JP6981750B2 - Silicon single crystal manufacturing method and silicon single crystal - Google Patents

Description

The present invention relates to a manufacturing method and silicon Tan'yui crystal of a silicon single crystal.

A silicon wafer used as a substrate for a semiconductor device (hereinafter, may be referred to as a "wafer") is generally cut from a silicon single crystal grown by the Czochralski method (hereinafter, may be referred to as a "CZ method"). It is manufactured through processes such as polishing and heat treatment.
FIG. 1 is a vertical cross-sectional view of a pulled-up silicon single crystal, schematically showing an example of the relationship between defect distribution and V / G. V is the pulling speed of the silicon single crystal, and G is the temperature gradient in the growth direction of the silicon single crystal immediately after pulling. The temperature gradient G is considered to be generally constant during the process of pulling the silicon single crystal due to the thermal properties of the hot zone structure of the CZ furnace. Therefore, V / G can be controlled by adjusting the pulling speed V.

In FIG. 1, COP (Crystal Originated Particle) is an aggregate of pores lacking atoms that should form a crystal lattice during growth of a silicon single crystal.
The OSF (Oxidation induced Stacking Fault) region is adjacent to the region where COP is generated (COP region), and is OSF when subjected to thermal oxidation treatment at a high temperature (generally 1000 ° C to 1200 ° C). The nucleus becomes apparent as OSF. Pulled obtained by adjusting the velocity V, by a U E Doha by slicing a silicon single crystal in the OSF region, OSF region is distributed in a ring shape in the wafer plane (the ring-shaped OSF region) Wafers can be obtained.
Also, P _V region, vacancy type point defects are dominant defect-free region. P _V region includes oxygen precipitation nuclei in as-grown state, when subjected to heat treatment, oxygen precipitate oxygen precipitate nuclei is bulk micro defects grown (BMD (bulk micro defect)) is generated easy.
P _I area, interstitial silicon type point defects are dominant defect-free region. P _I area does not include the most oxygen precipitation nuclei in as-grown state, BMD be subjected to a heat treatment hardly occurs.

Focusing on the characteristics of each region in such a silicon single crystal, studies have been made to improve the characteristics of the wafer (see, for example, Patent Documents 1 to 5).

Patent Document 1 discloses a wafer in which an OSF region does not exist in an outer peripheral portion and a portion located at the tip of the holding means when held by the holding means. It is disclosed that when the BMD density of the portion of such a wafer where the OSF region does not exist is 1 × 10 ⁹ pieces / cm ³ or more, the occurrence of slip dislocations is suppressed when the wafer is held by the holding means. Has been done.
In Patent Documents 2 and 3, heat treatment conditions for a wafer having a ring-shaped OSF region (hereinafter, may be referred to as “R-OSF region”) are controlled to make the radial BMD density of the wafer uniform. It is disclosed to let. Further, Patent Document 2 discloses a wafer having a BMD density of an outer peripheral portion (hereinafter, simply referred to as “outer peripheral BMD density”) of 1 × 10 ⁹ wafers / cm ³ or more, but Patent Document 3 discloses. , There is no disclosure of such wafers.
Patent Document 4 discloses that the size of the COP region is set to 80% or more of the area of the wafer to equalize the radial BMD density in the wafer.
In Patent Document 5, a silicon single crystal is manufactured so that the radius of the R-OSF region is ½ or more of the radius of the wafer, and the defect disappearing effect of void defects in the wafer due to hydrogen gas is exerted to the deep layer. Is disclosed.

Japanese Unexamined Patent Publication No. 2003-249501 Japanese Unexamined Patent Publication No. 2006-93645 Japanese Unexamined Patent Publication No. 2013-74139 Japanese Unexamined Patent Publication No. 2002-187794 Japanese Unexamined Patent Publication No. 2000-154095

However, Patent Documents 1 and 2 disclose a method for producing a silicon single crystal that can efficiently obtain a wafer having an outer peripheral BMD density of 1 × 10 ⁹ pieces / cm ^{3 or more and capable of suppressing the occurrence of slip dislocations.} Not.
In the wafer disclosed in Patent Document 3, since the outer peripheral BMD density is ^{less than 1 × 10 9} / cm ³ , the occurrence of slip dislocation cannot be suppressed.
Patent Documents 4 and 5 do not disclose that the outer peripheral BMD density is 1 × 10 ⁹ pieces / cm ³ or more, and there is a possibility that the occurrence of slip dislocations cannot be suppressed.

An object of the present invention is a silicon single crystal capable of efficiently obtaining a silicon wafer capable of suppressing the occurrence of slip dislocations on the outer peripheral portion after an inert atmosphere annealing treatment (hereinafter referred to as AN treatment) for eliminating void defects on the surface layer of the silicon wafer. and to provide a manufacturing method and silicon Tan'yui crystals.

The method for producing a silicon single crystal of the present invention is to produce a silicon single crystal ^{containing nitrogen of 2.89 × 10 13} atoms / cm ³ or more and 5.38 × 10 ¹⁴ atoms / cm ³ or less by the Czochralski method. In a method for manufacturing a silicon single crystal, the inner diameter of a ring-shaped OSF region in a region where the solidification rate in the straight body portion after grinding the outer circumference of the silicon single crystal is 9.6% or more is cut out from the straight body portion. It is characterized in that the silicon single crystal is pulled up so as to be within the range of 78% or more and 95% or less of the diameter of the silicon wafer.

According to the present invention, the inner diameter of the R-OSF region in the region where the solidification rate in the straight body portion after peripheral grinding is 9.6% or more is 78% or more of the diameter of the silicon wafer cut out from the straight body portion. By producing a silicon single crystal of 95% or less, a silicon wafer having ^{an outer peripheral BMD density of 1 × 10 9} pieces / cm ^{3 or more after AN treatment can be efficiently obtained from a region satisfying this condition.}
The boundary between the R-OSF region and the P _V region, i.e. to determine the outer peripheral edge of the R-OSF region is difficult, the boundary between the discrimination as compared with the boundary easy R-OSF region and the COP region That is, by discriminating the inner peripheral edge of the R-OSF region, ^{it is possible to efficiently obtain a silicon wafer having an outer peripheral BMD density of 1 × 10 9} pieces / cm ³ or more and capable of suppressing the occurrence of slip dislocations after AN treatment. Can be done.
The specific heat treatment conditions for the AN treatment are a temperature of 1150 ° C. or higher and 1250 ° C. or lower and a time of 30 minutes or longer and 120 minutes or lower under an Ar gas atmosphere.

In the method for producing a silicon single crystal of the present invention, it is preferable to pull up the silicon single crystal so that the inner diameter in the region where the solidification rate in the straight body portion is 93% or less is within the above range.

According to the present invention, it is possible to efficiently obtain a silicon wafer capable of suppressing the occurrence of slip dislocations on the outer peripheral portion after AN treatment from the region where the inner diameter of the R-OSF region is controlled.
The solidification rate is a value when the upper end of the straight body portion is 0% and the lower end is 100%.

In the method for producing a silicon single crystal of the present invention, a first pulling step of pulling up the first silicon single crystal at a pulling speed preset so that the inner diameter is within the above range, and the first silicon single crystal. A second silicon that is pulled up after the first pulling step based on the inner diameter measuring step of measuring the inner diameter of the OSF region in the straight body portion after the outer peripheral grinding and the inner diameter measured in the inner diameter measuring step. The second silicon single crystal at the speed setting step of setting the pulling speed and the pulling speed set in the speed setting step so that the inner diameter of the straight body portion after the outer peripheral grinding of the single crystal is within the above range. It is preferable to have a second pulling step for pulling up.

According to the present invention, in the first silicon single crystal, the inner diameter of the R-OSF region in the straight body portion after outer peripheral grinding is not 78% or more and 95% or less of the diameter of the silicon wafer cut out from the straight body portion. The region can be within the above range in the second silicon single crystal.

In the method for producing a silicon single crystal of the present invention, the first pulling step and the second pulling step are performed when the pulling drive unit is driven based on the set pulling speed to pull the silicon single crystal. It is preferable to control the pulling drive unit so that the actual pulling speed is within the range of ± 4.1% with respect to the set pulling speed.

According to the present invention, the inner diameter of the R-OSF region is a silicon wafer by controlling the pulling drive unit so that the actual pulling speed is within ± 4.1% of the set pulling speed. A silicon single crystal having a diameter of 78% or more and 95% or less can be stably produced.

The silicon single crystal of the present invention is a silicon single crystal ^{containing nitrogen of 2.89 × 10 13} atoms / cm ³ or more and 5.38 × 10 ¹⁴ atoms / cm ³ or less, and is a straight body portion after peripheral grinding. The inner diameter of the ring-shaped OSF region in the region where the solidification rate is 9.6% or more is within the range of 78% or more and 95% or less of the diameter of the silicon wafer cut out from the straight body portion. ..
The silicon wafer of the present invention is a silicon wafer containing nitrogen of ^{2.89 × 10 13} atoms / cm ³ or more and 5.38 × 10 ¹⁴ atoms / cm ^{3 or less.}
The inner diameter of the ring-shaped OSF region is within a range of 78% or more and 95% or less of the diameter of the silicon wafer.

The schematic diagram which shows an example of the relationship between the defect distribution and V / G in a silicon single crystal. The graph which shows the relationship between the solidification rate and the pulling rate ratio in Experiment 1 performed for deriving the present invention. The graph which shows the relationship between the R-OSF region inner diameter ratio and the pulling speed ratio in Experiment 1. The graph which shows the relationship between the R-OSF region inner diameter ratio in Experiment 1 and the outer peripheral BMD density after AN treatment. The graph which shows the relationship between the outer peripheral BMD density and the slip length when the temperature rise rate in Experiment 2 performed to derive this invention is 10 degreeC / min. The graph which shows the relationship between the outer peripheral BMD density and the slip length when the temperature rise rate in Experiment 2 is 4 degreeC / min. The graph which shows the relationship between the solidification rate, the pulling rate ratio, and the R-OSF region inner diameter ratio in the experiment 3 performed for deriving the present invention. The graph which shows the relationship between the R-OSF region inner diameter ratio and the pulling speed ratio in Experiment 4 performed for deriving the present invention. The schematic diagram which shows the schematic structure of the single crystal pulling apparatus which concerns on one Embodiment of this invention. The graph which shows the relationship between the solidification rate, the set pulling speed ratio, and the permissible speed threshold value in one embodiment. The explanatory view of the manufacturing method of the silicon single crystal using the single crystal pulling apparatus. The speed correction information in the one embodiment, and is a graph showing the relationship between the R-OSF region inner diameter ratio and the pulling speed ratio.

[Background to lead to the present invention]
[Experiment 1: Investigation of the relationship between the R-OSF region inner diameter ratio, the pulling speed of the silicon single crystal, and the BMD density of the outer peripheral portion after AN treatment]
When producing silicon single crystals with a nitrogen concentration of 2.89 × 10 ¹³ atoms / cm ³ or more and 5.38 × 10 ¹⁴ atoms / cm ³ or less, as shown by the solid line in FIG. 2, the pulling speed is increased according to the solidification rate. While changing, a straight body portion of the silicon single crystal of Experimental Example 1 was formed. The dopant was boron, and the electrical resistivity was 5 Ω · cm or more and 20 Ω · cm or less.
Note that FIG. 2 shows the ratio of the pulling speed (pulling speed ratio) at each solidification rate when the pulling speed is 1.0 when the solidification rate is 0%. Here, the pulling speed is a moving average speed. Further, also in other figures, the “pulling speed ratio” represents the same contents as in FIG. Further, the broken line in FIG. 2 is a general pulling speed ratio at the time of forming the straight body portion, and the pulling speed ratio is constant over the entire straight body portion.

Then, the outer circumference of the silicon single crystal of Experimental Example 1 was ground by about 3 mm to 7 mm to make the diameter 200 mm. After that, a plurality of silicon wafers were obtained from the straight body portion of the silicon single crystal, and the inner diameter of the R-OSF region in each silicon wafer was examined by the following method. A silicon wafer was obtained from a region having a solidification rate of 9.6% or more and 93% or less.

When examining the inner diameter of the R-OSF region, first, the silicon wafer was heat-treated for 2 hours in a wet oxygen atmosphere at 1100 ° C. Next, light etching of 2 μm was carried out to reveal the R-OSF region, and the inner diameter thereof was examined.
FIG. 3 shows the relationship between the R-OSF region inner diameter ratio (inner diameter of the R-OSF region in the straight body portion after outer peripheral grinding / the diameter of the silicon wafer cut out from the straight body portion after outer peripheral grinding) and the pulling speed ratio. .. In the following, the "inner diameter of the R-OSF region in the straight body portion after the outer peripheral grinding" is simply referred to as the "inner diameter of the R-OSF region", and the "diameter of the silicon wafer cut out from the straight body portion after the outer peripheral grinding". Is simply referred to as "the diameter of the silicon wafer".
As shown in FIG. 3 , there is a correlation between the R-OSF region inner diameter ratio and the pulling speed ratio, and the larger the pulling speed ratio (faster pulling speed), the larger the R-OSF region inner diameter ratio, and the pulling speed ratio becomes. It was found that the smaller the value (the slower the pulling speed), the smaller the R-OSF region inner diameter ratio.

Further, a silicon wafer was obtained from a position adjacent to the silicon wafer used for the inner diameter investigation of the R-OSF region, and the BMD after AN treatment in each silicon wafer was examined by the following method.
First, the silicon wafer after the AN treatment was subjected to the first heat treatment for 3 hours in a dry oxygen atmosphere at 780 ° C., and then further subjected to the second heat treatment for 16 hours in a dry oxygen atmosphere at 1000 ° C. Next, 2 μm light etching was performed to reveal the BMD, and the BMD density in the range of 5 mm from the outer edge of the silicon wafer was examined as the outer peripheral BMD density.

FIG. 4 shows the relationship between the R-OSF region inner diameter ratio and the outer peripheral BMD density. Since the same silicon wafer cannot be used for the OSF survey and the BMD survey, FIG. 4 was created by associating the OSF survey result of one of the two adjacent silicon wafers with the BMD survey result of the other. ..
As shown in FIG. 4, there is a correlation between the R-OSF region inner diameter ratio and the outer peripheral BMD density after AN treatment, and when the R-OSF region inner diameter ratio is less than 78% and when it exceeds 95%, that is, R. If the inner diameter of -OSF region exceeding if 95% of less than 78% of the diameter of the silicon wafer, it was found that in some cases the outer periphery BMD density is less than 1 × 10 ⁹ pieces / cm ^3. Here, the oxygen concentration was 11.0 × 10 ¹⁷ atoms / cm ³ or more and 13.5 × 10 ¹⁷ atoms / cm ³ or less (ASTM F-121 (1979)).

If the inner diameter of the R-OSF region is less than 78% of the diameter of the silicon wafer, why the outer peripheral portion BMD density is less than 1 × 10 ⁹ pieces / cm ³ is, BMD is hardly _{P I} region of the straight body portion occurs It is thought that it is located on the outer circumference. Further, even when the P _V region is located in the outer peripheral portion, the P _V region is close to P _I region, presumably because BMD hardly occurs.
On the other hand, when the inner diameter of the R-OSF region exceeds 95% of the diameter of the silicon wafer, the reason why the outer ^{peripheral BMD density is less than 1 × 10 9} / cm ³ is that there is no _{PV region on the outer peripheral.} Or even if it exists, it is considered to be due to a narrow range.

[Experiment 2: Investigation of the relationship between the outer peripheral BMD density after AN treatment and slip resistance]
The silicon single crystal of Experimental Example 1 described in Experiment 1 was produced. Further, as shown by the broken line in FIG. 2, the silicon single crystal of Experimental Example 2 was produced under the same conditions as in Experimental Example 1 except that the pulling speed ratio was made constant in the entire straight body portion.
Then, after performing outer peripheral grinding in the same manner as in Experiment 1 to make the diameter of the silicon single crystal of Experimental Examples 1 and 2 200 mm, a silicon wafer is obtained from the position shown in Table 1 below, and AN treatment is performed. The outer peripheral BMD density was evaluated by the same method as in Experiment 1. The results are shown in Table 1.

Further, the silicon wafer adjacent to the silicon wafer whose outer peripheral BMD density was evaluated was subjected to AN treatment and then a slip resistance test was performed. The reason why the outer peripheral BMD density evaluation and the slip resistance test were performed using silicon wafers adjacent to each other is that the evaluation and test cannot be performed on the same silicon wafer as in Experiment 1.
In the slip resistance test, thermal stress load heat treatment was performed using a horizontal furnace having a boat shape that supports the outer peripheral region of the silicon wafer. The thermal stress load heat treatment conditions were an input temperature of 900 ° C., a temperature rise rate of 10 ° C./min, holding at 1100 ° C. for 30 minutes, a temperature decrease rate of 2.5 ° C./min, and a take-out temperature of 900 ° C. Then, the silicon wafer after the heat treatment was observed by X-ray topography, and the length of the slip dislocation (hereinafter, simply referred to as “slip length”) was evaluated. Further, except that the temperature rise rate was set to 4 ° C./min, thermal stress load heat treatment was performed under the above conditions, and the slip length was evaluated. The test condition is a condition for forcibly causing slip, not a condition for quality assurance inspection of the product.
The results are shown in Table 1. Further, FIG. 5 shows the relationship between the outer peripheral BMD density and the slip length when the temperature rise rate is 10 ° C./min, and FIG. 6 shows the above relationship when the temperature rise rate is 4 ° C./min.

As shown in Table 1, FIGS. 5 and 6, the outer peripheral BMD density was 1 × 10 ⁹ pieces / cm ³ or more in Experimental Example 1 and less than ^{1 × 10 9} pieces / cm ^{3 in Experimental Example 2.} ..
The slip length was 9.7 mm or less in Experimental Example 1 and 13.5 mm or more in Experimental Example 2 when the heating rate was 10 ° C./min. When the temperature rising rate was 4 ° C./min, it was 8.7 mm or less in Experimental Example 1 and 9.2 mm or more in Experimental Example 2.
It was found that a silicon wafer with high slip resistance can be obtained by manufacturing a silicon single crystal so that the outer peripheral BMD density is 1 × 10 ⁹ pieces / cm ^{3 or more.}

From the results of Experiments 1 and 2, by producing a silicon single crystal having an inner diameter of the R-OSF region of 78% or more and 95% or less of the diameter of the silicon wafer, the outer peripheral portion BMD after AN treatment can be obtained from the region satisfying this condition. It was found that a silicon wafer having a density of 1 × 10 ⁹ pieces / cm ³ or more and capable of suppressing the occurrence of slip dislocations can be efficiently obtained.

[Experiment 3: Investigation of the relationship between the solidification rate of the straight body, the pulling speed ratio, and the R-OSF region inner diameter ratio]
Based on the relationship between the R-OSF region inner diameter ratio and the pulling speed ratio obtained in Experiment 1, as shown in FIG. 3, the inner diameter of the R-OSF region is the diameter of the silicon wafer over the entire length direction of the straight body portion. The pulling speed ratio so as to be 78% or more and 95% or less is set as shown by a solid line in FIG. Hereinafter, the pulling speed ratio shown by this solid line is referred to as a set pulling speed ratio.
Then, the silicon single crystal of Experimental Example 3 was manufactured at this set pulling speed ratio. The nitrogen concentration, dopant, and electrical resistivity were set to the same conditions as in Experiment 1.
Further, the actual pulling speed ratio is shown by a broken line in FIG.
As shown by the broken line in FIG. 7, the actual pull-up speed ratio could be made almost the same as the set pull-up speed ratio, although there were some variations.

Next, the silicon single crystal of Experimental Example 3 obtained by the control based on the set pull-up speed ratio was subjected to outer peripheral grinding in the same manner as in Experiment 1, and after the diameter was set to 200 mm, the positions corresponding to a plurality of solidification rates were obtained. Obtained a silicon wafer from. Then, the inner diameter and the outer diameter of the R-OSF region of this silicon wafer were evaluated by the same method as in Experiment 1.
The range of the R-OSF region corresponding to the solidification rate is shown in FIG. 7 by a vertical solid line thicker than the set pull-up speed ratio. The lower end of the solid line indicating the range of the R-OSF region represents the R-OSF region inner diameter ratio, and the upper end is the R-OSF region outer diameter ratio (outer diameter of the R-OSF region in the straight body portion after outer peripheral grinding / silicon). Wafer diameter).

As shown in FIG. 7, in the region where the solidification rate is less than 9.6%, the pulling speed ratio is not stable, and in the region where the solidification rate exceeds 93%, the region where the R-OSF region inner diameter ratio exceeds 95% It turned out to be more.
The reason why the above phenomenon occurs in the region where the solidification rate of the straight body is less than 9.6% is considered to be that the pulling speed is not stable because the elapsed time from the transition period from the shoulder to the straight body is short. ..
Further, it is considered that the reason why the above phenomenon occurs in the region where the solidification rate of the straight body portion exceeds 93% is that the nitrogen concentration increases due to the segregation phenomenon and the width of the R-OSF region expands.
From the above, it was found that it is difficult to control the R-OSF region inner diameter ratio to 78% or more and 95% or less in the region where the solidification rate is less than 9.6% or more than 93%.

[Experiment 4: Survey of allowable speed threshold for pulling speed]
The silicon single crystal of Experimental Example 1 described in Experiment 1 was produced. Next, the outer circumference of the silicon single crystal was ground to make the diameter 200 mm, and then a silicon wafer was obtained from a region having a solidification rate of 9.6% or more and 93% or less. Then, the inner diameter of the R-OSF region of these silicon wafers was evaluated by the same method as in Experiment 1.
FIG. 8 shows the relationship between the R-OSF region inner diameter ratio and the pulling speed ratio.

Next, an approximate expression between the R-OSF region inner diameter ratio and the pulling speed ratio is obtained, and from this approximate expression, the lower limit value V1 of the pulling speed ratio at which the R-OSF region inner diameter ratio is 78% and the pulling speed at 95% are obtained. The lower limit of the ratio V2 was obtained. V1 was 0.70 and V2 was 0.76. Then, the average value VA of V1 and V2 was obtained, and the difference between VA and V1 (or V2) with respect to VA was obtained as the allowable speed threshold value VB of the pulling speed ratio. The difference was 0.03 and the permissible speed threshold VB was 4.1%.

As described above, the allowable speed threshold value VB is obtained, and the pulling drive unit is controlled so that the actual pulling speed (ratio) is within the range of ± 4.1% with respect to the set pulling speed (ratio). Therefore, it is considered that a silicon single crystal having an inner diameter of the R-OSF region of 78% or more and 95% or less of the diameter of the silicon wafer can be stably produced.

[Embodiment]
Next, an embodiment of the present invention will be described with reference to the drawings.
[Structure of single crystal pulling device]
As shown in FIG. 9, the single crystal pulling device 1 is a device used in the CZ method (Czochralski method), and includes a pulling device main body 2, a memory 3, and a control unit 4.
The pulling device main body 2 includes a chamber 21, a crucible 22 arranged in the center of the chamber 21, a heating portion 23 for heating the crucible 22, a heat insulating cylinder 24, a pulling portion 25, and a heat shield 26. And have.

A gas introduction port 21A for introducing an inert gas such as Ar gas into the chamber 21 is provided in the upper part of the chamber 21. At the lower part of the chamber 21, a gas exhaust port 21B for discharging the gas in the chamber 21 by driving a vacuum pump (not shown) is provided.
Under the control of the control unit 4, the inert gas is introduced into the chamber 21 from the gas introduction port 21A at the upper part of the chamber 21 at a predetermined gas flow rate. Then, the introduced gas is discharged from the gas exhaust port 21B at the lower part of the chamber 21, so that the inert gas flows from the upper side to the lower side in the chamber 21.

The crucible 22 melts polycrystalline silicon, which is a raw material for a silicon wafer, to obtain a silicon melt M. The crucible 22 is supported by a support shaft 27 that can rotate and move up and down at a predetermined speed. The crucible 22 includes a bottomed cylindrical quartz crucible 221 and a carbon material support crucible 222 for accommodating the quartz crucible 221.

The heating unit 23 is arranged around the crucible 22 and melts the silicon in the crucible 22.
The heat insulating cylinder 24 is arranged so as to surround the crucible 22 and the heating portion 23.
The pull-up portion 25 includes a pull-up cable 251 to which a seed crystal SC is attached to one end, and a pull-up drive unit 252 that raises and lowers and rotates the pull-up cable 251. The pull-up unit 25 is a silicon single crystal SM by landing the seed crystal SC attached to the pull-up cable 251 on the dopant-added melt MD in the crucible 22 and then pulling it up while rotating it in a predetermined direction by the pull-up drive unit 252. Pull up.
The heat shield 26 blocks radiant heat radiated upward from the heating unit 23.

The memory 3 stores various information necessary for manufacturing the silicon single crystal SM, such as the gas flow rate in the chamber 21, the furnace pressure, the heating temperature of the crucible 22 by the heating unit 23, and the rotation speed of the crucible 22 and the silicon single crystal SM. is doing.
Further, the memory 3 stores information on the pulling speed of the silicon single crystal SM. The pulling speed information represents the relationship between the solidification rate of the straight body portion and the set pulling speed ratio as shown in FIG.
The set pull-up speed ratio is set so that in the region where the solidification rate is 9.6% or more and 93% or less, the portion where the R-OSF region inner diameter ratio is 78% or more and 95% or less is as large as possible.

The control unit 4 manufactures the silicon single crystal SM based on the information stored in the memory 3 and the setting input of the operator.

[Manufacturing method of silicon single crystal]
Next, a method for manufacturing the silicon single crystal SM will be described.
In this embodiment, the nitrogen concentration of the entire straight body portion is 2.89 × 10 ¹³ atoms / cm ³ or more and 5.38 × 10 ¹⁴ atoms / cm ³ or less, the dopant is boron, and the electrical resistivity is 5 Ω · cm or more and 20 Ω ·. An example is exemplified in the case of manufacturing a silicon single crystal SM having a diameter of 200 mm or less and a straight body portion SM3 after peripheral grinding.

The diameter of the straight body portion SM3 after grinding the outer circumference may be another size such as 300 mm or 450 mm.
Further, it is preferable that the memory 3 stores information on the pulling speed of different profiles according to the diameter and length of the silicon wafer cut out from the straight body portion.

First, the control unit 4 of the single crystal pulling device 1 sets the manufacturing conditions of the silicon single crystal SM, for example, the heating temperature, the Ar flow rate, the furnace pressure, the crucible 22 and the rotation speed of the silicon single crystal SM.
Next, the control unit 4 performs the pulling step S1 as shown in FIG. The pulling step S1 includes a pulling preparation step TP1 and a pulling implementation step TP2.
The pulling preparation step TP1 heats the crucible 22 to melt the polysilicon material (silicon raw material) and the dopant in the crucible 22 and dope with nitrogen to generate a dopant-added melt MD. After that, the control unit 4 introduces Ar gas into the chamber 21 from the gas introduction port 21A at a predetermined flow rate, and reduces the pressure in the chamber 21 to maintain the inside of the chamber 21 in an inert atmosphere under the reduced pressure. ..

Next, the control unit 4 performs the pulling implementation step TP2. This pulling-up implementation step TP2 directly includes a liquid landing step of landing the seed crystal SC on the dopant-added melt MD, a neck portion forming step of forming the neck portion SM1, and a shoulder portion forming step of forming the shoulder portion SM2. A straight body portion forming step for forming the body portion SM3, a tail portion forming step for forming a tail portion (not shown), a cooling step for cooling the silicon single crystal SM, and a taking-out step for taking out the silicon single crystal SM from the chamber 21 are performed. I have.

The period of the pull-up preparation step TP1 is a correctable period that does not affect the quality of the silicon single crystal SM even if the set pull-up speed ratio is corrected as described later.
The period of the pulling implementation step TP2 is an uncorrectable period that affects the quality of the silicon single crystal SM when the set pulling speed ratio is corrected.

In the straight body portion forming step at the time of manufacturing the first silicon single crystal SM, the control unit 4 drives the pulling drive unit 252 based on the set pulling speed ratio of each solidification rate shown in FIG. 10, and the silicon single crystal. While pulling up the SM, the pulling drive unit 252 is controlled so that the actual pulling speed ratio becomes the set pulling speed ratio of FIG. At the time of this pulling, the pulling drive unit 252 may be controlled so that the actual pulling speed ratio does not exceed the range of the allowable speed threshold value shown by the alternate long and short dash line in FIG. The permissible speed threshold value is preferably set to a value of ± 4.1% with respect to the set pull-up speed ratio of each solidification rate. The control for preventing the actual pulling speed ratio from exceeding the allowable speed threshold value may be manual control by the operator or automatic control by the control unit 4.
After that, the control unit 4 starts manufacturing the next silicon single crystal SM after a predetermined time has elapsed from the end of the taking-out step.
Of the two continuously manufactured silicon single crystal SMs, the front silicon single crystal SM corresponds to the first silicon single crystal, and the rear silicon single crystal SM corresponds to the second silicon single crystal. do. Further, the first silicon single crystal pulling step S1 corresponds to the first pulling step, and the second silicon single crystal pulling step S1 corresponds to the second pulling step.

Here, despite controlling the pull-up drive unit 252 so that the actual pull-up speed ratio becomes the set pull-up speed ratio or is within the range of ± 4.1% with respect to the set pull-up speed ratio. The R-OSF region inner diameter ratio may not be 78% or more and 95% or less. For example, there is a deterioration of the hot zone of the chamber 21 and the crucible 22.
Therefore, the following OSF evaluation step S2 is performed to correct the set pulling speed ratio of the second silicon single crystal as necessary.

In the OSF evaluation step S2, first, the straight body portion SM3 is cut out from the silicon single crystal SM, and the outer circumference is ground so that the diameter of the straight body portion SM3 becomes a desired size (200 mm in this embodiment).
Next, a plurality of cylindrical blocks are acquired from the straight body portion SM3. At this time, a cylindrical block that does not include a region having a solidification rate of less than 9.6% and a region having a solidification rate of more than 93% is acquired. The length of the cylindrical block is not particularly limited, but it is preferably selected according to the slicing ability of the wire saw used in the slicing step described later. For example, the length of the cylindrical block may be 100 mm or more and 400 mm or less.

Next, evaluation wafers were cut out from both ends of the cylindrical block, and the heat treatment and light etching performed when examining the inner diameter of the R-OSF region in Experiment 1 were performed on each evaluation wafer, and the R-OSF region inner diameter ratio was obtained. (Inner diameter measurement process).
After that, it is determined whether or not the R-OSF region inner diameter ratio of each evaluation wafer is 78% or more and 95% or less (hereinafter referred to as "passing range" in this embodiment), and if both are within the passing range, it is determined. The cylindrical block obtained from this evaluation wafer is sent to the next commercialization step S3. In the following, the evaluation wafer whose R-OSF region inner diameter ratio is within the pass range is referred to as a “passed wafer”, and the evaluation wafer outside the pass range is referred to as a “failed wafer”.
On the other hand, when at least one of the evaluation wafers is a failing wafer, the next evaluation wafer is acquired from the inside of the failing wafer acquisition position in the cylindrical block, and it is determined whether or not this evaluation wafer is a passing wafer. (Hereinafter referred to as "drive-in processing"). Then, in the case of a rejected wafer, the drive-in process is performed again, and in the case of a pass wafer, the remaining cylindrical block is sent to the next commercialization step S3.

Next, based on the evaluation result of the R-OSF region inner diameter ratio, the set pulling speed ratio is corrected as necessary (speed setting step).
When the R-OSF area inner diameter ratio is less than 78%, set the solidification rate corresponding to the rejected wafer. Increase the pulling speed ratio (faster pulling speed), and when it exceeds 95%, correspond to the rejected wafer. Setting the solidification rate Decrease the pull-up speed ratio (slow down the pull-up speed). On the other hand, the setting pull-up speed ratio of the solidification rate corresponding to the passing wafer is not corrected.

Specifically, when the R-OSF region inner diameter ratio is less than 78%, the actual pulling speed ratio is obtained from the R-OSF region inner diameter ratio based on the following equation (1) which is the speed correction information. This equation (1) expresses the relationship between the R-OSF region inner diameter ratio shown in FIG. 3 and the pulling speed ratio as an approximate equation, and represents an approximate straight line shown in FIG.
A = 0.004 x B + 0.393 ... (1)
A: Pulling speed ratio B: R-OSF area inner diameter ratio (%)

In order to put the R-OSF region inner diameter ratio within the pass range, it is preferable to set the target value of the R-OSF region inner diameter ratio to the center of the pass range.
Therefore, next, the pulling speed ratio at which the R-OSF region inner diameter ratio is 86.5% (the center value between the upper limit value (95%) and the lower limit value (78%) of the passing range) is expressed in the equation (1). The difference obtained by subtracting the actual pulling speed ratio from the obtained pulling speed ratio is obtained as the correction amount. Then, a correction amount is added to the setting pull-up speed ratio of the solidification rate corresponding to the rejected wafer at the time of manufacturing the second silicon single crystal SM.
For example, when the R-OSF region inner diameter ratio of the rejected wafer is 70%, the actual pulling speed ratio is 0.673 from the equation (1). By substituting 86.5% for the R-OSF region inner diameter ratio of the formula (1), 0.739 is obtained, so that the correction amount is 0.066 (= 0.739-0.673). When the set pull-up speed ratio of the solidification rate of the rejected wafer is 0.75, the set pull-up speed ratio in the solidification rate is corrected from 0.75 to 0.816.
In addition, in order to put the R-OSF region inner diameter ratio within the pass range, the target value of the R-OSF region inner diameter ratio is set to the center of the pass range, but a value other than the center within the pass range may be used.

On the other hand, when the R-OSF region inner diameter ratio exceeds 95%, the set pull-up speed ratio in the solidification rate of the rejected wafer is reduced by a predetermined amount without using the formula (1). At this time, if the correction amount is too small, the R-OSF region inner diameter ratio of the evaluation wafer in the second silicon single crystal SM remains over 95%, and if the correction amount is too large, it may be less than 78%. The correction amount is preferably 0.05 or more and 0.15 or less because of the property.

Further, in the above correction, the entire set pull-up speed ratio is corrected so as to connect the set pull-up speed ratio of the solidification rate corresponding to the rejected wafer and the pass wafer or the failing wafer in a linear, curvilinear or stepwise manner. Is preferable.
For example, as shown by the alternate long and short dash line in FIG. 10, it corresponds to the set pull-up speed ratio after correction of the solidification rate corresponding to the rejected wafer W2 having the R-OSF region inner diameter ratio of less than 78% and the passed wafer W1. The entire set pull-up speed ratio is corrected so as to connect with the uncorrected set pull-up speed ratio of the solidification rate.

Such an OSF evaluation step S2 is completed within the correctable period (pull-up preparation step TP1) of the second silicon single crystal SM. Therefore, even if the set pulling speed ratio in the pulling step S1 of the second silicon single crystal SM is corrected based on the processing result of the OSF evaluation step S2, the quality is not adversely affected and the second silicon single crystal is pulled. It is possible to increase the region where the R-OSF region inner diameter ratio in SM is 78% or more and 95% or less.
Further, by repeating such correction of the setting pull-up speed ratio, the R-OSF region inner diameter ratio is 78% or more and 95% or less in the entire region where the solidification rate in the straight body portion is 9.6% or more and 93% or less. It can be within the range.
In the production of the second and subsequent silicon single crystal SMs, the straight body portion forming step may be performed under conditions different from those at the time of manufacturing the immediately preceding silicon single crystal SM based on the result of the OSF evaluation step S2. The steps other than the part forming step are performed under the same conditions as the first step.

After performing the OSF evaluation step S2, the commercialization step S3 is performed.
In the commercialization step S3, the cylindrical block to be commercialized is sliced with a wire saw and mirror-polished to manufacture a silicon wafer for the commercial product.
The silicon wafer manufactured in this commercialization step S3 ^{contains nitrogen of 2.89 × 10 13} atoms / cm ³ or more and 5.38 × 10 ¹⁴ atoms / cm ³ or less, and has an R-OSF region inner diameter ratio of 78%. It is 95% or less. Such a silicon wafer has a characteristic that the outer peripheral BMD density is 1 × 10 ⁹ pieces / cm ³ or more, and slip dislocations are unlikely to occur after AN treatment.

After the commercialization step S3, the BMD evaluation step S4 is performed.
The BMD evaluation step S4 is a sampling evaluation for a silicon wafer for a product, and the heat treatment and light etching performed when examining the BMD in Experiment 1 are performed to obtain the outer peripheral BMD density.
If the result of the BMD evaluation step S4 is that the outer peripheral BMD density is ^{less than 1 × 10 9} pieces / cm ³ and the set pull-up speed ratio is corrected, the BMD evaluation step S4 is the second silicon single crystal SM. Since it ends after the pulling step S1 is completed and after the correctable period of the third silicon single crystal SM has elapsed, the set pulling speed ratio in the pulling step S1 of the fourth silicon single crystal SM is corrected. Therefore, two eyes, a silicon single crystal SM of 3 knots, becomes many areas peripheral portion BMD density after AN treatment is less than 1 × 10 ⁹ pieces / cm ^3, the production of the silicon wafer is reduced There is a risk that it will end up.
In the present embodiment, in order to correct the set pull-up speed ratio in the second silicon single crystal SM based on the result of the OSF evaluation step S2 for the first silicon single crystal SM, the set pull-up speed ratio is set after the BMD evaluation step S4. The production rate of the silicon wafer can be improved as compared with the case of correction.

[Action and effect of the embodiment]
According to the above embodiment, since a silicon single crystal having an R-OSF region inner diameter ratio of 78% or more and 95% or less is produced, the outer peripheral BMD density after AN treatment is 1 × 10 ^{9 from the region satisfying this condition.} Silicon wafers of / cm ³ or more can be efficiently obtained. In particular, by discriminating the inner peripheral edge of the R-OSF region, which is easier to distinguish than the outer peripheral edge of the R-OSF region, the outer peripheral BMD density after AN treatment is 1 × 10 ⁹ pieces / cm ³ or more. A silicon wafer capable of suppressing the occurrence of slip dislocations can be efficiently obtained.

Further, since the set pull-up speed ratio is set so that the R-OSF region inner diameter ratio in the region where the solidification rate is 9.6% or more and 93% or less is 78% or more and 95% or less, the R-OSF region. A silicon wafer capable of suppressing slip dislocations on the outer peripheral portion after AN treatment can be efficiently obtained from a region where the inner diameter of the wafer can be easily controlled.

Further, by controlling the pulling drive unit 252 so that the actual pulling speed ratio is within the range of ± 4.1% with respect to the set pulling speed ratio, the R-OSF region inner diameter ratio is the diameter of the silicon wafer. A silicon single crystal of 78% or more and 95% or less can be stably produced.

[Modification example]
The present invention is not limited to the above embodiment, and various improvements and design changes can be made without departing from the gist of the present invention.
For example, if the OSF evaluation step S2 is not completed within the correctable period of the second silicon single crystal SM, the set pull-up speed ratio may be corrected during the correctable period of the third silicon single crystal SM. Even in such a case, the decrease in the production rate can be suppressed as compared with the case where the set pull-up speed ratio is corrected after the BMD evaluation step S4.
Further, the permissible speed threshold value VB may be less than 4.1%, or the pull-up drive unit 252 may be controlled so as to have a set pull-up speed ratio without setting the permissible speed threshold value VB.

252 ... Pull-up drive unit, SM ... Silicon single crystal, SM3 ... Straight body unit.

Claims (4)

2.89 × 10 ¹³ atoms / cm ³ or more 5.38 × 10 ¹⁴ atoms / cm ³ or less This is a method for producing a silicon single crystal containing nitrogen by the Czochralski method.
The ratio of the inner diameter of the ring-shaped OSF region in the straight body portion after the outer peripheral grinding of the silicon single crystal to the diameter of the silicon wafer cut out from the straight body portion is defined as the inner diameter ratio.
In the region where the solidification rate in the straight body portion is 9.6% or more and 93% or less, the silicon single crystal is pulled at a preset pulling speed so that the inner diameter ratio is within the range of 78% or more and 95% or less. A method for producing a silicon single crystal, which is characterized by pulling up. In the method for producing a silicon single crystal according to claim 1,
The first pulling step of pulling the first silicon single crystal at a pulling speed preset so that the inner diameter ratio is within the range, and
An inner diameter measuring step for obtaining the inner diameter ratio in the straight body portion after grinding the outer circumference of the first silicon single crystal, and
Based on the inner diameter ratio obtained in the inner diameter measuring step, the inner diameter ratio in the straight body portion after the outer peripheral grinding of the second silicon single crystal to be pulled up after the first pulling step is within the above range. In addition, the speed setting process to set the pulling speed and
A method for producing a silicon single crystal, which comprises a second pulling step of pulling the second silicon single crystal at a pulling speed set in the speed setting step. In the method for producing a silicon single crystal according to claim 2.
In the first pulling step and the second pulling step, when the pulling drive unit is driven based on the set pulling speed to pull the silicon single crystal, the actual pulling speed is the set pulling speed. A method for producing a silicon single crystal, which comprises controlling the pulling drive unit so as to be within the range of ± 4.1% with respect to the above. 2.89 × 10 ¹³ atoms / cm ³ or more 5.38 × 10 ¹⁴ atoms / cm ³ or less Nitrogen-containing silicon single crystal.
The inner diameter of the ring-shaped OSF region in the region where the solidification rate in the straight body after peripheral grinding is 9.6% or more and 93% or less is 78% or more and 95% or less of the diameter of the silicon wafer cut out from the straight body. Is within the range of
A silicon single crystal characterized in that the BMD density in the range of 5 mm from the outer edge is 1 × 10 ⁹ pieces / cm ^{3 or more.}

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