JPH09199380A - Si substrate for epitaxial wafer and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an epitaxial wafer to be used for semiconductor devices required to realize a more high degree of integration; the wafer having a superior crystallinity without involving any dislocation in surface Si single crystal and no defect in view of the fine structure. SOLUTION: A Si substrate is heavily doped with B to provide a specified B concn. [B0 ]. Its surface B concn. Bs at its outermost face to grow an epitaxial film is 1.5×10<16> atoms/cm<3> or less and the B concn. increases at a gradient up to a B concn. [Bx ] higher than [B0 ]×0.5 in the depth of at least 2 microns from the outermost face. The substrate having the B concn. [B0 ] resulting from a heavy doping of B for epitaxial wafers can be produced by heat treating its surface to grow the epitaxial film in a H-containing gas atmosphere with [Bs ] of at least 1.5×10<16> atoms/cm<3> or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon substrate for an epitaxial wafer and a method for manufacturing the same, and more specifically, it is a boron-doped silicon substrate capable of epitaxially growing a silicon single crystal on the surface without warping or crystal lattice distortion with good crystallinity. TECHNICAL FIELD The present invention relates to a silicon substrate for an epitaxial wafer and a method for manufacturing the same, which makes it possible to manufacture semiconductor devices such as ultra-high performance ultra-LSI.

[0002]

2. Description of the Related Art In recent years, the degree of integration of semiconductor devices has been remarkably high, and a silicon wafer, which is a substrate thereof, is required to have high performance and to have better crystallinity. Therefore, an epitaxial silicon wafer has been conventionally used as a wafer for a DRAM or MPU substrate. Epitaxial silicon wafers generally have a carrier source, for example, boron (B) of 8.49 × 10 ¹⁸ to 2.
A silicon single crystal film was epitaxially grown to a thickness of several μm on a surface of a silicon substrate having a low specific resistance of about 5 to 10 mΩcm, which was heavily doped at a high concentration of 01 × 10 ¹⁹ atoms / cm ³ . The epitaxial silicon single crystal film formed on the surface of this epitaxial silicon wafer has, for example, a boron concentration of 1.34 × 10 ^{15 to} 2.70 × 10 ¹⁵ atoms / at a specific resistance of about 5 to 10 Ωcm.
It is in a lightly doped state of cm ³ . At present, high performance is ensured by forming devices on a highly crystalline silicon film epitaxially grown on such an epitaxial silicon wafer.

[0003]

However, in ultra-high integration semiconductor memories represented by VLSIs of recent years, it is usual to form sub-micron-order elements on the surface of an epitaxial wafer, and only silicon on the surface is formed. Even if the crystal has good crystallinity, if there are strains in the microstructure of the entire wafer and differences in trace amounts, these microstructural strains have a great impact on the final semiconductor device. It will be. On the other hand, a silicon epitaxial film on which a device is formed is epitaxially grown on a silicon substrate having a predetermined boron concentration with different boron concentrations as described above, and although there is an auto-doping phenomenon due to diffusion at the interface with the substrate, boron is formed. The concentration suddenly changes stepwise in a step function. The inventors are convinced that the abrupt change in the compositional composition in the epitaxial wafer as described above affects the entire epitaxial wafer and causes some inconvenience to the epitaxial film. We proceeded with a microstructural study of the epitaxial film on the surface. As a result, the change in the boron concentration at the interface between the silicon substrate and the epitaxial silicon film causes lattice structural distortion and structural warp in the epitaxial wafer, and the relaxation is also corresponding to the discontinuous change in the silicon lattice constant. The present inventors have found that there is a risk of dislocation in an epitaxial crystal due to stress, and have arrived at the present invention to provide a more complete and highly crystalline epitaxial wafer as a substrate of a semiconductor device for which higher integration is required.

[0004]

According to the present invention, a silicon substrate having a predetermined heavy-doped boron concentration [B ₀ ] and a surface boron concentration at the outermost surface of the substrate on which an epitaxial film is grown. [B _S ] is 1.5 ×
10 ¹⁶ atoms / cm ³ or less, and [B ₀ ]
There is provided a silicon substrate for an epitaxial wafer, wherein the boron concentration has a gradient and gradually increases from the outermost surface to a depth of at least 2 μm up to a boron concentration [B _X ] of 0.5 or more. In the silicon substrate for an epitaxial wafer of the present invention, the boron concentration [B ₀ ] is 1
It is preferably × 10 ¹⁷ atoms / cm ³ or more.

Further, according to the present invention, the surface of the silicon substrate having a predetermined heavy-doped boron concentration [B ₀ ] on which the epitaxial film is to be grown is heat-treated in a hydrogen-containing gas atmosphere to obtain at least the outermost boron concentration. Provided is a method for manufacturing a silicon substrate for an epitaxial wafer, characterized in that [B _S ] is set to 1.5 × 10 ¹⁶ atoms / cm ³ or less. In the method for producing a silicon substrate for an epitaxial wafer according to the present invention, it is preferable that the hydrogen-containing gas is a mixed gas of hydrogen gas and argon gas having a volume ratio H ₂ / Ar> 1.

The heat treatment in the method for producing a silicon substrate for an epitaxial wafer according to the present invention is carried out in a hydrogen-containing gas atmosphere at a temperature of 1000-1200 ° C. for 30-4.
Is preferably carried out for 60 minutes, for example, processing time, the following _{equation: D T △ t T = ∫} I F D (T) dt ( where, ∫ _I ^F D
(T) dt represents the diffusion of boron from the start of the heat treatment in the heat treatment step to the end of the heat treatment (including the temperature increase from substantially 1000 ° C. to the cooling step), and D _T represents the diffusion coefficient of boron at T ° C. ( cm ² / sec) and Δt _T is the heat treatment time corresponding to T ° C., that is, the heat treatment time (sec) required assuming that all the heat treatment steps are performed at T ° C. ) It is preferable that it is Δt _T.

The silicon substrate for an epitaxial wafer of the present invention is configured as described above, and the boron concentration of the carrier source on the surface of the silicon substrate on which the epitaxial film is formed is set to a predetermined value of 1.5 × 10 ¹⁶ atoms / cm ³ or less. Therefore, the boron concentration gap at the interface with the epitaxial film in the lightly doped state of 1 × 10 ¹⁵ to 1 × 10 ¹⁶ atoms / cm ³ can be significantly reduced, so that the crystal lattice strain can be reduced and the crystal of the epitaxial film can be reduced. Dislocations can also be suppressed, and a silicon crystal with better integrity can be obtained. Further, since the boron concentration is gradually decreased from the inside of the silicon substrate of a predetermined depth to the surface with a gradient to obtain the above predetermined concentration on the surface, the discontinuity of the lattice constant can be eliminated and the lattice strain can be reduced to reduce the epitaxial strain. It is possible to prevent the deterioration of the film characteristics, and to provide a highly reliable device having good element characteristics with high yield. Further, the silicon substrate for an epitaxial wafer as described above can be easily manufactured by heat-treating the silicon wafer in a hydrogen-containing atmosphere under predetermined conditions, and has extremely high industrial practicality.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. As the silicon substrate of the present invention, a conventionally well-known heavily-doped boron for p-type semiconductor at a concentration of 10 ¹⁷ atoms / cm ³ or more can be used, and its surface has a predetermined crystal plane like a normal wafer. Sliced and mirror-polished is used. Next, it will be described that when a silicon film is epitaxially formed on a silicon wafer heavily doped with boron as described above, inconvenience occurs in a fine structure such as crystal lattice distortion. The lattice constant of silicon doped with boron is, for example,
La metallurgia itallian
a) ”, Vol. 65, page 23 (1973), according to the lattice constant of silicon, 5.4305 Å, the boron concentration [B].
It has been reported that at ≧ 1 × 10 ¹⁹ atoms / cm ³ , it is less than or equal to 5.43038 Å, and [B] <1 × 10 ¹⁹ a
In the case of toms / cm ³ , (5.4305-5.43)
038) = 1.2 × 10 ⁻⁴ Å or less, and it is known that the change is slight. Therefore, it is presumed that the boron crystallite doping of 1 × 10 ¹⁶ atoms / cm ³ or less, which is a usual value in an epitaxial wafer, causes a small change in the silicon crystal lattice constant, and the distortion of the crystal lattice does not have to be a problem. In view of this point, the inventors have considered a heavy-doped silicon substrate having a boron concentration [B] = 1.3 × 10 ¹⁹ atoms / cm ³ and a boron concentration [B] = 2 × 10.
^The crystallinity of the light-doped silicon substrate of about ¹⁵ atoms / cm ³ was confirmed by Raman spectrum analysis. As a result, as shown in the Raman spectra of the light-doped silicon substrate in FIG. 1 and the heavy-doped silicon substrate in FIG. 2, as compared with the light-doped silicon substrate, the heavy-doped silicon substrate has a spectrum shifted to a lower wavenumber side and a crystal lattice. It is clear that the strain is generated, the full width at half maximum is increased, and the crystallinity is decreased. Also,
From these, it was also confirmed that when a light-doped silicon epitaxial film was formed on a heavy-doped silicon substrate, lattice strain occurred at the interface.

In the present invention, the surface boron concentration [B _S ] of the silicon substrate forming the epitaxial film is set to the boron concentration [B ₀ ]> 10 of the above heavy-doped silicon substrate.
¹⁷ atoms / cm ³ to 1.5 × 10 ¹⁶ atoms /
Reduce to cm ³ or less. In the above report, 1 × 10 ¹⁹ a
When the boron concentration is lower than toms / cm ^3, the change in the crystal lattice constant of silicon is small and the lattice strain is small. However, the boron concentration of the epitaxial film formed on the silicon substrate of the epitaxial wafer is 1 × 10 ¹⁵
-10 ¹⁶ atoms / cm ³ , and as described above, a sudden change in the boron concentration at the interface with the silicon substrate may cause crystal dislocation in the epitaxial film, and the same boron concentration [B _S ] 1.5 × A surface of 10 ¹⁶ atoms / cm ³ is preferable. If the surface boron concentration [B _S ] exceeds 1.5 × 10 ¹⁶ atoms / cm ³ , the lattice strain becomes large at the interface with the silicon substrate, which is not preferable.

The silicon substrate for an epitaxial wafer of the present invention has the above surface boron concentration, and the boron concentration gradually increases toward the inside of the silicon substrate at a depth of at least about 2 μm with a concentration gradient. Heavy-doped boron concentration [B ₀ ] (> 10 ¹⁷ atoms / cm 3)
A boron concentration of 50% or more of ³ , that is, a boron concentration [B _x ] of [B ₀ ] × 0.5 or more is reached, and finally the innermost portion is composed of the original heavy-doped boron silicon substrate. The reason that the boron concentration has a gradient in the inner direction at a depth of at least about 2 μm is to reduce the lattice strain at the interface between the silicon substrate and the epitaxial film. If the boron concentration has a gradient and the depth of increase is less than 2 μm, the boron concentration profile at the interface rises rapidly,
The situation is close to a step function, and the lattice strain at the interface cannot be ignored, which is not preferable. The reason that the boron concentration [B _X ] at a depth of 2 μm is 50% or more of the heavy doped boron concentration [B ₀ ] is that the profile of the boron concentration in the depth direction is asymptotic to the boron concentration in the bulk portion. To get closer to.

As described above, the silicon substrate for an epitaxial wafer according to the present invention has a predetermined boron concentration on the surface thereof, and a predetermined ratio of the boron concentration of the silicon substrate at a predetermined depth inward thereof. Since the silicon substrate is gradually increased to the above concentration and the original silicon substrate is retained internally, the crystallinity of the boron light-doped epitaxial film formed on the surface is small and the good crystallinity is not impaired. Therefore, it is possible to finally secure a good device formation region, it is possible to suppress the occurrence of crystal dislocation during the device manufacturing process, the characteristics of the device to be manufactured,
Reliability can be improved.

The method for producing a silicon substrate for an epitaxial wafer according to the present invention is not particularly limited as long as it can satisfy the above requirements. For example, it can be manufactured by the following method. That is, first, a silicon wafer having a boron concentration of 1 × 10 ¹⁷ atoms / cm ³ or more is manufactured by pulling it up by an ordinary Czochralski method or the like, and performing mirror polishing through various steps such as slicing and polishing by a known method. . Next, the manufactured silicon wafer can be heat-treated in a hydrogen-containing gas atmosphere so as to meet the predetermined requirements. The heat treatment in a hydrogen-containing gas atmosphere of the present invention is performed by treating a predetermined boron-doped silicon wafer with hydrogen gas or Ar,
1000 to 1200 ° C. in a hydrogen-containing gas atmosphere such as a mixed gas of 50% by volume or more of an inert gas such as nitrogen and hydrogen gas.
At a temperature of 30 to 460 minutes, the boron on the surface of the boron-heavy-doped silicon substrate is outwardly diffused, and at least the boron concentration on the outermost surface for epitaxial growth is 1.5 × 10 ¹⁶ atoms / cm ^3. Below.

In the heat treatment of the present invention, "substantially" means any of the following. That is, when the rate of temperature rise and rate of temperature drop in the furnace are extremely fast and a step function heat treatment schedule can be applied, for example,
A predetermined silicon wafer is set in a boat and placed in a heat treatment furnace, and the atmosphere in the furnace is set to a hydrogen-containing gas atmosphere at a temperature at which boron can diffuse outwardly at about 1100 ° C. for about 200 minutes or more, and at about 1150 ° C. for about 80 minutes. It is to hold for about 1 minute or more and to hold at about 1200 ° C. for about 30 minutes or more. Further, the profile of the boron concentration in the depth direction when the heat treatment is performed for t seconds in the heat treatment in this case is expressed by the following formula (1): [B
(x, t)] = [B _S ] + ([B ₀ ]-[B _S ]) erf (x / 2√D _T t) (However,
[B (x, t)] is the boron concentration at the depth of x μm from the outermost surface of the silicon substrate when heat-treated at T ° C. for t seconds,
D _T is the diffusion coefficient of boron at T ° C. (cm ² / sec). ).

Alternatively, when it takes time to raise and lower the temperature in the furnace, a heat treatment schedule is applied in consideration of outward diffusion of boron in the heating and cooling steps. For example,
A predetermined silicon wafer is set in a boat and placed in a heat treatment furnace, the atmosphere in the furnace is heated only by an inert gas, and when the temperature in the furnace reaches 1000 ° C., the atmosphere in the furnace is changed to the hydrogen-containing gas atmosphere. After substituting and continuing the temperature rise, the temperature is maintained at about 1150 ° C. for about 80 minutes or 1200 ° C. for about 30 minutes, and then the furnace is kept in a hydrogen-containing atmosphere for 10 minutes.
This means that the temperature is lowered to 00 ° C., and when the temperature becomes 1000 ° C. or less, the atmosphere in the furnace is replaced with an inert gas again and the temperature is cooled to room temperature.
When the temperature is 000 ° C. or higher, it is to be kept in a hydrogen-containing gas atmosphere. In this case, the profile of the boron concentration in the depth direction when the heat treatment is performed for t seconds is expressed by the following formula (2): [B (x, t)] = [B _S ] + ([B ₀ ]-[B _S ]) erf (x
/ 2√∫ _I ^F D (T) dt) ∫ _I ^F D (T) dt in this equation
And the following (3) _{formula: D T △ t T = ∫} I by ^F D (T) dt can be read as the heat treatment temperature T ° C. heat treatment time corresponding △ t _T. (However, [B (x, t)] is the boron concentration at a depth of x μm from the outermost surface of the silicon substrate when heat-treated at T ° C. for t seconds, ∫ _I ^F D (T) dt is substantially the heat-treatment in the heat-treatment step. During the heat treatment, for example, one of the heat treatment steps in the furnace
It shows the diffusion of boron from the temperature rise above 000 ° C to the cooling, and D _T is the diffusion coefficient (cm) of boron at T ° C.
A ² / sec), △ t _T is, T ° C. equivalent heat treatment time, i.e., a heat treatment time required assuming that the heat treatment of the heat treatment the entire process at T ° C.. )

The silicon substrate for an epitaxial wafer of the present invention can be manufactured by heat-treating a silicon substrate formed from a predetermined silicon ingot as described above. The obtained silicon substrate for an epitaxial wafer is an original boron heavy-doped silicon substrate, and the surface boron concentration corresponds to light doping. A silicon single crystal can be epitaxially grown on this surface in a conventional manner to form an epitaxial film having a predetermined thickness. The obtained epitaxial film is
Since the crystal lattice constant does not change sharply at the interface with the silicon substrate and the boron concentration does not change suddenly, there are no crystal dislocations and no microstructural distortion, and there are few defects with extremely high crystallinity. It becomes a silicon single crystal layer. In this case, the heat treatment and the epitaxial treatment of the silicon substrate may be performed in the same furnace, and the epitaxial treatment may be performed immediately after the heat treatment. Further, the heat treatment and the epitaxial treatment of the silicon substrate may be performed using different furnaces. It is possible to select which method is adopted according to various conditions such as a processing environment. It is known that a carrier-doped silicon wafer is heat-treated in an atmosphere of hydrogen gas, nitrogen, argon (Ar), etc. to change the dopant concentration on the surface (for example, Autumn 1995, 56th Annual Meeting of the Applied Physics Society of Japan). Meeting / Lecture Proceedings No.
1 pp. 198). However, the surface heat treatment for epitaxially growing a silicon single crystal on the surface of a silicon substrate for an epitaxial wafer, particularly a heavily-doped silicon substrate, has not been considered until now, and is the first one performed by the inventors.

[0016]

EXAMPLES The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples. The starting silicon substrate used in the following examples of the present invention is obtained by slicing a silicon single crystal ingot pulled up by the Czochralski method by a conventionally known method and polishing and mirror-polishing it.
These starting silicon substrates have a doped boron concentration of 3 × 10 5.
P type of ¹⁸ atoms / cm ³ , plane orientation (100),
The specific resistance was 21.4 mΩcm.

Example 1 Using the above starting silicon substrate, heat treatment was performed at 1200 ° C. for 2 hours in a 100% hydrogen gas atmosphere. First, the starting silicon substrate is charged into a furnace in an Ar gas atmosphere at 800 ° C., the temperature is raised from 800 ° C. to 1000 ° C. at a heating rate of about 10 ° C./min, and when the temperature reaches 1000 ° C., the atmosphere in the furnace is reached. Is replaced with a hydrogen-containing mixed gas of hydrogen gas: Ar gas = 1: 1 (volume ratio), and the temperature is further raised from 1000 ° C. to 1100 ° C. at a heating rate of about 3 ° C./min. Up to 1200 ° C. at a temperature rising rate of 2 ° C./min and held at 1200 ° C. for 2 hours. Then, after cooling to 1100 ° C. at a cooling rate of about 3 ° C./min and to 800 ° C. at a cooling rate of about 4 ° C./min, the atmosphere in the furnace was replaced with an inert gas and cooled to room temperature at 100 ° C./min. Then, a heat-treated silicon substrate was obtained. The relationship between the boron concentration and the depth from the surface of the obtained heat-treated silicon substrate was measured using SIMS (secondary ion mass spectrometry). The result is shown in Fig. 3A.
As shown.

Comparative Example 1 Similar to Example 1, the starting silicon substrate was heat-treated in the same manner as in Example 1 except that the atmosphere in the furnace was Ar gas. The relationship between the boron concentration and the depth from the surface of the obtained heat-treated silicon substrate was similarly measured by SIMS. The result is shown as B in FIG. In addition, in FIG. 3, the result of having measured the starting silicon substrate similarly by SIMS is shown as C. As is clear from FIG. 3, the surface boron concentration is 2 ×
It can be seen that the concentration is decreased to 10 ¹⁶ atoms / cm ³ or less, the depth is gradually increased to about 2 μm, and then the boron concentration is gradually increased to the initial concentration. On the other hand, it is understood that the doped boron is not reduced by the heat treatment in the Ar gas atmosphere.

Examples 2 to 5 In a hydrogen gas atmosphere, the temperature inside the furnace was 1000 ° C. and 1100.
C., 1150.degree. C. and 1200.degree. C., respectively, and the starting silicon substrate is placed in each furnace for 10 minutes and 30 minutes, respectively.
Minutes, 60 minutes, 100 minutes, 200 minutes, 300 minutes, 400
Min, 500 min and 600 min. For each of the obtained heat-treated silicon substrates, the relationship between the boron concentration and the surface depth was measured by SIMS in the same manner as in Example 1, and the initial boron concentration of the starting silicon substrate was 3 × 10 ¹⁸ atoms / cm ^3.
A depth (μm) showing a boron concentration value ([B _0.9 ]) of 90% of ([B ₀ ]) was calculated, and [B at each heat treatment temperature was calculated.
_0.9 ] and the processing time are shown in FIG. From these results, it can be seen that the required heat treatment time at each heat treatment temperature to reach [B _0.9 ] at a depth of 2 μm from the surface. For example, 12
About 30 minutes at 00 ° C, about 75 minutes at 1150 ° C
It is clear that at 1100 ° C, it takes 200 minutes.

Example 6 and Comparative Example 2 SiH ₂ Cl ₂ was used as a source gas on the heat-treated silicon substrate (Example 6) obtained in Example 1 and the starting silicon substrate (Comparative Example 2), respectively. After processing at 5 ° C. for 5 minutes, a silicon single crystal film was epitaxially grown to a thickness of about 5 μm to obtain an epitaxial wafer. SIMS of the obtained epitaxial wafer
Then, the boron concentration in the depth direction from the surface was measured and observed. The results of Comparative Example 2 are shown in FIG. From this result, it can be seen that the epitaxial silicon film formed on the conventional heavy boron-doped silicon substrate has a rapid boron concentration change with a width of about 0.1 μm at the interface with the silicon substrate. On the other hand, it was observed that on the heat-treated silicon substrate of the present invention, the boron concentration increased inward in a width of about 2 μm with a gentle gradient.

[0021]

EFFECTS OF THE INVENTION The silicon substrate for an epitaxial wafer of the present invention is such that the boron concentration of the outermost surface on which epitaxial growth is performed substantially corresponds to the light boron doping concentration of the epitaxial silicon single crystal film while maintaining the heavy boron doping inside. In addition, the epitaxially-doped epitaxial wafer obtained by epitaxially growing a silicon single crystal is free from the occurrence of distortion of the crystal lattice constant at the interface between the epitaxial film and the silicon substrate, since It has a good epitaxial silicon single crystal surface without any fine structural defects. Therefore, a good device formation region can be secured, and ultimately, a VLSI having excellent device characteristics without causing defects in the device formed thereon can be manufactured with high yield and reliability can be improved. it can.

[Brief description of drawings]

FIG. 1 Raman spectrum of lightly doped silicon substrate

FIG. 2 Raman spectrum of heavy-doped silicon substrate

FIG. 3 is a SIMS analysis of a hydrogen atmosphere heat treated silicon substrate (A) obtained in an example of the present invention, an argon atmosphere heat treated silicon substrate (B) obtained in a comparative example, and a starting silicon substrate (C) before heat treatment. result

FIG. 4 is a relational diagram between a boron concentration value ([B _0.9 ]) and a treatment time at a heat treatment temperature.

FIG. 5: SIMS analysis results of an epitaxial wafer manufactured by epitaxially growing a silicon single crystal on the surface of a conventional heavy boron-doped silicon substrate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenro Hayashi, 30 Soya, Hadano City, Kanagawa Prefecture, Toshiba Ceramics Co., Ltd.Development Research Laboratory (72) Inventor, Jun 30, Soya, Hadano City, Kanagawa In-house

Claims (6)

[Claims] 1. A silicon substrate having a predetermined heavy-doped boron concentration [B ₀ ] having a surface boron concentration [B _S ] of 1.5 × 10 5 at the outermost surface on which an epitaxial film is grown. A boron concentration of ¹⁶ atoms / cm ³ or less and [B ₀ ] × 0.5 or more [B
_X ]], wherein the boron concentration has a gradient and gradually increases from the outermost surface to a depth of at least 2 μm. 2. The boron concentration [B ₀ ] is 1 × 10 ¹⁷ a
The silicon substrate for an epitaxial wafer according to claim 1, which has a thickness of toms / cm ³ or more. 3. A surface of a silicon substrate having a predetermined heavy-doped boron concentration [B ₀ ] on which an epitaxial film is to be grown is heat-treated in a hydrogen-containing gas atmosphere,
At least the outermost surface boron concentration [B _S ] is 1.5 × 10 ¹⁶
A method of manufacturing a silicon substrate for an epitaxial wafer, which is characterized in that it is not more than atoms / cm ³ . 4. The method for producing a silicon substrate for an epitaxial wafer according to claim 3, wherein the hydrogen-containing gas is a mixed gas of hydrogen gas and argon gas having a volume ratio of H ₂ / Ar> 1. 5. The heat treatment is performed in a hydrogen-containing gas atmosphere at a temperature of 1000 to 1200 ° C. for 30 to 46.
The method for producing a silicon substrate for an epitaxial wafer according to claim 3, which is carried out for a processing time of 0 minutes. Wherein said processing time, the following _{equation: D T △ t T = ∫} I F
D (T) dt ^{_{(where, ∫ I F D (T)}} dt represents the diffusion of boron to completion of the heat treatment from the start of the heat treatment in the heat treatment step (including a substantially cooling process from Atsushi Nobori at 1000 ° C. or higher) , D
_T is a boron diffusion coefficient (cm ² / sec) at T ° C., and Δt _T is a T ° C. equivalent heat treatment time, that is, a heat treatment time required when it is assumed that all heat treatment steps are performed at T ° C. 6. The method for manufacturing an epitaxial wafer substrate according to claim 5, wherein Δt _T is represented by