JPH0317225B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a method of manufacturing a semiconductor device, and in particular, a semiconductor device having a cathode region and a gate region on one principal surface, the gate region being recessed into the cathode region. A method for manufacturing a semiconductor device that minimizes the step difference in the diffusion layer into the N _B gate region, which is formed by diffusion of the P _B layer directly under the recessed surface that becomes the gate region, in a semiconductor device formed as follows. Regarding.

[Technical background of the invention and its problems]

In high-power semiconductor devices, such as gate auxiliary turn-off thyristors, gate turn-off thyristors (GTO), and high-frequency thyristors, a cathode region and a gate region are provided with a step on one principal surface of the semiconductor substrate, so that the two regions are insulated from each other. There are many structures in which the gate region is separated and formed in a finely intricate shape in the cathode region.

When manufacturing a semiconductor device having the above structure, there are the following disadvantages.

That is, as shown in FIG. 1, an N _B layer 2 serving as a cathode region and a P _B layer 3 serving as a gate region are provided on one main surface side of a semiconductor substrate 1, and both these regions 2,
The portion where the gate electrode is provided so that the gate electrodes 3 and 3 are insulated and separated from each other is defined as a recessed surface 3a.

This recessed surface 3a is formed, for example, to a depth of about 50 μm by chemical etching or _the like.
It is generally created before the spread of.

That is, if the recessed surface 3a is formed by chemical etching or the like after the formation of the P _B layer 3, the resistance of the gate region surface will increase, and for example, when a gate-assisted turn-off thyristor is manufactured, this will adversely affect the turn-on and turn-off characteristics. result in giving.

Therefore, in general, a concave surface 3a is created in advance in a portion that will become the gate region, and then diffusion is performed to form the P _B layer 3.

However, if the above method is adopted, the concave surface 3a
This becomes the base region directly under the gate region where
N _B layer 4 has a diffusion layer step 4a corresponding to the depth of the recessed surface 3a, for example, about 50 μm in the above example.
is formed, and in order to maintain the required characteristics such as withstand voltage, the N _B layer 4 is
It becomes necessary to increase the thickness to, for example, about 230 μm or more.

However, increasing the thickness of the N _B layer 4 causes an undesirable increase in the forward voltage drop, which adversely affects the electrical characteristics.

[Purpose of the invention]

The present invention has been made based on the above circumstances, and it is possible to minimize the step difference in the diffusion layer formed in the N _B layer directly under the gate region where the concave surface is formed, and to suppress the increase in the thickness of the N _B layer. It is an object of the present invention to provide a method for manufacturing a semiconductor device that can improve electrical characteristics such as forward voltage drop.

[Summary of the invention]

The present invention provides a method for manufacturing a semiconductor device that has a cathode region and a gate region on one main surface of a semiconductor substrate, the gate region is recessed into the cathode region, and a step is provided between both regions to isolate them. , after making the surface roughness of the recessed surface that becomes the recessed gate region smaller than the surface roughness of the surface of the semiconductor substrate excluding the recessed surface and increasing the ratio of the surface roughnesses of the two, Impurities are diffused from one main surface side of the semiconductor substrate to form a base region with a small step of the diffusion layer directly under the recessed surface, and the thickness of the base region is prevented from increasing more than necessary. This is a method of manufacturing a semiconductor device that suppresses deterioration of physical characteristics.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

In the present invention, the diffusion rate of impurities into a silicon semiconductor substrate is greatly influenced by the surface roughness, and a surface with a large amount of processing strain, etc., and a rough surface condition has less processing strain, etc., and the surface condition is close to a mirror surface. It takes advantage of the phenomenon that the diffusion rate is extremely fast compared to the state.

To explain the present invention with reference to FIG. 2, for example, when manufacturing a thyristor structure, the semiconductor substrate 11
N _E layer 12 as a cathode region, P _B layer 13 as a gate region, and N _B layer 1 as a base region.
4. The _PE layer 15 as an anode region is created, but before creating the P _B layer 13, the following process is performed. First, one main surface of the semiconductor substrate 11,
That is, the surface of the semiconductor substrate 11 before the P _B layer 13 is diffused is lapped using, for example, a #600 abrasive.

Next, the surface of the part where the gate electrode will be attached is etched by chemical etching to a depth of approximately
A recessed surface 13a of about 50 μm is formed. Since this recessed surface 13a is formed by chemical etching, it has less processing distortion and the like and has a smaller surface roughness than the surface of the semiconductor substrate 11.

From the one main surface side of the semiconductor substrate 11 in the above state
When P-type impurities are diffused to form the P _B layer 13,
A diffusion layer step 14a is formed directly below the recessed surface 13a, but due to the difference in surface roughness between the two surfaces, the recessed surface 1
Since the diffusion rate is faster in other parts of the semiconductor substrate 11 than directly below the diffusion layer 3a, the diffusion layer step 14a becomes extremely small.

For example, the recessed surface 1 with an etching depth of about 50 μm
3a, the diffusion layer step 14a is approximately
As a result, the thickness of the N _B layer 11 can be reduced by about 30 μm compared to the conventional method, and electrical characteristics such as forward voltage drop can be improved. .

Note that the N _B layer 12 is formed in the P _B layer 13 by a normal selective diffusion method, and then a predetermined process is performed to produce a thyristor pellet.

〔Effect of the invention〕

As mentioned above, the present invention improves the surface roughness within the concave surface.
The difference in surface roughness of the semiconductor substrate surface before the P _B layer was formed was significantly changed, and the surface roughness of the semiconductor substrate surface was increased compared to the surface roughness within the concave surface, so that diffusion Due to the difference in speed, it is possible to reduce the step difference in the diffusion layer of the P _B layer that is formed directly under the concave surface, and as a result, it is possible to suppress the increase in the thickness of the N _B layer, and to reduce electrical problems such as forward voltage drop. Characteristics can be improved.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway sectional view showing an example of a semiconductor device manufactured by a conventional semiconductor device manufacturing method, and FIG. 2 is a semiconductor device manufactured by a semiconductor device manufacturing method according to the present invention. It is a partially cutaway sectional view showing an example. 11...Semiconductor substrate, 12...N _E layer, 13...
...P _B layer, 13a...concave surface, 14...N _B layer, 1
4a... Diffusion layer step, 15... P _E layer.

Claims (1)

[Claims] 1. In a method for manufacturing a semiconductor device having a cathode region and a gate region on one main surface of a semiconductor substrate, the gate region is recessed into the cathode region, and a step is provided between both regions to isolate them. After making the surface roughness of the recessed surface that will become the gate region smaller than the surface roughness of the surface of the semiconductor substrate excluding the recessed surface and increasing the ratio of the two surface roughnesses,
A method for manufacturing a semiconductor device, characterized in that impurities are diffused from one main surface side of the semiconductor substrate to form a base region with a small step difference in the diffusion layer directly under the recessed surface.