JPS58118148A - Light ignition type bidirectional thyristor - Google Patents

Abstract

PURPOSE:To contrive uniformity of ignition sensitivity for the titled thyristor by a method wherein the P-base located on one main surface of a bidirectional SCR and a part of the N- emitter of the second SCR located on the other main surface opposing to the above surface are used as light-irradiation surface, and the life time of the P-base layer on said light-irradiation surface is made larger than that of the other layer. CONSTITUTION:A P1 layer and a P2 layer 6 are provided on an N type substrate 5 by performing a B-diffusion, an N1 layer 3 and an N2 layer 7 are formed by selectively diffusing P, and the N1 layer 3 is formed into a short-circuit emitter structure using an electrode 2. The N1 layer 3 is removed by etching and the P1 layer 4 is exposed, and a light-receiving region 12 is formed. Then, a mesa etching is performed from both main surfaces, and the exposed junctions J3 and J4 are covered by a glass layer 9. At this point, a groove 11 is formed at the same time, and a photo-electric current generated on the irradiation surface is led out effectively. As the light-receiving region 12 is P-diffused from the opposing main surfaces, a life time which is higher than that of the other region is obtained by the gettering action of P, and the ignition sensitivity of the SCRT2 having a center junction J4 which is located away from the power source and the SCRT1having a center junction J3 is located close to the light source can be made uniform, thereby enabling to obtain the highly reliable bidirectional SCR.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light-triggered bidirectional thyristor that performs a switching operation based on an optical trigger signal.

Prior art and its problems Semiconductor controlled rectifiers exhibiting bidirectional switching characteristics generally have five successive layers of alternating conductivity, and these five layers have mutually opposite polarities with the inner and outer layers as one trend layer. a semiconductor substrate formed by forming a pair of four-layer regions; a pair of main electrodes that are electrically connected to an outer adjacent region of the semiconductor substrate;
and means for applying a trigger signal.

In such a device, when a voltage is applied between the main electrodes so that one main electrode has a higher potential than the other main electrode, when a signal is applied between the main electrodes, one main electrode is connected to the other main electrode. The four-layer region with the forward direction facing the main electrode is in a conductive state, and conversely, when a voltage is applied between the main electrodes so that the other main electrode has a higher potential than one main electrode, the gate When a trigger signal is applied, the four-layer region whose forward direction is from the other main electrode to one of the main electrodes becomes conductive. As a means for applying a trigger signal, a so-called electric gate method is generally used, in which a gate electrode is provided on any layer of a semiconductor substrate, and a gate signal is passed from this gate electrode to perform a #:wrinkle switching operation.

However, the electric gate method has the following drawbacks.

(1) In order to obtain symmetrical bidirectional switching characteristics, two gate electrodes are provided and two gate circuits electrically insulated from each other are required. (2) When the gate has only one pole, it is difficult to obtain symmetrical switching characteristics. (3) During commutation, there is a risk of so-called erroneous ignition in which conduction occurs before one stream of gate signal is applied.

J=J-)-, The disadvantages of the vI gate method can be overcome by using a so-called optical gate method in which a single electrically insulated light source irradiates a light trigger signal to ignite the at. Can be done. However, bidirectional thyristors employing the optical gate system also have the following drawbacks. It is a problem of imbalance in ignition sensitivity in the four-layer region of 2a.

A conventional example is shown in FIGS. 1 and 2. In Fig. 1, the thyristor (↓) consists of a thyristor T consisting of two 41-regions, and a thyristor IIN, with an N-type Jtji (3) at 1゛ and an N-type Iso (7) at T.
) is an electrode projected in one direction (overlapping only in part,
Preferably, it is formed into two pieces that do not overlap. Second
The figure is a cross-sectional view (enlarged view) of portions A- and N in FIG.

Of the pair of main electrodes, the first main electrode (2), excluding the light-triggered window (hereinafter referred to as the light receiving section), has an N-type layer (N1) in the dyristor T1 and a P-type layer (P) in the thyristor T. , ) are ohmically connected on one main surface. In addition, the second main electrode (8) has an N-type layer (Nri) at T, and a P-type layer (P,) at 1゛1 are ohmically connected on the other main surface.This thyristor (↓) can be ignited to its light receiving portion by an optical signal from the light source Ql.In this case, the carrier generation area effective for light ignition is the reverse biased central junction J.

and near J4, and in order to improve the light ignition sensitivity, it is necessary to irradiate light near the central junction.

When light is irradiated from one main surface of the semiconductor substrate, the distance between the light source and the reverse biased central junction, which is the carrier generation region effective for ignition of the two four-layer regions, is the center of the five-layer structure. h (Ns).

Therefore, the light necessary for ignition of the four-layer region formed by thyristor 'I', which has central junction J4 far from IS, is absorbed at the internal pressure of the central layer and attenuates in a linear function, so that its light ignition sensitivity will be significantly lower than the 41-chain plate formed by the thyristor T1 with the central junction J, close to the light source. As a result, the switching characteristics in both directions are uneven, and the light source is dim.
(The mode in which the thyristor T1 is fired is called the I+ mode, and the mode in which the thyristor T is fired is called the "mode").
There is a problem in that the drive current for a light source such as an ED becomes large, significantly shortening the life of the light source.

Purpose of the Invention The present invention has been made in view of the above circumstances, and its purpose is to uniformize the light ignition sensitivity and improve the light sensitivity itself by fully firing the two tilted thyristors. The purpose of the present invention is to provide an arc-shaped bidirectional thyristor. A further object of the present invention is to provide a light-ignited bidirectional thyristor with excellent switching characteristics, reliability, and economy.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be explained below with reference to the drawings. Third
The figure is a plan view of the light-triggered bidirectional thyristor of the present invention.
The figure is a partial cross-sectional view taken along the light receiving section A-A'.
It is manufactured by the method described below.

P-type impurities such as boron are diffused from both sides of the 200 μm thick N-type substrate (5) to a depth of 3077 m.
Form 7 layers (4) and 21 layers (6). Next, a predetermined oxide film is etched and etched using the well-known PEP technique, and using this oxide film as a mask, the thyristors T1 and T
, by selectively diffusing the N type region N,@(31) and the N2 layer (7) with impurities such as phosphorus.
An emitter region with a depth of about 15 μm is formed. At this time the third
Phosphorus is diffused only from the opposing main surface only in the light-receiving region μ4 shown in the figure. The emitter region has a so-called short-chit emitter structure in which a portion of the P base is exposed. Next, add 8% area A hot water to the receiving source, N, 1m +31
! 11+ Slightly deep <, R Heath Nti (41; 64
Chemically etch the area where it comes out to remove the highly concentrated N-type I- in this area. 7 around the thyristor
Mesa etching is performed from both sides to a depth of 0 to 80 .mu.m, and the surfaces of the junctions J and J4 exposed on the side surfaces are subjected to scivation using a glass film (9).

At the same time, a groove αυ is formed in the light receiving region to effectively guide the photocurrent generated on the irradiation surface. The light receiving area u3 has a longer lifetime than other areas due to the so-called getter action of phosphorus since phosphorus is diffused from the opposing main surfaces. Therefore, high photosensitivity can be obtained. Furthermore, by removing the phosphorous diffused in this area, no light absorption occurs, which can further contribute to improving quantum efficiency.

FIG. 5 is a partial cross-sectional view of another embodiment of the present invention taken along the direction of the light receiving section BB', and the difference from the above embodiment is that the N-type region NJ@t7 of the thyristor T. ) is formed deeper than the other N-type regions.

This makes the getter action of phosphorus even more effective, and at the same time increases the 1P base layer resistance in the mode (7
The effect is to increase the light sensitivity of the lever part. Furthermore, by attaching a thin antireflection film t+3, such as a SiO film, to the surface of the light receiving portion, light that is lost on the silicon surface can be effectively guided to the silicon shell.

Next, the effects of the present invention will be explained with reference to FIG.

In the figure, the solid line shows the conventional example, and the dotted line shows the change in doji efficiency when the present invention is implemented.

Wavelength person = 094μn1 LEI) as a light source 1 -)
By implementing the present invention, the quantum efficiency y of I mode hardly increases, while the quantum efficiency y of 1 mode improves from y=0.25 to y=05, and the quantum efficiency of C mode and 1 mode improves. It can be seen that the values are equalized. Furthermore, by increasing the lifetime of the N base layer, the photocurrent also increases, so the photosensitivity is approximately twice that of the conventional example.
The performance was improved by about 3.5 times in 1 mode.

Furthermore, when the thyristor turns off/off, it becomes easy to accumulate carriers during N-pace, so switching time such as play time can be greatly improved.

To describe the effects of the present invention numerically, compared to the minimum trigger power required for I+ mode in the conventional structure, Il
The minimum trigger power (war) that can be seen in the l+ mode is approximately twice as large, whereas in the present invention, light can be fired in both directions with approximately the same minimum trigger power. In mode, 4
It is possible to reduce the power to 1 below.

Modifications of the Invention Although the embodiments of the present invention have been described with respect to the case where the light receiving section is provided at the end, it is natural that the same effect can be obtained even if the light receiving section is provided at the center. The light-activated bidirectional thyristor of the present invention manufactured by such a method has a withstand voltage of 600 and a current carrying capacity of 16 A%.
/dt200V/...1 and can be triggered with the weak light of a small capacity LED of the order of 10mW output.

Effects of the Invention As described above, in the present invention, the optical trigger power of the I'' and III+ modes is made uniform, and a minimum trigger power of several mW enables optical ignition in both directions, and a high switching characteristic is achieved. The pressure-resistant light ignition type allows you to obtain a force-directed soy risk!

[Brief explanation of the drawing]

FIG. 1 is a plan view of a conventional light-triggered bidirectional thyristor, FIG. 2 is a cross-sectional view taken along line AA' in FIG. 4 is a partial sectional view taken along the line AA' in FIG. 3, FIG. 5 is a sectional view showing another embodiment of the present invention, and FIG. 6 is a diagram illustrating the relationship between doji efficiency. 1: Thyristor, 2: Main electrode of 1, 3: N, #. 4: 11 layers, 5: N type substrate, 6: P! Dove, 7:N, increase. 8: second main electrode, 9 glass layer, 10: light. 11: Groove, 12: Light receiving area, 13: Storm radiation prevention film 0Representative: Masu Rishi, Noriyuki Chika (and 1 other person) Fig. 1 Fig. 2 Fig. 3 Fig./f Fig. 4/ Fig. 5. Figure 6 o,'i o,%1.0 /, /

Claims (1)

[Claims] A first thyristor region in which semiconductor layers of different conductivity types are successively arranged in the order of NPNP from one main surface to the other main surface and a second thyristor region in which semiconductor layers of different conductivity types are successively arranged in the order of %PNPN are adjacent to each other. In a bidirectional thyristor in which the first and second thyristor regions are integrally formed and triggered by an external optical signal, a portion of the P pace region disposed on one main surface and a portion opposite thereto. N emitter of the second thyristor disposed on the other main surface,
A light-triggered bidirectional thyristor characterized in that a part of the region is used as an irradiation surface for optical signals, and the lifetime of the P pace and N base layers in this region is longer than the lifetime of the other regions.