JP4862884B2 - Method for producing silicon single crystal - Google Patents

Description

  The present invention relates to a method for producing a silicon single crystal in which a silicon single crystal rod is grown by necking (forming a reduced diameter portion) using a silicon seed crystal by a Czochralski method (hereinafter referred to as “CZ method”). It is about.

  Conventionally, in the production of a silicon single crystal by the CZ method, a single crystal rod is grown by using single crystal silicon as a seed crystal and bringing it into contact with a silicon melt and then slowly pulling it up while rotating. . At this time, after the seed crystal is brought into contact with the silicon melt, the constriction is formed by narrowing it to about 3 mm in diameter in order to eliminate dislocations propagating from slip dislocations generated in the seed crystal at high density by thermal shock. The so-called seed squeezing is performed, and then the crystal is thickened until a desired diameter is obtained, and the dislocation-free silicon single crystal is pulled up. Such seed drawing is a common sense when pulling up a silicon single crystal rod by the CZ method as the Dash Necking method.

  That is, the shape of the seed crystal that has been used in the past is, for example, a cylindrical or prismatic single crystal having a diameter or a side of about 8 to 20 mm provided with a notch for setting the seed holder. The lower tip shape in contact with the melt is a flat surface. In order to withstand the weight of a heavy single crystal rod and safely pull it up, it is difficult to reduce the thickness of the seed crystal below the above in view of the strength of the material.

  In the seed crystal having such a shape, since the heat capacity of the tip contacting the melt is large, a sudden temperature difference is generated in the crystal at the moment when the seed crystal contacts the melt, and slip dislocations are generated at a high density. . Therefore, seed squeezing by the above-mentioned Dash Necking method is necessary to eliminate this dislocation and grow a single crystal.

  However, in order to eliminate dislocations, it is necessary to narrow the minimum diameter to 4 to 6 mm. With the recent increase in the diameter of silicon single crystals, the strength is required to support the heavy single crystal rods. Insufficient, and during the pulling of the single crystal rod, there was a risk of causing a serious accident such as the thin throttle portion being broken and the single crystal rod falling.

  In order to solve such a problem, the shape of the tip of the seed crystal is a wedge shape or a shape having a hollow portion, and slip dislocation that occurs when the seed crystal contacts the silicon melt is reduced as much as possible. A method is disclosed that enables dislocation-free even when the diameter is relatively large (see, for example, Patent Document 1 and Patent Document 2).

  However, in the above-mentioned method, the diameter has become increasingly larger and longer in recent years. For example, the strength may be insufficient for lifting a single crystal rod of 200 kg or more. It was unsuitable. Therefore, using a silicon seed crystal with a sharp tip, the tip of the seed crystal is melted, a narrowed portion and a narrowed portion are formed, necking (formation of a reduced diameter portion) is performed, and then the diameter is expanded to obtain a single crystal rod Has been disclosed (see, for example, Patent Document 3). By this method, it was possible to increase the diameter and handle the lifting of a heavy single crystal rod, but in the narrowed-down portion, the narrowed portion, and the enlarged diameter portion before reaching the straight body portion, dislocations were generated. There was a problem.

  On the other hand, for a method of manufacturing a silicon single crystal using a seed crystal having a sharp tip without performing seed drawing by the Dash Necking method, the process proceeds to the growth of the single crystal after the dissolution of the seed crystal into the melt. And the growth rate is disclosed (for example, see Patent Document 4). However, in a manufacturing method in which necking (formation of a reduced diameter portion) is performed and a single crystal rod is pulled up, if the same growth rate is employed, the growth rate is too high and the diameter of the single crystal becomes too thin. However, the strength is insufficient for pulling up a single crystal rod that is long, for example, 200 kg or more, and is unsuitable for pulling up a heavy single crystal rod.

  Therefore, when necking (formation of reduced diameter part) is performed, formation of the reduced diameter part starts immediately after stopping the descent of the seed crystal and starting to pull up, while the expansion of the crystal diameter formed under the seed crystal begins. Then, the upper limit value of the pulling speed is disclosed in which the pulling speed is set to 0.5 mm / min or less and the single crystal is pulled (see, for example, Patent Document 5). However, even this method has a problem of causing dislocations in the narrowed portion and the enlarged diameter portion.

Japanese Patent Laid-Open No. 5-139880 Japanese Patent Application No. 9-255485 JP-A-11-292688 JP-A-11-240793 International Publication No. WO03 / 091483 Pamphlet

  In the present invention, when a single crystal is produced by carrying out necking (formation of a reduced diameter portion) by the CZ method, a single crystal rod is grown without reducing the dislocation-free rate in the narrowed portion and the enlarged diameter portion. Thus, an object of the present invention is to provide a method for producing a silicon single crystal that increases the diameter and improves the productivity of a heavy single crystal rod.

  In order to solve the above-mentioned problem, the present invention uses a Czochralski method to dissolve a silicon melt from a tip to a position of a predetermined diameter using a silicon seed crystal having a sharp tip, and performs necking to narrow the narrowed portion. In the silicon single crystal manufacturing method in which the seed crystal is formed and then expanded to form a diameter-expanded portion and a straight body portion and the single crystal rod is pulled up, the melting of the seed crystal is completed, and the seed crystal starts to be pulled upward The temperature of the silicon melt begins to be lowered by controlling the heater power before the start of pulling, and the pulling speed from the start of pulling to the start of formation of the straight body of the single crystal is set to at least two stages. The upper speed is less than 0.3 mm / min at the start of the pulling, and then 120% or more, or 50% or more and less than 75% with respect to the time when the diameter of the narrowed portion becomes the minimum. To be increased in the range of timing below 0.3 mm / min or more 0.7 mm / min to provide a method for manufacturing a silicon single crystal according to claim. (Claim 1).

In this way, by starting to lower the temperature of the silicon melt before the start of pulling, the pulling speed can be controlled thereafter to expand to the desired crystal diameter. Then, the pulling speed from the start of pulling to the start of formation of the straight body of the single crystal is set to at least two stages, and by increasing the pulling speed in the middle, the single crystal with high productivity is pulled up with high productivity. be able to. In that case, after pulling up at a predetermined pulling-up speed, by increasing the pulling-up speed at a predetermined timing, it does not increase in diameter in the narrowed-down part or decrease in diameter in the expanded part, A single crystal can be produced without causing dislocation.
Here, `` necking '' in the present invention, when using a silicon seed crystal with a sharp tip, after being dissolved in the silicon melt from the tip to a position of a predetermined diameter, when starting the growth of a single crystal, This means that the diameter is slightly reduced once, which is different from the seed drawing in the so-called Dash Necking method in which the diameter is once reduced to about 3 mm in order to eliminate dislocations. The diameter is reduced.

Further, in the manufacturing method of the present invention, the timing is such that the pulling speed at the start of pulling is fixed to less than 0.3 mm / min, the single crystal is prototyped, and the diameter of the narrowed portion is minimized. It is preferable to determine the timing of increasing the pulling speed by obtaining time.
In this way, by performing a trial manufacture of a single crystal with the pulling speed fixed, it is possible to accurately grasp the time when the diameter of the narrowed-down portion is minimum. And the timing which increases pulling speed from the calculated | required time can be determined in advance. Therefore, since the relationship between the pulling speed control and the heater power control can be derived in advance, the production of the single crystal can be surely automated, and the productivity of the single crystal can be improved.

Further, in the manufacturing method of the present invention, the narrowed portion is formed by continuously decreasing the diameter of the single crystal without increasing during the growth, and the enlarged diameter portion formed below the narrowed portion is thereafter It is preferable that the diameter of the single crystal is continuously increased without decreasing during the growth until reaching the straight body portion to be grown (claim 3).
As a result, the narrowed portion and the enlarged diameter portion do not repeat the diameter reduction or diameter expansion in the middle of their growth, so that dislocations in the narrowed portion and the enlarged diameter portion are prevented and a silicon single crystal is produced. be able to.

  As described above, in the present invention, the timing at which the pulling speed is determined in the method of manufacturing a single crystal by necking (forming a reduced diameter portion) using a seed crystal having a sharp tip by the CZ method. As a result of the increase, the dislocation of the narrowed portion and the enlarged diameter portion can be prevented and a silicon single crystal can be produced. In addition, since the pulling speed increases during the pulling of the single crystal, it is possible to manufacture a single crystal with high productivity and high weight.

Hereinafter, the present invention will be described more specifically.
As mentioned above, in order to cope with the pulling up of a single crystal rod with a large diameter and a heavy weight, necking is performed using a silicon seed crystal with a sharp tip to form a narrowed portion, a narrowed portion, and a large diameter portion. The method of pulling up the single crystal rod having the straight body portion was disclosed, but due to the shape of the narrowed portion, the narrowed portion, and the enlarged diameter portion before reaching the straight body portion, in particular, the narrowed portion has a monotonous diameter reduction. However, it has been found that dislocation occurs when a part of the diameter is expanded, or when a part of the diameter-expanded part following the throttle part is reduced.

  On the other hand, after the completion of the dissolution of the seed crystal into the melt, the time for starting to pull the seed crystal upward and the upper limit value of the pulling speed are disclosed. It has been found that the shape of the diameter portion repeatedly expands and decreases, which causes dislocations.

  Therefore, in order to prevent dislocation from occurring in the narrowed portion and the enlarged diameter portion, the shapes of the narrowed portion and the enlarged diameter portion are important. It is necessary not to repeat.

  However, in a manufacturing method in which a narrowed portion is formed by performing necking using a silicon seed crystal having a sharp tip, and then a single crystal rod is pulled up by forming a large diameter portion, the shape of the narrowed portion or the large diameter portion is expanded. It has been found that it is difficult to form the diameter and the diameter so as not to be repeated because the appropriate timing for changing the diameter of the narrowed portion or the enlarged portion and the pulling-up speed is not clear.

  Therefore, the present inventors started to lower the temperature of the silicon melt by the start of pulling up when the seed crystal starts to be pulled upward, the pulling speed at the start of pulling is set to be low, and then the diameter of the narrowed portion is minimized. An attempt was made to produce a single crystal having a desired shape by determining the timing for increasing the pulling speed with respect to a certain time and increasing the pulling speed at an appropriate timing to increase the speed.

  As a result, the diameter of the expanded part is increased during the growth by increasing the pulling speed from the low speed at the start of the pulling up to a timing in the range of 120% or more with respect to the time when the diameter of the narrowed part becomes the minimum after that. It was discovered that the diameter was not reduced.

  Further, the pulling-up portion and the diameter-expanding portion are increased by increasing the pulling-up speed from a low speed at the start of pulling up to a timing within a range of 50% or more and less than 75% with respect to the time when the diameter of the narrowing-down portion is minimized. It has been found that the shape of does not repeat the diameter expansion and the diameter reduction in the middle.

  On the other hand, when the pulling speed is increased from a low speed at the start of pulling up and then at a timing of less than 50% with respect to the time when the diameter of the narrowed portion becomes the minimum, the amount of reduction in the narrowed portion is large. When it becomes too large to be able to grow a heavy single crystal rod, and the increase timing is in the range of 75% or more and less than 120% with respect to the time when the diameter of the narrowed portion becomes the minimum. Discovered that the shape of the narrowed-down portion and the enlarged-diameter portion repeatedly expanded and reduced in the middle, and the produced silicon single crystal was converted to dislocations.

  In addition, the pulling speed is less than 0.3 mm / min when the pulling start is slow, and then increases to 0.3 mm / min or more and 0.7 mm / min or less when the pulling speed is high. It was also discovered that a single crystal can be raised with high productivity by increasing the speed at a midpoint and growing the single crystal with high productivity.

The present invention has been completed based on the above findings, and the present invention will be described in more detail below with reference to the drawings. However, the present invention is not limited to these.
FIG. 2 is a schematic view showing the shape of the narrowed portion and the enlarged diameter portion of the single crystal manufactured according to the present invention. The narrowed portion 3 is formed by melting the tip 2 of the seed crystal 1 having a sharp tip in a silicon melt (not shown) and performing necking. And it is the enlarged diameter part 4 and the straight trunk | drum 5 which are formed below the narrowing-down part 3 continuously.

  In the present invention, the silicon seed crystal 1 having a sharp tip is used to dissolve the silicon melt from the tip 2 to a predetermined diameter by the CZ method, and necking is performed to form the narrowed portion 3, and then the expansion is performed. In the method of manufacturing a silicon single crystal in which the single crystal rod is pulled up in diameter, the temperature of the silicon melt is controlled by controlling the heater power before the start of the pulling up of the seed crystal 1 after the melting of the seed crystal 1 is finished. Start to lower. This makes it possible to control the subsequent pulling speed to form a narrowed portion that reduces the diameter of the single crystal to a desired value, and then to form an enlarged portion that is then expanded.

  Here, FIG. 1 is a diagram showing the relationship between pulling speed, heater power, and single crystal diameter in the production of a silicon single crystal according to the present invention. As described above, the melting of the seed crystal is finished, the dial value of the heater power is lowered by the start of pulling up to start pulling the seed crystal upward, and then the pulling speed is controlled as in the present invention. It can be seen that the diameter of the single crystal decreases at the narrowed portion and increases at the expanded portion.

Next, in the manufacturing method of the present invention, the narrowing portion 3 is formed by performing necking at a pulling speed at the start of pulling at a low speed of less than 0.3 mm / min. Thus, by making the pulling speed less than 0.3 mm / min, the crystal growth does not catch up and the crystal diameter does not become too thin, and a heavy single crystal can be pulled up.
Then, the pulling speed is increased to 0.3 mm / min or more and 0.7 mm / min or less in the middle until the single crystal straight body portion 5 starts to be formed. As described above, the increase in the pulling speed enables the single crystal to be grown at a high speed, and the single crystal having a high weight can be pulled with good productivity.

  Moreover, in the manufacturing method of this invention, with respect to the time when the diameter of the narrowing-down part 3 becomes the minimum diameter W, the pulling-up speed is increased at a timing in the range of 120% or more. As a result, the single crystal has already formed a diameter-expanded portion, and the temperature of the silicon melt is sufficiently lowered, so that the diameter does not become thin even if the pulling speed is increased. The expanded diameter portion only expands. Therefore, it is possible to grow single crystal rods while preventing dislocations in the narrowed portion and the enlarged diameter portion.

Here, referring to FIG. 1, as described above, with respect to the time (about 20 minutes) in which the narrowing portion is formed with the pulling speed less than 0.3 mm / min and the diameter of the narrowing portion is minimized. At a timing of about 120% or more (about 25 minutes), the pulling speed is increased to 0.3 mm / min or more and 0.7 mm / min or less. When attention is paid to the diameter of the single crystal at this time, the diameter does not increase on the way from the formation of the narrowed portion to the minimum value. It can also be seen that the diameter does not decrease during the transition from the minimum value to the formation of the enlarged diameter portion. Therefore, by increasing the pulling speed at the timing as described above, it is possible to prevent dislocations in the narrowed portion and the enlarged diameter portion and to grow a single crystal rod.
In addition, the pulling speed at the start of pulling is, for example, the pulling speed is instantaneously increased immediately after the pulling start, and then reduced to form a narrowed portion with a constant pulling speed. The pulling speed may be varied as long as it is in a range of less than 0.3 mm / min.

  On the other hand, when the timing for increasing the pulling speed is within the range of 50% or more and less than 75% with respect to the time when the diameter of the narrowed portion 3 becomes the minimum diameter W, the single crystal starts to form the narrowed portion 3. Therefore, the narrowed portion is formed by reducing the diameter of the crystal by increasing the pulling speed, and after it reaches the minimum diameter, the reduced diameter and expanded diameter are not repeated alternately even if the enlarged diameter portion is formed. In addition, it is possible to grow single crystal rods by preventing dislocation from occurring in the narrowed portion and the enlarged diameter portion.

In this case, in the manufacturing method of the present invention, the pulling speed at the start of pulling is fixed to less than 0.3 mm / min, a single crystal is prototyped, and the time during which the diameter of the narrowed portion is minimized is obtained in advance. It is preferable to determine the timing for increasing the pulling speed.
In this way, it is possible to accurately grasp the time when the diameter of the narrowed-down portion is minimized by making the trial production by fixing the pulling speed in advance and stably growing the single crystal. The timing for increasing the speed can be determined in advance. And since it can be derived in advance that the relationship between the heater power and the pulling speed required for lowering the temperature of the silicon melt is as shown in FIG. 1, both can be controlled accurately. Therefore, the production of the single crystal can be surely automated, the efficiency can be promoted, and the productivity can be further improved.

Further, in the manufacturing method of the present invention, the narrowed portion is formed by continuously decreasing the diameter of the single crystal without increasing during the growth, and the expanded diameter portion is decreased by increasing the diameter of the single crystal during the growth. It can be formed by continuing to increase without doing.
In this way, the narrowed portion and the enlarged diameter portion do not repeat diameter reduction or diameter expansion in the middle of each growth, and a sudden change in the diameter of the single crystal does not occur. In addition, the growth time can be shortened. Therefore, it is possible to produce a silicon single crystal with high productivity by preventing dislocations in the narrowed portion and the enlarged diameter portion.

Next, the present invention will be described more specifically with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these.
First, in order to grow a silicon single crystal having a diameter of 300 mm by the CZ method, a seed crystal having a prismatic shape with a side of 20 mm and a sharp tip was dissolved in the silicon melt. At this time, the dial value of the heater power was lowered and the temperature of the silicon melt was started to decrease 10 minutes after the start of the dissolution of the seed crystal into the silicon melt. Then, when the diameter of the tip of the seed crystal reached 8.0 mm, the pulling speed was fixed at 0.1 mm / min and the seed crystal was pulled upward, and the pulling of the single crystal as a prototype was started. Then, it was confirmed that the time (hereinafter referred to as “X”) for the diameter of the single crystal to reach the target minimum diameter of 6.0 mm was 20 minutes after the start of pulling.
And as shown in Table 1, the timing (AF) which raises pulling speed as a factor, and pulling speed (ac) were changed, and the silicon single crystal of the Example and the comparative example was manufactured. .

(Example 1) (Factor B, a)
In order to grow a silicon single crystal having a diameter of 300 mm by the CZ method, the seed crystal was dissolved in a silicon melt under the same conditions as in the trial production, and when the diameter of the seed crystal reached 8.0 mm, the pulling speed was set to 0. The seed crystal was started to be pulled upward while being fixed at 1 mm / min. Thereafter, the timing for increasing the pulling speed was 10 minutes after starting pulling (50% of X), and the pulling speed was increased to 0.3 mm / min to grow a single crystal.
Then, a silicon single crystal was manufactured 20 times under these conditions, and the dislocation-free rate, the diameter reduction, and the number of times of diameter expansion were confirmed in the narrowed portion and the diameter-enlarged portion.

(Example 2 and Example 3) (Factor C, a and Factor F, a)
In the method for producing a silicon single crystal of Example 1 above, the timing for increasing the pulling speed is 14 minutes after the pulling start (less than 75% of X) and 24 minutes after (120% of X). The same evaluation as in Example 1 was also performed.

(Example 4) (Factors B and b)
In the method for producing a silicon single crystal of Example 1 above, the same evaluation as in Example 1 was performed when the pulling rate was increased to 0.7 mm / min.

(Example 5 and Example 6) (Factor C, b and Factor F, b)
In the silicon single crystal manufacturing method of Example 1 above, the pulling speed is increased to 0.7 mm / min, and the timing for increasing the pulling speed is 14 minutes after the pulling start (less than 75% of X). The same evaluation as in Example 1 was also performed in the case of the above and after 24 minutes (120% of X).

(Comparative Example 1 and Comparative Example 2) (Factor D, a and Factor E, a)
In the silicon single crystal manufacturing method of Example 1 above, when the timing for increasing the pulling speed is 15 minutes after starting pulling (75% of X) and after 23 minutes (less than 120% of X) The same evaluation as in Example 1 was also performed.

(Comparative Example 3 and Comparative Example 4) (Factor D, b and Factor E, b)
In the method for producing a silicon single crystal of Example 1 above, the pulling speed was increased to 0.7 mm / min, and the timing for increasing the pulling speed was 15 minutes after starting pulling (75% of X). The same evaluation as in Example 1 was performed for the case and after 23 minutes (less than 120% of X).

(Comparative Example 5 to Comparative Example 7) (Factor A, ac)
In the method for producing a silicon single crystal of Example 1 described above, the timing for increasing the pulling speed is 9 minutes after the pulling start (less than 50% of X), the pulling speed is 0.3 mm / min. The same evaluation as in Example 1 was performed for the cases of 7 mm / min and 0.8 mm / min.

(Comparative Examples 8 to 12) (Factors B to F, c)
In the method for producing a silicon single crystal of Example 1 above, the pulling speed is increased to 0.8 mm / min, and the timing for increasing the pulling speed is 10 minutes, 14 minutes, and 15 minutes after the start of pulling. , 23 minutes and 24 minutes later (50% of X, less than 75%, 75%, less than 120%, 120%), the same evaluation as in Example 1 was performed.

  From Table 1, it can be seen that a high dislocation-free rate can be obtained in all Examples. However, in most comparative examples, the dislocation-free rate was very low.

  Further, the number of times of switching between diameter reduction and diameter expansion in the narrowed portion and the enlarged diameter portion was only one time of switching from the narrowed portion to the enlarged diameter portion in all the examples. Moreover, although it was once also about Comparative Example 5-Comparative Example 9 and Comparative Example 12, it was 3 times in Comparative Example 1-Comparative Example 4, Comparative Example 10, and Comparative Example 11.

  As for the minimum diameter of the single crystal, Examples 1 and 4 had an average of 6.5 mm, Examples 2 and 5 had an average of 6.6 mm, and Examples 3 and 6 had an average of 7.2 mm. The single crystal could be pulled up. However, in Comparative Examples 5 to 7, the diameter of the single crystal was too thin than the target minimum diameter of 6.0 mm, and it was not possible to grow a high-weight single crystal.

  From the above, according to the method for producing a silicon single crystal of the present invention, in the narrowed-down portion and the diameter-expanded portion, without having to repeat the diameter reduction or diameter expansion, by having the minimum diameter of the target single crystal, High weight single crystal rods can be grown. In addition, it is possible to prevent dislocations in the narrowed portion and the enlarged diameter portion, and to produce a single crystal having a high dislocation-free rate. Furthermore, since the single crystal can be efficiently grown by increasing the pulling speed as much as possible, the silicon single crystal can be manufactured with high productivity.

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

It is the figure which showed the relationship between the pulling-up speed in the manufacture of the silicon single crystal in this invention, heater power, and the diameter of a single crystal. It is the schematic which shows the shape of the narrowing-down part and enlarged diameter part of the single crystal manufactured by this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Seed crystal, 2 ... Tip, 3 ... Restriction part, 4 ... Expanded diameter part, 5 ... Straight trunk | drum, W ... Minimum diameter.

Claims (3)

  Using the Czochralski method, a silicon seed crystal with a sharp tip is used to dissolve in the silicon melt from the tip to a position of a predetermined diameter, necking is performed to form a narrowed portion, and then the diameter is expanded to expand the diameter portion. In the method for producing a silicon single crystal in which a straight body portion is formed and the single crystal rod is pulled up, the melting of the seed crystal is completed, and the seed crystal starts to be pulled up to start the pulling up by controlling the heater power. The temperature of the silicon melt starts to decrease, and the pulling speed from the start of pulling to the start of formation of the straight body of the single crystal is at least two stages, and the pulling speed is 0 at the start of pulling. 0.3 mm / m at a timing within a range of 120% or more or 50% or more and less than 75% with respect to the time when the diameter of the narrowed-down portion becomes the minimum after that. Method for manufacturing a silicon single crystal, characterized by increased below n or 0.7 mm / min.   The timing is that the pulling speed at the start of the pulling is fixed to less than 0.3 mm / min, the single crystal is prototyped, the time when the diameter of the narrowed portion is minimized is determined, and the pulling speed is 2. The method for producing a silicon single crystal according to claim 1, wherein an increase timing is determined.   The narrowed portion is formed by continuously decreasing the diameter of the single crystal without increasing during the growth, and the expanded diameter portion formed below the narrowed portion reaches the straight body portion to be grown thereafter. 3. The method for producing a silicon single crystal according to claim 1, wherein the diameter of the single crystal is continuously increased without decreasing during the growth.

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