JP2009249253A - Method for manufacturing silicon single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a silicon single crystal, which copes with such a situation that a silicon raw material for a semiconductor is insufficient. <P>SOLUTION: After pulling a silicon single crystal 4, a solidified silicon 3b of a melt 3a remaining in a crucible 1 is obtained. The obtained solidified silicon 3b is charged into the crucible 1 in place of a portion of a silicon raw material 8. Then, the silicon single crystal 4 is pulled from a silicon melt 3 obtained by melting the solidified silicon 3b and the silicon raw material 8. The blending ratio of the solidified silicon 3b is calculated based on the solidification rate at the time when pulling in single crystal growth for obtaining solidified silicon 3b is finished. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a silicon single crystal by the Czochralski method (hereinafter referred to as “CZ method”), and in particular, production of a silicon single crystal using a solidified melt that remains in a crucible after pulling the single crystal. Regarding the method.

  There are various methods for producing a silicon single crystal as a material for a semiconductor substrate. Among them, the CZ method is widely adopted.

  FIG. 1 is a diagram schematically showing a main configuration of a single crystal pulling apparatus suitable for pulling a silicon single crystal by the CZ method. The single crystal pulling apparatus is configured with a chamber (not shown) in its outer shell, and a crucible 1 is disposed at the center thereof. The crucible 1 has a double structure, and is composed of an inner quartz crucible 1a having a bottomed cylindrical shape and an outer graphite crucible 1b.

  The crucible 1 is fixed to the upper end of a support shaft 6 that can rotate and move up and down. A resistance heating type heater 2 is disposed outside the crucible 1 so as to surround the crucible 1. Above the crucible 1, a pulling shaft 5 such as a wire rotating on the same axis as the support shaft 6 in the reverse direction or in the same direction at a predetermined speed is disposed. Is attached.

  When pulling up a silicon single crystal for semiconductors using such a single crystal pulling apparatus, a polycrystalline silicon raw material commonly used in the manufacture thereof is put into the crucible 1 and an inert gas atmosphere under reduced pressure. The silicon raw material is melted in the crucible 1 by heating with the heater 2. Thereafter, the seed crystal 7 held at the lower end of the pulling shaft 5 is immersed in the surface of the silicon melt 3 formed in the crucible 1 and the pulling shaft 5 is gradually moved while rotating the crucible 1 and the pulling shaft 5. Pull up. Thereby, the silicon single crystal 4 is grown below the seed crystal 7.

  And the end material generated by the cutting process from the pulled silicon single crystal 4 has high purity, and is reused as a silicon raw material for semiconductors (see, for example, Patent Document 1). The end material is a shoulder part and a tail part formed above and below a straight body part handled as a product, and a part included in the straight body part. However, slip dislocation, oxidation-induced stacking fault (OSF), etc. are remarkable. A crystal defect portion and a non-standard portion where the resistivity, oxygen concentration, etc. do not satisfy the standard correspond.

  On the other hand, the silicon melt remaining at the bottom of the quartz crucible after pulling up the silicon single crystal (hereinafter also referred to as “residual melt”) is discarded or solidified (hereinafter referred to as “silicon solidified material”). It is diverted to silicon raw materials for solar cells. In this diversion, it is necessary to remove the adhered quartz pieces, which are impurities harmful to the solar cell, from the silicon coagulated material. To realize this, for example, Patent Document 2 discloses a silicon coagulated material to which quartz is adhered, There has been proposed a quartz removal method in which a portion having a large particle size and having a small particle size is removed by sieving or specific gravity separation after pulverization under a predetermined condition using a rotary pulverizer.

  As a silicon raw material for solar cells, in addition to a silicon solidified material, a material that has a high impurity concentration and does not satisfy the purity required as a silicon raw material for semiconductors is used. This is because the quality standard of the silicon single crystal for solar cells is significantly looser than that of the silicon single crystal for semiconductor, and there is no problem even if the impurity concentration in the silicon raw material is somewhat high.

JP 2005-112669 A JP 2002-37617 A

  By the way, polycrystalline silicon raw materials used in the production of silicon single crystals for semiconductors are in a chronic shortage in the market due to factors such as the rapid increase in demand for silicon raw materials for solar cells in recent years. Is in the situation. For this reason, there is a possibility that the silicon raw material for the semiconductor may be insufficient, and it is not possible to sufficiently cope with this situation only by reusing the above-mentioned silicon single crystal end material.

  Under such circumstances, if the above-mentioned silicon solidified material that has been discarded or diverted into a silicon raw material for solar cells can be reused as a silicon raw material for semiconductors, there will be a shortage of silicon raw materials for semiconductors. Respond to the situation. However, as in the case of using the silicon coagulated material as a silicon raw material for solar cells, the following problems occur when the silicon solid material is used as a silicon raw material for semiconductors. In a silicon single crystal, not only the concentration of impurities such as metals increases extremely, but also the carbon concentration and lifetime value increase, and a portion that does not satisfy the quality standard is generated. Furthermore, when a silicon single crystal having a remarkably high impurity concentration flows into a subsequent process, especially in a wafer processing process, the entire line including the process may be contaminated, and the contamination may be spread to the wafer line or the entire factory.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a silicon single crystal that can cope with a situation where a silicon raw material for a semiconductor is insufficient.

  In order to achieve the above object, the present inventor has studied in detail the growth status of a silicon single crystal, and a silicon solidified product based on an uncrystallized residual melt remaining in the crucible after pulling up the silicon single crystal. Focused on.

  That is, when a silicon single crystal is grown by the CZ method, impurities contained in the silicon melt before pulling are distributed to the solid phase silicon single crystal and the liquid phase silicon melt. As a result, the impurity concentration in the silicon single crystal is much lower than the impurity concentration in the silicon melt.

  This is because the solubility of impurities in a silicon single crystal that is a solid phase is lower than the solubility of impurities in a silicon melt that is a liquid phase. The ratio “solubility in the solid phase / solubility in the liquid phase” is referred to as a segregation coefficient, which is constant when the impurity concentration is small, and is unique to each impurity element.

For example, taking copper (Cu), aluminum (Al), and carbon (Cs) as impurities, the segregation coefficients are 4 × 10 ^{−4 for} copper, 2 × 10 ^{−3 for} aluminum, and carbon for carbon. 7 × 10 ⁻² . Copper is an element used in a part of the pulling apparatus, and aluminum is an element contained as an impurity in the quartz crucible. Carbon is also used as a hot zone component in a lifting device such as a graphite crucible for holding a quartz crucible, a heater disposed around the crucible, and the like. All of these elements are easily mixed as impurities into the silicon single crystal, and among them, carbon used in many parts in the pulling apparatus is particularly easily mixed.

FIG. 2 is a diagram showing the relationship between the solidification rate in the growth of a silicon single crystal and the impurity concentration in the single crystal. The relationship shown in the figure is shown in accordance with a well-known formula (1) below that gives impurities concentration [C] _S in a silicon single crystal (solid phase) when copper, aluminum, and carbon are used as impurities and the solidification rate is g. . In FIG. 2, the vertical axis indicates the impurity concentration in the silicon single crystal, and the horizontal axis indicates the solidification rate. The “solidification rate” is a ratio of the mass ratio of the silicon single crystal to the amount of silicon melt in the crucible before pulling up the silicon single crystal.
[C] _S = k ₀ [C] ₀ (1-g) ^k0-1 (1)

From the above equation (1), the impurity concentration in the silicon single crystal corresponding to the change in the solidification rate can be obtained. In the equation, k ₀ is the segregation coefficient of each impurity, and [C] ₀ is the initial concentration of the impurity in the silicon melt (liquid phase) before solidification starts. FIG. 2 shows a state where the initial concentrations [C] ₀ of copper, aluminum, and carbon as impurities are all set to 1 × 10 ¹⁵ atoms / cm ³ .

As is apparent from FIG. 2, the concentration of each impurity in the silicon single crystal as a solid phase is significantly lower than the initial concentration (1 × 10 ¹⁵ atoms / cm ³ ) of each impurity in the silicon melt. In addition, for all of copper, aluminum, and carbon, the impurity concentration is low on the top side of the silicon single crystal (the solidification rate is close to 0), and gradually increases as the solidification rate increases, and the bottom side (solidification). On the side where the rate is close to 1.0), it increases rapidly.

After the silicon single crystal is pulled by such segregation of impurity elements, the impurity concentration [C] _S in the silicon single crystal is calculated from the above equation (1) based on the solidification rate g at the end of the pulling. Can be calculated. Furthermore, the impurity concentration [C] _L in the residual melt in the crucible at that time can be calculated from the impurity concentration [C] _S in the silicon single crystal according to the following known formula (2).
[C] _L = [C] _S / k ₀ = [C] ₀ (1-g) ^k0-1 (2)

The residual melt in the crucible is then solidified to a silicon solid. The impurity concentration in the silicon coagulum coincides with the impurity concentration [C] _L in the residual melt, and is calculated based on the solidification rate g at the end of the pulling of the silicon single crystal from the above formula (2). be able to. Therefore, as is clear from the above equation (2), the impurity concentration in the silicon solidified product increases as the solidification rate at the end of single crystal pulling increases, and can be calculated from the solidification rate at that time.

  Since the concentration of impurities in the silicon solidified material is clear, the silicon solidified material can be used as a silicon melt with an appropriate impurity concentration in growing a silicon single crystal using the silicon solidified material as a part of the silicon raw material. The compounding ratio of the product can be set.

  The present invention is based on such a technical idea, and is a method for producing a silicon single crystal by the CZ method, wherein the melt solidified material and the silicon raw material remaining in the crucible after the silicon single crystal is pulled up are used. The crucible is charged in a crucible and melted, and the silicon single crystal is pulled up from the melt.

  Here, it is preferable to calculate the blending rate of the solidified product based on the solidification rate at the end of the pulling of the silicon single crystal, and to charge the solidified product with the calculated blending rate as the upper limit. Further, the pulling of the silicon single crystal from the melt obtained by melting the solidified material and the silicon raw material can be repeated a plurality of times.

  According to the method for producing a silicon single crystal of the present invention, the melt solidified material remaining in the crucible after the silicon single crystal is pulled by the CZ method is reused as a part of the silicon material. As a result, it becomes possible to cope with a situation where the silicon raw material for semiconductor is insufficient.

  Hereinafter, an embodiment of the method for producing a silicon single crystal for semiconductor of the present invention will be described in detail. The method for producing a silicon single crystal according to the present embodiment is prepared by charging a melt solidified material remaining in the crucible and the silicon raw material into the crucible at a predetermined blending ratio after the silicon single crystal is pulled up. It is characterized by pulling up the silicon single crystal from the liquid.

  In a simple example, the silicon single crystal is pulled twice by the CZ method, and the first pulling is performed using a polycrystalline silicon raw material commonly used for the production of silicon single crystals for semiconductors. After the single crystal is pulled up to obtain a solidified product of the remaining melt, the single crystal is pulled up using the solidified product as a part of the silicon raw material in the second pulling up.

  FIG. 3 is a diagram schematically showing steps in a method for producing a silicon single crystal according to an embodiment of the present invention. As shown in FIG. 1A, a predetermined amount of polycrystalline silicon raw material 8 commonly used in the production of semiconductor silicon single crystals is put into a crucible 1 and heated by a heater. As a result, a silicon melt 3 in which the silicon raw material 8 is melted is obtained as shown in FIG.

  Subsequently, as shown in FIG. 3C, the seed crystal 7 is immersed in the surface of the silicon melt 3 in the crucible 1 and pulled upward according to normal manufacturing conditions. Thereby, the silicon single crystal 4 is grown below the seed crystal 7 as shown in FIG. Residual melt (silicon melt) 3a remains in the crucible 1 after pulling up the silicon single crystal 4. The remaining melt 3a is solidified to become a silicon solid 3b (see FIG. 5E).

  Next, as shown in FIG. 5E, the silicon solidified product 3b in the crucible 1 is taken out. At this time, a lot of quartz pieces peeled off from the crucible 1 (quartz crucible) are attached to the silicon solidified product 3b, and it is necessary to remove the quartz pieces in order to reuse the silicon solidified product 3b. For this purpose, the silicon solidified product 3b is washed. For this cleaning, for example, the silicon coagulated material 3b with the quartz piece adhered is immersed in hydrofluoric acid to dissolve the quartz piece, and further etched with hydrofluoric acid to remove contaminants attached to the surface. A method of performing pure water cleaning is preferred. Thereby, the quartz piece is completely removed from the silicon solidified product 3b.

  Furthermore, when the silicon solidified material 3b is reused, it can be crushed into a mass that can be easily melted. In this way, a silicon solidified product 3b that replaces a part of the silicon raw material 8 for semiconductor is obtained.

  Next, as shown in FIG. 5F, the high-purity silicon raw material 8 with very few impurities and the silicon coagulated material 3b are charged in the crucible 1 at a predetermined blending ratio and heated by a heater. As a result, as shown in FIG. 5G, a silicon melt 3 in which the silicon raw material 8 and the silicon solidified product 3b are melted is obtained.

  Subsequently, as shown in FIG. 6H, the seed crystal 7 is immersed in the silicon melt 3 in the crucible 1 and pulled upward in accordance with the same manufacturing conditions as in the step shown in FIG. As a result, as shown in FIG. 6I, the silicon single crystal 4 is grown below the seed crystal 7 as in the step shown in FIG.

  Even in the step shown in FIG. 6 (i), since the residual melt 3a remains in the crucible 1, the silicon solidified product 3b of the residual melt 3a is shown in FIG. The silicon single crystal 4 can be grown by performing the steps shown in (f) to (i) of FIG. That is, the steps shown in FIGS. 5E to 5I can be repeated a plurality of times.

  According to such a method for producing a silicon single crystal, the melt solidified material remaining in the crucible after pulling up the silicon single crystal is reused as a part of the silicon material. The amount can be reduced. As a result, it becomes possible to cope with a situation where the silicon raw material for semiconductor is insufficient.

  Here, in order to obtain a silicon single crystal having no problem in quality, it is important to determine the mixing ratio of the silicon solidified material and the silicon raw material charged in the crucible. Since the silicon solidified product contains impurities that were not taken into the silicon single crystal in the growth of the silicon single crystal to obtain this, if too much silicon solidified material is charged when growing the silicon single crystal, This is because the concentration of impurities in the grown single crystal may be out of specification.

For this reason, in this embodiment, the solidification rate is preferentially managed, and the blending ratio of the silicon solidified material and the silicon raw material charged in the crucible is set according to the following method. First, from the solidification rate g at the end of pulling of the silicon single crystal, the concentration [C] _L of the impurity in the residual melt, that is, the silicon coagulum, is calculated based on the equation (2).

Further, the impurity concentration in the silicon melt when the silicon solidified material is melted using a part of the silicon raw material is the initial concentration [C] of the impurity in the initial silicon melt employed in the single crystal growth. _From the concentration [C] _L of impurities in the silicon coagulum, the blending ratio of the silicon coagulum charged in the crucible is calculated so as to match ₀ . Then, together with the silicon raw material, the silicon solidified material is charged into the crucible with the calculated blending ratio as the upper limit, and the single crystal is pulled up from the silicon melt obtained by melting these. Thereby, a silicon single crystal having an impurity concentration that satisfies the standard can be grown.

For example, with reference to FIG. 1, the carbon having the largest segregation coefficient among the impurities will be considered. The initial concentration [C] ₀ of carbon in the initial silicon melt before pulling up the single crystal is set to 1 × 10 ¹⁵ atoms / cm ^3, and the solidification rate g is 0.9 by pulling up the silicon single crystal from the silicon melt. When the pulling is finished at the time, the carbon concentration [C] _S in the silicon single crystal becomes 5.96 × 10 ¹⁴ atoms / cm ³ based on the formula (1), and the residual melt, that is, in the silicon solidified material, The carbon concentration [C] _L is 8.51 × 10 ¹⁵ atoms / cm ³ based on the equation (2).

Using this silicon coagulum as part of the silicon raw material, the compounding ratio of the silicon coagulum at which the initial concentration [C] ₀ of carbon in the initial silicon melt is 1 × 10 ¹⁵ atoms / cm ³ is 1 × 10 ^{15 /} 8.51 × 10 ¹⁵ = 0.118 (11.8%). Therefore, if the silicon solidified material charged in the crucible together with the silicon raw material is 11.8% or less, the initial concentration [C] ₀ of carbon in the initial silicon melt obtained by melting these is 1 × 10 ¹⁵ atoms / Can be guaranteed to be cm ³ or less. As a result, the silicon single crystal pulled from the silicon melt has no problem in quality.

FIG. 4 is a diagram showing an example of the relationship between the impurity concentration in the silicon coagulum and the compounding ratio of the silicon coagulum. The relationship shown in the figure shows the blending ratio of silicon coagulum required for the impurities to be copper, aluminum, and carbon and the initial concentration of impurities in the initial silicon melt to be 1 × 10 ¹⁵ atoms / cm ³ . . As shown in the figure, the relationship between the impurity concentration in the silicon coagulum and the blending ratio of the silicon coagulum is substantially the same for any impurity element. From this figure, if the impurity concentration in the silicon solidified substance is clear, the blending ratio of the silicon solidified substance can be set.

  However, if the initial concentration of each impurity in the initial silicon melt is uniform in the growth of a single crystal to obtain a silicon solidified product, the concentration of each impurity in the silicon solidified product is theoretically the segregation coefficient. In order from the smallest element, that is, in the order of copper, aluminum, and carbon, the value is small but lower. Therefore, if the impurity element with the smallest segregation coefficient, that is, the concentration of copper is controlled and the compounding ratio of silicon coagulum is set, the silicon melt using the silicon coagulum as a part of the silicon raw material will contain other impurities. The concentration of elements, that is, aluminum and carbon is also sufficiently suppressed.

  By the way, in actuality, in the growth of a single crystal to obtain a silicon solidified product, the initial concentration of each impurity in the initial silicon melt is not uniform, and the carbon concentration is higher than the concentration of other impurity elements. Become. This is because carbon is used in many parts in the pulling device and is easily mixed into the silicon melt. For this reason, in actual operation, it is preferable to set the blending ratio of silicon coagulum by managing the concentration of carbon.

FIG. 5 is a diagram showing an example of the relationship between the solidification rate at the end of pulling of the single crystal from which the silicon solidified product was obtained and the blending rate of the silicon solidified product. The relationship shown in the figure is that the ratio of silicon coagulum in practical operation required for the impurity to be copper, aluminum, and carbon and the initial concentration of the impurity in the initial silicon melt to be 1 × 10 ¹⁵ atoms / cm ^3. Is shown. As the solidification rate at the end of the pulling of the single crystal increases due to segregation of the impurity elements, the concentration of impurities in the silicon solidified material increases, and actually, when the solidification rate is 0.9, carbon, aluminum, The concentrations of copper are about 1 × 10 ¹⁶ , 1 × 10 ¹³ , and 1 × 10 ¹¹ atoms / cm ³ , respectively. That is, even in the case of silicon solidified products having the same solidification rate, the concentration of carbon among impurities becomes the highest.

  For this reason, as shown in FIG. 5, it is necessary to set the reduction rate of the silicon solidified compound as the solidification rate at the end of the pulling of the single crystal increases. Thus, it is preferable to set the blending ratio of the silicon coagulum. This is because if the compounding ratio of the silicon coagulated material is set by paying attention to impurity elements other than carbon, the silicon melt using the silicon coagulated material as a part of the silicon raw material has an excessive carbon concentration.

  In any case, from the solidification rate at the end of pulling of the single crystal, it is possible to set an appropriate blending rate of silicon coagulum, and there is a quality problem from the silicon melt using this silicon coagulum as part of the silicon raw material. It is possible to grow a silicon single crystal without any defects.

  In order to confirm the effect of the method for producing a silicon single crystal of the present invention, the following test was conducted. In the test of this example, a crucible having an inner diameter of 22 inches was used. First, a polycrystalline silicon raw material was charged in a total weight of 140 kg, and the silicon single crystal was pulled up from the silicon melt obtained by heating and melting. It was. This was performed in three batches, and in each case, a silicon coagulated material based on the residual melt in the crucible was produced. At this time, the impurity concentration in the silicon coagulum is calculated from the solidification rate at the end of single crystal pulling for each batch, and these impurity concentrations are weighted and averaged, and three batches of silicon coagulum are obtained from this weighted average value. The upper limit of the blending ratio was calculated. The upper limit of the blending ratio of the three batches of silicon coagulum was 35%.

  Next, together with the polycrystalline silicon raw material, the three batches of silicon solidified material are mixed in a crucible at a blending ratio of 28%. After heating and melting, the silicon melt is pulled up to obtain a silicon single piece having a diameter of 200 mm. Crystals were grown. At that time, the temperature distribution in the apparatus and the pulling speed are adjusted, and pulling is performed under a growth condition in which a defect-free crystal region in which no grown-in defects such as infrared scatterer defects (COPs) and dislocation clusters exist is formed. Went.

  A sample wafer was sampled from the obtained silicon single crystal and evaluated for quality. Specifically, the oxygen concentration, specific resistance, OSF density, LPD (Light Point Defect) density, and BMD (Bulk Micro Defect) density of the sample wafer were evaluated. For comparison, the same evaluation was performed for the case where all the conventional polycrystalline silicon raw materials were used (normal raw materials).

Quality evaluation was performed by the following method.
Oxygen concentration: Based on the infrared absorption method prescribed | regulated to ASTMF121-1979, it measured using the Fourier transform type | mold infrared spectrophotometer (FTIR: Fourier Transform Infrared Spectrometer).

  Specific resistance: After a donor killer heat treatment (650 ° C. × 30 minutes) was performed on the silicon wafer, the specific resistance was measured by a specific resistance measuring device (four deep needle contact method).

OSF density: The silicon wafer was heat-treated at 1140 ° C. for 2 hours in a wet oxygen (Wet-O ₂ ) atmosphere, then the wafer surface was etched, and the OSF density on the wafer surface was measured with an optical microscope.

  LPD density: The number of LPDs having a size of 200 μm or more and LPDs having a size of 300 μm or more present on the wafer surface was counted using a light scattering particle counter (SP1 manufactured by KLA-Tencor) on the wafer surface.

  BMD density: After performing heat treatment on a silicon wafer at 780 ° C. for 3 hours and further at 1000 ° C. for 16 hours, the wafer was cleaved, and light etching was performed to etch the cross section by 2 μm, and then BMD in the cross section Was counted with an optical microscope.

  The evaluation results are shown in Table 1 below.

  From the results of Table 1, the quality of the sample wafer collected from the obtained silicon single crystal is different from the case of using the normal raw material even if the silicon solid based on the residual melt is used as a part of the silicon raw material. There wasn't.

  According to the method for producing a silicon single crystal of the present invention, the melt solidified material remaining in the crucible after the silicon single crystal is pulled up is reused as part of the silicon material, so that the amount of silicon material used can be reduced. As a result, it becomes possible to cope with a situation where silicon raw materials for semiconductors are insufficient. Therefore, the present invention is an extremely useful technique for producing a silicon single crystal by the CZ method.

It is a figure which shows typically the principal part structure of the single crystal pulling apparatus suitable for implementing the pulling of the silicon single crystal by CZ method. It is a figure which shows the relationship between the solidification rate in the growth of a silicon single crystal, and the impurity concentration in a single crystal. It is a figure which shows typically the process in the manufacturing method of the silicon single crystal which is one Embodiment of this invention. It is a figure which shows an example of the relationship between the impurity concentration in a silicon solidified material, and the compounding ratio of a silicon solidified material. It is a figure which shows an example of the relationship between the solidification rate at the time of completion | finish of a single crystal pulling with which the silicon solidified material was obtained, and the compounding rate of a silicon solidified material.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crucible 1a Quartz crucible 1b Graphite crucible 2 Heater 3 Raw material melt 3a Remaining melt 3b Solidified material 4 Nitrogen dope silicon single crystal 5 Lifting shaft 6 Support shaft 7 Seed crystal 8 Silicon material 9 High purity nitrogen dopant material 10 Crushed material

Claims (3)

A method for producing a silicon single crystal by the Czochralski method,
A method for producing a silicon single crystal, comprising: melting and solidifying a melt solidified in a crucible and a silicon raw material in a crucible after the silicon single crystal is pulled up; and pulling the silicon single crystal from the melt.   2. The silicon single crystal according to claim 1, wherein a blending ratio of the solidified substance is calculated based on a solidification ratio at the end of pulling of the silicon single crystal, and the solidified substance is charged with the calculated blending ratio as an upper limit. Manufacturing method.   3. The method for producing a silicon single crystal according to claim 1, wherein the pulling of the silicon single crystal from a melt obtained by melting the solidified material and the silicon raw material is repeated a plurality of times.

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