JPH1084101A - Manufacture of soi substrate and soi substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a SOI substrate with a low COP(crystal originated particle) density in an SOI layer particularly for a thin film SOI substrate with the SOI layer thickness of at most 1 micron. SOLUTION: An oxide film is formed on at least a first silicon single crystal substrate by this manufacturing method, a second single crystal substrate is tightly adhered to the oxide film and strongly coupled by giving a heat treatment and, when an SOI substrate is produce for forming a thin film on the first silicon single crystal substrate, a high temperature heat treatment exceeding 1100 deg.C is effected before forming an oxide film on the surface of a first silicon single crystal substrate. Alternatively the oxidation temperature for forming an oxide film on the surface of the first silicon single crystal substrate is made higher than 1100 deg.C and the thickness of oxide film is made at least 700nm, or the thickness of the oxide film formed on the surface of the first silicon single crystal substrate is made at most 200nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called bonded SOI substrate manufacturing method and a bonded SOI substrate which are manufactured by bonding two silicon single crystal substrates via a silicon oxide film, and more particularly to an SOI layer. Of COP (Crystal Or
The present invention relates to a method for manufacturing a thin film SOI substrate having a small density.

[0002]

2. Description of the Related Art A technique of bonding two silicon single crystal substrates through a silicon oxide film is disclosed in, for example, Japanese Patent Publication No. 5-4.
As shown in Japanese Patent No. 6086, an oxide film is formed on at least one of the substrates and is bonded to each other without intervening foreign matter on the bonding surface, and then heat-treated at a temperature of about 200 to 1200 ° C. to increase the bonding strength. Methods are conventionally known.

[0003] Since a bonded substrate whose bonding strength has been increased by heat treatment can be subjected to subsequent grinding and polishing steps, it is necessary to reduce the thickness of either one of the substrates to a desired thickness by grinding and polishing. Thereby, an SOI layer for forming an element can be formed.

That is, since the manufactured SOI substrate uses the bulk crystal of a silicon single crystal substrate having excellent crystallinity as it is, an SOI layer having excellent crystallinity can be obtained. Law (Separation by
Other SOIs such as Implanted Oxgen) and melt recrystallization
It is superior to the fabrication method.

On the other hand, a silicon single crystal substrate as a raw material of a bonded substrate, in particular, a CZ manufactured from a silicon single crystal ingot pulled up by the Czochralski method,
A crystal defect called COP (Crystal Originated Particle) exists in the substrate, and it has recently been clarified that this is one of the causes of deterioration of the oxide film breakdown voltage characteristics (J. Ryuta, E. Morita, T.). .Tanaka and Y.Shimanuki; Jpn.J.
Appl. Phys. 29 (1990) L1947).

[0006] Therefore, using such a CZ substrate, SO
When an I substrate is manufactured, the COP naturally exists in the manufactured SOI layer, and the oxide withstand voltage characteristic of the SOI layer is deteriorated. In this case, especially in the case of a thin-film SOI substrate in which the thickness of the SOI layer to be manufactured is, for example, 1 μm or less, the COP may penetrate the SOI layer and form a pinhole.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above problems, and is directed to an SOI substrate having a low COP density in an SOI layer, particularly a thin film SOI substrate having an SOI layer having a thickness of 1 micron or less. The purpose of the present invention is to provide a method for producing the same.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, an oxide film is formed on at least a surface of a first silicon single crystal substrate, and a second silicon single crystal substrate is formed. A method for manufacturing an SOI substrate in which the first silicon single crystal substrate is thinned after the substrate is brought into close contact with the substrate via the oxide film and subjected to heat treatment so as to be firmly bonded to the first silicon single crystal substrate. A method for manufacturing an SOI substrate, comprising performing a high-temperature heat treatment at a temperature exceeding 1100 ° C. on the substrate before forming an oxide film on the surface.

As described above, the COP density near the substrate surface can be reduced by previously performing a high-temperature heat treatment at a temperature exceeding 1100 ° C. on the first silicon single crystal substrate serving as the active-side substrate. Therefore, if an oxide film is formed on this substrate and bonded to the second silicon single crystal substrate, an SOI substrate having a low COP density in the SOI layer can be manufactured.

In this case, the high-temperature heat treatment at a temperature exceeding 1100 ° C. is desirably performed in a reducing atmosphere, an inert gas atmosphere, or a mixed atmosphere thereof. Thus, if the substrate is heat-treated in a reducing atmosphere or an inert gas atmosphere, the COP density near the substrate surface can be efficiently reduced.

Further, in the present invention, the oxidation temperature for forming an oxide film on the surface of the first silicon single crystal substrate is 11
It is preferable that the temperature be higher than 00 ° C. (claim 3).
As described above, by setting the oxidation temperature at which the oxide film is formed on the surface of the first silicon single crystal substrate to a temperature exceeding 1100 ° C., the density of COP generated near the substrate surface due to the oxidation heat treatment can be suppressed. Can be. In this case, the COP density can be further reduced by setting the thickness of the oxide film to be formed to 700 nm or more (claim 5).

In the present invention, the thickness of the oxide film formed on the surface of the first silicon single crystal substrate is 200 nm.
By the following, C generated near the substrate surface
The density of OP can be suppressed and reduced.
Claim 6). In this case, if the thickness of the oxide film formed on the first silicon single crystal substrate is 200 nm or less, if the thickness of the buried oxide film is insufficient, the surface of the second silicon single crystal substrate also has an oxide film. May be formed and the thickness thereof may be adjusted (claim 7).

[0013] The invention described in claim 8 of the present invention is the invention according to any one of claims 5 to 7.
In the method for manufacturing an OI substrate, the oxide film formed on the surface of the first silicon single crystal substrate is once removed, and then the oxide film is formed again on the surface of the first silicon single crystal substrate, and the oxidation temperature exceeds 1100 ° C. Temperature and oxide film thickness 700n
m, or a film thickness of an oxide film to be formed is set to 200 nm or less, and then the oxide film is brought into close contact with a second silicon single crystal substrate.

As described above, the oxide film formed on the surface of the first silicon single crystal substrate is once removed, and then the oxide film is formed again by the method according to the present invention. By contacting with the substrate, the COP density near the substrate surface can be reduced, and the quality of the buried oxide film can be improved.

According to the method of the present invention, the SOI layer having a low COP density in the SOI layer.
I substrate can be obtained, which
It is particularly useful for a thin film SOI substrate having an OI layer thickness of 1 micron or less (claims 9 and 10).

Hereinafter, the present invention will be described in more detail.
The present invention is not limited to these. In the case where an SOI substrate is manufactured by using the bonding method, the SOI layer is formed near the surface of the silicon single crystal substrate as a raw material.
The OP density is a problem. In particular, with the recent high integration of devices, the required thickness of the SOI layer has been further reduced, and a thin film S having an SOI layer of 1 micron or less has been required.
There is a need for an OI substrate. Therefore, in such a thin-film SOI substrate, the vicinity of the surface of the silicon single crystal substrate, which is particularly problematic, is a region of about 1 micron or less from the surface, more precisely, an oxide film formed on the substrate surface. Approximately 1
It is the area within a micron.

Accordingly, the present inventors have conceived of applying a heat treatment to a raw silicon single crystal substrate in advance to reduce the COP density in the vicinity of the surface and using the substrate as a bonded substrate. As a result of investigating the relationship between the heat treatment conditions and the COP density near the substrate surface after the heat treatment, it was found that a high temperature heat treatment at a temperature exceeding 1100 ° C. could be performed, and the present invention was completed. It was made.

The present inventors further investigated the relationship between the heat treatment conditions for forming an oxide film on the surface of the silicon single crystal substrate and the COP density near the surface, and found that the COP density near the surface was low.
It has been found that the P density is greatly affected by the oxidation temperature and the thickness of the oxide film (oxide film thickness), and the present invention has been completed by determining these optimum conditions.

That is, in manufacturing a bonded SOI substrate, the SOI
One substrate to be a layer (hereinafter referred to as a bond wafer)
When an oxide film is formed on the substrate and bonded to the other substrate (hereinafter, referred to as a base wafer), the COP density near the surface increases as compared to before the oxide film is formed unless the oxide film forming conditions of the bond wafer are appropriate. The SOI substrate manufactured by using this bond wafer has a high COP density.
In other words, it has a layer, and the defect rate after forming the element becomes high.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto. Here, FIG. 1 is an explanatory view showing a schematic process in the case where a high-temperature heat treatment according to the present invention is performed on a bond wafer to produce an SOI substrate.

In FIG. 1, first, a bond wafer and a base wafer which are raw material wafers for producing a thin film SOI substrate are prepared. Then, among the prepared silicon single crystal substrates, a high-temperature heat treatment is performed on the bond wafer 1 (FIG. 1A) to form a COP reduction region 2 near the substrate surface (FIG. 1B).

In this case, the heat treatment temperature needs to be higher than 1100 ° C., and the upper limit temperature may be lower than the melting point of the silicon substrate (about 1420 ° C.). , Usually less than 1250 ° C. When the heat treatment is performed at around 1100 ° C., the heat treatment is preferably performed for at least one hour. If the time is shorter than this, the effect of reducing the COP existing near the surface of the bond wafer cannot be sufficiently obtained.

In order to effectively reduce the COP near the substrate surface, the atmosphere during the high-temperature heat treatment is preferably performed in hydrogen or argon or a mixed atmosphere thereof. It may be performed in an inert gas atmosphere other than the above. in this case,
For simple and low-cost operation, it is preferable to use hydrogen or argon.

The details of the theory that the COP density near the substrate surface is improved by such a high-temperature heat treatment are unknown, but when a silicon single crystal substrate is subjected to a hydrogen heat treatment, the surface morphology is improved by reflow of Si and crystal defects are reduced. Recovery is known to occur, and a similar phenomenon may occur (M. Horiuchian
d S. Aoki, J. Electrochem. Soc. Vol. 139, p. 2586 (1992)).

Next, an oxide film 3 to be a buried oxide film of the SOI substrate is formed on the surface of the bond wafer (FIG. 1).
(C)). At this time, since the region 2 in which the COP has been reduced near the surface of the bond wafer has already been formed by the high-temperature heat treatment, the heat treatment conditions for forming the oxide film 3 are not particularly limited, but preferably 1100 as described later. By oxidizing at a temperature exceeding 100 ° C. or by making the formed oxide film thickness 200 nm or less, the SOI
The COP density in the layer can be reduced.

Further, by setting the oxidation condition of the bond wafer to a temperature exceeding 1100 ° C. or setting the thickness of the oxide film to be formed to 200 nm or less, the high-temperature heat treatment of the substrate before the oxidation is omitted. It is also possible. These will be described below with reference to FIG.

FIG. 2 shows the relationship between COP density, oxide film thickness and oxidation temperature. After oxidizing a bond wafer made of a CZ substrate having a diameter of 200 mm under various oxidation conditions, the oxide film was removed with hydrofluoric acid. Then, the substrate was washed with a mixed aqueous solution of ammonia and hydrogen peroxide, and the density of COP generated on the surface was measured. The COP was measured using a particle inspection apparatus (LS-6000: manufactured by Hitachi Electronics Engineering Co., Ltd.) using a detection voltage of 700 V and a detection size of 0.1.
The test was performed under the condition of 5 to 0.20 microns.

From the results shown in FIG. 2, when the oxidation temperature is 1000 ° C. or less, the COP density increases as the oxide film thickness increases.
Above 1050 ° C., the tendency changes, surprisingly 1
It can be seen that at 150 ° C., it decreases conversely. Such a phenomenon was first discovered by the present inventors. Therefore, the oxidation condition of the bond wafer is 1100
It is found that the temperature is desirably higher than 0 ° C., whereby it is understood that the generation and increase of COP due to the oxidation heat treatment can be suppressed. In this case, it can be seen that the COP density can be further reduced by setting the oxide film thickness to 700 nm or more. However, when the oxidation heat treatment is performed at normal pressure, the upper limit of the oxide film thickness is about 3 μm, and a heat treatment for a considerably long time is required to form a film having a thickness larger than that, which is not practical.

FIG. 2 also shows that, regardless of the oxidation temperature, when the oxide film thickness is 200 nm or less, particularly 100 nm or less,
It can be seen that the COP density shows a constant value at a very low level. Therefore, by setting the thickness of the oxide film formed on the surface of the bond wafer to 200 nm or less, particularly 100 nm or less, generation of COP can be suppressed and reduced. In this case, as the lower limit of the oxide film thickness, the minimum film thickness that can be generally formed by thermal oxidation is 5 nm.
Since it is on the order, it means that the thickness is more than this.

As described above, the COP density of the bond wafer depends on the conditions for forming the oxide film formed on the bond wafer. Then, the COP density of the thin film SOI layer formed from the bond wafer is also affected by the oxidation conditions of the bond wafer.

Therefore, in order to manufacture an SOI substrate having a low COP density, the bond wafer is oxidized at a temperature exceeding 1100.degree.
In this case, the thickness of the oxide film to be formed is set to 200 nm or less. ) Must be satisfied, and by adopting such oxidation conditions, a thin film SOI substrate having a low COP density can be obtained without necessarily performing the high-temperature heat treatment before the oxidation of the bond wafer. .

FIG. 3 shows the effect when the high-temperature heat treatment is applied to the bond wafer. The high-temperature heat treatment at 1200 ° C. in a hydrogen atmosphere is performed before the bond wafer is oxidized.
This is a result of investigating the relationship between the oxide film thickness and the COP density by forming an oxide film on the surface at an oxidation temperature of 1050 ° C. after performing the test for a time. The measurement conditions for COP were the same as those in FIG.

As shown in FIG. 2, at the oxidation temperature of 1050 ° C., the COP density should increase with the increase of the oxide film thickness. According to the results of FIG. 3, the bond wafer was subjected to a high-temperature heat treatment in a hydrogen atmosphere. After that, the low COP density is maintained irrespective of the oxide film thickness, and it can be seen that the COP does not increase. Therefore, it is effective to apply a high-temperature heat treatment to the bond wafer. If the high-temperature heat treatment is applied before forming an oxide film, the oxidation temperature can be increased to 1100.
Temperature exceeding 200 ° C. and an oxide film thickness of 200
It is understood that it is not always necessary to set the diameter to nm or less.

FIG. 4 shows the result of investigation of the influence of the atmosphere during the high-temperature heat treatment. The bond wafer was subjected to a high-temperature heat treatment at 1200 ° C. for 1 hour in a hydrogen atmosphere and an argon atmosphere, and the reference wafer was not subjected to the high-temperature heat treatment. The COP density of the sample was measured. As a result, it can be seen that even when the high-temperature heat treatment is performed in an argon atmosphere, which is an inert gas, there is a COP reduction effect as in the case of a hydrogen atmosphere.

As described above, high-temperature heat treatment is performed before forming an oxide film on a bond wafer, or oxidation is performed at a temperature exceeding 1100 ° C. without performing high-temperature heat treatment, and the oxide film thickness is reduced to 700 nm. By setting the oxide film thickness to 200 nm or less as described above, a bond wafer with an oxide film having a region 2 having a low COP density near the surface (FIG. 1C) can be obtained.

Then, a bond wafer with an oxide film having a region 2 having a low COP density near the surface is brought into close contact with a base wafer 4 having no oxide film on the surface at room temperature,
When heat treatment for improving the bonding strength is added to this,
A bonded substrate in which two silicon single crystal substrates are firmly bonded can be obtained (FIG. 1D). In this case, the heat treatment conditions for improving the bonding strength are not particularly limited as long as the bonding strength that can withstand the subsequent thinning step is obtained, but the heat treatment is usually performed in an oxidizing atmosphere at a temperature of 800 ° C. or more. Will be

In this case, CO 2 on the surface of the bond wafer
If the P density is reduced by reducing the oxide film thickness to be formed to 200 nm or less, the buried oxide film thickness of the SOI substrate may be insufficient for a desired thickness.
In other words, when the buried oxide film thickness needs to be 200 nm or more, an insufficient oxide film may be formed on the base wafer and then bonded.

The bond wafer 1 side of the bonded substrate thus obtained is thinned to a desired thickness by a thinning technique such as grinding and polishing, and the thickness of the SOI layer is, for example, 1 μm or less, particularly 0 μm. A thin film SOI substrate having a thickness of 0.1 μm is obtained (FIG. 1E).

The COP density in the SOI layer of the substrate obtained as described above is determined by the above high temperature heat treatment or 1100 ° C.
Since the measures taken to form an oxide film at a temperature exceeding 200 nm or to reduce the thickness of the oxide film to be formed to 200 nm or less have been taken, the number of the oxide films is much smaller than that of an SOI substrate manufactured by a conventional method.

[0040]

Next, examples of the present invention will be described. (Examples and Comparative Examples) First, the diameter was 200 mm and the thickness was 725.
Twelve mirror-polished CZ substrates having a thickness of 4 μm, conductivity type p, and resistivity of 4 to 6 Ω · cm are prepared, and six are used for bond wafers.
Six were classified for the base wafer. Then, the six bond wafers were individually heat-treated under the conditions shown in Table 1 to obtain Examples 1, 2, 3, and 4 and Comparative Examples 1 and 2, respectively.

That is, the high-temperature heat treatment was performed on the bond wafer in the first and second embodiments. The high-temperature heat treatment was performed in the hydrogen atmosphere in the first embodiment and in the argon atmosphere in the second embodiment. In Example 3, the oxidation temperature for forming an oxide film on the surface of the bond wafer was set to a temperature exceeding 1100 ° C. (1150 ° C.), and the oxide film thickness to be formed was set to 700 n.
In Example 4, the thickness of the oxide film formed on the surface of the bond wafer was 200 nm or less.
On the other hand, in Comparative Examples 1 and 2, the heat treatment according to the present invention was not added, and only the bonding heat treatment temperature was changed to Comparative Example 2.

Then, the six bond wafers, which had been subjected to the bond oxidation heat treatment, were brought into close contact with six base wafers having no oxide film, respectively, and were subjected to heat treatment under the bonding heat treatment conditions shown in Table 1 to form a firm bond. . This bonding heat treatment was performed in an oxidizing atmosphere containing water vapor.

Then, in order to fabricate a target thin film SOI substrate, the bond wafer side of the bonded substrate, which has been subjected to the bonding heat treatment, is ground with a surface grinder or the like, and
After reducing the thickness of the layer to about 20 microns, an SOI layer having a thickness of 1 micron or less is formed by a thinning method such as polishing. When you make an SOI substrate,
Since it becomes very difficult to measure the COP density in the SOI layer, the following method was used to evaluate this example and the comparative example.

That is, the base wafer side of the bonded substrate after the completion of the bonding heat treatment is ground with a surface grinder to make the base wafer about 10 μm thick.
The remaining 10 μm is etched away using an aqueous solution of potassium hydroxide (concentration: 5% by weight, 70 ° C.) to expose the oxide film of the bond wafer that has become the bonding surface. Further, after immersion in dilute hydrofluoric acid with a concentration of 5% to completely remove the oxide film,
After washing with an aqueous solution of ammonia and hydrogen peroxide for 5 minutes and drying, the number of COPs present on the surface was determined using a particle inspection device (LS-6000: manufactured by Hitachi Electronics Engineering Co., Ltd.) at a detection voltage of 700 V. And the detection size was 0.15 to 0.20 microns. The results are shown in Table 1.

[0045]

[Table 1]

As is clear from the results shown in Table 1, the COP densities of the bond wafer surfaces of Examples 1 to 4 where the heat treatment according to the present invention was performed were low. Therefore, this can form an SOI layer having a low COP density. On the other hand, the surface of the bond wafer of the comparative example not subjected to the heat treatment of the present invention has a high COP density. The reason why the data in Table 1 tends to increase from the data in FIGS. 2 to 4 is probably due to the measurement after the bonding heat treatment.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, in the above embodiment, the description has been made mainly on the case where the oxide film is formed only on the bond wafer side. However, the present invention is not limited to this, and the oxide film is also formed on the base wafer side. Later, the two are stuck together and SOI
The present invention is naturally applied to the case of manufacturing a substrate.

In the above embodiment, the heat treatment according to the present invention, that is, a high-temperature heat treatment is performed before forming an oxide film on the bond wafer, or the oxide film is oxidized at a temperature exceeding 1100 ° C. as an oxidation condition. Although the heat treatment for controlling the thickness to 700 nm or more or the oxide film thickness to be formed to 200 nm or less has been mainly described,
The present invention is not limited to this, and it goes without saying that heat treatment may be performed by combining these with one bond wafer.

Further, after forming an oxide film on the surface of the first silicon single crystal substrate at a temperature exceeding 1100 ° C., or reducing the thickness of the formed oxide film to 200 nm or less,
The oxide film formed on the surface of the first silicon single crystal substrate is once removed, and then the oxide film is again formed on the surface of the first silicon single crystal substrate. The oxide film may be formed to have a thickness of 700 nm or more, or may have a thickness of 200 nm or less, and may be in close contact with the second silicon single crystal substrate.

This is because the oxide film on the surface of the first silicon single crystal substrate that is formed first may incorporate COP originally present on the substrate surface, and the breakdown voltage characteristics of the buried oxide film may be reduced. Because it can cause
If this is once removed by etching or the like, and then an oxide film is formed again by the method according to the present invention, and then the oxide film is brought into close contact with the second silicon single crystal substrate, the COP density near the substrate surface can be reduced. This is because it is possible to improve the quality of the buried oxide film as well as to improve the quality of the buried oxide film.

[0052]

As described above, according to the present invention, a high-temperature heat treatment is performed before an oxide film is formed on a bond wafer.
By oxidizing at a temperature exceeding 1100 ° C. as an oxidizing condition and forming an oxide film with a thickness of 700 nm or more or a formed oxide film with a thickness of 200 nm or less, a region having a low COP density near the surface can be created. it can. Therefore, an SOI substrate having an SOI layer with a low COP density can be manufactured. Such an SOI substrate having a small COP density is particularly useful in a recently required thin film SOI in which the thickness of the SOI layer is 1 μm or less, since generation of pinholes is suppressed. Further, the SOI substrate manufactured according to the present invention has element characteristics excellent in oxide film breakdown voltage and the like due to low COP.

[Brief description of the drawings]

FIGS. 1 (a) to 1 (e) are explanatory views showing schematic steps in a case where a high-temperature heat treatment according to the present invention is performed on a bond wafer to produce an SOI substrate.

FIG. 2 shows the relationship between COP density, oxide film thickness and oxidation temperature.

FIG. 3 shows an oxide film formed on a bond wafer subjected to a high-temperature heat treatment at an oxidation temperature of 1050 ° C.
It is a figure as a result of having investigated the relationship with P density.

FIG. 4 is a result of investigating an influence of an atmosphere during a high-temperature heat treatment.

[Explanation of symbols]

1. Bond wafer, 2. COP reduction region, 3. Oxide film, 4. Base wafer.

Continued on the front page (72) Inventor Masatake Katayama 2-13-1, Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Semiconductor Co., Ltd.

Claims (10)

[Claims] 1. An oxide film is formed on at least a surface of a first silicon single crystal substrate, and the second silicon single crystal substrate is brought into close contact with the oxide film via the oxide film. Thereafter, in a method for manufacturing an SOI substrate in which the first silicon single crystal substrate is thinned, before forming an oxide film on the surface of the first silicon single crystal substrate, the substrate is subjected to a high-temperature heat treatment at a temperature exceeding 1100 ° C. A method for manufacturing an SOI substrate. 2. The SOI substrate manufacturing method according to claim 1, wherein the high-temperature heat treatment at a temperature exceeding 1100 ° C. is performed in a reducing atmosphere, an inert gas atmosphere, or a mixed atmosphere thereof. How to make a substrate. 3. The SOI according to claim 1 or claim 2.
In the method for manufacturing a substrate, an oxidation temperature for forming an oxide film on a surface of the first silicon single crystal substrate is higher than 1100 ° C. 4. The method for manufacturing an SOI substrate according to claim 1, wherein an oxide film formed on a surface of the first silicon single crystal substrate has a thickness of 200 nm or less. SOI characterized by the following:
How to make a substrate. 5. An oxide film is formed on at least the surface of the first silicon single crystal substrate, and is closely adhered to the second silicon single crystal substrate via the oxide film. Then, in the method for manufacturing an SOI substrate for thinning the first silicon single crystal substrate, the oxidation temperature for forming an oxide film on the surface of the first silicon single crystal substrate is set to a temperature exceeding 1100 ° C. A method for manufacturing an SOI substrate, wherein the thickness of the film is 700 nm or more. 6. An oxide film is formed on at least a surface of a first silicon single crystal substrate, and is brought into close contact with a second silicon single crystal substrate via the oxide film, and is heat-treated to be firmly bonded thereto. Then, in a method for manufacturing an SOI substrate for thinning a first silicon single crystal substrate, the thickness of an oxide film formed on the first silicon single crystal substrate is set to 200 nm or less. Method. 7. After forming an oxide film on the surfaces of the first and second silicon single crystal substrates, the two are brought into close contact with each other via the oxide film, and heat-treated to bond them firmly to form a first film. A method for manufacturing an SOI substrate, wherein the thickness of an oxide film formed on the first silicon single crystal substrate is set to 200 nm or less. 8. The method for manufacturing an SOI substrate according to claim 5, wherein the oxide film formed on the surface of the first silicon single crystal substrate is temporarily removed, and then the second silicon single crystal substrate is removed again. (1) forming an oxide film on the surface of the silicon single crystal substrate at an oxidation temperature of over 1100 ° C. and an oxide film thickness of 700 nm or more, or forming the oxide film thickness of 200 nm or less and thereafter A method for manufacturing an SOI substrate, which is in close contact with a second silicon single crystal substrate. 9. An SOI substrate manufactured by the method according to claim 1. 10. A thin film SOI substrate manufactured by the method according to claim 1, wherein the thickness of the SOI layer is 1 μm or less.