Method for manufacturing single crystal

Abstract

To provide a method for producing a single crystal that can produce a defect-free single crystal by suppressing variation in crystal pulling-up speed while suppressing variation in oxygen density in a crystal pulling-up direction.SOLUTION: A method for producing a single crystal includes a step of pulling-up a single crystal while applying a horizontal magnetic field to a crucible storing a melt of raw material of the single crystal so that a magnetic flux density becomes 0.58×M or more at a point A (0 mm, 0 mm, -400 mm) and a magnetic flux density becomes 1.47×M or more at a point B (400 mm, 0 mm, 0 mm) where M represents a magnetic flux density at a magnetic field center O (0 mm, 0 mm, 0 mm) at a magnetic field neutral plane.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Generally, substrates for semiconductor devices are made of single crystals of semiconductors such as silicon. A typical method for manufacturing such single crystals of semiconductors is the Czochralski (CZ) method. The CZ method is a method in which semiconductor raw materials are placed in a crucible and melted, and a seed crystal is immersed in the molten single crystal raw material and pulled up, growing a single crystal below the seed crystal.

[0003] The crucible in which the single crystal raw material is contained is generally made of quartz. Therefore, if the single crystal raw material melt contained in the crucible convects quickly, the amount of dissolved oxygen contained in the quartz crucible increases, and the oxygen concentration of the single crystal increases. Therefore, the oxygen concentration of the single crystal is controlled by applying a horizontal magnetic field to the raw material melt in the crucible to suppress the convection of the raw material melt while pulling the single crystal (see, for example, Patent Document 1).

[0004] Fig. 1 shows an example of a single crystal manufacturing apparatus using a horizontal magnetic field application method. The single crystal manufacturing apparatus 100 shown in this figure includes a crucible 12 that contains a raw material (e.g., polycrystalline silicon) for a single crystal (e.g., silicon) 16 in a chamber 11, 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 at the bottom of the crucible 12 and rotates the crucible 12 in a 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 pull up the single crystal 16, the seed crystal 17, and the seed crystal holder 18. Further, a magnet 21 having a plurality of coils 22 for applying a horizontal magnetic field (transverse magnetic field) to the silicon melt 13 in the crucible 12 is disposed on the lower outside of the chamber 11 .

[0005] Using such a single crystal manufacturing apparatus 10, a single crystal 16 can be manufactured as follows. That is, first, a predetermined amount of single crystal raw material is placed in a crucible 12 and heated by a heater 14 to form raw material melt 13, and a predetermined horizontal magnetic field is applied to the raw material melt 13 by a magnet 21.

[0006] 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, a single crystal having a predetermined diameter can be produced.

[0007] In recent years, with the miniaturization and high integration of semiconductor devices, semiconductor wafers such as silicon wafers, which are 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 wafer and cause degradation of the gate oxide film and leakage current in semiconductor devices.

[0008] The behavior of vacancies and interstitial atoms in a crystal is explained by the Voronkov model, which states that when the ratio v / G of the crystal pulling speed v to the temperature gradient G in the pulling direction of the single crystal ingot near the solid-liquid interface is greater than a critical value (hereinafter also referred to as ``critical v / G''), vacancies are dominant, and when it is smaller than the critical v / G, interstitial atoms are dominant (for example, see non-patent document 1). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2007-204312 A [Non-patent literature]

[0010] [Non-Patent Document 1] VVVoronkov, J.Crystal Growth,59,625(1982) Summary of the Invention [Problem to be solved by the invention]

[0011] When the value of v / G is the critical value, a defect-free single crystal is obtained. In general, the margin of the pulling speed v for obtaining a defect-free single crystal is extremely narrow, and must be controlled within ±2% of the critical value of v / G. However, during pulling of the single crystal, the pulling speed v of the crystal fluctuates due to fluctuations in the temperature of the solid-liquid interface, and as a result, the value of v / G may deviate from the above condition, making it impossible to obtain a defect-free single crystal.

[0012] In addition, the oxygen concentration in the produced single crystal can be significantly reduced by applying a horizontal magnetic field to the raw material melt, but this causes a problem of variation in the oxygen concentration in the direction of pulling the crystal (i.e., the axial direction of the single crystal).

[0013] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to propose a method for producing a single crystal that can suppress fluctuations in the oxygen concentration in the crystal pulling direction while suppressing fluctuations in the crystal pulling speed, thereby producing a defect-free single crystal. [Means for solving the problem]

[0014] The present invention which solves the above problems is as follows. [1] A method for producing a single crystal by the Czochralski method, comprising applying a horizontal magnetic field to a crucible containing a melt of a single crystal material while pulling the single crystal, A method for producing a single crystal, comprising applying the horizontal magnetic field to the melt so that, when the magnetic flux density at the magnetic field center O (0 mm, 0 mm, 0 mm) of the magnetic field neutral plane is M, the magnetic flux density at point A (0 mm, 0 mm, -400 mm) is 0.58 x M or more and the magnetic flux density at point B (400 mm, 0 mm, 0 mm) is 1.47 x M or more.

[0015] [2] The method for producing a single crystal described in [1] above, wherein the horizontal magnetic field is applied using a magnet comprising four or more coils, at least one of which has a height-to-width ratio exceeding 1, and a control unit capable of generating a magnetic field for each of the four or more coils independently of each other.

[0016] [3] The method for producing a single crystal according to [2] above, wherein the coil is rectangular and annular.

[0017] [4] The method for producing a single crystal according to [2] or [3] above, wherein the height of the coil is 600 mm or more.

[0018] [5] The method for producing a single crystal according to any one of [1] to [4] above, wherein the single crystal is a silicon single crystal. Effect of the Invention

[0019] According to the present invention, it is possible to produce a defect-free single crystal by suppressing fluctuations in the oxygen concentration in the crystal pulling direction and fluctuations in the crystal pulling speed. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing an example of a single crystal manufacturing apparatus using a horizontal magnetic field application method. [Diagram 2] 1A and 1B are diagrams for explaining the position at which the magnetic flux density is controlled in the present invention, where (a) is a top view of a crucible and (b) is a side view of the crucible. [Diagram 3]FIG. 1 shows a preferred example of a coil constituting a magnet of a single crystal production apparatus that can be used in the present invention, where (a) is an overall view, (b) is a front view, (c) is a side view, and (d) is a bottom view. [Figure 4] FIG. 13 is a diagram illustrating a coil angle. [Diagram 5] FIG. 13 shows (c) the magnetic flux density in the x direction and (d) the magnetic flux density in the z direction for the bobbin-type coil arrangement shown in (a) and the vertical rectangular coil arrangement shown in (b). [Figure 6] FIG. 13 shows (c) the magnetic flux density in the x direction and (d) the magnetic flux density in the z direction for the bobbin-type coil arrangement shown in (a) and the vertical rectangular coil arrangement shown in (b). [Figure 7] 1 is a diagram showing the variation in oxygen concentration in the axial direction of a silicon single crystal, where (a) is for a comparative example, (b) is for example 1 of the invention, and (c) is for example 2 of the invention. [Figure 8] 1A to 1C are diagrams showing the time variation of the temperature at the solid-liquid interface by a three-dimensional fluid simulation, where (a) is for a comparative example, (b) is for example 1 of the invention, and (c) is for example 2 of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The method for producing a single crystal according to the present invention is a method for producing a single crystal by applying a horizontal magnetic field to a crucible containing a melt of a raw material of the single crystal by the Czochralski method while pulling the single crystal. Here, the method is characterized in that, when the magnetic flux density at the magnetic field center O (0 mm, 0 mm, 0 mm) of the magnetic field neutral plane is M, the magnetic flux density at point A (0 mm, 0 mm, -400 mm) is 0.58×M or more and the magnetic flux density at point B (400 mm, 0 mm, 0 mm) is 1.47×M or more, a horizontal magnetic field is applied to the melt to pull the single crystal.

[0022] The present inventors have intensively studied ways to produce defect-free single crystals by suppressing the fluctuation of the oxygen concentration in the crystal pulling direction while suppressing the fluctuation of the crystal pulling speed. In the process, they discovered that in a coordinate system with the origin at the magnetic field center O, which is the intersection of the magnetic field neutral plane (a plane including the centers of gravity of all the coils constituting magnet 21) and the crystal pulling axis, the magnetic flux density at a specific position (point) is closely related to the fluctuation of the oxygen concentration in the crystal pulling direction and the fluctuation of the crystal pulling speed.

[0023] That is, when a magnetic field is applied to the crucible 12 by the magnet 21 and the magnetic field neutral plane is located at the same position as the surface of the raw material melt 13 (when there is no crystal, the magnetic field center O is located on the surface of the raw material melt 13), as shown in Figures 2(a) and (b), the magnetic field center O is the origin, the axis passing through the origin and parallel to the direction of the magnetic field is the y-axis, the axis perpendicular to the direction of the magnetic field is the x-axis, and the axis passing through the origin and perpendicular to the magnetic field neutral plane is the z-axis. In this case, the inventors have found that when a point on the inside (inner surface) of the crucible 12 on the z-axis at the start of pulling the crystal is designated as point A, the magnetic flux density at point A is closely related to the variation in oxygen concentration of the single crystal in the direction of pulling the crystal. This is thought to be because when the magnetic flux density at the bottom of crucible 12 is low, the strength of the Lorentz force controlling the convection of raw material melt 13 becomes smaller, and the effect of the shear force due to the rotation of crucible 12 becomes greater, resulting in greater fluctuations in the flow distribution of raw material melt 13, which in turn affects the fluctuations in the oxygen concentration.

[0024] The inventors also discovered that when a point on the inside (inner surface) of crucible 12 on the x-axis is designated as point B, the magnetic flux density at point B is closely related to the fluctuation in the crystal pulling speed when pulling up a defect-free single crystal. This is thought to be because, when a horizontal magnetic field is applied to raw material melt 13 of a conductor such as silicon, a roll-shaped convection current revolving around the direction of the horizontal magnetic field is generated, and when the magnetic flux density at point B is high, the damping of the upward and downward currents is enhanced, and the fluctuation in temperature at the solid-liquid interface is suppressed, thereby suppressing the fluctuation in the crystal pulling speed v.

[0025] Thus, the inventors have found that in order to produce a defect-free single crystal while suppressing the variation in oxygen concentration in the crystal pulling direction, it is essential to maintain the magnetic flux density within a predetermined range at points A and B. The inventors have found that it is possible to produce a defect-free single crystal while suppressing the variation in oxygen concentration in the crystal pulling direction by pulling a single crystal while applying a horizontal magnetic field to the melt so that, when the magnetic flux density at the magnetic field center O (0 mm, 0 mm, 0 mm) is M, the magnetic flux density at point A (0 mm, 0 mm, -400 mm) is 0.58×M or more and the magnetic flux density at point B (400 mm, 0 mm, 0 mm) is 1.47×M or more, thereby completing the present invention.

[0026] As described above, in the present invention, when the magnetic flux density at the magnetic field center O is M, the magnetic flux density at point A is set to 0.58 M or more. As shown in the examples described later, by setting the magnetic flux density at point A to 0.58 M or more, it is possible to suppress the variation in oxygen concentration in the crystal pulling direction in the single crystal. Preferably, the magnetic flux density at point A is set to 0.64 M or more. This makes it possible to further suppress the variation in oxygen concentration in the crystal pulling direction in the single crystal.

[0027] Furthermore, in the present invention, when the magnetic flux density at the magnetic field center O is M, the magnetic flux density at point B is set to 1.47 M or more. As shown in the examples described later, by setting the magnetic flux density at point B to 1.47 M or more, it is possible to suppress fluctuations in the crystal pulling speed of a defect-free single crystal. Preferably, the magnetic flux density at point B is set to 2.23 M or more. This makes it possible to further suppress fluctuations in the crystal pulling speed of a defect-free single crystal.

[0028] 2(a), it is preferable to set the magnetic flux density at point C (0 mm, 400 mm, 0 mm) on the y-axis inside (inner surface) of crucible 12, which is at the same height as point B, smaller than the magnetic flux density at point B. This can further suppress the convection fluctuation of raw material melt 13.

[0029] Control of the magnetic flux density at points A and B depends on the configuration of magnet 21, but can be achieved by placing the coil in an appropriate position and adjusting the magnitude and direction of the current applied to the coil. Conventionally, an annular (bobbin type) coil has been widely used as coil 22 constituting magnet 21 (see, for example, JP 2009-173536 A).

[0030] By placing a bobbin-type coil in an appropriate position and adjusting the magnitude and direction of the current applied to the coil, it is possible to control the magnetic flux density at points A and B. However, the position at which the coil is placed may be limited due to restrictions on the device configuration. In such cases, with a bobbin-type coil, it is necessary to reduce the coil width, i.e., the diameter, in order to alleviate the positional restrictions.

[0031] However, when the diameter of the bobbin-type coil is reduced, the height of the coil is also reduced at the same time, which affects the magnetic field applied in the height direction to the raw material melt 13 contained in the crucible 12. Thus, when the coil 22 constituting the magnet 21 is of the bobbin type, there is a problem that the degree of freedom in designing the magnetic field distribution applied to the raw material melt 13 is low.

[0032] After extensive research into ways to solve the above problems, the inventors came up with the idea of ​​configuring the coils that make up the magnet so that the ratio of their height to their width exceeds 1, i.e., making them vertical. This makes it possible to deal with cases where the arrangement of the coils is limited due to restrictions on the device configuration by only reducing the width of the coils without changing their height. In this way, by configuring the magnet with vertical coils, the freedom of designing the magnetic field distribution can be increased compared to bobbin-type coils.

[0033] 3 shows a preferred example of a coil constituting a magnet of a single crystal manufacturing apparatus that can be used in the method for manufacturing a single crystal according to the present invention, where (a) is an overall view, (b) is a front view, (c) is a side view, and (d) is a bottom view. The coil 2 shown in FIG. 3 is configured so that the ratio of its height to its width exceeds 1, that is, it is configured vertically. More specifically, the coil 2 constituting the magnet 1 is rectangular and annular, and has two first parts 3 that are longitudinal members extending in the vertical direction, two second parts 4 that are transverse members extending in the horizontal direction, and four connection parts 5 that connect the first parts 3 and the second parts 4.

[0034] In the coil 2, the height Hi of the first portion 3 is configured to be greater than the length Wi of the second portion 4. As a result, the height of the coil 2 is also greater than the width, and the ratio of the height to the width exceeds 1. In the present invention, the "height of the coil" means the length of the longest part of the opening 2a of the annular coil in the up-down direction (vertical direction) (in FIG. 3, the height Hi of the first portion 3), and the "width of the coil" means the length of the longest part of the opening 2a in the horizontal direction (in FIG. 3, the length Wi of the second portion 4). In addition, when the coil 2 is curved toward the outer surface 2b as shown in FIG. 3(d), the width of the coil 2 is the length along the inner surface 2c of the coil 2.

[0035] The coils 2 constituting the magnet are preferably rectangular as shown in Fig. 3, but are not limited thereto and may be elliptical, for example. It is also preferable that all the coils 2 are vertical and have the same shape. This allows for the formation of a highly symmetrical magnetic field distribution.

[0036] With the coil 2 having such a configuration, even if the arrangement of the coil 2 is limited due to restrictions on the device configuration, it is possible to reduce only the width of the coil 2 without reducing the height of the coil 2. This makes it possible to suppress the effect of the magnetic field applied to the raw material melt 13 in the height direction, and to increase the degree of freedom in designing the magnetic field distribution.

[0037] The height Hi of the coil 2 is preferably 600 mm or more. This allows a horizontal magnetic field to be applied satisfactorily to the molten raw material 13 contained in the crucible 12 when producing a single crystal having a diameter of 300 mm or more (for example, a diameter of 301 to 340 mm for a silicon single crystal for a φ300 mm wafer, and a diameter of 451 to 500 mm for a silicon single crystal for a φ450 mm wafer). More preferably, the height Hi of the coil 2 is 750 to 1000 mm when producing a silicon single crystal for a φ300 mm wafer, and 1125 to 1500 mm when producing a silicon single crystal for a φ450 mm wafer.

[0038] As shown in Fig. 3(d), it is preferable that the second portion 4 of the coil 2 be curved toward the outer surface 2b of the coil 2. This allows the coil 2 to be arranged along the outer wall of the chamber 11, saving the space required for arranging the coil 2 and making the entire magnet 1 compact, but the second portion 4 may be configured in a straight line to form a flat coil 2.

[0039] The external width Wo of coil 2 (i.e. the length of second portion 4 plus the two connecting portions 5) is 1 / 4 or less of the circumference L of magnet 1, more preferably 1 / 6 or less of the circumference L of magnet 1, even more preferably 1 / 8 or less, and most preferably 1 / 12 or less. By making the external width Wo of coil 2 smaller relative to the circumference L of the magnet, more coils 2 can be arranged, increasing the freedom to space coils 2 tightly and tightly, and increasing the freedom to design the magnetic field distribution.

[0040] In addition, when the coil 2 is curved toward the outer surface 2b as shown in FIG. 3(d), the width Wo of the outer shape of the coil 2 is the length along the inner surface 2c of the coil 2 as shown in FIG. 3(d). By making the width Wo of the outer shape of the coil 2 smaller than the circumference L of the magnet, more coils 2 can be arranged, increasing the degree of freedom in the density between the coils 2, and increasing the degree of freedom in the design of the magnetic field distribution. In addition, when the coil 2 is curved toward the outer surface 2b and the inner surfaces 2c of four or more coils 2 form a circle, the "circumference of the magnet" refers to the length of the circumference of the circle formed by the inner surfaces 2c of the coils 2 when the magnet 1 is viewed from above. In addition, when the coil 2 is flat or the inner surfaces 2c of the coils 2 do not form a circle, the "circumference of the magnet" refers to the length of the circumference of the circle (a circle passing through the four midpoints) formed by the center (the midpoint of the line segment corresponding to the inner surface 2c) of the inner surface 2c of the coil 2 when the magnet 1 is viewed from above.

[0041] In relation to the relationship between the width Wo of the coil 2 and the circumference L of the magnet 1, it is preferable that the number of coils 2 is four or more, and at least one of them is vertical. By making the number of coils 2 four or more, it is possible to ensure sufficient freedom in designing the magnetic field distribution applied to the raw material melt 13 contained in the crucible 12. It is preferable that the number of coils 2 is a multiple of two. By making the number of coils 2 a multiple of two, it is possible to arrange the coils 2 with high symmetry. It is more preferable that the number of coils 2 is six or more, even more preferable that it is eight, and most preferable that it is twelve. In addition, it is preferable that the number of coils 2 is 40 or less. This makes it possible to avoid the magnetic field design becoming complicated and to perform the magnetic field design with a high degree of freedom, and also to suppress the cost of the magnet 1. Furthermore, it is preferable that the coils 2 are arranged so that the centers of gravity of all the coils 2 are located at the same height, and the magnetic field neutral plane is a horizontal plane.

[0042] The coil 2 can be constructed by preparing an annular support as shown in Fig. 3, providing a recess in the outer peripheral surface 2d that defines the outer shape of the support when viewed from above as shown in Fig. 3(b), or in the inner peripheral surface 2e that defines the opening of the support, and winding the wire housed in the recess. The coil 2 can also be constructed by winding the wire into the shape shown in Fig. 3 and solidifying it with resin without providing a support.

[0043] Furthermore, when the winding is wound around the outer peripheral surface 2d or inner peripheral surface 2e of the support, it is preferable that the outer peripheral surface 2d or inner peripheral surface 2e of the connection portion 5 constituting the coil 2 has a radius (rounded) at its corners so as to smoothly wind the winding that constitutes the coil 2. Furthermore, when the winding is not wound around the support, it is preferable to wind the winding with a radius at the portion corresponding to the connection portion 5.

[0044] Furthermore, in order to realize the desired magnetic field distribution using the coil 2, it is necessary to configure a control system that can independently control the current value flowing through each of the four or more coils, so that magnetic fields can be generated independently of each other.

[0045] It is preferable that the four or more coils 2 are arranged symmetrically with respect to an axis perpendicular to an axis extending vertically through the center of the magnet 1 when the magnet 1 is viewed from above. This makes it possible to form a symmetrical magnetic field distribution.

[0046] By setting the coil angle θ to 90° or more for four or more coils and pulling up a single crystal by aligning the surface of the raw material melt 13 with the magnetic field neutral plane, it is possible to suppress the fluctuation in oxygen concentration in the crystal pulling direction and the fluctuation in the crystal pulling speed, thereby producing a defect-free single crystal. Note that the coil angle θ is the angle between two coils 2 that sandwich the magnetic flux line at the center of the magnetic field, as shown in Figure 4.

[0047] FIG. 5 shows (c) the magnetic flux density in the x direction and (d) the magnetic flux density in the z direction (vertical up-down direction) for the arrangement of the bobbin type coil shown in (a) and the arrangement of the vertical rectangular coil shown in (b). The circle in FIG. 5(a) and FIG. 5(b) indicates the chamber 11, but there is no technical meaning in that the coils 22, 2 are in contact with the chamber 11. As shown in FIG. 5(d), the magnetic flux density at point A can be made 0.58M or more for both the bobbin type coil shown in FIG. 5(a) and the vertical rectangular coil shown in FIG. 5(b). However, as shown in FIG. 5(c), the magnetic flux density at point B can be made 2.23M or more for the vertical rectangular coil shown in FIG. 5(b), but not for the bobbin type coil shown in FIG. 5(a).

[0048] Figure 6 shows (c) the magnetic flux density in the x direction and (d) the magnetic flux density in the z direction (vertical up-down direction) for the bobbin coil arrangement shown in (a) and the vertical rectangular coil arrangement shown in (b). As shown in Figure 6(c), the magnetic flux density at point B can be made 2.23M or more for both the bobbin coil shown in Figure 6(a) and the vertical rectangular coil shown in Figure 6(b). However, as shown in Figure 6(d), while the magnetic flux density at point A can be made 0.58M or more for the vertical rectangular coil shown in Figure 6(b), it cannot be made for the bobbin coil shown in Figure 6(a).

[0049] Thus, while a bobbin-type coil cannot realize the magnetic flux density at points A and B of the present invention, the use of a vertical rectangular coil makes it possible to realize the magnetic flux density at points A and B of the present invention. However, the shape of the coil constituting the magnet of the single crystal production apparatus used in the present invention is not limited to a vertical rectangular coil, and any coil may be used as long as it can generate a magnetic field distribution that satisfies the requirements for the magnetic flux density at points A and B.

[0050] The single crystal produced by the present invention is not particularly limited as long as it can be produced by the CZ method, but it is possible to suitably produce a silicon single crystal with small fluctuations in oxygen concentration. EXAMPLES

[0051] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0052] (Example 1) A silicon single crystal with a diameter of 310 mm was produced using a single crystal production apparatus equipped with a magnet having a vertical rectangular annular coil as shown in Figure 3. The rectangular annular coil was configured so that the height of the magnetic field neutral plane was the same as point A in Figure 2(b), and four coils were arranged with a coil angle of 60°. Each coil was vertical and had the same shape, and the magnetic field neutral plane was configured to be a horizontal plane. Then, the magnitude and direction of the current flowing through the coils were adjusted to generate a magnetic field distribution with a magnetic flux density of 0.58 M at point A and a magnetic flux density of 1.43 M at point B. In this state, polycrystalline silicon, which is the silicon raw material contained in the crucible, was melted, and a seed crystal was immersed in the molten silicon and pulled up, and a silicon single crystal was grown below the seed crystal.

[0053] (Example 2) Silicon single crystals were produced in the same manner as in Example 1. However, the height of the magnetic field neutral plane relative to point A was changed so that the magnetic flux density at point A was 0.64 times the magnetic flux density M at the magnetic field center O, and the magnetic flux density at point B was 2.23 times. All other conditions were the same as in Example 1.

[0054] (Comparative Example) Silicon single crystals were produced in the same manner as in Example 1. However, the height of the magnetic field neutral plane relative to point A was changed so that the magnetic flux density at point A was 0.53 times the magnetic flux density M at the magnetic field center O, and the magnetic flux density at point B was 1.03 times. All other conditions were the same as in Example 1.

[0055] <Oxygen concentration in the axial direction of single crystal> FIG. 7 shows the variation in oxygen concentration in the axial direction of a silicon single crystal, where (a) is for a comparative example, (b) is for example 1, and (c) is for example 2. In FIG. 7, the axial position and oxygen concentration of the single crystal are normalized by a predetermined value. For the comparative example shown in FIG. 7(a), the variation in oxygen concentration in the axial direction of the single crystal was large and did not fall within the specified oxygen concentration range. On the other hand, for examples 1 and 2 shown in FIGS. 7(b) and 7(c), the variation in oxygen concentration was reduced compared to the comparative examples, and especially for example 2, the variation in oxygen concentration was reduced to about 1 / 5 compared to the comparative examples.

[0056] FIG. 8 shows the time variation of the temperature of the solid-liquid interface by a three-dimensional fluid simulation, where (a) is for the comparative example, (b) is for the invention example 1, and (c) is for the invention example 2. In FIG. 8, the time and the temperature of the solid-liquid interface are normalized by a predetermined value. For the comparative example shown in FIG. 8(a), the time variation of the temperature of the solid-liquid interface is large, and due to this temperature variation, the crystal pulling speed varies greatly, and it was found that a defect-free silicon single crystal could not be obtained. On the other hand, for the invention examples 1 and 2 shown in FIG. 8(b) and (c), the time variation of the temperature of the solid-liquid interface is reduced and the crystal pulling speed varies less than the comparative example, and it was found that a defect-free silicon single crystal could be obtained in both cases. In particular, for the invention example 2, the time variation of the temperature of the solid-liquid interface was reduced to about 1 / 50 compared to the comparative example. [Industrial Applicability]

[0057] INDUSTRIAL APPLICABILITY The present invention is useful in the semiconductor wafer manufacturing industry because it can produce defect-free silicon single crystal for semiconductor use by suppressing fluctuations in the oxygen concentration in the crystal pulling direction and fluctuations in the crystal pulling speed. [Explanation of symbols]

[0058] 1,21 Magnet 2,22 Coil 2a opening 2b External surface 2c Inside 2d outer surface 2e Inner surface 3. First Part 4. Second Part 5 Connection part 100 Single crystal manufacturing equipment 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, comprising applying a horizontal magnetic field to a crucible containing a melt of a single crystal material while pulling the single crystal, The magnetic field center O of the magnetic field neutral plane is the origin, the axis passing through the origin and parallel to the direction of the horizontal magnetic field is the y-axis, the axis passing through the origin and perpendicular to the direction of the horizontal magnetic field is the x-axis, the axis passing through the origin and perpendicular to the magnetic field neutral plane is the z-axis, the intersection of the z-axis and the inner surface of the crucible is point A, and the intersection of the x-axis and the inner surface of the crucible is point B. Before the start of pulling the single crystal, the magnetic field center O of the magnetic field neutral plane is positioned on the surface of the melt of the raw material of the single crystal, a magnetic flux density at point A of the magnetic field center O of the magnetic field neutral plane being M, the magnetic flux density at point A being 0.58×M or more and the magnetic flux density at point B being 1.47×M or more; and a single crystal is pulled up by applying the horizontal magnetic field to the melt so that the magnetic flux density at point A is 0.58×M or more and the magnetic flux density at point B is 1.47×M or more, the coordinates of the magnetic field center O being (0 mm, 0 mm, 0 mm), the coordinates of the point A being (0 mm, 0 mm, -400 mm), and the coordinates of the point B being (400 mm, 0 mm, 0 mm).

2. The method for producing a single crystal according to claim 1, wherein the horizontal magnetic field is applied using a magnet comprising four or more coils, at least one of which has a height-to-width ratio exceeding 1, and a control unit capable of generating a magnetic field for each of the four or more coils independently of one another.

3. The method for producing a single crystal according to claim 2 , wherein the coil is rectangular and annular.

4. The method for producing a single crystal according to claim 2 or 3, wherein the height of the coil is 600 mm or more.

5. The method for producing a single crystal according to any one of claims 1 to 4, wherein the single crystal is a silicon single crystal.

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