Method for producing silicon single crystal

Abstract

This contributes to the removal of bubbles in the melt.SOLUTION: A melting step of heating and melting a crystal raw material in a quartz crucible by a heater to generate a raw material melt, and a growing step of immersing a seed crystal in the raw material melt and pulling up the seed crystal to grow a silicon single crystal, before the growth step, a first soaking step of applying a magnetic field to the raw material melt and leaving the raw material melt to stand while increasing an applied intensity, and a second soaking step of leaving the raw material melt to stand while decreasing the applied intensity are included, and at least one or more of a gas flow rate, a furnace pressure, a quartz crucible position, a radiation shield position, or a quartz crucible rotation speed are set to different conditions between the first soaking step and the second soaking step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a silicon single crystal. [Background technology]

[0002] The Czochralski method (hereinafter referred to as the "CZ method") is widely used for growing silicon single crystals. In this method, a seed crystal is brought into contact with the surface of molten silicon contained in a crucible, and while the crucible is rotated, the seed crystal is pulled upward while rotating in the opposite direction, thereby forming a single crystal at the bottom of the seed crystal.

[0003] In the CZ method, polysilicon is first loaded into a quartz glass crucible and heated to form a silicon melt. A seed crystal attached to a pulling wire is then brought into contact with the silicon melt and pulled to grow a silicon single crystal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-201757 Summary of the Invention [Problem to be solved by the invention]

[0005] The disclosures of the above-mentioned prior art documents are incorporated herein by reference. The following analysis has been carried out by the present inventors.

[0006] During the pulling of silicon single crystals, bubbles present in the silicon melt can become trapped in the silicon single crystal, resulting in defects known as air pockets. To address this issue, in some silicon single crystal manufacturing methods, a "soaking" process is performed to remove bubbles from the melt after polycrystalline silicon melting, before starting single crystal growth. The bubbles in the melt are believed to be primarily attached to the inner surface of the quartz crucible. The soaking process is expected to stimulate convection in the melt, thereby removing the bubbles attached to the inner surface of the quartz crucible. For example, Patent Document 1 describes a method for removing bubbles from the melt during the soaking process by increasing the heater output and lowering the furnace pressure compared to when pulling the silicon single crystal.

[0007] However, in the soaking process, maintaining the melt in the quartz crucible at a high temperature was not enough to remove bubbles from the melt, so a more effective method for removing bubbles from the melt was required.

[0008] In view of the above-mentioned problems, an object of the present invention is to provide a method for producing a silicon single crystal that contributes to removing bubbles in the melt. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a method for producing a silicon single crystal by the Czochralski method, which includes a melting step in which a crystal raw material is heated and melted in a quartz crucible by a heater to produce a raw material melt, and a growing step in which a silicon single crystal is grown by immersing a seed crystal in the raw material melt and pulling the seed crystal upward, and which includes, before the growing step, a first soaking step in which a magnetic field is applied to the raw material melt and the raw material melt is left standing while the applied strength is increased, and a second soaking step in which the raw material melt is left standing while the applied strength is decreased, and is characterized in that the first soaking step and the second soaking step have different conditions for at least one of the gas flow rate, furnace pressure, quartz crucible position, radiation shield position, and quartz crucible rotation speed.

[0010] Furthermore, the present invention provides a method for producing a silicon single crystal by the Czochralski method, which includes a melting step in which a crystal raw material is heated and melted in a quartz crucible with a heater to produce a raw material melt, a growth step in which a silicon single crystal is grown by immersing a seed crystal in the raw material melt and pulling the seed crystal upward, a melt-back step in which, when dislocations occur in the silicon single crystal in the growth step, the silicon single crystal is re-melted in the raw material melt, and a second growth step after the melt-back step, and the method further includes, before the second growth step, a first soaking step in which a magnetic field is applied to the raw material melt obtained by remelting the silicon single crystal and the raw material melt is left standing while increasing the applied magnetic field strength, and a second soaking step in which the raw material melt is left standing while decreasing the applied magnetic field strength, and the first soaking step and the second soaking step have different conditions with respect to at least one of the gas flow rate, furnace pressure, quartz crucible position, radiation shield position, and quartz crucible rotation speed.

[0011] Furthermore, the present invention provides a method for producing a silicon single crystal by the Czochralski method, which includes a melting step in which a crystal raw material is heated and melted in a quartz crucible with a heater to produce a raw material melt, a growth step in which a silicon single crystal is grown by immersing a seed crystal in the raw material melt and pulling the seed crystal upward, a melt-back step in which, when dislocations occur in the silicon single crystal in the growth step, the silicon single crystal is re-melted in the raw material melt, and a second growth step after the melt-back step. The method further includes, before the growth step and the second growth step, a first soaking step in which a magnetic field is applied to the raw material melt or the raw material melt obtained by remelting the silicon single crystal, and the raw material melt is left standing while the applied magnetic field strength is increased, and a second soaking step in which the raw material melt is left standing while the applied magnetic field strength is decreased, and the first soaking step and the second soaking step are characterized in that at least one of the gas flow rate, furnace pressure, quartz crucible position, radiation shield position, and quartz crucible rotation speed is set to be different conditions.

[0012] In the method for producing a silicon single crystal of the present invention, bubbles can be removed from the melt more effectively by performing the first soaking step and the second soaking step under different conditions.

[0013] The first soaking step and the second soaking step in the method for producing a silicon single crystal are preferably performed in the following order: first soaking step, second soaking step, first soaking step, second soaking step. This is because a method for producing a silicon single crystal in which the first soaking step and the second soaking step are combined into one set and two sets of soaking are performed is more effective in removing bubbles from the melt than a method for producing a silicon single crystal in which only one set of soaking is performed.

[0014] In the method for producing a silicon single crystal, the gas flow rate in the first soaking step is preferably 0.8 times or less or 1.2 times or more the gas flow rate in the second soaking step. Furthermore, in the method for producing a silicon single crystal, the furnace pressure in the first soaking step is preferably 0.5 times or less or 2 times or more the furnace pressure in the second soaking step. This is because bubbles adhering to the inner surface of the crucible change in volume due to pressure changes, and bubbles in the melt are more effectively removed.

[0015] In the method for producing a silicon single crystal, it is preferable to relatively move the crucible position in either one of the first soaking step and the second soaking step (preferably the first soaking step) so that the upper end of the crucible is lower than the upper end of the heater, and to relatively move the crucible position in the other soaking step (preferably the second soaking step) so that the upper end of the crucible is at the same height as the upper end of the heater. Furthermore, in the method for producing a silicon single crystal, it is preferable to relatively move the radiation shield in either one of the first soaking step and the second soaking step (preferably the first soaking step) so that it is closer to the melt surface, and to relatively move the radiation shield in the other soaking step (preferably the second soaking step) to a height that ensures the flow rate of gas generated from the melt. This is because changes in melt convection due to changes in melt temperature more effectively remove bubbles in the melt.

[0016] In the method for producing silicon single crystals, it is preferable that the rotation speed of the quartz crucible in either the first soaking step or the second soaking step (preferably the first soaking step) is maintained at a speed that prevents the melt from spilling from the quartz crucible, and that the rotation speed of the quartz crucible in the other soaking step (preferably the second soaking step) is maintained at a relatively low speed. Furthermore, in the method for producing silicon single crystals, when the magnetic field is a horizontal magnetic field, it is preferable that the applied magnetic field strength (magnetic flux density) in the first soaking step is increased between steps from 1000 G or more, preferably 2000 G or more, and more preferably from 0 G to 2000 G or more, and that the applied magnetic field strength (magnetic flux density) in the second soaking step is decreased between steps from 1000 G or more, preferably 2000 G or more, and more preferably from 2000 G or more to 0 G. When the magnetic field is a cusp magnetic field, it is preferable to increase the applied magnetic field strength (magnetic flux density) in the first soaking step from 100 G or more, preferably 200 G, and more preferably 0 G to 200 G or more between steps, and to decrease the applied magnetic field strength (magnetic flux density) in the second soaking step from 100 G or more, preferably 200 G or more, and more preferably 200 G or more to 0 G between steps. This is because the change in friction between the melt and the crucible more effectively removes bubbles in the melt. [Effects of the Invention]

[0017] According to each aspect of the present invention, it is possible to provide a method for producing a silicon single crystal that contributes to removing bubbles in the melt. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a block diagram showing the overall configuration of a single crystal pulling apparatus 1 for carrying out a silicon single crystal manufacturing method according to the present invention. [Figure 2] FIG. 2 is a flowchart showing the steps of the method for producing a silicon single crystal according to the present invention. [Figure 3] FIG. 3 is a flowchart showing the procedures of the first soaking step and the second soaking step. [Figure 4]FIG. 4 is a diagram showing the configuration of the apparatus around the crucible in the first soaking step and the second soaking step. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the embodiments described below. In addition, the same or corresponding elements in each drawing are appropriately designated by the same reference numerals. Furthermore, it should be noted that the drawings are schematic, and the dimensional relationships and ratios of each element may differ from those in reality. There may also be parts in which the dimensional relationships and ratios differ between the drawings.

[0020] FIG. 1 is a block diagram showing the overall configuration of a single crystal pulling apparatus 1 for implementing the silicon single crystal manufacturing method according to the present invention. The apparatus configuration is shown, as an example, when the magnetic field is horizontal. The single crystal pulling apparatus 1 includes a furnace body 2 formed by stacking a pull chamber 2b on top of a cylindrical main chamber 2a, a crucible 3 provided within the furnace body 2, a heater 4 for melting a semiconductor raw material (raw polysilicon) M loaded into the crucible 3, and a pulling mechanism 5 for pulling a single crystal C to be grown. The crucible 3 has a double structure, with an inner quartz glass crucible 3a and an outer graphite crucible 3b. The pulling mechanism 5 includes a motor-driven winding mechanism 5a and a pulling wire 5b wound around the winding mechanism 5a, with a seed crystal P attached to the tip of the wire 5b.

[0021] Within the main chamber 2a, a radiation shield 6 is provided above and near the crucible 3. The radiation shield 6 has openings at the top and bottom to surround the single crystal C, and prevents the single crystal C from receiving unnecessary radiant heat from the heater 4 or the like during growth. The distance (gap) between the bottom end of the radiation shield 6 and the melt surface is set to be changeable to a predetermined distance (gap) depending on the characteristics of the single crystal to be grown.

[0022] Furthermore, in the single crystal pulling apparatus 1, an electric coil 13 for applying a magnetic field is installed outside the main chamber 2a, and the MCZ method (Magnetic field applied CZ method) is used, in which a horizontal magnetic field (a cusp magnetic field when a cusp-type magnetic field is applied) is applied to the silicon melt in the crucible 3 to grow a single crystal.

[0023] 1 also includes a heater control unit 9 that controls the amount of power supplied to a heater 4 that controls the temperature of the silicon melt M, a motor 10 that rotates the crucible 3, and a motor control unit 10a that controls the rotation speed of the motor 10. It also includes an elevator 11 that controls the height of the crucible 3, an elevator control unit 11a that controls the elevator 11, and a wire reel rotation device control unit 12 that controls the pulling speed and rotation speed of the growing crystal. It also includes an electric coil control unit 13a that controls the operation of an electric coil 13 for applying a magnetic field. Each of these control units 9, 10a, 11a, 12, and 13a is connected to an arithmetic and control device 8b of a computer 8.

[0024] The method for producing a silicon single crystal according to the present invention is carried out using the single crystal pulling apparatus 1 configured as described above. Figure 2 is a flowchart showing the steps of the method for producing a silicon single crystal according to the present invention.

[0025] As shown in FIG. 2, the method for producing a silicon single crystal includes a melting step (S1), a soaking step (S2), a growing step (S3), and a melt-back step (S4).

[0026] In the melting step (S1), a predetermined atmosphere (e.g., Ar gas) is created inside the furnace body 2 by the atmosphere control means, and the heater control unit 9 is activated by command from the arithmetic and control device 8b to heat the heater 4, thereby heating and melting the crystal raw material in the quartz crucible 3a to produce a raw material melt.

[0027] In the soaking step (S2), a predetermined process is performed on the silicon melt M to remove bubbles from the silicon melt M. The soaking step (S2) includes a first soaking step in which a magnetic field is applied to the raw material melt and the raw material melt is left standing while increasing the applied magnetic field strength, and a second soaking step in which the raw material melt is left standing while decreasing the applied magnetic field strength. Details of the processes in the first and second soaking steps will be described later, but in the present invention, the first and second soaking steps have different conditions for one or more of the gas flow rate, furnace pressure, quartz crucible position, radiation shield position, and quartz crucible rotation speed. Furthermore, in the soaking step (S2) of the present invention, after the change in the applied magnetic field strength has ended, the raw material melt can be left standing while maintaining the same conditions for any or all of the gas flow rate, furnace pressure, quartz crucible position, radiation shield position, and quartz crucible rotation speed.

[0028] Thereafter, in the growth step (S3), a seed crystal P is immersed in the raw material melt M and then pulled up to grow a silicon single crystal. In response to a command from the arithmetic and control device 8b, the wire reel rotation device control unit 12 is activated, and the winding mechanism 5a is activated to lower the wire 5b. Then, the seed crystal P attached to the wire 5b is brought into contact with the silicon melt M, and the winding mechanism 5a pulls up the wire 5b while growing a silicon single crystal C.

[0029] In the melt-back step (S4), the silicon single crystal C is remelted. During the pulling and growing of a silicon single crystal, dislocations may occur due to various disturbances. If dislocations occur, the value of the silicon single crystal grown thereafter as a product will be diminished. Therefore, if dislocations occur in the single crystal at a relatively early stage in the growing step (S3), the grown single crystal is remelted and the growing step (S3) is performed again. In the present invention, a soaking step (S2) can be performed before this growing step (S3) again.

[0030] 3 is a flowchart showing the procedures of the first soaking step and the second soaking step. As shown in FIG. 3, the soaking step (S2) is performed in the order of the first soaking step (S21a), the second soaking step (S22a), the first soaking step (S21b), and the second soaking step (S22b). In other words, if the first soaking step and the second soaking step constitute one set, then two sets of these will be performed. Note that the first soaking step (S21a) and the first soaking step (S21b), and the second soaking step (S22a) and the second soaking step (S22b) performed in this order can each be performed under the same conditions.

[0031] Below, we will explain the phenomena that are presumed to occur in the melt when the present invention is implemented, using as examples the following conditions: in the first soaking step, the gas flow rate is 0.8 times or less the gas flow rate in the second soaking step, the furnace pressure is at least twice the furnace pressure in the second soaking step, the crucible position is moved relatively so that the top of the crucible is lower than the top of the heater, the radiation shield is moved relatively so that it is closer to the melt surface, the quartz crucible rotation speed is set to a speed at which the melt does not spill out of the quartz crucible, and the applied magnetic field strength is increased between steps; and in the second soaking step, the crucible position is moved relatively so that the top of the crucible is at the same height as the top of the heater, the radiation shield is moved relatively to a height that ensures the gas flow rate generated from the melt, the quartz crucible rotation speed is set to a relatively slow speed, and the applied magnetic field strength is decreased between steps. In the first soaking process, the Ar gas flow is throttled while ensuring a flow rate that allows the SiO generated from the melt to be exhausted. As shown in Figure 4(a), the crucible 3 is moved relative to the heater so that its upper end is lower than the upper end of the heater. The radiation shield 6 is positioned so that it is close to the melt surface. The rotation of the crucible 3 is maintained at a speed that prevents the melt from spilling out of the quartz crucible. The pressure inside the furnace is set high enough to ensure that the SiO generated from the melt is exhausted. The strength of the applied magnetic field is gradually increased during this process.

[0032] In the second soaking process, the Ar gas is increased while ensuring the flow rate at which SiO generated from the melt is exhausted. As shown in Figure 4(b), the crucible 3 is raised until the top of the heater 4 and the top of the crucible are roughly the same height. The radiation shield 6 is raised relatively while ensuring the gas flow rate at which SiO generated from the melt is exhausted. The rotation of the crucible 3 is kept slow. The temperature inside the furnace is set low enough to prevent the melt from boiling. The strength of the applied magnetic field is gradually reduced during this process.

[0033] By changing the Ar gas flow rate and furnace pressure during the first and second soaking processes, the volume changes (expansion and contraction) caused by pressure changes in the bubbles adhering to the inner surface of the quartz crucible are promoted, facilitating their removal. The positions of the crucible 3 and radiation shield 6 promote the removal and dissolution of bubbles and microscopic scratches that are the source of bubbles that occur on the inner surface of the quartz crucible due to changes in melt convection caused by changes in melt temperature. The lower limit of friction between the melt and the quartz crucible can be changed by changing the rotation of the crucible 3 and the strength of the applied magnetic field, promoting the removal and dissolution of bubbles and microscopic scratches that are the source of bubbles that occur on the inner surface of the quartz crucible.

[0034] By including the above soaking step in the method for producing a silicon single crystal, it is possible to suppress the occurrence of air pockets in the silicon single crystal, and by promoting stirring of the melt, it is possible to eliminate temperature variations in the melt in the quartz crucible, thereby creating a stable environment for growing the single crystal. In the present invention, the soaking step can be performed before the growth step or before the second growth step when performing the melt-back step, and it is preferable to apply it before either the growth step or the second growth step.

[0035] [Example] Here, we will explain the effects of a silicon single crystal manufacturing method in which the conditions for the first soaking step and the second soaking step were specifically defined. Experiment 1 is a manufacturing example in which the magnetic field was horizontal, and Experiment 2 is a manufacturing example in which the magnetic field was a cusp field. In both cases, multiple manufacturing runs were performed under the same conditions, and the average values ​​of the results are shown below.

[0036] (Experiment 1) First soaking process The Ar gas flow rate was 105 liters / min, the crucible was positioned so that its top was 200 mm lower than the top of the heater, and the radiation shield was positioned so that its bottom was 35 mm above the melt surface so that it was close to the melt surface. The crucible was rotated at 1.0 rpm so that the melt would not spill out of the quartz crucible, the furnace pressure was 30 Torr, and the magnetic flux density was increased to 3000 G over approximately 50 minutes. Second soaking process The Ar gas flow rate was set to 250 liters / min, the crucible was positioned so that its upper end was at the same height as the upper end of the heater, and the radiation shield was positioned so that its lower end was 100 mm above the melt surface to ensure the gas flow rate generated from the melt. The crucible rotation speed was set to a slow 0.5 rpm, the furnace pressure was set to 15 Torr, and the magnetic flux density was reduced to 0 G over approximately 50 minutes.

[0037] [Table 1]

[0038] The first and second soaking steps under the above soaking conditions were considered as one set, and a verification experiment was conducted to verify the loss of production time (operational loss) due to dislocations and the rate of air pocket occurrence for a silicon single crystal manufacturing method in which only one set of soaking was performed, and a silicon single crystal manufacturing method in which two sets of soaking were performed for comparison, with a silicon single crystal manufacturing method in which no soaking was performed.The experimental results are as follows.

[0039] [Table 2]

[0040] (Experiment 2) First soaking process The Ar gas flow rate was 100 liters / min, the crucible was positioned in the same position as in the melting process, and the radiation shield was positioned 25 mm above the melt surface so that its bottom edge was close to the melt surface. The crucible was rotated at 15 rpm to prevent the melt from spilling out of the quartz crucible, the furnace pressure was 90 Torr, and the magnetic flux density was increased to 300 G over approximately 5 minutes. After that, the sample was left at the same 300 G magnetic flux density for approximately 120 minutes with the same gas flow rate, furnace pressure, quartz crucible position, radiation shield position, and quartz crucible rotation speed. Second soaking process The Ar gas flow rate was 130 liters / min, the crucible was positioned in the same position as in the melting process, and the radiation shield was positioned so that its bottom end was 75 mm above the melt surface to ensure the gas flow rate generated from the melt. The crucible rotation was slow at 0.5 rpm, the furnace pressure was 15 Torr, and the magnetic flux density was reduced to 0 G over approximately 5 minutes. After that, the sample was left at 0 G magnetic flux density for approximately 40 minutes with the same gas flow rate, furnace pressure, quartz crucible position, radiation shield position, and quartz crucible rotation speed.

[0041] [Table 3]

[0042] A first soaking step and a second soaking step under the above soaking conditions constitute one set, and a verification experiment was conducted to examine the loss of production time (operational loss) due to dislocation generation and the rate of air pocket occurrence for a silicon single crystal manufacturing method in which one set of soaking was performed, as well as a silicon single crystal manufacturing method in which no soaking was performed for comparison. The experimental results are as follows. Furthermore, when the manufactured silicon single crystals were processed into silicon wafers, the number of silicon wafers in which air pockets were confirmed was compared, and it was confirmed that the soaking of the present invention reduced the frequency of air pocket occurrence by 91%.

[0043] [Table 4]

[0044] As can be seen from the above experimental results, the silicon single crystal manufacturing method according to the present invention includes a first soaking step and a second soaking step before the growth step, which removes bubbles that occur on the inner surface of the crucible and dissolves minute scratches that are the source of the bubbles, thereby preventing dislocations and reducing operational losses. Furthermore, the stirring of the melt is promoted, eliminating temperature variations and creating a stable single crystal growth environment. In particular, a silicon single crystal manufacturing method that performs two soaking sets, consisting of the first soaking step and the second soaking step, can reduce operational losses more than a silicon single crystal manufacturing method that performs only one soaking set. The rate of air pocket generation is also reduced.

[0045] The disclosures of the above-cited patent documents and other documents are incorporated herein by reference. Modifications and adjustments of the embodiments and examples are possible within the scope of the entire disclosure of the present invention (including the claims), and further based on the basic technical concepts thereof. Furthermore, various combinations and selections (including partial deletions) of various disclosed elements (including elements of each claim, each element of each embodiment or example, each element of each drawing, etc.) are possible within the scope of the entire disclosure of the present invention. In other words, the present invention naturally embraces various modifications and alterations that would be possible by a person skilled in the art in accordance with the entire disclosure and technical concepts, including the claims. In particular, with regard to the numerical ranges set forth herein, any numerical value or subrange within that range should be construed as specifically set forth, even if not otherwise specified. Furthermore, the disclosures of the above-cited documents, when used in part or in whole in combination with the disclosures herein as part of the disclosure of the present invention, in accordance with the spirit of the present invention, are also deemed to be included in the disclosures of this application. [Explanation of symbols]

[0046] 1. Single crystal pulling device 2 Furnace body 2a Main Chamber 2b Pull chamber 3 Crucible 3a Quartz glass crucible 3b Graphite crucible 4 heater 5. Lifting mechanism 6 Radiation Shield 8. Computers 8a Storage device 8b Arithmetic storage unit 13 Electric coil for applying magnetic field C single crystal M raw material melt P seed crystal

Claims

1. A method for producing a silicon single crystal by the Czochralski method, comprising: a melting step of heating and melting a crystal raw material in a quartz crucible with a heater to produce a raw material melt; and a growing step of immersing a seed crystal in the raw material melt and pulling the seed crystal upward to grow a silicon single crystal, a first soaking step of applying a magnetic field to the raw material melt and leaving the raw material melt while increasing the strength of the applied magnetic field before the growing step, and a second soaking step of leaving the raw material melt while decreasing the strength of the applied magnetic field, The first soaking step and the second soaking step are different in at least one of the gas flow rate, the furnace pressure, the quartz crucible position, the radiation shield position, and the quartz crucible rotation speed.

1. A method for producing a silicon single crystal.

2. A method for producing a silicon single crystal by the Czochralski method, comprising: a melting step of heating and melting a crystal raw material in a quartz crucible with a heater to produce a raw material melt; a growing step of growing a silicon single crystal by immersing a seed crystal in the raw material melt and pulling the seed crystal upward; a melt-back step of remelting the silicon single crystal in the raw material melt when dislocations occur in the silicon single crystal in the growing step; and a second growing step after the melt-back step, a first soaking step of applying a magnetic field to the raw material melt obtained by remelting the silicon single crystal and leaving the raw material melt while increasing the strength of the applied magnetic field before the second growing step; and a second soaking step of leaving the raw material melt while decreasing the strength of the applied magnetic field, The first soaking step and the second soaking step are different in at least one of the gas flow rate, the furnace pressure, the quartz crucible position, the radiation shield position, and the quartz crucible rotation speed.

1. A method for producing a silicon single crystal.

3. A method for producing a silicon single crystal by the Czochralski method, comprising: a melting step of heating and melting a crystal raw material in a quartz crucible with a heater to produce a raw material melt; a growing step of growing a silicon single crystal by immersing a seed crystal in the raw material melt and pulling the seed crystal upward; a melt-back step of remelting the silicon single crystal in the raw material melt when dislocations occur in the silicon single crystal in the growing step; and a second growing step after the melt-back step, a first soaking step of applying a magnetic field to the raw material melt or the raw material melt obtained by remelting the silicon single crystal and leaving the raw material melt while increasing the strength of the applied magnetic field before the growing step and the second growing step, and a second soaking step of leaving the raw material melt while decreasing the strength of the applied magnetic field; The first soaking step and the second soaking step are different in at least one of the gas flow rate, the furnace pressure, the quartz crucible position, the radiation shield position, and the quartz crucible rotation speed.

1. A method for producing a silicon single crystal.

4. The method for producing a silicon single crystal according to any one of claims 1 to 3, characterized in that the first soaking step and the second soaking step are performed in the following order: first soaking step, second soaking step, first soaking step, second soaking step.

5. The method for producing a silicon single crystal according to any one of claims 1 to 3, wherein the gas flow rate in the first soaking step is 0.8 times or less or 1.2 times or more the gas flow rate in the second soaking step.

6. The method for producing a silicon single crystal according to any one of claims 1 to 3, wherein the furnace pressure in the first soaking step is 0.5 times or less or 2 times or more the furnace pressure in the second soaking step.

7. The method for producing a silicon single crystal according to any one of claims 1 to 3, characterized in that the crucible position in either the first soaking step or the second soaking step is moved relatively so that the upper end of the crucible is lower than the upper end of the heater, and the crucible position in the other soaking step is moved relatively so that the upper end of the crucible is at the same height as the upper end of the heater.

8. 4. The method for producing a silicon single crystal according to claim 1, wherein the radiation shield in either the first soaking step or the second soaking step is relatively moved so as to approach the melt surface, and the radiation shield in the other soaking step is relatively moved to a height that ensures a flow rate of gas generated from the melt.

9. The method for producing a silicon single crystal according to any one of claims 1 to 3, characterized in that the rotation speed of the quartz crucible in either the first soaking step or the second soaking step is maintained at a speed at which the melt does not spill from the quartz crucible, and the rotation speed of the quartz crucible in the other soaking step is maintained at a relatively low speed.

10. The method for producing a silicon single crystal according to any one of claims 1 to 3, characterized in that the magnetic field is a horizontal magnetic field, the applied strength (magnetic flux density) of the magnetic field in the first soaking step is increased by 1000 G or more between steps, and the applied strength (magnetic flux density) of the magnetic field in the second soaking step is decreased by 1000 G or more between steps.

11. The method for producing a silicon single crystal according to any one of claims 1 to 3, characterized in that the magnetic field is a cusp magnetic field, and the applied strength (magnetic flux density) of the magnetic field in the first soaking step is increased by 100 G or more between steps, and the applied strength (magnetic flux density) of the magnetic field in the second soaking step is decreased by 100 G or more between steps.

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