JPH0235459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor substrate, and particularly to a method for manufacturing a semiconductor substrate used for manufacturing a power transistor for electric power.

To manufacture power transistors for electric power, a two-layer structure (NonN ⁺ or
A PonP ⁺ ) semiconductor substrate is used. This is because in a power transistor for electric power, the collector electrode is taken out from the back side of the substrate, so a high concentration impurity layer is required on the back side of the substrate in order to reduce the saturation resistance of the collector. The conventional manufacturing method for a semiconductor substrate having the above two-layer structure is used to manufacture an NPN bipolar power transistor.
The following is an explanation using a NonN ⁺ type silicon substrate as an example.

(i) First, phosphorus was diffused at 1200°C for 3 hours using phosphorus oxychloride (POCl ₃ ) as a diffusion source on an n ^- type silicon substrate 1 with a thickness of 500μ and a #1000 lap finish, and then diffused phosphorus on both sides of the substrate 1. Diffusion depth 15μ,
An n ⁺ type deposition layer 2 having a surface impurity concentration of 4 to 6×10 ²¹ /cm ³ is formed (as shown in FIG. 1A).

(ii) Next, the n ⁺ type deposition layer 2 is slumped by heat treatment at 1270°C for 270 hours to form an n ⁺ type slumping layer 3 with a diffusion depth of 190 μ and an impurity surface concentration of 1 × 10 ²⁰ /cm ³ or more. (Figure b
(Illustrated).

(iii) Next, remove 220μ from the surface of one slumping layer 3 by #1000 wrapping. This also removes n ^- type layer 1 by 220μ - 190μ = 30μ, so that the unwrapped n ⁺
having an n ^- type layer 1 on the slumping layer 3 of the mold
A NonN ⁺ type silicon substrate is obtained (Fig.
(Illustrated).

At this time, the surface of the n ^- type layer 1 becomes a #1000 wrapping surface 4.

(iv) Next, by mirror wrapping the surface of the n ^- layer 1, the crushed layer on the wrapping surface 4 is removed and the surface is finished into a mirror surface 5. As a result, there is an n ⁺ type slumping layer 3 with a depth of 190μ for forming the collector electrode on the back side, and an n ^- type region 1 with a thickness of 60μ that will become the collector region on top of it, and the total thickness is 250μ. A NonN ⁺ type silicon substrate is obtained (as shown in figure d).

The two-layer semiconductor substrate obtained in this way is an OSL substrate (One Side Mirror) due to its manufacturing method.
Lapping board).

By the way, in the above conventional manufacturing method, the thickness
In order to obtain a 250μ OSL substrate, it was necessary to start from a substrate that was approximately twice as thick, resulting in a problem of large material loss. In addition, there were problems in that it required a long wrapping time to wrap and remove 220μ on one side, and that high-density wrapping required sophisticated technology, resulting in high costs. Furthermore,
The removal method is #1000 wrapping, and the subsequent mirror surface finishing is also mechanical wrapping, so it is not possible to use the above conventional manufacturing method.
Devices fabricated using OSL substrates have had the problem of reduced minority carrier lifetime.

The present invention was made in view of the above circumstances, and
A semiconductor that can manufacture a two-layer structure semiconductor substrate with the same thickness as a conventional one starting from a thinner substrate at low cost and with high material efficiency, and also has a high minority carrier lifetime. A method for manufacturing a substrate is provided.

That is, the present invention includes a step of forming an oxide film on both sides of a semiconductor substrate of one conductivity type with a low impurity concentration, applying a liquid silica compound on the oxide film on one side of the substrate, and applying a liquid silica compound to the oxide film on one side of the substrate. A process of forming a bonded body in which two substrates are closely bonded together, and a process of forming a highly concentrated impurity layer of the same conductivity type as the substrate on the non-bonded side of the substrate by diffusing impurities into the bonded body. , a step of growing an oxide film on the non-bonded surface side of the substrate by oxidizing the entire surface of the adhered body, and silamping of the high concentration impurity layer in a stacked state in which a large number of adhered bodies were laminated and pressurized. Thereafter, the method for manufacturing semiconductor substrates comprises the steps of separating individual substrates from this stacked state, and finishing the non-slumping surfaces of the separated substrates by mirror etching.

Hereinafter, an embodiment in which the present invention is applied to the manufacture of a silicon substrate for an NPN bipolar power transistor will be described with reference to FIGS. 2a to 2g.

Example (i) First, 270μ thick, #1000 lap finished ^n-
By heat-treating the mold silicon substrate 11 in a dry oxygen atmosphere at 1000 DEG C. for 20 minutes, thermal oxide films 12 having a thickness of 500 to 700 Å are formed on both surfaces thereof (as shown in FIG. 2A).

(ii) Next, a liquid silica compound solution is applied onto the thermal oxide film 12 on one side of the substrate 11 using a spinner or the like, for example, at 2000 rpm for 15 seconds. Attach two similar boards together. Next, the liquid silica compound film is solidified by heat treatment in an oxygen atmosphere at 1000°C or higher, thereby forming the two substrates 1.
1 and 11' are closely fixed through the silica compound layer 13 (as shown in FIG. 2b).

Note that this heat treatment removes the thermal oxide films 12, 1 previously formed on the surfaces of the substrates 11, 11'.
2' reacts with the silica compound 13 to achieve a strong bond.

(iii) Next, use e.g. phosphorus oxychloride as a diffusion source.
Phosphorus was diffused for about 3 hours in an oxidizing atmosphere at 1200℃, with a diffusion depth of 15μ and an impurity surface concentration of 4.
~6×10 ²¹ /cm ³ n ⁺ type high concentration impurity layer 14,1
4' (as shown in Figure 2e).

(iv) Next, oxidation was performed at 1000℃ for 4 hours in a steam atmosphere to form an oxide film 15,1 with a thickness of 1.0 to 1.2μ.
5' (as shown in Figure 2d).

(v) Next, as shown in Fig. 2d, two substrates 11, 1
1′ in close contact with 1270℃ N ₂ /O ₂ = 2/1
Slumping was performed for 270 hours under a mixed glass atmosphere of 100 mL of mixed glass, and an n ⁺ type slumping layer 16 with a diffusion depth of 190 μ and an impurity surface concentration of 1×10 ²⁰ /cm ³ or more was formed.
16' (as shown in FIG. 2e).

In this slumping, as shown in FIG. 3, the substrates 11 and 11' are tightly bonded as shown in FIG. This is carried out on a quartz diffusion boat 101.

(vi) After the above-mentioned slumping is completed, the completely stacked substrates 11 and 11' shown in FIG. The substrates are separated into individual substrates by dipping (as shown in FIG. 2f).

(vii) Next, the surface of the n ^- type layer 11 on each separated substrate is coated with, for example, a mixed solution of hydrofluoric acid, nitric acid, and acetic acid (HF:HNO ₃ :CH ₃ COOH=1:
3:2) to a mirror surface finish by etching about 20μ (as shown in Figure 2g).

In this way, the slumping layer 1 with a diffusion depth of 190μ
6 and an n ^- type layer 11 with a film thickness of 60μ, the entire structure is
A double-layered NonN ⁺ type silicon substrate with a thickness of 250μ is fabricated. Note that a semiconductor substrate that has one side mirror-finished by etching is called an OSE substrate (one side substrate) as opposed to an OSL substrate.
We will call it mirror etching board).

According to the above embodiment, since the n ⁺ type slumping layer 16 can be formed only on one side of the starting substrate 11, a raw material substrate with a thickness of 270 μm may be used when manufacturing an OSE substrate with a thickness of 250 μm. Therefore, compared to conventional manufacturing methods, raw material loss is significantly reduced, and material efficiency can be dramatically improved. Also, when finishing the mirror surface, it is possible to use etching to finish the mirror surface since it is sufficient to remove about 20 μm of the n ^- type layer 11.
Therefore, the mirror surface finishing process is extremely easy and takes a shorter time than conventional wrapping, which makes it possible to reduce costs, while there is no need to mechanically wrap the n ^- type layer 1.
The fracture layer and strain of 1 are reduced, and the lifetime of minority carriers can be improved compared to conventional manufacturing methods. By the way, when using both the conventional OSL substrate and the OSE substrate of the above example,
A planar structure PN junction was formed at the depth of , electrodes were formed, and the lifetime was measured.
As shown in the figure. Figure A is a lifetime distribution chart when the conventional OSL board is used, and Figure B is a lifetime distribution diagram when the OSE board of the above embodiment is used. This result is based on the above example.
This shows that the OSE board has a longer minority carrier lifetime.

In addition, some methods have been used in the past in which a highly concentrated slumping layer is formed on only one side of the starting substrate, but in this method, as shown in Figure 5, highly concentrated slumping is performed on one side. At this time, the n-type impurity that jumped out from the surface of the n ⁺ layer becomes n ^-
There was a problem in that it was impossible to avoid penetrating into the surface of the layer, and as a result, the control of the thickness of the n ^- layer became unstable. On the other hand, it is clear that the method of the above embodiment can completely solve this problem.

It goes without saying that the present invention can be applied not only to the production of NonN ⁺ type semiconductor substrates but also to the production of PonP type semiconductor substrates.

As described in detail above, according to the present invention, it is possible to manufacture a two-layer structure semiconductor substrate for use in manufacturing power transistors with high material efficiency and low cost, and also to have excellent minority carrier lifetime characteristics. It is possible to provide a method for manufacturing a semiconductor substrate that can be obtained.

[Brief explanation of drawings]

1A to 1D are cross-sectional views showing the manufacturing process of a conventional OSL substrate, FIGS. 2A to 2G are cross-sectional views showing the manufacturing process of a semiconductor substrate according to an embodiment of the present invention, and FIG. FIG. 4 is a distribution diagram showing a comparison of the lifetime characteristics of minority carriers in a conventional OSL board and an OSE board manufactured according to an embodiment of the present invention. The figure is an explanatory diagram showing problems in conventional manufacturing methods other than the conventional examples shown in FIGS. 1a to 1d. 11,11'...n ^- type silicon substrate, 12,1
2'...Thermal oxide film, 13...Silica compound layer, 1
4,14'...n ⁺ type high concentration impurity layer, 15,1
5'...Oxide film, 16,16'...n ⁺ type slumping layer, 100...Quartz guide plate, 101...Quartz boat.

Claims (1)

[Claims] 1. A step of forming an oxide film on both sides of a semiconductor substrate of one conductivity type with a low impurity concentration, and applying a liquid silica compound on the oxide film on one side of the substrate, and bonding the two substrates through the liquid silica compound. a step of forming a bonded body in which the bonded body is tightly adhered; a step of forming a highly concentrated impurity layer of the same conductivity type as the substrate on the non-bonded side of the substrate by diffusing impurities into the bonded body; After a process of growing an oxide film on the non-bonded side of the substrate by oxidizing the entire surface of the substrate, and slumping the high concentration impurity layer in a stacked state in which a large number of bonded bodies are laminated and pressurized, this stack is 1. A method for manufacturing a semiconductor substrate, comprising the steps of separating individual substrates from a state, and finishing a non-slumping surface of the separated substrates by mirror etching.