Aihiko Fukushi (and 2 others) Pole 3
figure,? 4 IFT (rrL勺Fig. 5%) + ＼) q η'l! & I Fr (mA),
? Figure 6

Claims (1)

[Claims] 1. In a horizontal photothyristor made of PNPN, the base width of the PNP transistor included in the photothyristor is set to a value that can maximize the critical off-voltage rise rate <dv>, and further hFE is 1. A semiconductor device characterized in that the critical off-state voltage rise rate is improved by increasing the size and reducing the gate resistance. 2. The semiconductor device according to claim 1, wherein the photothyristor is provided with a phosphorus diffusion layer on the back surface of the semiconductor substrate to increase the hFE of the PNP transistor. 3. In the photothyristor, a phosphorus diffusion layer is formed around the element region, so that the h of the PNP transistor is
The semiconductor device according to claim 1, wherein the FE is increased. 4. The semiconductor device according to claim 1, wherein the gate resistor is integrally formed on the same semiconductor substrate as the photothyristor main body.