JP3294722B2 - Method for manufacturing silicon wafer and silicon wafer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon wafer for semiconductor devices such as VLSI and a method for manufacturing the same.

[0002]

2. Description of the Related Art In a manufacturing process of a semiconductor device for an VLSI, a semiconductor in which a trace amount of metal impurities mixed in a wafer and a minute defect existing in a device active region (about 10 μm deep from the wafer surface) of the wafer are manufactured. It may cause deterioration of device characteristics and reliability. Therefore, various measures have conventionally been taken to minimize these metal impurities and minute defects.

As a method of reducing metal impurities, there is a back side damage method (BSD method) in which minute distortion is provided on the back surface of the wafer by sand blasting or the like to capture (getter) the metal impurities. Further, a method of depositing polycrystalline silicon on the back surface of the wafer has also been used.

As a countermeasure for the latter, an epitaxial wafer having a vapor-grown single-crystal silicon layer having no minute defects in a device active region is used.

Further, an intrinsic gettering method (IG method) has been developed in order to perform both measures simultaneously. In the IG method, by subjecting the wafer to high-temperature heat treatment, oxygen on the surface of the wafer is diffused outward to reduce interstitial oxygen serving as nuclei of minute defects, and a denuded zone (DZ layer) having no minute defects in a device active region is formed. Let it form. Further, in a deep region (bulk portion) below the DZ layer, excessive interstitial oxygen contained therein is precipitated by high-temperature heat treatment, and BMD typified by fine SiO ₂ precipitates is generated. These BMDs give strain to the bulk silicon matrix, induce secondary dislocations and stacking faults, and getter metal impurities.

In the IG method, a plurality of stages of heat treatment are performed in order to be unaffected by the thermal history of the pulled single crystal silicon ingot and to use a wafer having a wider oxygen concentration range. . First,
In the pre-heat treatment, heat treatment is performed at a high temperature (up to 1200 ° C.) in an oxygen-containing inert gas atmosphere to diffuse oxygen outward from the wafer surface, thereby reducing BMD nuclei caused by oxygen originally present. Extinguish. Next, BMD nuclei are generated in the bulk portion by performing a middle-stage low-temperature (500 to 900 ° C.) heat treatment in an oxygen atmosphere. Finally, the BMD is subjected to a medium temperature (up to 1000 ° C.) heat treatment in an oxygen atmosphere.
BMD is generated and grown by growing nuclei. Various ideas have been devised for the middle heat treatment, for example, isothermal annealing, multi-stage annealing from a low temperature, and ramping annealing from a low temperature.

In the above-mentioned IG method, actually, the outward diffusion of oxygen by the heat treatment in the preceding stage is not sufficient, and minute oxygen precipitates (such as BMD) may remain in the device active region. Further, since a plurality of heat treatment steps are required, practical use has not progressed much due to workability problems and cost problems.

Recently, instead of such a method requiring a multi-stage heat treatment, 100% reducing gas or 100%
By performing a high-temperature heat treatment in an atmosphere of an inert gas or a mixed gas of a reducing gas and an inert gas, a DZ layer is formed on the wafer surface and a BMD is formed on the bulk portion to provide an intrinsic gettering effect (IG effect). Wafer manufacturing methods have also been implemented. Regarding these production methods, the present applicant has disclosed in Japanese Patent Application Laid-Open Nos.
193458, JP-A-61-193449, JP-A-61-193456, JP-A-62-123098,
We have filed applications such as Japanese Patent Application Laid-Open No. 2-177541.

A typical heat treatment in an inert gas atmosphere in this method is performed by the following temperature process. The temperature raising process for raising the temperature to the heat treatment temperature is about 10 ° C./min from room temperature to 1000 ° C., 3 ° C./min or less from 1000 ° C. to 1200 ° C., and the heat treatment is about 12 ° C.
Over 1 hour at 00 ° C, 1200 ° C cooling process
To 900 ° C. to 3 ° C./min or less. FIG. 1 shows a typical temperature process. In the heat treatment operation of FIG. 1, the temperature rise process is 10 ° C./mi from room temperature to 1000 ° C.
n, 3 ° C./min between 1000 ° C. and 1200 ° C., heat treatment at 1200 ° C. for 1 hour, temperature drop process at 1200 ° C.
3 ° C./min. To 1000 ° C .;
It is performed at 0 ° C./min.

In this heat treatment operation, in the temperature raising process in the region of 1000 ° C. or higher, if the temperature raising rate is higher than about 3 ° C./min, there is a possibility that the wafer being processed may slip. In addition, the heat treatment furnace that is usually used has not been heated at a high speed because of heat insulation and restrictions on heating elements.

The mechanism of the formation of the wafer structure by the above heat treatment process can be estimated as follows. Since the heating rate is slow during the heating process, BMD
At the same time as oxygen grows, outward diffusion of oxygen occurs in the surface layer, and the oxygen concentration in the surface layer decreases. After reaching the heat treatment temperature, oxygen in the surface layer is further diffused outward, so that interstitial oxygen serving as BMD nuclei in the surface layer decreases, and the BMD in the surface layer decreases.
Disappearance is accelerated. In the bulk portion, oxygen diffuses in the wafer due to the high-temperature heat treatment, and the BMD shrinks. However, BMD does not disappear due to a small amount of oxygen reduction. During the temperature lowering process, the rate of temperature rise is slow, so that theoretically BMD growth occurs even in the surface layer portion of the wafer, but since oxygen in the surface layer portion is reduced by outward diffusion, BMD is not formed and BMD is not formed.
It becomes a Z layer. On the other hand, BMD grows and precipitates again in the bulk portion.

FIG. 2 shows that the wafer is 100% argon gas.
The relationship between the initial oxygen concentration of the wafer and the BMD density of the bulk portion of the wafer after the heat treatment when the heat treatment as shown in FIG. FIG. 2 shows that B in the bulk portion after heat treatment
It is understood that the MD density depends on the initial oxygen concentration of the wafer, and the BMD density of the bulk portion increases as the initial oxygen concentration increases.

In recent years, in order to improve the characteristics of memory devices and the like, which have been highly integrated, a silicon wafer as a starting material is required to have a more completely defect-free device active layer on the surface, and is complicated. It is necessary and important to have a structure that can getter metal impurities mixed during the device manufacturing process.

In order to satisfy the former requirement, that is, to form a more complete defect-free layer, it is preferable that the concentration of interstitial oxygen which causes defects is low. Therefore, it is difficult to manufacture, and there are many problems in terms of productivity, cost, and the like. Further, in such a wafer, it is difficult to form a sufficient amount of BMD sufficient to perform a gettering function in an internal bulk portion by a conventional heat treatment process.

The present invention has been made in order to solve the above-described problems. Even if the wafer has a relatively low oxygen concentration range, the device active layer is more defect-free and the BMD is formed in the bulk portion. It is an object of the present invention to provide a method of manufacturing a silicon wafer capable of producing a silicon wafer at a high density and exhibiting a sufficient gettering effect, and to provide such a silicon wafer.

[0016]

According to a first aspect of the present invention, an interstitial oxygen concentration [Oi] manufactured from a single crystal silicon ingot manufactured by the Czochralski method is reduced.
A silicon wafer having a density of 1.50 × 10 ¹⁸ atoms / cm ³ or less was heated at a heat treatment temperature of 11 in an argon gas atmosphere.
00 ° C to 1300 ° C, heat treatment time 1 minute to 48 hours,
By heat treatment in conditions <br/> matter that the heating rate 5 to 10 ° C. / min in the temperature range from 1000 ° C. the Atsushi Nobori process up to the heat treatment temperature, at least the depth 10μm from the wafer surface It has a defect-free layer having a BMD having a size of 20 nm or more and 10 ³ / cm ³ or less, and has an oxygen precipitate density [BMD] of a bulk portion inside a wafer.
Is [BMD] ≦ 1 × 10 ¹⁰ pieces / cm ³ and [BM
D] ≧ exp ｛1.151 × 10 ⁻¹⁷ × [Oi] +1.
A gist of the present invention is a method for manufacturing a silicon wafer, which is characterized by manufacturing a wafer having a size of 151｝ / cm ³ . In the second invention of the present application, the interstitial oxygen concentration [Oi] manufactured from a single crystal silicon ingot manufactured by the Czochralski method is 1.50 × 10 ¹⁸ atoms / c.
Heat treatment of silicon wafers of m ³ or less in an argon gas atmosphere at a heat treatment temperature of 1100 ° C. to 1300 ° C., a heat treatment time of 1 minute to 48 hours, and a temperature increase process of 1000 ° C.
The heating rate in the temperature range up to the temperature is 5 to 1
0 ℃ produced by heat treatment in the conditions and / min, size over at least a depth 10μm from the wafer surface has a defect-free layer BMD more than 20nm is 10 ³ / cm ³ or less, When the oxygen precipitate density [BMD] of the bulk portion inside the wafer is [BMD] ≦ 1 ×
10 ¹⁰ pieces / cm ³ and [BMD] ≧ exp ｛1.15
A gist of the present invention is a silicon wafer characterized by 1 × 10 ⁻¹⁷ × [Oi] + 1.151 ° / cm ³ .

In this specification, all oxygen concentrations are Ol
d Value based on a conversion coefficient according to ASTM.

Generally, BMD when heat-treating a wafer
The behavior of will be described.

According to the classical nucleation theory, BMD grows and contracts by attaching and detaching supersaturated oxygen with oxygen clusters as uniform nuclei.

Whether a BMD existing at a certain time grows or shrinks / disappears is determined by the critical nuclear radius determined by the size of the BMD at that time and the temperature (and oxygen concentration) at that time. The critical nuclear radius depends on the temperature,
As the temperature increases, the critical nuclear radius increases. When the wafer is held at a certain temperature, the BMD that has already grown larger than the critical nucleus radius at that temperature continues to grow, and the BMD with a diameter smaller than the critical nucleus radius shrinks or disappears.

Based on the above findings, the present inventors can control the BMD by applying the present invention to a wafer manufacturing method, know that a wafer suitable for manufacturing a highly integrated device can be manufactured, and can accomplish the present invention. It is a thing.

The present invention is directed to a silicon wafer manufactured from a silicon ingot manufactured by a general Czochralski method, in which the oxygen concentration is relatively low.
It is applied to the heat treatment of a wafer of 1.50 × 10 ¹⁸ atoms / cm ³ or less . A wafer having a higher oxygen concentration can increase the BMD density without performing the heat treatment of the present invention as described above.

The heat treatment of the present invention is performed in a 100% inert gas atmosphere. Performing in a 100% inert gas atmosphere is similar to a 100% hydrogen gas atmosphere in terms of formation of a defect-free layer, easiness of outward diffusion of oxygen, and difficulty in roughening during heat treatment. preferable.

The heat treatment of the present invention is performed at 1100 ° C. to 1300 ° C.
Done in At 1100 ° C. or lower, the effect of the present invention cannot be obtained. At 1300 ° C. or higher, the outward diffusion effect of oxygen is excellent, but there is a problem in the safety and reliability of the device.

The heat treatment time of the present invention is 1 minute to 48 hours. If the time is less than 1 minute, the effect of the present invention cannot be obtained, and even if the heat treatment is performed for more than 48 hours, the effect cannot be expected to be improved.

In the heat treatment process of the present invention, the heating rate is set to 5 within the temperature range from 1000 ° C. or higher to the heat treatment temperature.
It is necessary to raise the temperature at -10 ° C / min.

If the rate of temperature rise is less than 5 ° C./min in the region of 1000 ° C. or more, the rate of increase of the critical nucleus radius does not overtake the growth rate of BMD.
MD seems to grow. However, a low oxygen content wafer such as the present invention has a small amount of attached oxygen itself,
Further, since the effective heat treatment time including the temperature raising process becomes longer, the amount of desorbed oxygen becomes larger than the amount (probability) of oxygen adhering to existing BMD nuclei, so that the size of the BMD becomes smaller. Furthermore, it disappears. Therefore, the density is also reduced.

When the temperature rise rate is 5 to 10 ° C./min as defined in the present invention in the region of 1000 ° C. or more, the adhesion is reversed when compared throughout the heat treatment operation. It is considered that the size and density of BMD increase because the amount of oxygen is larger than the amount of oxygen to be desorbed.

If the rate of temperature rise is higher than 10 ° C./min in the region of 1000 ° C. or higher, the rate of increase of the critical nucleus radius becomes larger than the growth rate of the existing BMD at that temperature. Since the time of the temperature raising process is shortened, the difference between the critical nucleus radius and the diameter of the existing BMD becomes larger, and the BMD does not grow but heads in the direction of reduction.

As described above, the heating rate is 5 to 10 ° C./min.
BMD can be formed at a high density only when

At the heat treatment temperature, the outward diffusion of oxygen proceeds in the surface region, so that the oxygen concentration around the BMD near the surface decreases and disappears and the DZ layer is formed. In the bulk portion, the effect of out-diffusion of oxygen is difficult to achieve, and the decrease in oxygen concentration is small. When the temperature is raised at the temperature raising rate of the present invention,
Since the size of the BMD is already larger than the critical nuclear radius at the heat treatment temperature, the BMD grows.

During the cooling process, the BM is already
Since D is decreased and the oxygen concentration is further decreased, it is considered that BMD does not occur or grow even when the temperature decreasing rate is changed. In the bulk part, BMD has already grown, and there is no significant effect even if the temperature drop rate is changed. However, the rate of temperature drop is 2 to 2 due to productivity, wafer quality (prevention of slip and surface roughening), and structural problems of the furnace used.
It is desirable to be 300 ° C./min.

By performing such a heat treatment, the initial oxygen concentration is 1.50 × 10 ¹⁸ atoms / cm ³ or less.
From the wafer surface using a silicon wafer
BM having a size of 20 nm or more over a depth of at least μm
D has a DZ layer of 10 ³ / cm ³ or less, and
BMD density [BMD] of bulk part in a region deeper than DZ layer
≦ 1 × 10 ¹⁰ pieces / cm ³ and [BMD] ≧ exp
{1.151 × 10 ⁻¹⁷ × [Oi] +1.151} pieces /
It is possible to produce wafers that are cm ³ .

Such a wafer is indicated by the area A + B + C in the graph of FIG.

A wafer having the above-mentioned initial oxygen concentration, which has a good DZ layer in the surface layer portion, and has a BMD density in the bulk portion within the above-mentioned range has not existed conventionally. It is provided for the first time.

A more preferable range of the BMD density is as follows:
1 × 10 ⁸ pieces / cm ³ ≦ [BMD] ≦ 1 × 10 ¹⁰ pieces / c
m ³ (region B + C in FIG. 2), and [BMD]
≦ 1 × 10 ¹⁰ pieces / cm ³ and [BMD] ≧ exp
{4.605 × 10 ⁻¹⁸ × [Oi] +12.434} pieces / cm ³ (region C in FIG. 2).

A wafer having a BMD density in such a range has a sufficient gettering function, and the surface device active layer is a good defect-free DZ layer.

It is preferable that the BMD in the DZ layer in the surface layer is substantially 0. The reason for defining the BMD in the DZ layer as described above is that the detection limit of the size of the BMD of the current device is 20 nm, and when the BMD density exceeds 10 ³ / cm ³ , it is no longer defect-free. However, this is because the characteristics of the manufactured device are adversely affected.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, all the wafers used for explaining the embodiments of the present invention were cut out from a silicon ingot pulled up by the Czochralski method, manufactured by a usual method, and used mirror-finished silicon wafers. These wafers are of N type, plane orientation (10
0), specific resistance 1 to 1000 Ω / cm, initial interstitial oxygen concentration [Oi] is 1.45 to 1.74 × 10 ¹⁸ atoms /
cm ³ .

Example 1 [Oi] of the wafer was 1.50 × 10 ¹⁸ at.
The oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% argon gas atmosphere. However, 1
The heating rate in the range from 000 ° C to 1200 ° C is 6.3 ° C /
min, and the cooling rate was 10 ° C./min.

Example 2 [Oi] of the wafer was 1.45 × 10 ¹⁸ at.
The oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% argon gas atmosphere. However, 1
The heating rate in the range from 000 ° C to 1200 ° C is 8.5 ° C /
min, and the temperature drop rate was 3.8 ° C./min.

Comparative Example 1 [Oi] was 1.72 × 10 ¹⁸ at among the wafers.
An oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% hydrogen gas atmosphere. However, 10
The heating rate in the range of 00 ° C to 1200 ° C is 30 ° C / mi.
n, the temperature decreasing rate was 300 ° C./min.

Comparative Example 2 [Oi] of the wafer was 1.61 × 10 ¹⁸ at.
An oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% hydrogen gas atmosphere. However, 10
The heating rate in the range of 00 ° C to 1200 ° C is 30 ° C / mi.
n, the temperature decreasing rate was 300 ° C./min.

Comparative Example 3 Among the wafers, [Oi] was 1.50 × 10 ¹⁸ at.
An oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% hydrogen gas atmosphere. However, 10
The heating rate in the range of 00 ° C to 1200 ° C is 30 ° C / mi.
n, the temperature decreasing rate was 300 ° C./min.

Comparative Example 4 [Oi] of the wafer was 1.61 × 10 ¹⁸ at.
The oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% argon gas atmosphere. However, 1
The heating rate in the range from 000 ° C to 1200 ° C is 6.3 ° C /
min, and the cooling rate was 10 ° C./min.

Comparative Example 5 Among the wafers, [Oi] was 1.70 × 10 ¹⁸ at.
The oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% argon gas atmosphere. However, 1
The rate of temperature rise in the range from 000 ° C to 1200 ° C is 3.8 ° C /
min, and the temperature drop rate was 3.8 ° C./min.

Comparative Example 6 Among the wafers, [Oi] was 1.50 × 10 ¹⁸ at.
An oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% hydrogen gas atmosphere. However, 10
A heating rate in the range of 00 ° C to 1200 ° C is set to 2-3 ° C / m
in, and the temperature drop rate was 2-3 ° C./min.

Comparative Example 7 Among the wafers, [Oi] was 1.56 × 10 ¹⁸ at.
An oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% hydrogen gas atmosphere. However, 10
A heating rate in the range of 00 ° C to 1200 ° C is set to 2-3 ° C / m
in, and the temperature drop rate was 2-3 ° C./min.

Comparative Example 8 Among the wafers, [Oi] was 1.60 × 10 ¹⁸ at.
An oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% hydrogen gas atmosphere. However, 10
A heating rate in the range of 00 ° C to 1200 ° C is set to 2-3 ° C / m
in, and the temperature drop rate was 2-3 ° C./min.

Comparative Example 9 Of the above wafers, [Oi] was 1.74 × 10 ¹⁸ at.
An oms / cm ³ wafer was heat-treated at 1200 ° C. for 1 hour in a 100% hydrogen gas atmosphere. However, 10
A heating rate in the range of 00 ° C to 1200 ° C is set to 2-3 ° C / m
in, and the temperature drop rate was 2-3 ° C./min.

From the cross-sections ((110) planes) of the wafers subjected to the heat treatments of these Examples and Comparative Examples, the density of BMD generated by infrared tomography was measured. The minimum detectable BMD size in the infrared tomography method used is 20 nm. This method depends on the measurement area.
The detection limit of MD density is different. In this measurement, the measurement was performed on a rectangular parallelepiped region of 4 × 200 μm and a depth of 185 μm on the wafer surface. In this case, the measurement limit of the BMD density is 6.8 × 10 ⁶ / cm ³ . Under such conditions, the BMD having a size of 20 nm or more defined by the present invention is 10
The thickness of ³ / cm ³ or less DZ layer first BMD typical field of view corresponds to the depth from the surface to be detected.

Table 1 and Table 2 show the measurement results together with the heat treatment conditions.
Shown in FIG. 2 shows the initial oxygen concentration of the wafer and the BMD.
A graph showing the relationship between the densities is shown.

[0053]

[Table 1]

[Table 2] As is clear from Tables 1 and 2 and FIG. 2, a good DZ layer is formed on the wafer subjected to the heat treatment of the present invention even if the initial oxygen concentration [Oi] is low, and the wafer is further formed on the bulk portion. BMD can have a high density. That is, a BMD having a size of 20 nm or more and a BMD having a size of 20 nm or more from the surface at least 10 μm or more has a defect-free layer of 10 ³ / cm ³ or less, and the oxygen precipitate density [BMD] of the bulk portion inside the wafer is [BMD]. ] ≦ 1 × 10 ¹⁰ pieces / cm
³ and [BMD] ≧ exp ｛1.151 × 10 ⁻¹⁸ ×
[Oi] + 1.151 ° wafers / cm ³ can be manufactured.

On the other hand, as can be understood from the comparative example, in the case of a wafer heat-treated under conditions outside the range of the present invention, the higher the initial oxygen concentration, the more BMDs are formed. It can be seen that the BMD density to be formed becomes low. In Comparative Examples 1 to 3 and 6, a defect-free layer was formed, but B in the bulk portion inside the wafer was
There is a possibility that the MD has a low density and a sufficient gettering function cannot be performed.

Further, since the wafer of the present invention is constructed as described above, the device active layer becomes defect-free and the BMD is sufficiently formed in the bulk portion, so that devices having good characteristics can be obtained with a high yield. Can be manufactured.

[0056]

According to the present invention, it is possible to increase the BMD density formed even on a wafer having a low initial oxygen concentration, and as a result, it has a sufficient gettering function, so that highly integrated devices having good characteristics can be manufactured with high yield. be able to. Further, such a wafer can be provided.

[Brief description of the drawings]

FIG. 1 is a view showing a temperature process of a conventional heat treatment.

FIG. 2 is a diagram showing a relationship between an initial oxygen concentration of a wafer and a BMD density after a heat treatment.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuka Kashima 30 Soya, Hadano-shi, Kanagawa Toshiba Ceramics Co., Ltd. (72) Yoshio Kirino 30 Soya, Hadano-shi, Kanagawa Toshiba Ceramics Co., Ltd. Inside the development laboratory (56) References JP-A-57-167637 (JP, A) JP-A-8-97222 (JP, A) JP-A-6-295913 (JP, A) JP-A-6-252154 (JP, A A) JP-A-4-69937 (JP, A) JP-A-2-177542 (JP, A) JP-A-61-193458 (JP, A) JP-A-59-202640 (JP, A) JP-A-58 -56343 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/322 H01L 21/02 H01L 21/324

Claims (2)

(57) [Claims] 1. A silicon wafer having an interstitial oxygen concentration [Oi] of 1.50 × 10 ¹⁸ atoms / cm ³ or less manufactured from a single-crystal silicon ingot manufactured by the Czochralski method is treated with argon. In a gas atmosphere, heat treatment temperature is 1100 ° C. to 1300 ° C., heat treatment time is 1 minute to
48 hours, the temperature rises from 1000 ° C to the heat treatment temperature
Up to 5-10 ° C / mi in the temperature range up to
By performing the heat treatment under the condition of n , the BMD having a size of 20 nm or more and a BMD having a size of 20 nm or more and having a defect density of 10 ³ / cm ³ or less from the surface of the wafer at a depth of at least 10 μm or less is provided. When the precipitate density [BMD] is [BMD] ≦ 1 × 10 ¹⁰ / cm ³ and [BMD] ≧ exp ｛1.151 × 10 ⁻¹⁷ × [O
i] A method of manufacturing a silicon wafer, which manufactures a wafer having an amount of +1.151｝ / cm ³ . 2. A silicon wafer having an interstitial oxygen concentration [Oi] of 1.50 × 10 ¹⁸ atoms / cm ³ or less manufactured from a single-crystal silicon ingot manufactured by the Czochralski method is treated with argon. In a gas atmosphere, heat treatment temperature is 1100 ° C. to 1300 ° C., heat treatment time is 1 minute to
48 hours, the temperature rises from 1000 ° C to the heat treatment temperature
Up to 5-10 ° C / mi in the temperature range up to
manufactured by performing a heat treatment under the condition of n.
A BMD having a size of 20 nm or more and a BMD having a size of 20 nm or more at a depth of at least 10 μm from the wafer surface has a defect-free layer of 10 ³ pieces / cm ³ or less, and the oxygen precipitate density [BMD] of the bulk portion inside the wafer is [BMD]. ≦ 1 × 10 ¹⁰ /
cm ³ and [BMD] ≧ exp ｛1.151 × 10
^-17 × [Oi] + 1.151 ° wafers / cm ³ .