JP2010018494A - Growing method of silicon single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a growing method of a single crystal which can be suitably used for enhancing controllability of seed diameter in a necking process and controllability of single crystal diameter during the drawing-up in a diameter increasing process and a diameter fixing process. <P>SOLUTION: In the growing method of a silicon single crystal by CZ method, in the necking process where the seed diameter is reduced, rotation number of a crucible is set not higher than 0.1 rpm in the normal or reverse direction to the direction of the rotation of the seed crystal. In the necking process and the following diameter increasing process, the rotation number of the crucible is set similarly not higher than 0.1 rpm. It is desirable to adopt an embodiment in which the growth of silicon single crystal is carried out under a horizontal magnetic field of not lower than 0.1 T but not higher than 0.4 T. Since the target seed diameter can be set to the minimum diameter corresponding to the breaking limit at the weight of the drawing-up single crystal, dislocation is easy to come away and the dangerousness of the breaking at the neck part can be remarkably reduced. Variation in the drawing-up speed can be controlled by improving the controllability of the single crystal diameter and the yield of the product can also be enhanced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for growing a silicon single crystal by the Czochralski method (hereinafter referred to as “CZ method”), and more specifically, to prevent the fluctuation of the neck diameter in the drawing step, the rotational speed of the crucible. The present invention relates to a method for growing a silicon single crystal to be controlled.

  A silicon single crystal growth method by the CZ method is a method in which a silicon raw material for semiconductor is put into a crucible, heated and melted, and the seed crystal immersed in the melt is pulled up while rotating, so that the silicon single crystal is formed at the lower end of the seed crystal. This is a method for growing a crystal and is widely used as a method for producing a silicon single crystal used for a semiconductor substrate.

  FIG. 1 is a longitudinal sectional view schematically showing a configuration example of a main part of a single crystal pulling apparatus suitable for growing a silicon single crystal by the CZ method. As shown in FIG. 1, in this pulling device, a heater 1 for heating the silicon raw material supplied into the crucible 2 and maintaining it in a molten state is disposed substantially concentrically outside the crucible 2, and the vicinity of the outer periphery thereof. The heat insulating material 3 is attached to. The crucible 2 is composed of a quartz crucible 2a having a bottomed cylindrical shape and a graphite crucible 2b that holds the quartz crucible 2a, and is fixed to the upper end of a support shaft 4 that can rotate and move up and down. Has been.

  On the central axis of the crucible 2 filled with the molten liquid 5, a pulling wire 6 that rotates on the same axis as the support shaft 4 in the reverse direction or in the same direction at a predetermined speed is disposed. Holds the seed crystal 7.

  When pulling up a silicon single crystal using the pulling apparatus configured as described above, a predetermined amount of silicon raw material (generally using massive or granular polycrystalline silicon) is put into the crucible 2. The raw material is heated and melted by a heater 1 disposed around the crucible 2 in an inert gas (usually Ar) atmosphere under reduced pressure, and then the lower end of the pulling wire 6 is placed near the surface of the formed melt 5. The seed crystal 7 held in is immersed. Subsequently, the wire 6 is pulled up while rotating the crucible 2 and the pulling wire 6, and the single crystal 8 is grown on the lower end surface of the seed crystal 7.

  When pulling up, after adjusting the speed and the temperature of the silicon melt and reducing the diameter of the seed crystal 7 to form the neck portion 9, the neck portion diameter (hereinafter referred to as "seed diameter", Alternatively, the process proceeds to a diameter increasing step in which the cone 10 and further the shoulder 11 are formed. Subsequently, in the constant diameter step, a constant diameter body portion (straight body portion) 12 used as a material for the product wafer is formed. After the body portion 12 reaches a predetermined length, its diameter is gradually reduced to form a tail portion (not shown), and the foremost portion is pulled away from the melt 5 to form a silicon single crystal 8 having a predetermined shape. can get.

  In addition, when growing a silicon single crystal, a temperature distribution near the crystal growth interface is reduced by applying a transverse magnetic field to the silicon melt in the crucible, resulting in a uniform concentration distribution of dopants and other impurities. In recent years, the application of a transverse magnetic field at the time of pulling a single crystal has become widespread because of the advantage that the crystal growth rate can be increased. Usually, the strength of the magnetic field is 0.3 to 0.4 T (Tesla) in the constant diameter process.

  The drawing step is an essential step performed to remove high-density dislocations introduced into the seed crystal by heat shock when the seed crystal is brought into contact with the silicon melt. Dislocations are removed.

  However, in this squeezing process, the seed diameter may vary with temperature fluctuations (melt temperature fluctuations) due to convection of the silicon melt, and it may be difficult to maintain a single crystal that is partially thinned and grown. is there. In order to solve this problem, attempts have been made to prevent variation in the seed diameter by applying a magnetic field in the throttling step and further in the subsequent diameter increasing step.

  For example, in Patent Document 1, a crucible rotation speed is set to 1 rpm or less in a drawing process, a lateral magnetic field of 0.1 T or less is applied, and the magnetic field application is stopped at the stage of shifting from a drawing process to a diameter increasing process. A crystal growth method has been proposed.

  However, in the method described in Patent Document 1, the strength of the applied lateral magnetic field is adjusted to stabilize the seed diameter in the squeezing process. Since there was a fluctuation in the melt temperature (that is, over a long span in time) and there was a variation in the seed diameter, the controllability of the seed diameter was not sufficient. For this reason, it is necessary to increase the target seed diameter somewhat in consideration of the variation of the seed diameter, which makes it difficult for the dislocation to fall out, resulting in a decrease in yield.

  In particular, in response to the recent trend toward higher integration, lower cost, and improved productivity of semiconductor devices, wafers are also becoming larger in diameter, and the diameter and weight of silicon single crystal as the material has increased. Therefore, it is necessary to further improve the controllability of the seed diameter and to set the minimum diameter according to the fracture limit with the weight of the single crystal to be pulled up.

Moreover, in the diameter increasing process and the constant diameter process, the diameter of the single crystal during the pulling fluctuates due to the instability of the melt temperature, and the pulling speed must be changed to correct the fluctuation of the diameter. In other words, as a result, the target pulling speed deviates, and a single crystal having a predetermined quality may not be obtained.
JP 2004-83320 A

  The present invention has been made in view of such a situation, and by improving the controllability of the seed diameter in the squeezing process and stabilizing the seed diameter, dislocations are eliminated particularly when pulling up a large single crystal. A method for growing a silicon single crystal that can make the seed diameter as thin as possible and avoid the risk of breakage at the neck, and further, a diameter-increasing step following the drawing step, a constant diameter An object of the present invention is to provide a method for growing a silicon single crystal that can improve the controllability of the diameter of the single crystal during the pulling process, suppress the fluctuation of the pulling speed, and improve the product yield.

  In the course of repeated studies to solve the above problems, the present inventors have found that when the single crystal is pulled under application of a transverse magnetic field, the melt temperature fluctuates when the rotational speed of the crucible is zero. The experimental fact was obtained that it was the smallest and the seed diameter variation was minimized.

  When the crucible rotates too quickly, the melt temperature fluctuates greatly. On the other hand, there is also a meaning of avoiding local heating to the quartz crucible, and usually within the range of 2 rpm to 0.1 rpm. The inventors paid attention to the experimental facts described above, and examined the details by rotating the crucible at various rotational speeds, including the range outside the conventional range. As a result, it has been found that the variation in the seed diameter is minimized when the rotational speed of the crucible is 0.1 rpm or less (zero, that is, including a stationary state). It was found that the direction of rotation may be either the forward direction or the reverse direction with respect to the rotation direction of the seed crystal.

  Furthermore, the diameter controllability of the single crystal during the pulling is improved by performing the diameter increasing process from the drawing process in the same crucible rotation speed range (that is, 0.1 rpm or less) and then shifting to the constant diameter process. As a result, it was also found that the single crystal pulling rate can be maintained within a predetermined range, so that a single crystal having a predetermined quality can be obtained and the product yield can be improved.

  The present invention has been made based on such knowledge, and the gist thereof is the following method for growing a silicon single crystal.

  That is, in a method for growing a silicon single crystal by the CZ method in which a silicon single crystal is grown on the lower end of the seed crystal by rotating the seed crystal immersed in the silicon melt in the crucible while rotating the seed crystal, In the growing process, the crucible rotation speed is set to 0.1 rpm or less in the forward or reverse direction with respect to the rotation direction of the seed crystal. The above “0.1 rpm or less” includes the case where the crucible rotation speed is zero, that is, the case where only the seed crystal is rotated without rotating the crucible.

  In the silicon single crystal growth method of the present invention, the crucible rotation speed is set to 0.1 rpm or less in the forward or reverse direction with respect to the rotation direction of the seed crystal in the drawing step and the subsequent diameter increasing step (this) Can be referred to as “Embodiment 1”).

  In the silicon single crystal growth method (including the first embodiment) of the present invention, an embodiment is adopted in which the silicon single crystal is grown under application of a transverse magnetic field of 0.1 T or more and 0.4 T or less. It is desirable.

  According to the method for growing a silicon single crystal of the present invention (including the first embodiment), in the drawing step for reducing the seed diameter, controllability of the seed diameter can be improved and the seed diameter can be stabilized. As a result, the target seed diameter can be set to the minimum diameter according to the breaking limit in terms of the weight of each pulled single crystal, and it is possible to easily escape dislocations and avoid the risk of breaking at the neck portion. Become. Since the seed diameter can be minimized as required, this growing method is particularly effective for pulling a large weight single crystal. Further, according to the growing method of the present invention, the controllability of the diameter can be improved in the drawing step and the subsequent diameter increasing step, and the yield of the product can be improved by suppressing fluctuations in the pulling speed. .

  As described above, the method for growing a silicon single crystal according to the present invention is a squeezing step in which the seed crystal immersed in a silicon melt is pulled down to reduce the seed diameter in the method for growing a silicon single crystal by the CZ method. The method is characterized in that the speed is 0.1 rpm or less in the forward or reverse direction with respect to the rotation direction of the seed crystal. In the growth of a silicon single crystal, since a transverse magnetic field is generally applied, a single crystal under a transverse magnetic field application of 0.1 T or more and 0.4 T or less, which is a preferred embodiment of the present invention, will be described below. On the premise of growth, the method for growing a silicon single crystal of the present invention will be described.

  In the silicon single crystal growth method of the present invention, the crucible rotation speed is set to 0.1 rpm or less in the squeezing step to improve the controllability of the seed diameter to suppress the variation, and to increase the seed diameter. This is because each crystal is minimized according to the breaking limit of its weight. As shown in the examples described later, when the crucible rotation speed exceeds 0.1 rpm, the seed diameter varies due to the influence of the fluctuation of the melt temperature, but when the rotation speed is 0.1 rpm or less, the seed diameter is changed. No change is allowed. That is, in the growing method of the present invention, the seed diameter can be controlled by controlling the number of rotations of the crucible.

  In this case, it is desirable that the strength of the transverse magnetic field applied in the drawing process be in the range of 0.1T to 0.4T. Within this range, the concentration distribution of dopants and other impurities can be made uniform, the crystal growth rate can be increased, and the effect of applying a transverse magnetic field can be obtained. The effect of the present invention that it is possible to avoid the risk of breakage at the portion is also sufficiently exhibited. In actual operation, the strength of the transverse magnetic field is normally set to 0.3T to 0.4T. Therefore, it is sufficient to apply a transverse magnetic field at the level of actual operation or a range close to that level. It can be said that it may be adapted to the normal manufacturing conditions.

  The rotation direction of the crucible may be either the forward direction or the reverse direction with respect to the rotation direction of the seed crystal. The same effect can be obtained regardless of whether the rotation direction is normal or reverse.

  Note that the low speed control of the crucible rotation speed of 0.1 rpm or less performed in the growing method of the present invention can be carried out without problems by using an existing transmission.

  In the silicon single crystal growth method of the present invention, the crucible rotation speed is set to 0.1 rpm or less in the forward direction or the reverse direction with respect to the rotation direction of the seed crystal in the drawing step and the subsequent diameter increasing step. be able to. This is the growing method of the first embodiment.

  The reason why the rotation speed of the crucible is set to 0.1 rpm or less without changing the crucible rotation speed in the expansion process to the diameter increasing process is to prevent a change in convection due to the change in the crucible rotation speed. The crystal diameter controllability can be further improved.

  Conventionally, the melt temperature was not stable, and the diameter of the single crystal during the pulling was changed, so the pulling speed had to be changed. However, according to the growing method of this embodiment 1, the single crystal during the pulling was changed. Therefore, it is not necessary to change the pulling rate of the single crystal, and a single crystal having a predetermined quality can be obtained, so that the product yield can be improved.

  Also in this case, the strength of the applied transverse magnetic field is desirably set to a level (0.3T to 0.4T) in actual operation or within a range of 0.1T to 0.4T close to the level. Thereby, the effect of applying a transverse magnetic field is obtained, and the effect of improving the diameter controllability of the single crystal is sufficiently exhibited.

  As described above, in the method for growing a silicon single crystal of the present invention including the first embodiment, the seed diameter is controlled in the drawing process by controlling the number of revolutions of the crucible. In the subsequent diameter increasing step, the diameter of the single crystal being pulled is controlled to suppress and stabilize the variation of the seed diameter or the diameter of the single crystal.

  On the other hand, all of the conventionally proposed methods including the silicon single crystal growth method described in the above-mentioned Patent Document 1 are based on various changes in the strength of the applied magnetic field. In the method described in Patent Document 1, the rotational speed of the crucible is also important for suppressing variation in seed diameter, and it is necessary to keep the rotational speed as small as possible. When a transverse magnetic field of 1 T or less is applied, the rotational speed of the crucible is set to 1 rpm or less, but there is no change in the idea that the main body that suppresses the variation in seed diameter is the application of a transverse magnetic field.

  Table 1 compares the problem solving means for the method described in Patent Document 1 and the growing method of the present invention. Desired conditions are listed in parentheses. As for the problems, both of them are substantially the same, stabilizing the seed diameter in the drawing process and improving the controllability of the single crystal diameter in the diameter increasing process.

  As shown in Table 1, in the method described in Patent Document 1, the main means for solving the problem is the application of a transverse magnetic field, and the magnetic field strength is 0.1 T or less in each step of drawing, diameter increasing, and constant diameter, Zero and re-applying a magnetic field (preferably 0.1T to 0.4T) are changed for each step, and accordingly, the number of rotations of the crucible is changed for each step. On the other hand, in the growing method of the present invention, the crucible rotation speed is defined as ± 0.1 rpm or less in the drawing step and the diameter increasing step, and the desirable magnetic field strength is also constant within the range of 0.1T to 0.4T. It is. In the growth method of the present invention, “±” of the number of rotations of the crucible means “forward direction (+) or reverse direction (−)” with respect to the rotation direction of the seed crystal.

  As is clear from Table 1 (contrast table), the method for solving the problems of the growing method of the present invention is clearly different from the method described in Patent Document 1. Furthermore, in the growing method of the present invention, the control range of the number of revolutions of the crucible is ± 0.1 rpm or less in the drawing process and the diameter increasing process for growing a single crystal and is unchanged. In the constant diameter process, a crucible rotation speed suitable for the target crystal quality can be appropriately employed. Further, the strength of the magnetic field to be applied may be constant between 0.1T and 0.4T including the level (0.3T to 0.4T) in actual operation, and the application condition of the magnetic field is changed every time the process proceeds. There is also an advantage that it is easy to operate because it is not necessary.

  As described above, according to the method for growing a silicon single crystal of the present invention (including the first embodiment), in the drawing process, by controlling the number of revolutions of the crucible, the seed diameter is controlled and the fluctuation is suppressed. The seed diameter can be set to the minimum diameter corresponding to the breaking limit in terms of weight for each pulled single crystal. As a result, dislocation can be easily removed, and the risk of breakage at the neck portion can be remarkably reduced, so that the product yield can be improved.

  Further, in the drawing step and the subsequent diameter increasing step, the diameter of the single crystal being pulled can be controlled to suppress fluctuations in the diameter of the single crystal being pulled, so that the single crystal pulling speed can be kept within a predetermined range. It becomes possible to obtain a single crystal having a predetermined quality while maintaining it, and a silicon single crystal can be manufactured with a high product yield.

  A silicon single crystal having a diameter of 300 mm and a weight of about 300 kg was grown using the single crystal growth apparatus having the schematic configuration shown in FIG.

  At the time of pulling up, the target seed diameter is set to 5.0 mm in the drawing process, and the rotation speed of the crucible is set to 0 rpm (stationary), 0 in the positive direction with respect to the rotation direction of the seed crystal through the drawing process and the diameter increasing process. .1 rpm, 0.2 rpm or 0.5 rpm was changed, and the deviation of the seed diameter from the target value (difference from the target value) was investigated. The strength of the magnetic field to be applied was set to 0.3 T through the drawing, diameter increasing and constant diameter processes in accordance with normal manufacturing conditions.

  Table 2 shows the survey results. The numerical value in the column of “seed diameter” is the maximum value of the difference (absolute value) between the seed diameter measured over the entire neck portion and the target seed diameter, and is indicated by the sign “±”. For example, when the crucible rotation speed is 0.2 rpm, the seed diameter may be 5.0 ± 0.1 (mm) or 5.0 ± 0.2 (mm), but the difference from the target seed diameter (absolute Value) is 0.5 (mm), so it is 5.0 ± 0.5 (mm).

  As shown in Table 2, when the rotation speed of the crucible was 0.2 rpm or 0.5 rpm, a variation in the seed diameter was observed, but when the rotation speed was 0 rpm (stationary) and 0.1 rpm, the variation in the seed diameter was It was not recognized and could be controlled to the target seed diameter. Although not shown, it was confirmed that there was no difference in the survey results even if the crucible rotation direction was either the forward direction or the reverse direction with respect to the seed crystal rotation direction. In addition, when the crucible rotation speed was 0.2 rpm or 0.5 rpm, a change in diameter was observed in the diameter increasing process, but when the rotation speed was 0 rpm (stationary) and 0.1 rpm, the target diameter was increased in the diameter increasing process. Could be controlled on the street.

  The method for growing a silicon single crystal according to the present invention is a growth method in which the number of rotations of the crucible is set to 0.1 rpm or less in a drawing step for reducing the seed diameter in the method for growing a silicon single crystal by the CZ method. Controllability can be improved. This makes it possible to set the target seed diameter to the minimum diameter according to the breaking limit at the weight of each pulled single crystal, making it easy to escape dislocations and significantly reducing the risk of breaking at the neck. It becomes. This growing method is particularly effective in pulling a large single crystal.

  Moreover, according to the growing method of the present invention, the controllability of the diameter can be improved in the drawing step and the subsequent diameter increasing step, and a single crystal having a predetermined quality can be obtained while maintaining the pulling speed within a predetermined range. Product yield can be improved.

  Therefore, the method for growing a silicon single crystal of the present invention can be effectively used for manufacturing a silicon single crystal in the field of semiconductor device manufacturing.

It is a longitudinal cross-sectional view which shows typically the structural example of the principal part of the single crystal pulling apparatus suitable for the growth of the silicon single crystal by CZ method.

Explanation of symbols

1: heater, 2: crucible, 2a: quartz crucible, 2b: graphite crucible,
3: insulation material, 4: support shaft, 5: melt,
6: Pull-up wire, 7: Seed crystal, 8: Single crystal,
9: Neck part, 10: Cone,
11: Shoulder, 12: Body

Claims (3)

In the method of growing a silicon single crystal by the Czochralski method of growing a silicon single crystal on the lower end of the seed crystal by pulling up the seed crystal immersed in the silicon melt in the crucible while rotating,
Growing a silicon single crystal characterized in that, in the drawing step of reducing the seed diameter while pulling up the seed crystal, the rotational speed of the crucible is set to 0.1 rpm or less in the forward or reverse direction with respect to the rotation direction of the seed crystal. Method.   2. The silicon single unit according to claim 1, wherein in the drawing step and the subsequent diameter increasing step, the crucible rotation speed is set to 0.1 rpm or less in the forward direction or the reverse direction with respect to the rotation direction of the seed crystal. Crystal growth method.   The method for growing a silicon single crystal according to claim 1, wherein the silicon single crystal is grown under application of a transverse magnetic field of 0.1 T or more and 0.4 T or less.

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