JPH10144696A - Silicon wafer and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon wafer and its manufacturing method to avoid bad influence of BMD on device characteristics by arranging a BMD concentrated layer away from a device active layer. SOLUTION: Heat treatment is performed on a CZ silicon wafer in a hydrogen atmosphere at 1000 deg.C or higher, then a part of or entire cooling treatment is performed in an argon gas atmosphere. In the silicon wafer manufactured by this method, having a denuded zone layer(DZ layer) on its front surface, a BMD high-concentrated region where oxygen products are concentrated is located at a position inner from an inner boundary of the denuded zone layer(DZ layer) by a predetermined distance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silicon wafer used for a semiconductor device and a method for manufacturing the same.

[0002]

2. Description of the Related Art A silicon single crystal as a raw material of a silicon wafer can be manufactured by the Czochralski (CZ) method. Using raw material polysilicon as quartz glass (Si
It is put into an O ₂ ) crucible, heated and melted, and a silicon single crystal is pulled up using a seed crystal.

[0003] In a silicon single crystal manufactured by the Czochralski method, oxygen is usually dissolved in a solid solution. The dissolved oxygen precipitates as ultrafine oxygen precipitates (emprio) in the cooling process after the single crystal is pulled.

[0004] Oxygen precipitates on the wafer surface layer are IC, LS
It becomes an obstacle when I, ULSI, etc. operate, and causes a loss of device reliability. That is, in the device active region, electrons move and diffuse by a circuit formed on the substrate, so that the presence of oxygen precipitates easily causes device defects.

On the other hand, the oxygen precipitate in the bulk portion of the wafer has a function of getting impurities, and is useful as a carrier of a so-called intrinsic gettering (IG) effect.

For this reason, conventionally, a silicon wafer is heat-treated in a hydrogen atmosphere, and oxygen of the wafer surface layer is diffused outward to form a defect-free layer (DZ layer). Defects). Further, the heat treatment improves the pressure resistance of the oxide film formed on the surface of the silicon wafer.

[0007]

However, when a defect-free layer is formed by heat treatment in a hydrogen atmosphere, BMDs are concentrated just below the defect-free region, and the BMD density tends to become the peak of the BMD density.

Since the BMD dense region is located near the device active layer, the device characteristics may be adversely affected. In that case, the yield of the device has decreased.

In view of the above problems of the prior art, the present invention provides a silicon wafer and a method of manufacturing the same, in which the BMD is hardly affected by the device characteristics by keeping the BMD dense layer away from the device active layer. The purpose is.

[0010]

The first invention of the present application is characterized in that a heat treatment step of 1000 ° C. or more is performed on a CZ silicon wafer in a hydrogen atmosphere, and then a part or all of the temperature lowering step is performed in an argon gas atmosphere. The gist of the present invention is a method of manufacturing a silicon wafer.

The second invention of the present application is directed to a silicon wafer manufactured by the above method and having a defect-free layer (DZ layer) on a surface layer, wherein a BMD high-density region in which oxygen precipitates (BMD) are concentrated is a defect-free layer. The gist of the present invention is a silicon wafer, which is located at a predetermined distance inside from an inner boundary of the (DZ layer).

[0012]

EXAMPLES The present inventors have conducted intensive studies and made the following considerations and studies on the BMD density in a silicon wafer, thereby completing the present invention.

In a CZ silicon wafer that was heat-treated at 1200 ° C. for 1 hour in an atmosphere of hydrogen and argon, an IR tomographic image was binarized to obtain a distribution of BMD density. FIG. 1 is a diagram showing a BMD density depth distribution (see Comparative Examples 2 and 1).

As a result, when the high-temperature treatment is performed in an argon atmosphere, the BMD density distribution becomes almost uniform except that oxygen in the surface layer diffuses outward to form a defect-free region (DZ layer). (See Comparative Example 1 in FIG. 1). On the other hand, when the heat treatment is performed in a hydrogen atmosphere, the BMD density becomes uniform in a region deeper than about 100 μm from the wafer surface as in the case where the argon treatment is performed, but the BMD density range is from just below the DZ layer to about 100 μm. (Peak portion of BMD density) was found to occur (see Comparative Example 2 in FIG. 1).

In particular, the BM at the peak of this BMD
The D density [BMD] _peak was about three times that of [BMD] _{bulk in} the bulk part (about 100 μm or less). That is, the following equation 1 is obtained.

[0016]

(Equation 1) This can be confirmed again from the measurement results of IR absorption. That is, FIG. 2 shows the result of examining the oxygen concentration of the silicon wafer after the heat treatment by IR absorption measurement. Compared to an unheated wafer, the oxygen reduction amount [ _Oi ] _Ar of the wafer treated with argon is 1.2 × 10
^Although it was ¹⁷ cm ^-3 ,
[O _i ] _H became 1.6 × 10 ¹⁷ cm ⁻³ . Assuming that the difference between the oxygen reduction amounts due to the two processes is generated only in the peak portion, the ratio between the oxygen reduction amount in the peak portion and the oxygen reduction amount in the bulk portion is as shown in the following Expression 2.

[0017]

(Equation 2) Since this value coincides with the BMD measurement result (Equation 1), it is estimated that the difference in the oxygen precipitation behavior between the hydrogen treatment and the argon treatment is the difference in the deposition method immediately below the DZ layer.

Since the BMD density in the hydrogen-treated wafer becomes higher, the hydrogen atoms have an advantageous effect on the precipitation of oxygen. Therefore, the occurrence of the BMD peak is related to the hydrogen distribution in the silicon wafer in the temperature range where oxygen is precipitated. As shown in FIG. 1, the distribution of BMD has a high concentration near the surface and a low concentration inside.

The present inventors have considered the reason why the BMD distribution becomes as described above as follows.

First, it is considered that the distribution of hydrogen is uniform during high-temperature treatment of the wafer, but the distribution of hydrogen increases near the surface in the course of cooling. Regarding this phenomenon, it has been reported that hydrogen is turned into plasma in a medium temperature range from 300 ° C. to 500 ° C., and when silicon wafers are rapidly cooled, a high concentration of hydrogen (H ₂ ) is distributed near the surface thereof ( JIPankove and NMJhonson, Hydrog
en in Semiconductors, Academic Press, San Diego, (199
1) pp273). However, since the temperature of the hydrogen treatment in the present invention is much higher than this report, the heat capacity of the heat treatment furnace is large, and the temperature drop rate is low, it is considered that the above phenomenon is hardly realized.

Therefore, the present inventors have considered that the concentration of hydrogen atoms may decrease due to the presence of oxygen atoms. This discussion is based on the results of the Muonium μSR experiment, a hydrogen atom analogue. Among the FZ samples having a low oxygen concentration, normal Mu (Td position), abnormal Mu ^* (centered position of boned), and magnetic μ ⁺ [probability ω (M
u): ω (Mu ^* ): ω (μ ⁺ ) 〓60%: 35%: 7
%] Were observed, but CZ with a high oxygen concentration was observed.
Only abnormal Mu ^* signals were left in the sample (BDPa
tterson, Rev. Mod. Phys. 60 , 69 (1988))). According to this result, the low-concentration oxygen region formed by outward diffusion of oxygen atoms, that is, the hydrogen concentration in the so-called DZ layer is higher than that in the bulk portion, and the interaction between hydrogen atoms and oxygen atoms is strong immediately below the DZ layer, Promotes BMD precipitation. In particular, assuming that the concentration of hydrogen atoms corresponds to the probability of Muonium at each position, the ratio between the concentration of hydrogen atoms and the concentration in bulk immediately below the DZ layer (the oxygen concentration corresponds to the value in the FZ sample) The following equation (3) is obtained, which is consistent with the results of the IR tomography and the IR absorption.

[0022]

(Equation 3) From the above considerations, it has been found that in order to control the distribution of BMD, the hydrogen concentration must be changed within the oxygen deposition temperature range. However, when the wafer is treated in a hydrogen atmosphere, the distribution of the hydrogen concentration in the wafer is determined by the distribution of the oxygen concentration. The distribution of the hydrogen concentration according to the distribution of the oxygen concentration formed by the outward diffusion cannot be changed. Therefore, it is necessary to treat the silicon wafer in an argon atmosphere within a temperature range in which oxygen is precipitated.

Therefore, in the present invention, a heat treatment step of 1000 ° C. or more is performed on the CZ silicon wafer in a hydrogen atmosphere,
Thereafter, part or all of the temperature lowering step is performed in an argon gas atmosphere. That is, the atmosphere gas is replaced with an argon gas at the start of or during the cooling step. The replacement of the atmosphere is performed at a temperature at which oxygen is precipitated. That is, in the case of a normal CZ silicon wafer, it is necessary to perform atmosphere replacement at 1200 ° C. to 500 ° C.

As described above, the temperature-lowering atmosphere is replaced with argon gas, and a part or all of the temperature-lowering step is performed in an argon gas atmosphere.
It can move inward from the boundary position of the (Z layer).

It is desirable that the peak of the BMD density be located at least about 60 μm inward from the inner boundary of the DZ layer. As described above, by moving the BMD density peak inward, the BMD high-density region can be kept away from the device active layer. And the possibility that a device defect will occur can be reduced significantly.

Hereinafter, Embodiment 1 of the present invention will be described.

In the first embodiment, a P-type electric resistance of 15Ωc
A 6 inch CZ mirror silicon wafer was used, which had an oxygen concentration of 1.54 × 10 ₁₈ cm by IR absorption and a plane orientation of (100). 1200 ° C.1 for this silicon wafer
After heating in a hydrogen atmosphere for an hour, a heat treatment was performed in which the atmosphere was replaced with argon gas and the temperature was lowered to room temperature.

In Comparative Example 2, the same silicon wafer as in Example 1 was heated at 1200 ° C. for 1 hour in an argon atmosphere, and then heat-treated to lower the temperature to room temperature. In Comparative Example 3, heat treatment was performed at 1200 ° C. for 1 hour in a hydrogen atmosphere, and then the temperature was lowered to room temperature.

The results of IR tomography and IR absorption for Example 1 and Comparative Examples 1 and 2 are shown in FIGS. 1 and 2, respectively.

As can be seen from FIG. 1, in Example 1, the BMD density was reduced as compared with Comparative Example 2, and a peak occurred in the inner layer. That is, by lowering the temperature of the hydrogen-treated wafer in an argon gas atmosphere, the BMD density of the wafer subjected to the hydrogen treatment and temperature reduction can be reduced as a whole.
It was confirmed that the density peak can be moved inward from immediately below the defect-free region (DZ layer). Further, as can be seen from FIG. 2, in Example 1, the oxygen concentration was reduced to about the same level as in Comparative Example 2 (in the case of argon treatment).

In Example 1, the BMD concentration at a depth of 0 to about 60 μm was reduced to the same level as that of a wafer subjected to argon treatment and temperature reduction. Also, the BM of the first embodiment
The D concentration peak value was reduced to about half of the peak value of Comparative Example 2.

As described above, in the silicon wafer of Example 1, since the peak position of the BMD density is far from the device active layer, device defects caused by BMD hardly occur as compared with the wafer of Comparative Example 2. Further, the silicon wafer of Example 1 had a larger I compared to the wafer of Comparative Example 1.
G effect can be expected.

[0033]

According to the present invention, the BMD dense layer is kept away from the device active layer, so that the adverse effect of the BMD can hardly reach the device characteristics. Therefore, by using the silicon wafer of the present invention, a high-quality semiconductor device can be manufactured with high yield.

The present invention is not limited to the above embodiment. For example, by changing the temperature at which the hydrogen gas is replaced with the argon gas in the range of 1200 ° C. to 500 ° C., the BMD density immediately below the defect-free region (DZ layer) and the peak position and peak width of the BMD density can be controlled. For example, 900
C., the BMD density peak width becomes 120
0 ° C., 1 hH ₂ , smaller than 1200 ° C.
° C. 1HH ₂ and can to come between 1200 ℃ 1hH ₂ + Ar cooling.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in BMD concentration in an example of the present invention and a comparative example.

FIG. 2 is a graph showing oxygen concentrations in Examples of the present invention and Comparative Examples.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kenro Hayashi 30 Soya, Hadano-shi, Kanagawa Toshiba Ceramics Co., Ltd. Inside

Claims (3)

[Claims] 1. A method in which a CZ silicon wafer is subjected to hydrogen atmosphere in a hydrogen atmosphere.
A method for producing a silicon wafer, comprising: performing a heat treatment step at 000 ° C. or higher, and then performing a part or all of the temperature lowering step in an argon gas atmosphere. 2. The method for producing a silicon wafer according to claim 1, wherein the temperature in the temperature lowering step performed in an argon gas atmosphere is in a range of 1200 ° C. to 500 ° C. 3. A silicon wafer having a defect-free layer (DZ layer) on a surface layer manufactured by the method according to claim 1, wherein a BMD high-density region in which oxygen precipitates (BMD) are concentrated is defect-free. A silicon wafer which is located at a predetermined distance inside from an inner boundary of a layer (DZ layer).