JPS6221277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a reverse conducting thyristor.

Conventionally, there has been a reverse conduction thyristor as shown in FIG. This reverse conducting thyristor is N _B
After selectively diffusing a predetermined position on one main surface of layer 1 to form an N ⁺ region, a P-type impurity such as gallium is diffused from both sides of the N _B layer to invert the N ⁺ region into an N region. forming a P _B layer 2 and a P _E layer 3;
After that, N-type impurities are selectively diffused into the P _B layer 2,
N _E layer 4 is formed and manufactured. In this method, gallium is used to make the P _B layer 2 a deep and uniform diffusion layer, but since gallium cannot be selectively diffused,
The thickness H ₁ of P _E layer 3 is approximately equal to the thickness H ₂ of P _B layer 2.
It becomes 40-50μ. Since a reverse conduction thyristor is a combination of a thyristor part and a diode part, there is no need for reverse breakdown voltage in the thyristor part, and the thickness of the P _E layer is only a few microns.
However, in the reverse conduction thyristor manufactured by the method described above, the _PE layer 3 was thicker than necessary. Furthermore, when a reverse conduction thyristor is used in an inverter, etc., a certain level of high speed is required, and in order to increase the speed, gold is diffused into the thyristor, especially in the N _B layer 1, to shorten the carrier lifetime. Efforts were being made to shorten the turn-off time.
However, when the P _E layer 3 is thick, in order to obtain a predetermined turn-off time, the gold diffusion temperature has been raised to diffuse a large amount of gold into the N _B layer.
When the gold diffusion temperature is high, the on-voltage increases and power loss increases. For example, a manufacturing method for making the P _E layer thinner than the P _B layer is to form a PN bonded substrate consisting of a P _B layer and an N _B layer, selectively diffuse into the P _B layer to form the N _E layer, and then , the entire main surface on the P _B layer side is covered with an oxide film, and the P type impurity is diffused from the main surface on the N _B layer side to form a thin P _E layer compared to the P _B layer.
One that forms layers can be considered. However, this has the problem that when forming the P _E layer, the entire main surface on the P _B layer side must be covered with an oxide film, which increases manufacturing costs.

An object of the present invention is to provide a method of manufacturing a reverse conduction thyristor having a P _E layer thinner than the P _B layer at low cost.

The present invention will be explained below based on one embodiment shown in FIGS. 2 to 8.

First, as shown in Figure 2, gallium is diffused into the N-type silicon semiconductor substrate from both its main surfaces.
An N-type semiconductor layer 6 and P-type diffusion layers 8, 8 are formed. Next, one of the P-type diffusion layers 8, 8 in FIG. 2 is removed by etching or wrapping to form a PN junction substrate as shown in FIG. 3. Hereinafter, the N-type semiconductor layer 6 will be referred to as the N _B layer 6,
The remaining P-type semiconductor layer 8 is referred to as a P _B layer 8. Note that when removing the P-type diffusion layer 8, even a part of the N _B layer 6 may be removed.

Next, as shown in FIG. 4, an N-rich N _E layer 24 is formed in the thyristor portion of the P _B layer 8, and an N ⁺ region 26 is formed in the diode portion of the N _B layer 6 by selectively diffusing phosphorus. Next, the main surface 28 shown in FIG.
By diffusing gallium thinner than 30, a P _E layer 32 with a thickness of several μm is formed on the N _B layer 6, as shown in FIG. At this time, the N ⁺ region 26 is N
However, since the N _E layer 24 is formed to be N-rich, it does not invert to P type. Finally, as shown in FIG.
4, the exposed surfaces 28 and 30 are coated with gold.
Make it more diffuse.

FIG. 7 shows the relationship between on-voltage and turn-off time of the thyristor portion of the reverse conduction thyristor manufactured in this manner and the thyristor portion of the reverse conduction thyristor manufactured by the conventional method. Curve 36 represents the characteristics of a conventional thyristor section, and curve 38 represents the characteristics of a thyristor section according to the invention. As can be seen from the figure, the reverse conduction thyristor according to the present invention has P _E
Since the layer 32 is formed thin, gold can be diffused up to the N _B layer 6 at a lower temperature than before, thereby shortening the turn-off time and at the same time reducing the on-voltage to approx.
It is 0.3V low. Furthermore, since the P _E layer 32 is thin, the thyristor and diode are completely separated, and commutation failure does not occur. Further, FIG. 8 shows the relationship between diode voltage and diode recovery time between a diode of a reverse conduction thyristor manufactured by the present invention and a diode of a reverse conduction thyristor manufactured by the conventional method. Curve 40 represents the characteristics of a conventional reverse conducting thyristor, and curve 42 represents the characteristics of a reverse conducting thyristor according to the invention.
As can be seen from the figure, even with the same recovery time, the diode voltage of the reverse conduction thyristor according to the present invention is lower by about 0.2V.

As described above, in the method for manufacturing a reverse conduction thyristor of the present invention, since the N _E layer 24 is formed to be N-rich and the N ⁺ region 26 is formed, impurities can be diffused from the main surfaces 28 and 30. , N _E layer 24
is not inverted to P type, and the main surface 30 side except for the N ⁺ region 26 is inverted to P _E layer 32. Therefore, without using selective diffusion, the P _E layer 32 is replaced with the P _B layer 8.
It can be made thinner compared to . In this way, the P _E layer 32 can be formed thin without using selective diffusion, so that the manufacturing cost of a reverse conduction thyristor that does not require reverse breakdown voltage can be reduced.

In the above embodiment, as shown in FIG. 3, immediately after removing one of the P-type diffusion layers 8, gallium is diffused to be thinner than the main surfaces 12, 14, 28, and 30 to form the _PE layer 32. After that, it is possible to selectively diffuse phosphorus to form the _NE layer 24, but the heat generated when selectively diffusing phosphorus causes gallium to penetrate deeply, making the _PE layer 32 thicker and increasing the on-state voltage. So I don't like it.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a reverse conduction thyristor manufactured by a conventional manufacturing method, FIGS. 2 to 6 are longitudinal sectional views showing the process of manufacturing a reverse conduction thyristor by the manufacturing method according to the present invention, and FIG. On-voltage-turn-off time characteristic diagram of the thyristor portion of the reverse conduction thyristor manufactured by the manufacturing method according to the present invention and the reverse conduction thyristor manufactured by the conventional manufacturing method, and Fig. 8 is a diode suppression-recovery time characteristic diagram of the same reverse conduction thyristor. It is. 6... First N-type semiconductor layer, 8... First P-type semiconductor layer, 24... Second N-type semiconductor layer, 32... Second P-type semiconductor layer, 33, 34... Silicon dioxide film (mask film) ), 26...N ⁺ area.

Claims (1)

[Claims] 1. Diffusing P-type impurities from both main surfaces of the N-type semiconductor layer to form P-type semiconductor layers from both main surfaces to predetermined depths, and removing one of the P-type semiconductor layers. forming a PN junction semiconductor base including a first N-type semiconductor layer and a first P-type semiconductor layer; selectively diffusing N-type impurities into a second predetermined position that is not opposite to the first predetermined position on the main surface of the N-type semiconductor layer to form a second N-rich N-type semiconductor layer in the first predetermined position; A step of forming an N ⁺ type semiconductor layer at a second predetermined position, and shortening P type impurities that cannot be selectively diffused from the main surface on the first P type semiconductor layer side and the main surface on the first N type semiconductor layer side, respectively. By time-diffusion, a second P-type semiconductor layer having a thickness thinner than that of the first P-type semiconductor layer is formed on a surface other than the second predetermined position of the main surface on the side of the first N-type semiconductor layer. A method for manufacturing a reverse conduction thyristor, comprising the step of forming a reverse conducting thyristor.