JPH1032168A - Method of forming protective film on surface of silicon substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate cleaning of a silicon substrate subsequent to a carrying-out of the substrate in the atmosphere and to reduce adverse effects to the substrate pertaining to the cleaning by a method, wherein a germanium film is deposited on the surface of the substrate to coat the surface of the substrate and the thickness of the germanium film is formed preferably with a thickness of a specified value or lower. SOLUTION: A germanium film 1 is applied on the surface of a silicon substrate 2. In the application of the film 1, the substrate 2 is heated for one minute at about 1100 deg.C in an ultrahigh vacuum container at a pressure of about 1×10<-8> Torr or lower to clean the surface of the substrate 2. Then, the germanium film is deposited on the substrate 2 with a film thickness of 100Å or thinner, such as a film thickness of 50Å. The deposition is conducted by evaporating the solid germanium film from a heating crucible. This substrate 2 is carried out in the atmosphere, is exposed to the atmosphere for 5 hours or thereabouts and is again returned to the ultrahigh vacuum container. In this a way, when the germanium film 1 is kept being applied on the substrate 2, the clean surface of the substrate 2 can be easily reproduced by a heating treatment at a comparatively low temperature, even if the substrate is exposed to the atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a protective film on a silicon substrate surface. More specifically, the present invention relates to a technique for preventing contamination of a silicon substrate used for forming a semiconductor electronic device when the silicon substrate is stored or transported in the air, due to oxidation of the substrate or adsorption of impurities.

[0002]

2. Description of the Related Art Semiconductor electronic components such as transistors and integrated circuits are usually formed by laminating various types of films on a silicon substrate or by performing surface processing such as etching by lithography.

[0003] Before the silicon substrate is processed, impurities on the surface, for example, silicon oxide (Si)
A cleaning process for removing O ₂ ), hydrocarbons (C ₂ H ₆ , CH ₄ ), etc., must be performed to create a clean surface with only silicon atoms.

[0004] When such impurities are present, when semiconductor electronic components are subsequently formed, the characteristics of the components are degraded and the yield is degraded. Further, even if the silicon substrate once produces a clean surface, once it is exposed to the atmosphere, it is instantaneously oxidized and adsorbs impurities, and is contaminated with such impurities.

Therefore, when an electronic component is formed, if it is carried out of the apparatus to the atmosphere for the purpose of moving between the apparatuses or temporarily storing the same, a cleaning process is always performed before the subsequent processing.

[0006] Cleaning requires high-temperature heating at a temperature of 1000 ° C or higher, plasma irradiation, or the like. However, such processing is suppressed as few times as possible because it degrades the quality of the substrate. Is desired.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to facilitate the cleaning of a silicon substrate after being carried out to the atmosphere and to reduce the adverse effect of the cleaning on the substrate.

[0008]

According to a first aspect of the present invention, there is provided a method of forming a protective film on a surface of a silicon substrate, wherein a germanium film is deposited and coated on the surface of the silicon substrate. To achieve the above object, a method for forming a protective film on a silicon substrate surface according to claim 2 of the present invention comprises:
In claim 1, the thickness of the germanium film is 10
0 ° or less.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, as shown in FIG.
The germanium film 1 is thinned on the cleaned silicon substrate 2 by vapor phase growth or vapor deposition.
Å or less, preferably about 20 to 50Å is deposited to cover the surface. If the thickness of the germanium film is too large, it takes a long time to remove sublimation, which may cause deterioration of the silicon substrate 2, whereas if it is too thin, the protective effect on the substrate surface is weakened. Experience has shown that a germanium film thickness of 100 ° or less has a practical effect as a protective film and can be processed in a short time.

Next, as shown in FIG. 2 (2), when the silicon substrate 2 covered with the germanium film 1 is exposed to the air, only the surface layer of the germanium film 1 is thinly oxidized to form a germanium oxide layer (GeO). ₂ , GeO). Also,
The impurities are also adsorbed only on the surface layer.

Thereafter, as shown in FIG. 2 (3), the silicon substrate 2 covered with the germanium film 1 is heated to about 800 ° C. in a vacuum or an inert gas atmosphere, so that the coated germanium film is The film 1 is easily volatilized. At the same time, all of the germanium oxide and the adsorbed impurities are volatilized.

Therefore, a clean silicon surface is finally exposed as shown in FIG.

As described above, by covering the surface of the silicon substrate 2 with the germanium film 1, generation of adsorbed impurities and oxides occurs only on the surface layer of the germanium film 1, and the silicon substrate 2 is not contaminated.

The germanium film 1 itself can be removed by sublimation at a relatively low temperature of 800 ° C., and at the same time, oxides and impurities can be removed. That is, the coated germanium film 1 functions as a protective film for the silicon substrate 2 which can be easily removed.

[Action] Conventionally, a silicon substrate carried out to the atmosphere requires a cleaning treatment due to the attachment of impurities or the formation of an oxide layer. However, according to the present invention, the germanium film functions as a protective film. This prevents the silicon substrate itself from being contaminated.

Therefore, the germanium film may be removed instead of the cleaning process. The removal of germanium may be performed by a relatively low-temperature heat treatment at about 800 ° C., and the adverse effect on the silicon substrate can be reduced.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. FIG. 1 shows a silicon substrate covered with a germanium film manufactured by applying one embodiment of the present invention.
Shown in As shown in the figure, the surface of a silicon substrate 2 is covered with a germanium film 1.

The coating of the germanium film 1 is performed as follows. First, the surface of the silicon substrate 2 is cleaned by heating it at 1100 ° C. for 1 minute in an ultrahigh vacuum vessel of 1 × 10 ⁻⁸ Torr or less.

Next, germanium is deposited on the silicon substrate 2 by about 50 °. The deposition was performed by a method of depositing solid germanium from a heating crucible. In addition, the substrate temperature at the time of vapor deposition was room temperature, and amorphous germanium was laminated on the substrate surface.

The silicon substrate 2 was carried out to the atmosphere, exposed to the air for about 5 hours, and returned to the ultrahigh vacuum vessel again. When the surface was observed using Auger electron spectroscopy,
It was found that oxygen and carbon of 10 ¹⁴ atm / cc or more were present on the surface, the germanium film 1 was oxidized, and carbon-based impurities were adsorbed.

This substrate was heated at 800 ° C. for about 30 minutes in an ultra-high vacuum vessel of 1 × 10 ⁻⁸ Torr or less to sublimate the germanium coating on the surface, and the surface was observed again by Auger electron spectroscopy. Surface oxygen and carbon concentration of 1
0 ¹³ atm / cc or less was found.

This indicates that impurities on the surface have been removed to the extent that there is no practical problem. It was found that the concentration of germanium on the surface was below the measurement limit and was almost completely removed. As described above, in the present embodiment, if the silicon substrate 2 is covered with the germanium film 1, the clean surface can be easily reproduced by the heat treatment at a relatively low temperature of about 800 ° C. even when exposed to the atmosphere. it can.

Here, in the above-described embodiment, a heat treatment at about 800 ° C. is performed to re-clean the surface. This is only 200 times less than the conventional 1000 ° C.
Although it seems that the effect is only as low as about ° C, much research has been done in the world of semiconductor processes to avoid the following problems.

Reduction of Solid Solution Diffusion Many Si semiconductor devices are made by joining a p-type semiconductor film and an n-type semiconductor film.
The mold film is formed by introducing boron B into Si as a doping material. The boron in this Si is 1000
If heated above ℃, it will diffuse. For example, 100
Diffusion about 1 micron by heating at 0 ° C. for about 1 hour. In a semiconductor device, since a film having a thickness of 1 micron or less is formed by laminating layers, boron is diffused from a boron-doped film to another film by heating at 1000 ° C. It becomes a mold and causes a device operation failure. However, when the heating is performed at about 800 ° C., the diffusion can be suppressed to about several hundreds of square meters, so that such a defect can be solved.

Reduction of Defects In a Si substrate, dissolved oxygen is diffused inside the substrate by heating at about 1000 ° C. to form stacking faults inside. This stacking fault causes a malfunction of the device. This stacking fault can be significantly suppressed when the heating temperature is about 800 ° C.

In the above embodiment, the substrate surface is first
Cleaning is performed by heating at about 100 ° C. for 1 minute, but such heat treatment is inevitable. The reason is that when an electronic device is usually formed on a Si substrate, the surface of the purchased substrate is first cleaned by heating at 1100 ° C.
After that, an electronic device is formed by forming a film on the surface or performing an etching process.

The present invention is applied not to such an initial cleaning process but to a case where the substrate surface after the electronic device has been formed is cleaned again. That is, as described in the related art, if a substrate on which an electronic device is formed is once taken out of the apparatus and brought into contact with the atmosphere, the surface becomes dirty, and re-cleaning by heating is required.

According to the present invention, in order to solve such a problem, there is an effect that the temperature for re-cleaning can be reduced by attaching a germanium film as a protective film to the surface of the silicon substrate. Therefore, the first heat treatment at 1100 ° C. in the examples is inevitably necessary, and has an effect that the surface can be re-cleaned at a low temperature even when exposed to the atmosphere thereafter.

[0029]

As described above in detail with reference to the embodiments, in the present invention, the silicon substrate is covered with the germanium film, so that the cleaning process after the silicon substrate is carried out to the atmosphere is facilitated, and can be performed at a low temperature. Therefore, the deterioration of the silicon substrate related to this can be suppressed. Thus, the performance of the manufactured electronic component is stabilized, and the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a silicon substrate coated with a germanium film manufactured according to one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a state after a silicon substrate is coated with a germanium film, exposed to the air, heated and sublimated, and after sublimation.

[Explanation of symbols]

 1 germanium film 2 silicon substrate

Claims (2)

[Claims] 1. A method for forming a protective film on a surface of a silicon substrate, comprising depositing and covering a germanium film on the surface of the silicon substrate. 2. The thickness of the germanium film is 100 °.
2. The method for forming a protective film on a silicon substrate surface according to claim 1, wherein: