Single crystal manufacturing method

Abstract

Proposed is a single crystal manufacturing method capable of suppressing deterioration in controllability of the crystal pulling rate as the manufacture of a single crystal progresses. This single crystal manufacturing method is a method for manufacturing a single crystal by the Czochralski method in which a single crystal is pulled up while a horizontal magnetic field is applied to a raw material melt 13 accommodated in a crucible 12. The method is characterized in that, when, in a horizontal plane including the surface of the raw material melt 13, the direction of the component of a magnetic field line at origin C that is parallel to the horizontal plane is defined as the x-axis and the direction perpendicular to the x-axis and passing through origin C is defined as the y-axis, the magnetic flux density ratio Bp / Bc is lowered during the pulling of the single crystal, where Bp is the magnetic flux density at an intersection point P of the y-axis and the inner wall surface of the crucible, and Bc is the magnetic flux density at the origin C.

Description

Single crystal manufacturing method

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

[0002] Generally, semiconductor wafers made of single crystals of semiconductors such as silicon are used as substrates for semiconductor devices. A typical method for producing such semiconductor single crystals is the Czochralski (CZ) method. The CZ method involves placing semiconductor raw material in a crucible and melting it, immersing a seed crystal in the molten single crystal raw material, and then lifting it up to grow a single crystal below the seed crystal. Semiconductor wafers can be obtained by subjecting the grown single crystal ingot (hereinafter also referred to as "single crystal" or simply "crystal") to wafer processing.

[0003] In recent years, with the further miniaturization and high integration of semiconductor devices, the semiconductor wafers used as substrates are required to be free of grown-in defects, i.e., defect-free. Grown-in defects refer to void defects formed by the aggregation of vacancies and interstitial dislocation clusters formed by the precipitation of interstitial atoms, and can remain in the manufactured semiconductor wafers and cause degradation of the gate oxide film and leakage current in semiconductor devices.

[0004] The defect-free crystal is produced by suppressing convection of the raw material melt in the crucible and controlling the crystal pulling speed within a speed range that allows defect-free crystal to be obtained (see, for example, Patent Document 1).

[0005] Fig. 1 shows an example of a single crystal manufacturing apparatus using a horizontal magnetic field application method. The single crystal manufacturing apparatus 10 shown in Fig. 1 includes, within a chamber 11, a crucible 12 that contains a raw material (e.g., polycrystalline silicon) for a single crystal (e.g., silicon) 16, a heater 14 that heats the raw material in the crucible 12 to form a raw material melt 13, a crucible rotation mechanism 15 that is provided below the crucible 12 and rotates the crucible 12 in the circumferential direction, a seed crystal holder 18 that holds a seed crystal 17 for growing the single crystal 16, a wire rope 19 to which the seed crystal holder 18 is attached at its tip, and a winding mechanism 20 that rotates the wire rope 19 to rotate and pull up the single crystal 16, the seed crystal 17, and the seed crystal holder 18. Further, a magnet 1 having a plurality of coils 2 for applying a horizontal magnetic field (transverse magnetic field) to the raw material melt 13 in the crucible 12 is arranged on the outside of the lower part of the chamber 11 .

[0006] Using such a single crystal manufacturing apparatus 10, a single crystal 16 can be manufactured as follows: First, a predetermined amount of single crystal raw material is placed in a crucible 12 and heated by a heater 14 to form a raw material melt 13, and a predetermined horizontal magnetic field is applied to the raw material melt 13 by a magnet 2.

[0007] Next, with a horizontal magnetic field applied to the raw material melt 13, the seed crystal 17 held by the seed crystal holder 18 is immersed in the raw material melt 13. Then, the crucible 12 is rotated at a predetermined rotation speed by the crucible rotation mechanism 15, and the seed crystal 17 (i.e., the single crystal 16) is wound up by the winding mechanism 20 while being rotated at the predetermined rotation speed, thereby pulling up the seed crystal 17 and the single crystal 16 grown below the seed crystal 17. In this manner, the single crystal 16 having a predetermined diameter can be produced.

[0008] JP 2017-57127 A

[0009] R. Suewaka and K. Nakamura, Jpn. J. Appl. Phys. 59, 015502 (2020).

[0010] 1, when a defect-free silicon single crystal is produced using the horizontal magnetic field type single crystal production apparatus 10, the diameter of the crystal fluctuates if the temperature of the silicon melt supplied to the region near the solid-liquid interface between the silicon single crystal and the silicon melt changes. Therefore, when producing a defect-free silicon single crystal, the crystal pulling speed is controlled so that the diameter of the pulled crystal does not fluctuate.

[0011] However, when the present inventors produced silicon single crystals using the single crystal production apparatus 10 shown in Figure 1, they found that as the crystal was pulled, variations in the crystal pull-up speed (i.e., fluctuations in the crystal pull-up speed) increased, sometimes resulting in poor controllability of the crystal pull-up speed. As described above, when producing defect-free silicon single crystals, the crystal pull-up speed is controlled within a speed range that allows defect-free crystals to be obtained, but this speed range is extremely narrow. Therefore, fluctuations in the pull-up speed can cause the speed to fall outside the speed range that allows defect-free crystals to be obtained, making it impossible to obtain defect-free crystals, and reducing the yield of defect-free crystal production.

[0012] Thus, if the crystal pulling speed varies and the controllability of the crystal pulling speed deteriorates, it may not be possible to obtain a crystal with the desired characteristics. Therefore, there is a need to propose a method for producing a single crystal that can suppress the deterioration of the controllability of the crystal pulling speed.

[0013] The present invention has been made in consideration of the above-mentioned problems, and its object is to propose a method for producing a single crystal that can suppress deterioration in controllability of the crystal pulling rate as the production of the single crystal progresses.

[0014] The present invention, which solves the above problems, is as follows.

[0015] [1] A method for producing a single crystal by the Czochralski method, in which a single crystal is pulled up while a horizontal magnetic field is applied to a raw material melt contained in a crucible, the method comprising the steps of: in a horizontal plane including the surface of the raw material melt, defining an intersection point with a central axis of the crucible as the origin; defining an x-axis as the direction of a component of a magnetic field line parallel to the horizontal plane at the origin; defining a y-axis as the direction passing through the origin and perpendicular to the x-axis; defining a ratio of a magnetic flux density Bp at the intersection point of the y-axis with an inner wall surface of the crucible to a magnetic flux density Bc at the origin, and defining Bp / Bc as the ratio of the magnetic flux density Bp at the intersection point of the y-axis with the inner wall surface of the crucible to the magnetic flux density Bc at the origin; and reducing the magnetic flux density ratio Bp / Bc of the magnetic flux density Bp to the magnetic flux density Bc during pulling up of the single crystal.

[0016] [2] The method for producing a single crystal according to [1], wherein the single crystal is pulled under conditions in which the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.7 is smaller than the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.1.

[0017] [3] The method for producing a single crystal according to [1] or [2], wherein the single crystal is pulled under a condition in which the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.7 is smaller than the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.2.

[0018] [4] The method for producing a single crystal according to [3], wherein the single crystal is pulled with a difference of 0.1 or more between the magnetic flux density ratio Bp / Bc when the solidification rate of the single crystal is 0.2 and the magnetic flux density ratio Bp / Bc when the solidification rate of the single crystal is 0.7.

[0019] [5] The method for producing a single crystal according to any one of [1] to [4], wherein the single crystal is pulled under a condition in which the magnetic flux density ratio Bp / Bc is 1.0 or more when the solidification rate of the single crystal is 0.2.

[0020] [6] The method for producing a single crystal according to any one of [1] to [5], wherein the single crystal is pulled under conditions in which the magnetic flux density ratio Bp / Bc is 1.3 and the magnetic flux density Bc is 3500 G when the solidification rate of the single crystal is 0.2, and the magnetic flux density ratio Bp / Bc is 1.0 and the magnetic flux density Bc is 3500 G when the solidification rate of the single crystal is 0.7.

[0021] [7] The method for producing a single crystal according to any one of [1] to [6], wherein the single crystal is a silicon single crystal.

[0022] According to the present invention, it is possible to suppress deterioration in the controllability of the crystal pulling rate as the production of a single crystal progresses.

[0023] 1 is a diagram illustrating an example of a horizontal magnetic field type single crystal manufacturing apparatus; 2 is a diagram illustrating a main stream of silicon melt in a crucible; 3 is a diagram illustrating a side stream of silicon melt in a crucible; 4 is a schematic diagram illustrating the relationship between the magnetic flux density ratio Bp / Bc of the magnetic flux density Bp at the origin C to the magnetic flux density Bp at point P and the magnetic flux distribution, where (a) is for the case where Bp / Bc is 1.0, (b) is for the case where Bp / Bc is 1.3, and (c) is for the case where Bp / Bc is 1.5; 5 is a diagram illustrating the change in magnetic field distribution when Bp / Bc is reduced during crystal pulling, where (a) is for the case where the remaining amount of silicon melt is large and the magnetic flux density ratio is 1.3, and (b) is for the case where the remaining amount of silicon melt is small and the magnetic flux density ratio Bp / Bc is 1.0; 6 is a diagram illustrating the positions of the origin C and point P; and 7 is a diagram illustrating the positions in the crystal corresponding to the solidification rates of the crystal of 0.2 and 0.7. 1 is a graph showing the relationship between the solidification rate of the crystal and the variation in the pulling rate for invention examples 1 to 3 and conventional example 1. 2 is a graph showing the relationship between the solidification rate of the crystal and the variation in the pulling rate for invention examples 4, 5, conventional example 2, and comparative example 1. 3 is a graph showing the relationship between the solidification rate of the crystal and the variation in the pulling rate for invention example 6, conventional example 3, and comparative examples 2 and 3. 4 is a graph showing the relationship between the solidification rate of the crystal and the variation in the pulling rate for conventional example 4 and comparative examples 4 to 6. 5 is a graph showing the relationship between the solidification rate of the crystal and the variation in the pulling rate for invention example 7, conventional example 5, and comparative example 7. 6 is a graph showing the relationship between the solidification rate of the crystal and the variation in the pulling rate for invention example 8 and conventional example 6. 7 is a graph showing the relationship between the solidification rate of the crystal and the variation in the pulling rate for invention example 9 and conventional example 7. 8 is a graph explaining how to reduce the magnetic flux density ratio.

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings. A method for producing a single crystal according to the present invention is a method for producing a single crystal by the CZ method, in which a single crystal is pulled while a horizontal magnetic field is applied to a raw material melt contained in a crucible. Here, in a horizontal plane including the surface of the raw material melt, the intersection point with the central axis of the crucible is defined as the origin, the direction of the component of the magnetic field lines at the origin parallel to the horizontal plane is defined as the x-axis, and the direction passing through the origin and perpendicular to the x-axis is defined as the y-axis. The ratio of the magnetic flux density Bp at the intersection point of the y-axis with the inner wall surface of the crucible to the magnetic flux density Bc at the origin is defined as Bp / Bc. During the pulling of the single crystal, the magnetic flux density ratio Bp / Bc of the magnetic flux density Bp to the magnetic flux density Bc is reduced. The direction of the component of the magnetic field lines at the origin parallel to the horizontal plane refers to the direction of the component parallel to the horizontal plane when the magnetic field lines at the origin are decomposed into a component perpendicular to the horizontal plane and a component parallel to the horizontal plane.

[0025] In diligently studying ways to solve the above problems, the present inventors have focused on convection of the raw material melt 13 in the crucible 12. Hereinafter, an example will be described in which the single crystal 16 is a silicon single crystal.

[0026] Conventionally, when producing silicon single crystals by the horizontal magnetic field CZ method, it has been believed that the silicon melt in the crucible 12 convects by forming two roll-shaped vortex flows that convect in opposite directions around an axis parallel to the direction of the horizontal magnetic field. However, as shown in Figure 2, the latest three-dimensional flow analysis has shown that the silicon melt convects by forming one large flow (hereinafter referred to as the "main flow") along the inner wall of the crucible 12 and the free surface of the silicon melt. The three-dimensional flow analysis also shows the existence of small flows (hereinafter referred to as "side flows") that convect within the main flow, as shown in Figure 3.

[0027] According to the above three-dimensional flow analysis, the behavior of the main stream does not change significantly during crystal pulling. On the other hand, the number and location of side streams fluctuate during crystal pulling. For example, side streams are formed in the region near the free surface of the silicon melt (i.e., a relatively high region), move downward in the crucible 12, then rise again and are absorbed into the main stream and disappear. In addition, multiple side streams may merge to form a single side stream. In this way, side streams of silicon melt exhibit complex behavior of generation, movement, and disappearance during crystal pulling.

[0028] The behavior of such a side flow of silicon melt immediately below the solid-liquid interface is thought to affect the temperature of the silicon melt supplied to the region near the solid-liquid interface, causing fluctuations in the diameter of the silicon single crystal and ultimately leading to fluctuations in the crystal pulling speed. Therefore, in order to suppress deterioration of the controllability of the crystal pulling speed as the single crystal production progresses, it is thought to be essential to control the behavior of the side flow of silicon melt. Therefore, the inventors have studied the horizontal magnetic field distribution applied to the silicon melt.

[0029] The influence of the magnetic field distribution on the silicon melt can be evaluated to some extent based on Bp / Bc, where the direction of the component of the magnetic field line at origin C that is parallel to the horizontal plane including the surface of raw material melt 13 is defined as the x-axis, the direction passing through origin C and perpendicular to the x-axis is defined as the y-axis, and the ratio of magnetic flux density Bp at intersection P between the y-axis and the inner wall surface of crucible 12 and magnetic flux density Bc at origin C is defined as Bp / Bc.

[0030] FIG. 4 is a schematic diagram showing the relationship between the magnetic flux density ratio Bp / Bc and the magnetic field distribution in the silicon melt. Here, FIG. 4(a) shows the case where the magnetic flux density ratio Bp / Bc is 1.0, FIG. 4(b) shows the case where the magnetic flux density ratio Bp / Bc is 1.3, and FIG. 4(c) shows the case where the magnetic flux density ratio Bp / Bc is 1.5. The positions of the origin C and point P are shown in FIG. 6. Taking the case where Bp / Bc is 1.0 shown in FIG. 4(a) as a reference, when the magnetic flux density ratio Bp / Bc is increased to more than 1.0, a region with high magnetic flux density is generated on the outer periphery of the crucible, as shown in FIG. 4(b). Furthermore, when the magnetic flux density ratio Bp / Bc is further increased, the region with high magnetic flux density becomes larger, as shown in FIG. 4(c).

[0031] In the region where the magnetic flux density is high, the damping effect of the silicon melt is high, and in the region where the magnetic flux density is low, the damping effect of the silicon melt is low. According to three-dimensional flow analysis, the side flow exists in the region where the magnetic flux density is low, and by increasing the magnetic flux density ratio Bp / Bc, the region where the side flow exists is narrowed. Therefore, in order to stabilize the behavior of the side flow of the silicon melt, it is considered that the "size of the region below the magnetic flux density at the origin C" and the "balance of the damping force between the region below the magnetic flux density at the origin C and the region where the magnetic flux density is higher than the magnetic flux density at the origin C" are important.

[0032] As described above, it has been found that as the crystal pulling progresses, variations in the crystal pulling speed occur, and the controllability of the pulling speed may deteriorate. As the crystal pulling progresses, the amount of silicon melt remaining in the crucible 12 decreases, and it is thought that as the crystal pulling progresses, the area in which the silicon melt sideflows exist also narrows.

[0033] For these reasons, the inventors of the present invention have hypothesized that as the crystal pulling process progresses, the area in which the silicon melt side flow exists becomes narrower, causing the behavior of the side flow to become unstable, which may be adversely affecting the temperature of the silicon melt supplied to the area near the solid-liquid interface. As a result of extensive research into ways to stabilize the behavior of the silicon melt side flow, they have come up with the idea of ​​reducing Bp / Bc during crystal pulling.

[0034] FIG. 5 illustrates the change in magnetic field distribution when Bp / Bc is reduced during crystal pulling. Here, FIG. 5(a) illustrates the case where the remaining amount of silicon melt is large and the magnetic flux density ratio is 1.3, and FIG. 5(b) illustrates the case where the remaining amount of silicon melt is small and the magnetic flux density ratio Bp / Bc is 1.0. The positions of the origin C and point P are as shown in FIG. 6. As shown in FIG. 5(a), when the remaining amount of silicon melt is large and the magnetic flux density ratio Bp / Bc is large, the region in which a side flow can exist is limited. In contrast, as shown in FIG. 5(b), when the remaining amount of silicon melt is small and the magnetic flux density ratio Bp / Bc is reduced, the region in which a side flow can exist is expanded, and it is believed that the side flow can exist stably. As shown in the examples described below, it has been found that reducing Bp / Bc during crystal pulling can reduce variations in the crystal pulling speed and suppress deterioration of the crystal pulling speed controllability. This is how the present invention was completed. Each step of the method for producing a single crystal will be described below.

[0035] First, the raw material for the single crystal 16 is filled into the crucible 12. When the single crystal 16 is a silicon single crystal, the raw material is, for example, polycrystalline silicon. At this time, the pressure inside the chamber 11 is reduced and an inert gas atmosphere such as Ar gas is maintained.

[0036] Next, the raw material in the crucible 12 is heated and melted by the heater 14 to form a raw material melt 13 in the crucible 12 .

[0037] Next, the crucible 12 is raised to the lifting start position.

[0038] Thereafter, the wire rope 19 is lowered by the winding mechanism 20, causing the seed crystal 17 held in the seed crystal holder 18 to immerse in the raw material melt 13, and the seed crystal 17 and ultimately the single crystal 16 are pulled up from the raw material melt 13. Specifically, while the crucible 12 and the wire rope 19 are rotated in a predetermined direction, the wire rope 19 is wound up by the winding mechanism 20, and the single crystal 16 is grown below the seed crystal 17. As the growth of the single crystal 16 progresses, the amount of raw material melt 13 decreases, but the crucible 12 is raised to maintain the height position of the surface of the raw material melt 13.

[0039] When pulling the seed crystal 17 (single crystal 16), seed necking is first performed by the Dash method to eliminate dislocations in the single crystal 16, forming a neck portion. Next, a shoulder portion is grown, and when the single crystal 16 reaches a desired diameter, the diameter is kept constant and a body portion is grown. After the straight body portion is grown to a predetermined length, tail necking is performed to separate the single crystal 16 from the raw material melt 13 in a dislocation-free state, forming a tail portion.

[0040] The seed crystal 17 (single crystal 16) is pulled while a horizontal magnetic field is applied to the raw material melt 13 by the magnet 1 composed of coils 2. The distribution of the horizontal magnetic field can be adjusted by the magnitude and direction of the current flowing through the coils 2 constituting the magnet 1. Specifically, the magnet 1 is composed of multiple coils 2, some of which are designated as a main coil set and the rest as sub-coil sets, and various magnetic field distributions can be formed by changing the magnitude and direction of the current flowing through the coils 2 between the main coil set and the sub-coil set. Various magnetic field distributions can also be formed by configuring the magnitude and direction of the current flowing through each of the coils 2 constituting the magnet 1 to be controllable, and setting the magnitude and direction of the current flowing through each coil 2.

[0041] As described above, the horizontal magnetic field distribution can be evaluated based on Bp / Bc, where Bc is the magnetic flux density at the origin C, the x-axis is the direction of the magnetic field lines at the origin C, and the y-axis is the direction passing through the origin C and perpendicular to the x-axis. Bp / Bc is the ratio of the magnetic flux density Bp at the intersection P of the y-axis and the inner wall surface of the crucible 12 to the magnetic flux density Bc at the origin C.

[0042] In the present invention, the value of the magnetic flux density ratio Bp / Bc at the start of pulling the crystal 16 is 0.5 or more and 2.3 or less. The value of the magnetic flux density ratio Bp / Bc is preferably 1.0 or more and 1.5 or less, and more preferably 1.1 or more and 1.3 or less. The value of Bp / Bc may be adjusted by changing both Bp and Bc, or by keeping one of Bp and Bc constant and changing the other. For example, this can be done by keeping Bc constant and changing Bp.

[0043] As described above, in the present invention, the magnetic flux density ratio Bp / Bc of the magnetic flux density Bp to the magnetic flux density Bc is reduced during the pulling of the seed crystal 17 (crystal 16), thereby suppressing variations in the pulling speed of the crystal 16 and preventing deterioration in the controllability of the crystal pulling speed.

[0044] The method for decreasing the magnetic flux density ratio Bp / Bc is not particularly limited, and as shown in FIG. 9 , it can be decreased at a constant rate from the start of pulling to the end of pulling. Alternatively, it can be kept constant until the solidification rate of the crystal 16 reaches a predetermined value, and then decreased at a constant rate until the end of pulling. Furthermore, it can be kept constant until the solidification rate of the crystal reaches a predetermined value from the start of pulling the crystal, and then decreased at a constant rate until the end of pulling. In this specification, the term "solidification rate" refers to the rate at which the raw material melt 13 has solidified, with 1 being the rate when all of the raw material melt 13 has solidified. For example, a state in which 1 / 10 of the entire raw material melt 13 has solidified is represented as a solidification rate of 0.1, and a state in which 1 / 5 has solidified is represented as a solidification rate of 0.2.

[0045] The seed crystal 17 (single crystal 16) is preferably pulled under a condition in which the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal 16 is 0.7 is smaller than the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal 16 is 0.1. This makes it possible to suppress the increase in the variation in the crystal pulling speed.

[0046] The seed crystal 17 (single crystal 16) is preferably pulled under conditions in which the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal 16 is 0.7 is smaller than the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal 16 is 0.2. This can suppress the increase in the variation in the crystal pulling rate. Note that the positions in the single crystal 16 corresponding to the times when the solidification rates of the single crystal are 0.2 and 0.7 are as shown in FIG. 7.

[0047] Furthermore, it is preferable that the seed crystal 17 (single crystal 16) is pulled with the difference between the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal 16 is 0.2 and the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal 16 is 0.7 being 0.1 or more. This makes it possible to suppress variations in the crystal pulling speed over the entire length of the crystal.

[0048] The magnetic flux density Bc at the origin C is set to 1000 G or more and 4000 G or less. The magnetic flux density Bc at the origin C is preferably set to 2000 G or more and 4000 G or less, and more preferably set to 2500 G or more and 3500 G or less.

[0049] The seed crystal 17 (single crystal 16) is preferably pulled under a condition in which the magnetic flux density ratio Bp / Bc is 1.0 or more when the solidification rate of the single crystal 16 is 0.2. This makes it possible to suppress the increase in the variation in the crystal pulling speed.

[0050] The seed crystal 17 (single crystal 16) is preferably pulled under conditions where the magnetic flux density ratio Bp / Bc is 1.3 and the magnetic flux density Bc is 3500 G when the solidification rate of the single crystal 16 is 0.2, and where the magnetic flux density ratio Bp / Bc is 1.0 and the magnetic flux density Bc is 3500 G when the solidification rate of the single crystal 16 is 0.7. This makes it possible to suppress variations in the crystal pulling speed over the entire length of the crystal.

[0051] The single crystal 16 is not particularly limited as long as it can be produced by the CZ method, but it is possible to suitably produce a single crystal of semiconductor silicon with small fluctuations in oxygen concentration or a defect-free silicon single crystal.

[0052] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0053] (Example 1) A silicon single crystal with a diameter of 310 mm was produced by the CZ method using a single crystal production apparatus equipped with a magnet having six coils. First, 400 kg of polycrystalline silicon, a silicon raw material, was melted in a crucible to form molten silicon. Next, a seed crystal was immersed in the molten silicon and rotated at 10 rpm while the crucible was rotated at 0.5 rpm while being pulled up, producing a silicon single crystal below the seed crystal. The magnitude and direction of the current flowing through the coil were adjusted to set the magnetic flux density at origin C to 3500 G. During the production of the silicon single crystal, Bp was adjusted to adjust the magnetic flux density ratio Bp / Bc to 1.5 at a solidification rate of 0.2, and Bp / Bc was lowered so that the magnetic flux density ratio Bp / Bc was 1.0 at a solidification rate of 0.7. Figure 8A shows the relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate.

[0054] (Invention Example 2) A silicon single crystal was produced in the same manner as in Invention Example 1. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was reduced so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.1. All other conditions were the same as in Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8A.

[0055] (Invention Example 3) A silicon single crystal was produced in the same manner as in Invention Example 1. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was reduced so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.3. All other conditions were the same as in Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8A.

[0056] Conventional Example 1 A silicon single crystal was produced in the same manner as in Invention Example 1. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was not reduced, and the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 was maintained at 1.5. All other conditions were the same as in Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8A.

[0057] (Invention Example 4) A silicon single crystal was produced in the same manner as in Invention Example 1. However, the magnetic flux density ratio Bp / Bc was adjusted to 1.3 at a solidification rate of 0.2. All other conditions were the same as in Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8B.

[0058] (Invention Example 5) A silicon single crystal was produced in the same manner as in Invention Example 4. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was reduced so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.1. All other conditions were the same as in Invention Example 4. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8B.

[0059] Conventional Example 2 A silicon single crystal was produced in the same manner as in Inventive Example 4. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was not reduced, and the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 was maintained at 1.3. All other conditions were the same as in Inventive Example 4. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8B.

[0060] Comparative Example 1 A silicon single crystal was produced in the same manner as in Inventive Example 4. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was increased so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.5. All other conditions were the same as in Inventive Example 4. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8B.

[0061] (Invention Example 6) A silicon single crystal was produced in the same manner as in Invention Example 1. However, the magnetic flux density ratio Bp / Bc was adjusted to 1.1 at a solidification rate of 0.2. All other conditions were the same as in Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8C.

[0062] Conventional Example 3: A silicon single crystal was produced in the same manner as in Inventive Example 6. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was not reduced, and the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 was maintained at 1.1. All other conditions were the same as in Inventive Example 6. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8C.

[0063] Comparative Example 2 A silicon single crystal was produced in the same manner as in Inventive Example 6. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was increased so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.3. All other conditions were the same as in Inventive Example 6. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8C.

[0064] Comparative Example 3 A silicon single crystal was produced in the same manner as in Inventive Example 6. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was increased so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.5. All other conditions were the same as in Inventive Example 6. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8C.

[0065] Conventional Example 4 A silicon single crystal was produced in the same manner as in Invention Example 1. However, the value of the magnetic flux density ratio Bp / Bc before the start of pulling the silicon single crystal was set to 1.0, and the magnetic flux density ratio Bp / Bc was not reduced during the production of the silicon single crystal, and the magnetic flux density ratio Bp / Bc was maintained at 1.0 at a solidification rate of 0.7. All other conditions were the same as in Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8D.

[0066] (Comparative Example 4) A silicon single crystal was produced in the same manner as in Conventional Example 4. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was increased so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.1. All other conditions were the same as in Conventional Example 4. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8D.

[0067] (Comparative Example 5) A silicon single crystal was produced in the same manner as in Conventional Example 4. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was increased so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.3. All other conditions were the same as in Conventional Example 4. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8D.

[0068] (Comparative Example 6) A silicon single crystal was produced in the same manner as in Conventional Example 4. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was increased so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.5. All other conditions were the same as in Conventional Example 4. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8D.

[0069] (Invention Example 7) A silicon single crystal was produced in the same manner as in Invention Example 1. However, the magnetic flux density at the origin C was set to 3000 G. Furthermore, during the production of the silicon single crystal, Bp was adjusted to adjust the magnetic flux density ratio Bp / Bc to 1.2 at a solidification rate of 0.2, and Bp / Bc was lowered so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 became 1.0. All other conditions were the same as Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8E.

[0070] Conventional Example 5 A silicon single crystal was produced in the same manner as in Inventive Example 7. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was not reduced, and the magnetic flux density Bp / Bc at a solidification rate of 0.7 was maintained at 1.2. All other conditions were the same as in Inventive Example 7. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8E.

[0071] Comparative Example 7 A silicon single crystal was produced in the same manner as in Inventive Example 7. However, during the production of the silicon single crystal, the magnetic flux density Bp / Bc was increased so that the magnetic flux density Bp / Bc at a solidification rate of 0.7 became 1.3. All other conditions were the same as in Inventive Example 7. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8E.

[0072] (Invention Example 8) A silicon single crystal was produced in the same manner as in Invention Example 1. However, the magnetic flux density at the origin C was set to 2500 G. Furthermore, during the production of the silicon single crystal, Bp was adjusted to adjust the magnetic flux density ratio Bp / Bc to 1.3 at a solidification rate of 0.2, and Bp / Bc was lowered so that the magnetic flux density ratio Bp / Bc was 1.2 at a solidification rate of 0.7. All other conditions were the same as in Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8F.

[0073] Conventional Example 6 A silicon single crystal was produced in the same manner as in Inventive Example 8. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was not reduced, and the magnetic flux density Bp / Bc at a solidification rate of 0.7 was maintained at 1.3. All other conditions were the same as in Inventive Example 8. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8F.

[0074] (Invention Example 9) A silicon single crystal was produced in the same manner as in Invention Example 1. However, the magnetic flux density at the origin C was set to 2000 G. Furthermore, during the production of the silicon single crystal, Bp was adjusted to adjust the magnetic flux density ratio Bp / Bc to 2.3 at a solidification rate of 0.2, and Bp / Bc was lowered so that the magnetic flux density ratio Bp / Bc at a solidification rate of 0.7 was 1.5. All other conditions were the same as in Invention Example 1. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8G.

[0075] Conventional Example 7 A silicon single crystal was produced in the same manner as in Inventive Example 9. However, during the production of the silicon single crystal, the magnetic flux density ratio Bp / Bc was not reduced, and the magnetic flux density Bp / Bc at a solidification rate of 0.7 was maintained at 2.3. All other conditions were the same as in Inventive Example 9. The relationship between the solidification rate of the silicon single crystal and the variation in the pulling rate is shown in Figure 8G.

[0076] As shown in Figure 8B, in the case of Conventional Example 2, in which the magnetic flux density ratio Bp / Bc before crystal pulling is 1.3 and this value is maintained, the pull-up rate fluctuates as the solidification rate increases, i.e., as the crystal is pulled. However, as shown in Figure 8B, by decreasing the magnetic flux density ratio Bp / Bc during crystal pulling, as in Inventive Examples 4 and 5, the pull-up rate fluctuates less than when the magnetic flux density ratio Bp / Bc is maintained constant at 1.3.

[0077] As shown in Figure 8C, a similar trend is observed when the magnetic flux density ratio Bp / Bc is set to 1.1 before the start of crystal pulling, indicating that by lowering the magnetic flux density ratio Bp / Bc during crystal pulling, the variation in the pulling rate can be reduced compared to when the magnetic flux density ratio Bp / Bc is maintained constant at 1.1. Also, as shown in Figure 8F, a similar trend is observed when the magnetic flux density at the origin C at the start of crystal pulling is set to 2500 G, indicating that by lowering the magnetic flux density ratio Bp / Bc during crystal pulling, the variation in the pulling rate can be reduced.

[0078] On the other hand, as shown in Figure 8A, when the magnetic flux density ratio Bp / Bc before the start of crystal pulling is maintained at 1.5, the variation in the pulling rate remains almost constant even as the solidification rate increases, i.e., the crystal pulling progresses, resulting in a large variation in the pulling rate. However, it can be seen that the variation in the crystal pulling rate can be reduced by lowering the magnetic flux density ratio Bp / Bc during crystal pulling.

[0079] According to the present invention, it is possible to suppress deterioration in the controllability of the crystal pulling rate as the production of a single crystal progresses.

[0080] REFERENCE SIGNS LIST 1 magnet 2 coil 10 single crystal manufacturing apparatus 11 chamber 12 crucible 13 raw material melt 14 heater 15 crucible rotation mechanism 16 single crystal 17 seed crystal 18 seed crystal holder 19 wire rope 20 winding mechanism

Claims

1. A method for producing a single crystal by the Czochralski method, in which a single crystal is pulled up while a horizontal magnetic field is applied to a raw material melt contained in a crucible, characterized in that, within a horizontal plane including the surface of the raw material melt, the point of intersection with the central axis of the crucible is defined as the origin, the direction of the component of the magnetic field line parallel to the horizontal plane at the origin is defined as the x-axis, and the direction passing through the origin and perpendicular to the x-axis is defined as the y-axis, and the ratio of magnetic flux density Bp at the intersection of the y-axis with the inner wall surface of the crucible to magnetic flux density Bc at the origin is defined as Bp / Bc, and the magnetic flux density ratio Bp / Bc of magnetic flux density Bp to magnetic flux density Bc is reduced during pulling of the single crystal.

2. The method for producing a single crystal according to claim 1, wherein the single crystal is pulled under conditions in which the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.7 is smaller than the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.

1.

3. A method for producing a single crystal according to claim 1 or 2, wherein the single crystal is pulled under conditions in which the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.7 is smaller than the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.

2.

4. The method for producing a single crystal according to claim 3, wherein the single crystal is pulled with a difference of 0.1 or more between the magnetic flux density ratio Bp / Bc when the solidification rate of the single crystal is 0.2 and the magnetic flux density ratio Bp / Bc when the solidification rate of the single crystal is 0.

7.

5. The method for producing a single crystal according to claim 1 or 2, wherein the single crystal is pulled under a condition in which the magnetic flux density ratio Bp / Bc at the time when the solidification rate of the single crystal is 0.2 is 1.0 or more.

6. A method for producing a single crystal according to claim 1 or 2, wherein the single crystal is pulled under conditions in which the magnetic flux density ratio Bp / Bc is 1.3 and the magnetic flux density Bc is 3,500 G when the solidification rate of the single crystal is 0.2, and the magnetic flux density ratio Bp / Bc is 1.0 and the magnetic flux density Bc is 3,500 G when the solidification rate of the single crystal is 0.

7.

7. The method for producing a single crystal according to claim 1 or 2, wherein the single crystal is a silicon single crystal.

Images