JPH04162777A - Bidirectional voltage checking semiconductor device - Google Patents

Abstract

PURPOSE:To facilitate manufacturing and improve reliability by exposing the junction on the side of a supporting plate on the bevel face by mesa-etching thereby making it into a mesa structure, and exposing the junction on the opposite side on the main face thereby making it into a planar structure. CONSTITUTION:The third semiconductor layer 3 is the region selectively made in one side of the first semiconductor layer 1, and the junction 13 between the first and third semiconductor layers 1 and 3 is covered with the first protective film, and the other side of the first semiconductor layer 1 is in contact with the second semiconductor layer 2, and the junction 12 between the first and second semiconductor layers 1 and 2 is exposed on the side 41, which has an inclination such that the area of the second semiconductor layer 2 decreases as the distance from the junction increases, and is covered with the second protective film 42. That is, the third semiconductor layer side 3 is of a planar structure, and the second semiconductor layer side 2 is of a mesa structure, and the junction between the first and second semiconductor layers 1 and 2 is apart from a conductive supporting plate 6. Hereby, the facilitation of the manufacturing and the improvement of reliability can be realized.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is characterized in that two semiconductor layers of opposite conductivity type are provided with one semiconductor layer of higher resistivity sandwiched therebetween, and a semiconductor layer of a forward direction is formed between the two semiconductor layers of opposite conductivity type. The present invention relates to bidirectional voltage blocking semiconductor devices such as reverse blocking thyristors, triacs, diacs, etc., which have opposite PN junctions.

[Conventional technology]

In a bidirectional voltage blocking semiconductor device, it is desirable that the blocking voltages in both directions be equal. However, since the plate-shaped semiconductor element is supported on a support by one side, it is difficult to make the conditions on the front and back sides the same, and various methods have been devised to solve this problem.

In the planar thyristor shown in FIG. 2, there are a p-type diffusion layer 2, which becomes an n-emitter layer, and a p-type expansion layer 3, which becomes a p-base layer, sandwiching an n-silicon substrate 1. The part where n<- becomes a layer, and n
An n-diffusion layer 4 serving as an emitter layer is formed. The n-emitter layer 2 is extended to the surface where the n-emitter layer 4 is present by p-type diffusion layers 21, 22 from both sides. This results in a PN junction 12. between the high resistivity n-base III and the 21472 layer 2. PN junction 1 between p base layer 3
3 is exposed on the same surface of the substrate and protected by an oxide film 5 used as a diffusion mask. And 21
The back electrode 6 in contact with the 472 layer 2 has a 7 node terminal 7, the upper electrode 8i81 in contact with the n← emitter layer 4 has a cathode/terminal 9, and the upper electrode in contact with the exposed surface of the p base layer 3 The gate terminal 10 is connected to 8i82.

In this way, in this thyristor, the two PN junctions are exposed on the same surface of the substrate, thereby making the conditions for breakdown voltage the same.

In the case of the double-sided planar thyristor shown in Figure 3, n-
A 21472 layer 2 and a p base layer 3 are formed symmetrically by selective diffusion from both sides of the silicon substrate.
PN junctions 12 and 13 are exposed on both sides, respectively. In order to improve the breakdown voltage of these PN junctions, two p-type guard rings 31 are formed on the back side, and two p-type guard rings 32 are formed on the front side, surrounding the n emitter layer 2 and the p base layer 3. .

In the double-sided mesa type thyristor shown in Fig. 4, the PN junction 12
．． 13 are both formed parallel to the substrate surface, and mesa-etched so that the exposed portion thereof becomes a positive helical surface 41. Each beveled surface 41 is covered with a glass film 42 serving as a protective film.

The silicon substrates of these semiconductor devices are supported by a conductive support plate on the electrode 6 side and electrically connected to the support plate.

[Problem B to be Solved by the Invention] Among the bidirectional voltage blocking semiconductor devices described above, in the case of the single-sided planar shown in FIG. 2, in order to extend the nine layers 2 on the back side to the front surface, Since the deep diffusion layers 21 and 22 are formed by a diffusion process called through-diffusion, which requires a very long time, the operating rate of the device decreases.

There were drawbacks that led to deterioration of characteristics and a decrease in the rate of non-defective products. Also, the third
In the case of the double-sided planar shown in the figure, since the passivation film 5 is thin, the passivation film 5 on the back side is easily damaged, and the reliability is insufficient. Furthermore, since there is not a sufficient distance between the end surface of the silicon substrate 1 on the back side, the back electrode 6, and the conductive support plate having the same potential, there is a drawback that discharge occurs between the silicon substrate and the support plate.

Furthermore, in the case of the double-sided mesa type shown in FIG. 4, when a large number of such semiconductor pieces are made from one silicon wafer, the strength of the wafer is reduced due to mesa grooves because mesa etching is performed from both sides. There is a drawback that care must be taken in handling the wafer in the process before dividing into semiconductor pieces.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bidirectional voltage blocking semiconductor device that is easy to manufacture and has high reliability, while eliminating the above-mentioned drawbacks.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a semiconductor substrate in which a first semiconductor layer of a first conductivity type having a higher voltage resistance is sandwiched between second and third semiconductor layers of a second conductivity type,
In a bidirectional voltage blocking semiconductor device supported by a conductive support plate on the second semiconductor layer side, the third semiconductor layer is a region selectively formed from one surface of the first semiconductor layer; The junction between the semiconductor layers is covered with a first protective film, the other surface of the first semiconductor layer is entirely in contact with the second semiconductor layer, and the first semiconductor layer is in contact with the second semiconductor layer.

It is assumed that the junction between the second semiconductor layers is exposed and covered with the second protective film on a side surface having a slope such that the area of the second semiconductor layer decreases as the distance from the junction increases. It is effective that the first protective film is made of an oxide of a semiconductor material and the second protective film is made of glass, or that both the first and second protective films are made of glass. Furthermore, such semiconductor devices include a reverse aiming type thyristor, a tritic, and a dianoch.

[Effect]

The above semiconductor device has a brainer structure on the third semiconductor layer side,
The second semiconductor layer side has a mesa-type structure and does not require through-diffusion. Since no passivation film is present on the support plate side surface of the semiconductor substrate, there is no problem of damage to the passivation group.

In addition, since the junction between the first and second semiconductor layers is separated from the conductive support plate, there is no risk of electrical discharge occurring between the first semiconductor layer and the support plate. Even when a large number of pieces are made from one wafer, it is only necessary to form the mesa groove on one side, so there is little deterioration in the strength of the wafer, and wafer handling during the process becomes easier.

〔Example〕

FIG. 1 shows a reverse blocking thyristor according to an embodiment of the present invention, in which the same parts as in FIGS. 2 to 4 are given the same reference numerals, and the upper surface side has a brainer structure and the lower surface side has a mesa type structure. It becomes. This thyristor is manufactured as follows. First, p is applied to the n-silicon substrate 1 by full diffusion from one side and selective diffusion using the oxide film 5 as a mask from the other side.
A type diffusion layer 2 and a plurality of p-type diffusion layers 3 are formed. At the same time, an oxide film mask is formed again for the 0th order to form a double p-type guard ring 32 surrounding the p-type diffusion layer 3, and each
An n' diffusion layer 4 is selectively formed in the type diffusion layer 3. Then, on the lower surface side, a mask having openings in a grid pattern is formed using, for example, a resist film, and mesa etching is performed to form the beveled surface 41.
form. Thereafter, an upper electrode 81 in contact with the 0 layer 4 and an upper electrode 82 in contact with the 9 layer 3 are formed on the upper surface through a window opened in the oxide film 5, and an electrode 6 is formed on the lower surface. Thereafter, the electrode 81 is divided at the mesa groove to obtain a plurality of semiconductor pieces as shown in FIG.
82 is connected to the gate terminal 10, and the electrode 6 is connected to the anode terminal 7. The beveled surface 41 is covered with a glass film 42 . In this way, p emitter layer 2 + n base layer 1
．． I) base layer 3 + n emitter layer 4, having 2
The exposed surface of the junction 12 between layer 2 and n-layer 1 is covered with a glass membrane 42.
The junction 13 between the 9-layer 3 and the n-layer l and the junction 13 between the 9-layer 3 and the 0-layer 4 and between the p-type guard ring 32 and the n-
A thyristor is obtained in which all the junctions between layers 1 are protected by an oxide film.

FIG. 5 shows a reverse blocking thyristor according to another embodiment of the present invention, which differs from the thyristor in FIG. The exposed part of the PN junction between the guard ring 32 is covered with a glass film (
It is protected by a glacivation layer) 42.

〔Effect of the invention〕

According to the present invention, the junction on the support plate side of a bidirectional voltage blocking semiconductor device is exposed on the bevel surface by mesa etching to form a mesa-type structure, and the junction on the opposite side is exposed on the main surface of the semiconductor substrate to form a brainer structure. This eliminates the need for through-diffusion in a single-sided planar structure, and eliminates the problem of reduced reliability of the retainer II membrane on the support plate side and discharge between the support plate and the mesa-type structure in a double-sided planar structure. Highly reliable reverse blocking thyristors, triacs or diacs can be obtained by solving the problem of wafer strength reduction in the case of be able to.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a thyristor according to an embodiment of the present invention, and FIG.
3 and 4 are cross-sectional views showing different structures of conventional thyristors, respectively, and FIG. 5 is a cross-sectional view of a thyristor according to another embodiment of the present invention. 1: n-silicon substrate, 2.3: 1) type diffusion layer, 4: n
゛Diffusion layer, 5 dioxide film, 7: anode terminal, 9: cathode terminal, 10: gate terminal, 32: p-type guard ring,
41: Beveled surface, 42 Niglass film.

Claims (1)

[Claims] 1) A first semiconductor layer of a first conductivity type having a higher specific resistance is sandwiched between second and third semiconductor layers of a second conductivity type in the semiconductor substrate, and the second semiconductor layer is sandwiched between second and third semiconductor layers of a second conductivity type. In the case where the third semiconductor layer is supported by a conductive support plate on the side, the third semiconductor layer is a region selectively formed from one side of the first semiconductor layer, and the junction between the first and third semiconductor layers is the first protection layer. The other surface of the first semiconductor layer is covered with a film, the entire other surface of the first semiconductor layer is in contact with the second semiconductor layer, and the area of the second semiconductor layer decreases as the junction between the first and second semiconductor layers moves away from the junction. A bidirectional voltage blocking type semiconductor device characterized by having an exposed side surface with an inclined surface and covered with a second protective film. 2) A bidirectional voltage blocking semiconductor device according to claim 1, wherein the first protective film is made of an oxide of a semiconductor material and the second protective film is made of glass. 3) A bidirectional voltage blocking semiconductor device according to claim 1, wherein both the first and second protective films are made of glass. 4) A bidirectional voltage blocking semiconductor device according to claim 1, which is a reverse blocking thyristor. 5) A bidirectional voltage blocking semiconductor device according to claim 1, 2 or 3, which is a triac. 6) A bidirectional voltage blocking semiconductor device according to claim 1, 2 or 3, which is a diac.