JPH0569296B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A method of manufacturing a semiconductor device according to the present invention will be explained according to the following items.

A. Industrial application field B. Summary of the invention C. Prior art [Figure 2] D. Problem to be solved by the invention E. Means for solving the problem F. Example [Figure 1] a. Manufacturing method [Figure 1] Figure] b Effect of the invention (A Field of industrial application) The present invention relates to a novel method for manufacturing a semiconductor device. More specifically, the present invention relates to a method of manufacturing a semiconductor device in which an oxide film, ie, a sidewall, is formed on the inner surface of an opening formed in a semiconductor layer on a semiconductor substrate.

(B. Summary of the Invention) The method for manufacturing a semiconductor device of the present invention enables the thickness of a sidewall made of an oxide film to be controlled with high precision, and by forming the sidewall, a sidewall is formed on the side surface of a semiconductor substrate. In order to prevent damage to the surface facing the opening where the semiconductor layer is formed, after forming the opening in the semiconductor layer on the semiconductor substrate, oxidizing the semiconductor layer and the surface facing the opening of the semiconductor substrate, Of the oxide film formed by the oxidation, the portion formed on the surface of the opening of the semiconductor substrate is removed, and then an oxidation-resistant film is formed on the surface of the semiconductor substrate facing the opening, and then the opening is removed. A sidewall made of an oxide film is formed by oxidizing the inner surface of the oxide film.

(C. Prior Art) [Figure 2] A bipolar element, for example, a bipolar element for ECL, cannot obtain the required characteristics unless the emitter is aligned with the base by self-alignment. A technique for positioning the emitter with respect to the base using a side wall has been introduced, for example, in Japanese Patent Publication No. 59-2187. FIG. 2 shows the technology in the order of steps. The technology is explained in the second section below.
This will be briefly explained according to the diagram.

(A) A polycrystalline silicon layer b containing an N-type impurity for forming a graft base is formed on a P-type semiconductor substrate a, and a silicon oxide film c is formed on the polycrystalline silicon layer b. Then, an opening d is formed in the polycrystalline silicon layer b and the silicon oxide film c to form a base. Then, a P-type impurity for forming a base is doped into the surface of the semiconductor substrate a through the opening d by ion implantation. e is the base region formed by the ion implantation. FIG. 2A shows the state after ion implantation for forming the base region e.

(B) Next, a silicon oxide film f is formed on the surface of the semiconductor substrate a by CVD [see FIG. 2B].

Since the film formed by CVD has good step coverage, the thickness of the silicon oxide film f on the inner surface of the opening d is relatively close to the film thickness on the semiconductor a.

(C) Next, the silicon oxide film f is removed by CVD by anisotropic etching, for example, RIE [see FIG. 2C].

Since the silicon oxide film f is removed by anisotropic etching, a portion g of the silicon oxide film f located on the inner surface of the opening d is not removed much and remains as a sidewall. On the other hand, the portion of the surface of the base region e of the semiconductor substrate a where the sidewall g is not formed is completely exposed.

(D) After that, using silicon oxide film c and sidewall g as a mask, apply N to the surface of base region e.
The emitter h is formed by implanting impurity ions into the mold, and then annealing is performed. By this annealing, the emitter h is activated, and the P-type impurity in the polycrystalline silicon layer b is diffused to the surface of the semiconductor substrate a, and the graft base i
is formed.

After that, an electrode j made of aluminum is formed. FIG. 2D shows the state after the electrode j is formed.

In this way, after forming the base region, a sidewall g is formed on the inner surface of the opening d for impurity introduction to form the base region e, and the emitter region h is formed through the opening narrowed by the sidewall g. By introducing impurities for
It is possible to position the emitter region h with respect to the base region e by self-alignment. Such a self-alignment method was also introduced in Japanese Patent Application Laid-Open No. 54-44474,
Furthermore, details regarding the method of forming the sidewalls are introduced in Japanese Patent Application Laid-Open No. 54-44477.

(D Problems to be Solved by the Invention) By aligning the emitter region with respect to the base region using the self-alignment method described above, a bipolar IC with a narrow base width and excellent high-speed performance can be obtained. However, CVD
It is very difficult to control the thickness of the sidewall formed from a silicon oxide film according to the method described above, and large variations in the film thickness tend to occur. That is, although the silicon oxide film formed by CVD has good step coverage, it is very difficult to control the film thickness at step portions, apart from the film thickness on a flat base. Furthermore, when a silicon oxide film is etched by anisotropic etching using RIE or the like, the amount of etching progress in the lateral direction (in the thickness direction of the sidewall) with respect to the portion of the silicon oxide film located above the stepped portion is also not constant. Therefore, the reproducibility of the sidewall is very poor. Moreover, it is very difficult to make the sidewalls thicker, and since the polycrystalline etching layer b must be made thicker in order to make the sidewalls thicker, the surface of the substrate becomes more uneven, which is not preferable. This has resulted in problems such as variations in the characteristics (cutoff frequency, etc.) of the transistor elements and shorting between the emitter and base.

In addition, according to the above method, since the silicon oxide film f formed by CVD is subjected to an anisotropic etching process such as RIE to expose the surface of the base region e, the surface of the portion where the emitter region h is to be formed is damaged. As a result, there was a problem that the characteristics deteriorated.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to control the thickness of the oxide film that is the sidewall with high precision, and also prevents damage to the surface facing the opening of the semiconductor substrate due to the formation of the oxide film. The purpose is to protect against

(E. Means for Solving Problems) In order to solve the above problems, the method for manufacturing a semiconductor device of the present invention includes forming an opening in a semiconductor layer on a semiconductor substrate, and then forming an opening between the semiconductor layer and the semiconductor substrate. oxidize the surface facing the opening of the semiconductor substrate, remove the portion of the oxide film formed by the oxidation that is formed on the surface of the opening of the semiconductor substrate, and then form an oxidation-resistant film on the surface of the semiconductor substrate facing the opening. The method is characterized in that an oxide film serving as a sidewall is formed by oxidizing the inner surface of the opening.

Therefore, according to the method for manufacturing a semiconductor device of the present invention, an oxide film serving as a sidewall is formed by heating and oxidizing the inner surface of an opening in a semiconductor layer, and the thickness of the oxide film can be greatly reduced by adjusting the oxidation time. Can be controlled with high precision. After forming an oxide film with good step coverage, the oxide film is
Since a sidewall formation method in which an oxide film is left only on the inner surface of the opening by anisotropic etching using RIE or the like is not used, anisotropic etching is not required to form the sidewall. Therefore, damage to the semiconductor substrate surface caused by anisotropic etching such as RIE for forming sidewalls can be avoided.

(Embodiment F) [FIG. 1] A method of manufacturing a semiconductor device of the present invention will be described below with reference to an embodiment shown in the accompanying drawings.

(a Manufacturing method) [FIG. 1] FIGS. 1A to 1H show an example of the implementation of the method for manufacturing a semiconductor device of the present invention in the order of steps.

(A) A polycrystalline silicon layer 2 containing an N-type impurity for forming a graft base is formed on an N-type semiconductor substrate 1, a silicon oxide film 3 is formed on the polycrystalline silicon layer 2, and then a silicon oxide film 3
Then, an opening 4 for forming a base region is formed in the polycrystalline silicon layer 2 by etching.

Thereafter, a base region 5 is formed by implanting P-type impurity ions into the surface of the semiconductor substrate 1 through the opening 4. FIG. 1A shows the state after ion implantation of P-type impurities.

(B) Next, the surface of the semiconductor substrate 1 is heated and oxidized by about 50 to 500 Å. Then, polycrystalline silicon layer 2
An oxide film 6 is formed on the inner surface of the opening 4 and on the surface of the portion of the semiconductor substrate 1 facing the opening 4.
The thickness t of the oxide film 6 on the inner surface of the opening 4 is thicker than the thickness t' on the surface of the semiconductor substrate 1. This oxide film 6 is formed to prevent the inner surface of the opening 4 of the polycrystalline silicon layer 2 from being nitrided in a later nitriding step. FIG. 1B shows the state after the oxide film 6 is formed by thermal oxidation.

(C) Next, the portion of the silicon oxide film 6 formed on the surface of the semiconductor substrate 1 is removed by anisotropic etching of the silicon oxide film 3, for example, RIE. Since anisotropic etching is used, most of the portion of silicon oxide film 6 located on the inner surface of opening 4 remains intact. FIG. 1C shows the state after anisotropic etching.

(D) Next, the surface of the semiconductor substrate 1 is directly nitrided to form a silicon oxide film (thickness:
Å) form 7. Specifically, this nitriding treatment is preferably performed by nitrogen ion implantation or plasma nitriding using an ammonia-based gas. FIG. 1D shows the state after the silicon nitride film 7 is formed.

(E) Next, a sidewall (thickness: 3000 Å, for example) 8 is formed on the inner surface of the opening 4 of the polycrystalline silicon layer 2 by thermal oxidation. The thickness of the sidewall 8 made of a silicon oxide film formed on the inner surface of the opening 4 can be controlled with very high precision by adjusting the heating oxidation time.

Furthermore, since the silicon nitride film 7 has oxidation resistance, it functions as a mask against this thermal oxidation.
The surface of semiconductor substrate 1 is not oxidized. FIG. 1E shows the state after this heating and oxidation treatment.

(F) Next, the silicon nitride film 7 is removed by etching. This etching is performed on the silicon nitride film 7.
If wet etching is performed using an etching solution that is corrosive to the semiconductor substrate 1, the surface of the semiconductor substrate 1 will not be damaged. Note that even if the silicon nitride film 7 is first etched by dry etching such as RIE to a certain thickness, and then the remaining silicon nitride film 7 is wet etched, the surface of the area where the emitter will be formed will be damaged. It is possible to prevent this from happening. FIG. 1F shows the state after the silicon nitride film 7 is removed.

(G) Next, N is applied to the surface of the base region 5 through the opening 4' narrowed by the sidewall 8.
An emitter region 9 is formed by doping type impurities. Then, by annealing, the impurities in the base region 5 and the emitter region 9 are activated, and at the same time, the P-type impurity doped in the polycrystalline silicon layer 2 is diffused into the surface of the semiconductor substrate 1 to form the graft base 10. form. FIG. 1G shows the state after the emitter region 9 and graft base 10 have been formed.

(H) After that, an electrode 11 made of aluminum is formed. FIG. 1H shows the state after electrode formation.

(b Effect) According to the above-described method for manufacturing a bipolar element,
Since the sidewall 8 is formed by heating and oxidizing the opening 4 formed in the polycrystalline silicon layer 2 on the semiconductor substrate 1, the film thickness of the sidewall 8 can be adjusted with high precision by adjusting the heating oxidation time. can be controlled. Therefore, the positional relationship between the base region 5 and the emitter region 9 can be controlled very accurately.

Further, according to the method for manufacturing a bipolar element described above, it is possible to prevent the surface of the semiconductor substrate 1 from being seriously damaged by anisotropic etching such as RIE. That is, according to the manufacturing method shown in FIG. 2, a silicon oxide film f with good step coverage is formed by CVD, and then the silicon oxide film f is anisotropically etched by RIE to form the opening d. A sidewall g is formed by leaving a silicon oxide film on the inner surface.
Therefore, it is inevitable that the surface of the active region of the semiconductor substrate will be damaged by anisotropic etching such as RIE for forming sidewalls. However, according to the manufacturing method according to an embodiment of the present invention shown in FIG. No anisotropic etching is required to form the sidewalls 8. Therefore, there is no fear that the surface of the semiconductor substrate 1 will be damaged due to the formation of the sidewall 8 and that the characteristics of the transistor will deteriorate. Of course, anisotropic etching is performed to remove the silicon oxide film 6 on the semiconductor substrate 1 [see FIG. 1B], but since the silicon oxide film 6 is very thin at 50 to 500 Å, There is no problem because it can be removed without causing major damage to the surface. Furthermore, after forming the sidewall 8, the silicon nitride film 7 is removed.
This removal itself does not necessarily have to be done by anisotropic etching, and even if removed by anisotropic etching, the silicon nitride film 7 is thin, for example, about 80 Å, so the surface of the semiconductor substrate 1 may be damaged. This can be avoided.

(G Effect of the invention) As is clear from the above,
The method for manufacturing a semiconductor device of the present invention includes a step of forming an opening in a semiconductor layer formed on a semiconductor substrate, a step of oxidizing the semiconductor layer and a surface of the semiconductor substrate facing the opening, and a step of oxidizing the semiconductor layer and the surface of the semiconductor substrate facing the opening. removing the oxide film formed on the surface facing the opening of the semiconductor substrate, forming an oxidation-resistant film on the surface of the semiconductor substrate from which the oxide film has been removed, and performing oxidation treatment to remove at least the semiconductor layer. forming an oxide film on the inner surface of the opening.

Therefore, according to the method for manufacturing a semiconductor device of the present invention, an oxide film serving as a sidewall is formed by heating and oxidizing the inner surface of an opening in a semiconductor layer, and the thickness of the oxide film can be greatly reduced by adjusting the oxidation time. Can be controlled with high precision. In addition, after forming an oxide film with good step coverage, the oxide film is RIE
Since the sidewall formation method of leaving an oxide film only on the inner surface of the opening by anisotropic etching is not used, anisotropic etching is not required to form the sidewall. Therefore, damage to the semiconductor substrate surface caused by anisotropic etching such as RIE for forming sidewalls can be avoided.

[Brief explanation of the drawing]

1A to 1H are cross-sectional views showing an example of the method for manufacturing a semiconductor device according to the present invention in the order of steps, and FIGS. 2A to D are cross-sectional views showing a conventional example of the method for manufacturing a semiconductor device in the order of steps. . Explanation of symbols: 1... Semiconductor substrate, 2... Semiconductor layer, 4... Opening, 6... Oxide film, 7... Oxidation resistant film, 8... Oxide film (side wall).

Claims (1)

[Claims] 1. A step of forming an opening in a semiconductor layer formed on a semiconductor substrate; A step of oxidizing the semiconductor layer and a surface of the semiconductor substrate facing the opening; a step of removing an oxide film formed on a surface facing the opening; a step of forming an oxidation-resistant film on the surface of the semiconductor substrate from which the oxide film has been removed; and an oxidation treatment to remove at least the semiconductor layer. A method for manufacturing a semiconductor device, comprising the steps of: forming an oxide film on the inner surface of the opening.