Single crystal pulling device and single crystal pulling method

Abstract

The present invention is a single crystal pulling device, comprising: a pulling furnace having a central axis; and a magnetic field generating device, which is arranged around the pulling furnace and has a superconducting coil, and suppresses convection in a crucible by applying a horizontal magnetic field to a molten semiconductor raw material, wherein the superconducting coil is saddle-shaped, and two pairs of saddle-shaped superconducting coils are provided, and the two coil axes of the two pairs of superconducting coils are contained in the same horizontal plane, and in the horizontal plane, when the direction of the magnetic field line of the central axis of the pulling furnace is set as the X axis, the center angle α between the two coil axes sandwiching the X axis is greater than 100 degrees and less than 120 degrees. Thus, a single crystal pulling device and a single crystal pulling method are provided, which can reduce the coil height by improving the magnetic field generation efficiency, and can raise the magnetic field center to the vicinity of the molten liquid surface of the semiconductor raw material, thereby obtaining a single crystal with a lower oxygen concentration than before.

Description

Technical Field

[0001] The present invention relates to a single crystal pulling device and a single crystal pulling method using the single crystal pulling device. Background Art

[0002] Semiconductors such as silicon and gallium arsenide are composed of single crystals and are used in memory of small to large computers, and memory devices are required to have larger capacity, lower cost, and higher quality.

[0003] In the past, as one of the single crystal pulling methods for manufacturing single crystals that meet the requirements of these semiconductors, the following method is known: applying a magnetic field to a molten semiconductor raw material contained in a crucible, thereby suppressing the heat convection generated in the molten liquid and manufacturing large-diameter and high-quality semiconductors (generally referred to as the magnetic field applied Czochralski (MCZ) method).

[0004] pass Figure 8 An example of a single crystal pulling apparatus based on the conventional CZ method will be described.

[0005] The single crystal pulling device 100 includes a pulling furnace 101 having an opening on the upper surface, and a crucible 102 is installed in the pulling furnace 101. In addition, a heater 103 for heating and melting a semiconductor raw material 106 in the crucible 102 is provided around the crucible 102 inside the pulling furnace 101, and a superconducting magnet 130 is arranged outside the pulling furnace 101, in which a pair (two) of superconducting coils 104 (104a, 104b) are installed in a refrigerant container (hereinafter also referred to as a cylindrical refrigerant container) 105 which is a cylindrical container.

[0006] When manufacturing a single crystal, a semiconductor raw material 106 is placed in a crucible 102 and heated by a heater 103 to melt the semiconductor raw material 106. A seed crystal (not shown) is lowered from, for example, the center of the crucible 102 to contact the molten liquid, and a pulling mechanism (not shown) is used to pull the seed crystal in a pulling direction 108 at a predetermined speed. Thus, the crystal grows in the solid-liquid interface layer to generate a single crystal. At this time, when the fluid movement of the molten liquid caused by the heating of the heater 103, that is, the heat convection, occurs, the pulled single crystal is prone to dislocation, and the yield rate of the single crystal generation is reduced.

[0007] Therefore, as a countermeasure, a superconducting coil 104 using a superconducting magnet 130 is used. That is, the semiconductor raw material 106 in the molten liquid receives the action-restraining force by the magnetic field lines 107 generated by energizing the superconducting coil 104, and does not generate convection in the crucible 102, and is slowly pulled upward along with the pulling of the seed crystal, thereby manufacturing a solid single crystal 109. In addition, although not shown in the figure, a pulling mechanism for pulling the single crystal 109 along the center line of the crucible (the center axis 110 of the pulling furnace 101) is provided above the pulling furnace 101.

[0008] Next, through Fig. 9 Yes Figure 8 An example of the superconducting magnet 130 used in the single crystal pulling apparatus 100 shown in FIG. 1 will be described.

[0009] The superconducting magnet 130 is a structure in which the superconducting coils 104 (104a, 104b) are housed in a cylindrical vacuum container 119 via a cylindrical refrigerant container. The superconducting magnet 130 houses a pair of superconducting coils 104a, 104b facing each other across the center of the cylindrical vacuum container 119. The pair of superconducting coils 104a, 104b are Helmholtz-type magnetic field coils that generate magnetic fields in the same direction in the lateral direction, such as Figure 8 As shown, magnetic lines of force 107 are generated that are symmetrical with respect to the central axis 110 of the pulling furnace 101 and the cylindrical vacuum container 119 (the position of the central axis 110 is referred to as the magnetic field center).

[0010] In addition, if Figure 8 , Fig. 9 As shown in FIG. 1 , the superconducting magnet 130 includes a current lead 111 for introducing current into the two superconducting coils 104a and 104b, a small helium refrigerator 112 for cooling the first radiation cover 117 and the second radiation cover 118 stored in the cylindrical vacuum container 119, a gas release pipe 113 for releasing the helium gas in the cylindrical refrigerant container 105, and a maintenance port 114 having a supply port for supplying liquid helium. A Figure 8 The pulling furnace 101 is shown.

[0011] Fig.10 The magnetic field distribution of the above-mentioned conventional superconducting magnet 130 is shown.

[0012] If the Fig.10 As shown, in the conventional superconducting magnet 130, since a pair of superconducting coils 104a and 104b are arranged facing each other, the arrangement direction of each coil ( Fig.10 In the X direction), the magnetic field gradually increases to both sides. In the direction orthogonal to this direction ( Fig.10 In the Y direction), the magnetic field gradually decreases in the upward and downward directions. In such an existing structure, Fig. 9 , Fig.10 As shown in FIG. 1 , since the magnetic field gradient in the range of the hole 115 is too large, the heat convection generated in the molten liquid is unevenly suppressed and the magnetic field efficiency is poor. Fig.10 As shown by the diagonal lines in the figure, the magnetic field is not uniform in the area near the center of the magnetic field (i.e. Fig.10, formed into a cross shape that is elongated vertically and horizontally), so the accuracy of suppressing thermal convection is poor, and there is a problem that high-quality single crystals cannot be pulled.

[0013] Patent Document 1 discloses a technique for solving the above-mentioned problems. Fig.11A , Fig. 11B The technology disclosed in Patent Document 1 will be described.

[0014] It shows another example of a superconducting magnet, Fig.11A It is a stereogram. Fig. 11B show Fig.11A In patent document 1, in order to solve the above-mentioned problem, as Fig.11A , Fig. 11B As shown in FIG. 1 , it is disclosed that the number of superconducting coils 104 is set to 4 or more (for example, 104a, 104b, 104c, and 104d), the center of each superconducting coil 104 is arranged on a plane in a cylindrical vacuum container 119 coaxially arranged around a pulling furnace, and the arranged superconducting coils 104 are set to face each other across the axis of the cylindrical vacuum container 119, and the arrangement angle θ between each pair of adjacent superconducting coils facing the inside of the cylindrical vacuum container 119 is set to θ (refer to FIG. 1 ). Fig. 11B ) is set to a range of 100°-130° (i.e., the center angle α between the adjacent coil axes sandwiching the X axis (refer to Fig. 11B ) is 50°-80°).

[0015] Thus, a transverse magnetic field with a small magnetic field gradient and good uniformity can be generated inside the hole 115, and a concentric or square magnetic field distribution can be generated on the plane, which can greatly suppress the unbalanced electromagnetic force. In addition, as a result, the uniform magnetic field area in the pulling direction is increased, and the magnetic field in the transverse magnetic field direction is roughly horizontal. By suppressing the unbalanced electromagnetic force, high-quality single crystals can be manufactured. In addition, it is also disclosed that according to this single crystal pulling method, high-quality single crystals can be pulled with a good yield. In addition, Fig. 11B The symbol d in is the diameter (inner diameter) of the superconducting coil, and the symbol 1 is the distance between a pair of coils.

[0016] According to this method, since the magnetic field distribution applied to the molten semiconductor material is made uniform and the unbalanced electromagnetic force is suppressed, heat convection is suppressed even at a lower magnetic flux density than in the conventional technology using two coils.

[0017] However, even with such a uniform magnetic field distribution, in the transverse magnetic field where the magnetic lines of force are directed toward the X-axis, a comprehensive heat transfer analysis including three-dimensional melt convection shows that there is a difference in heat convection in the section parallel to the X-axis and in the section parallel to the Y-axis (see patent document 2).

[0018] When a conductive fluid moves in a magnetic field, an induced current is generated in a direction orthogonal to the magnetic force lines and the velocity component perpendicular to the magnetic force lines. When a quartz crucible with electrical insulation is used, the crucible wall and the free surface of the molten semiconductor raw material form an insulating wall, so the induced current in these directions orthogonal to the magnetic force lines no longer flows. Therefore, the convection suppression force based on the electromagnetic force is weakened in the upper part of the molten semiconductor raw material. In addition, if the cross section parallel to the X-axis (cross section parallel to the magnetic force lines) and the cross section perpendicular to the X-axis (cross section perpendicular to the magnetic force lines) are compared, the convection in the cross section perpendicular to the X-axis (cross section perpendicular to the magnetic force lines) is stronger.

[0019] In this way, when a uniform magnetic field distribution is formed by the above four coils, although the velocity difference of convection becomes slightly smaller, an uneven flow velocity distribution is formed in the circumferential direction. In particular, since the flow field connecting the growth interface from the crucible wall remains in the cross section perpendicular to the magnetic field lines, the oxygen dissolved from the quartz crucible reaches the crystal, so the effect of reducing the oxygen concentration due to the application of the magnetic field is limited, and it is difficult to cope with the requirements of extremely low oxygen concentrations such as the semiconductor crystals for power components or image sensors that have recently increased in demand. In addition, the presence of an uneven flow field in the circumferential direction causes growth stripes in the crystal that is pulled while rotating the crystal. When evaluating the cross section parallel to the growth direction, the resistivity and oxygen concentration changes during the crystal rotation period are observed, so the distribution becomes annular in the wafer surface sliced ​​perpendicular to the growth direction.

[0020] In order to solve this problem, Patent Document 2 discloses Fig. 12A , Fig. 12B The single crystal pulling device shown. Fig. 12A is a schematic diagram of the device. Fig. 12B A cross section of an example of a superconducting magnet is shown.

[0021] In a horizontal plane 120 including two coil axes 121 passing through the centers of the pairs of superconducting coils 104 (104a and 104c, 104b and 104d), a magnetic field distribution is generated such that when the direction of the magnetic force lines of the central axis 110 of the pulling furnace is taken as the X-axis, the magnetic flux density distribution on the X-axis is a convex distribution, and when the magnetic flux density of the central axis 110 in the horizontal plane 120 is taken as the magnetic flux density setting value, the magnetic flux density on the X-axis is less than 80% of the magnetic flux density setting value at the crucible wall, and at the same time, in the horizontal plane 12 0 and passing through the center axis 110 is a convex distribution, and the magnetic flux density on the Y axis is more than 140% of the set value of the magnetic flux density at the crucible wall. In the magnetic field generating device, two pairs of superconducting coils 104 (104a and 104c, 104b and 104d) arranged opposite to each other are arranged so that their respective coil axes 121 are contained in the same horizontal plane 120, and the center angle α between the two coil axes 121 with respect to the X axis is set to be greater than 100 degrees and less than 120 degrees.

[0022] Thus, the following effects can be obtained in the technology disclosed in Patent Document 2. That is, even in a cross section perpendicular to the X-axis where the convection suppression force based on the electromagnetic force is insufficient, the flow rate of the molten semiconductor raw material can be reduced, and the flow rate of the cross section of the molten semiconductor raw material parallel to the X-axis can be balanced with the flow rate of the cross section of the molten semiconductor raw material perpendicular to the X-axis.

[0023] In addition, the single crystal pulling device can be configured to significantly reduce the concentration of oxygen taken into the single crystal by reducing the flow rate of the molten semiconductor raw material even in the cross section perpendicular to the X-axis, thereby lengthening the time for oxygen dissolved from the crucible wall to reach the single crystal and increasing the amount of oxygen evaporated from the free surface of the molten semiconductor raw material. In addition, the single crystal pulling device can be configured to suppress growth stripes in the cultivated single crystal by balancing the flow rate of the cross section of the molten semiconductor raw material parallel to the X-axis and the flow rate of the cross section of the molten semiconductor raw material perpendicular to the X-axis.

[0024] Prior art literature

[0025] Patent Literature

[0026] Patent Document 1: Japanese Patent Application Publication No. 2004-51475

[0027] Patent Document 2: Japanese Patent Application Publication No. 2017-57127

[0028] Patent Document 3: Japanese Patent Application Laid-Open No. 10-291892 Summary of the invention

[0029] 1. Technical issues to be resolved

[0030] However, the inventors of this case analyzed the magnetic field distribution in various coil configurations and found that the magnetic field distribution described in Patent Document 2 can be achieved even in coil configurations other than those described in Patent Document 2.

[0031] In addition, in order to improve the magnetic field efficiency with the coil configuration, the coil diameter needs to be as large as possible, but the height of the container containing the coil also needs to be increased accordingly. In the case of a cylindrical container magnet device (also called a magnetic field generating device or a superconducting magnet), it needs to be disassembled and installed at the end of the crystal pulling stage, but at this time, the magnet device needs to be lowered and raised, so the magnet device needs to be installed on a lifting device.

[0032] Regarding the positional relationship between the magnet and the molten raw material, as described in Patent Document 3, it is known that when the height of the magnetic field center of the transverse magnetic field is raised to near the molten liquid surface of the molten raw material, the oxygen concentration in the crystal decreases, and when it is lowered to the depth of the molten liquid, the oxygen concentration increases. The upper limit position of this magnet device is determined by the stroke of the lifting device and the interference on the side of the pulling furnace. Usually, in order to enable the chamber of the pulling furnace to be lifted and rotated, an arm is connected to a hydraulic cylinder located on the outside of the magnet device. Fig.13 An example of the lifting device 122 of the pulling furnace and the lifting device 123 of the superconducting magnet are shown in FIG. Therefore, this determines the upper limit position of the magnet device. Since the greater the total height of the magnet device, the more difficult it is to raise the center of the coil in the height direction, that is, the center of the magnetic field, upward, it is not conducive to obtaining low-oxygen crystals.

[0033] The present invention is made in view of the above-mentioned problems, and its purpose is to provide a single crystal pulling device and a single crystal pulling method that can reduce the coil height by improving the magnetic field generation efficiency and raise the center of the magnetic field to near the molten liquid surface of the semiconductor raw material, thereby obtaining a single crystal with a lower oxygen concentration than before.

[0034] (II) Technical solution

[0035] To achieve the above-mentioned object, the present invention provides a single crystal pulling device, comprising: a pulling furnace, which is equipped with a heater and a crucible for accommodating molten semiconductor raw material and has a central axis; and a magnetic field generating device, which is arranged around the pulling furnace and has a superconducting coil, and applies a horizontal magnetic field to the molten semiconductor raw material by energizing the superconducting coil, thereby suppressing the convection of the molten semiconductor raw material in the crucible, characterized in that:

[0036] The superconducting coil of the magnetic field generating device is in a saddle shape that is bent along the outer shape of the pulling furnace, and two pairs of the saddle-shaped superconducting coils that are arranged opposite to each other are provided around the pulling furnace.

[0037] When the axis passing through the centers of the pair of superconducting coils arranged opposite to each other is defined as the coil axis,

[0038] The two coil axes of the two sets of superconducting coils are contained in the same horizontal plane,

[0039] In the horizontal plane, when the direction of the magnetic force lines on the central axis of the pulling furnace is defined as an X-axis, a center angle α between the two coil axes sandwiching the X-axis is not less than 100 degrees and not more than 120 degrees.

[0040] The center angle α between the two coil axes sandwiching the X-axis is within a range of 100 degrees or more and 120 degrees or less, so that near the cross section perpendicular to the X-axis, the magnetic force lines are perpendicular to the component of the crucible, so that it is easy to suppress natural convection near the cross section perpendicular to the X-axis, and it can be balanced with the flow rate of the cross section parallel to the X-axis. Even in the cross section perpendicular to the X-axis, by reducing the flow rate of the molten semiconductor raw material, the time for the oxygen dissolved from the crucible wall to reach the single crystal becomes longer, and the amount of oxygen evaporated from the free surface of the molten semiconductor raw material increases, thereby forming a single crystal pulling device that can significantly reduce the concentration of oxygen taken into the single crystal.

[0041] Furthermore, by balancing the flow velocity in the cross section parallel to the X-axis and the flow velocity in the cross section perpendicular to the X-axis of the molten semiconductor raw material, a single crystal pulling apparatus can be provided that is capable of suppressing growth streaks in a grown single crystal.

[0042] In addition, adjacent superconducting coils can be appropriately arranged without coming too close to each other and colliding with each other.

[0043] In addition, since the superconducting coil is not a circular coil as in the prior art but a saddle-shaped coil, the circumference of the coil can be increased, and thus a magnetic field with a larger magnetic flux density can be generated with the same current value. That is, the efficiency of magnetic field generation can be improved.

[0044] In addition, due to the saddle shape, the total height of the coil is smaller than that of a circular coil, so that the center height position of the coil in the magnetic field generating device can be increased. Therefore, when the lifting device is raised to the upper limit, the center of the magnetic field can be set at a higher position relative to the melt, and a single crystal with a lower oxygen concentration can be obtained compared to the existing single crystal pulling device such as Patent Document 2.

[0045] In addition, in order to achieve the above-mentioned purpose, the present invention provides a single crystal pulling device, comprising: a pulling furnace, which is equipped with a heater and a crucible for accommodating molten semiconductor raw material and has a central axis; and a magnetic field generating device, which is arranged around the pulling furnace and has a superconducting coil, and applies a horizontal magnetic field to the molten semiconductor raw material by energizing the superconducting coil, thereby suppressing the convection of the molten semiconductor raw material in the crucible, characterized in that

[0046] The superconducting coil of the magnetic field generating device is saddle-shaped and curved with a curvature greater than the shape along the outer shape of the pulling furnace. Two pairs of the saddle-shaped superconducting coils are arranged opposite to each other around the pulling furnace.

[0047] When the axis passing through the centers of the pair of superconducting coils arranged opposite to each other is defined as the coil axis,

[0048] The two coil axes of the two sets of superconducting coils are contained in the same horizontal plane,

[0049] In the horizontal plane, when the direction of the magnetic force lines on the central axis of the pulling furnace is defined as an X-axis, a center angle α between the two coil axes sandwiching the X-axis is not less than 100 degrees and not more than 120 degrees.

[0050] The center angle α between the two coil axes sandwiching the X-axis is within a range of 100 degrees or more and 120 degrees or less, so that near the cross section perpendicular to the X-axis, the magnetic force lines are perpendicular to the component of the crucible, so that it is easy to suppress natural convection near the cross section perpendicular to the X-axis, and it can be balanced with the flow rate of the cross section parallel to the X-axis. Even in the cross section perpendicular to the X-axis, by reducing the flow rate of the molten semiconductor raw material, the time for the oxygen dissolved from the crucible wall to reach the single crystal becomes longer, and the amount of oxygen evaporated from the free surface of the molten semiconductor raw material increases, thereby forming a single crystal pulling device that can significantly reduce the concentration of oxygen taken into the single crystal.

[0051] Furthermore, by balancing the flow velocity of the molten semiconductor raw material in the cross section parallel to the X-axis and the flow velocity in the cross section perpendicular to the X-axis, a single crystal pulling apparatus can be provided that is capable of suppressing growth streaks in a grown single crystal.

[0052] In addition, adjacent superconducting coils can be appropriately arranged without coming too close to each other and colliding with each other.

[0053] In addition, since the superconducting coil is not a circular coil as in the prior art but a saddle-shaped coil, the circumference of the coil can be increased, so a magnetic field with a larger magnetic flux density can be generated with the same current value. That is, the efficiency of magnetic field generation can be improved.

[0054] In addition, since the saddle-shaped coil has a total height smaller than that of a circular coil, the center height position of the coil in the magnetic field generating device (the height position of the coil axis) can be increased. Therefore, when the lifting device is raised to the upper limit, the center of the magnetic field can be set at a higher position relative to the melt, and a single crystal with a lower oxygen concentration can be obtained compared to the existing single crystal pulling device such as Patent Document 2.

[0055] In addition, in a region (coil axis angle region) at an angle corresponding to (or close to) the center region of the paired superconducting coils (i.e., near the position of the coil axis described above), the magnetic flux density component orthogonal to the crucible becomes stronger than in other angle regions, and the diffusion boundary layer of oxygen in the melt near the inner wall of the crucible becomes thinner, so oxygen is easily dissolved from the crucible. However, in the present invention, by utilizing the fact that the magnetic flux density at a position far from the coil is inversely proportional to the square of the distance to the coil, the saddle shape of the superconducting coil is curved with a curvature greater than the shape along the outer shape of the pulling furnace, so that the magnetic flux density in the coil axis angle region can be reduced, and the dissolution of oxygen from the crucible in this angle region can be suppressed, and as a result, a single crystal with a lower oxygen concentration can be obtained.

[0056] In this case, a ratio of the curvature of the saddle-shaped superconducting coil to the curvature of the shape along the outer shape of the pulling furnace may be 1.2 or more and 2.0 or less.

[0057] If the ratio (also called curvature ratio) is 1.2 or more, the above-mentioned reduction in magnetic flux density and suppression of oxygen dissolution can be performed more effectively. In addition, if it is 2.0 or less, the outer shape of the housing storing the coil can be prevented from being too large, and the reduction in the maximum magnetic field strength due to the reduction in the central magnetic field strength can be prevented.

[0058] At this time, the magnetic field generating device may be disposed on a lifting device that can move up and down in a vertical direction.

[0059] Thus, when disassembling and installing after the operation is completed, the magnetic field generating device is lowered, and the operator can easily disassemble and clean the hot area in the furnace. In addition, even during single crystal pulling, the height position of the magnetic field generating device can be more easily adjusted to make the oxygen concentration in the single crystal reach a desired value.

[0060] In addition, the saddle-shaped superconducting coil may have a longitudinal width shorter than a lateral width.

[0061] With such a superconducting coil, the total height of the coil can be more reliably reduced, and the center height position of the coil can be increased, the magnetic field center can be set at a higher position, and a single crystal with a low oxygen concentration can be obtained more easily.

[0062] In addition, the present invention provides a single crystal pulling method, characterized in that a semiconductor single crystal is pulled using the above-mentioned single crystal pulling apparatus.

[0063] Such a single crystal pulling method can grow a semiconductor single crystal in which the concentration of oxygen taken in is greatly reduced and growth streaks are suppressed.

[0064] At this time, when the semiconductor single crystal is pulled up, the height position of the magnetic field generating device can be adjusted according to a target value of the oxygen concentration contained in the semiconductor single crystal.

[0065] In this way, the oxygen concentration can be finely controlled, and a semiconductor single crystal with a low oxygen concentration can be grown more reliably.

[0066] (III) Beneficial effects

[0067] As described above, the single crystal pulling apparatus of the present invention can be configured as a single crystal pulling apparatus capable of significantly reducing the concentration of oxygen taken into the single crystal and suppressing growth streaks in the grown single crystal.

[0068] In addition, if it is the single crystal pulling device of the present invention, it can be constructed as the following single crystal pulling device, which can increase the height position of the coil center and increase the time for oxygen from the crucible to reach the single crystal. In addition, it can inhibit the dissolution of oxygen from the crucible in the coil axis angle area, and can greatly reduce the concentration of oxygen taken into the single crystal, and can inhibit the growth stripes in the cultivated single crystal.

[0069] Furthermore, according to the single crystal pulling method of the present invention, it is possible to grow a semiconductor single crystal in which the concentration of oxygen taken in is greatly reduced and growth streaks are suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 This is a schematic diagram showing an example of a single crystal pulling apparatus according to the present invention.

[0071] Figure 2A This is a perspective view showing an example of the shape of the superconducting coil of the present invention.

[0072] Figure 2B This is a cross-sectional view showing an example of the arrangement of the superconducting coil of the present invention.

[0073] Figure 3 This is an analysis diagram showing the magnetic flux density distribution in Example 1.

[0074] Figure 4 This is an analysis diagram showing the velocity vector and oxygen concentration distribution in the melt in Example 1.

[0075] Figure 5 This is an analysis diagram showing the velocity vector and oxygen concentration distribution in the melt in Example 2.

[0076] Figure 6 This is an analysis diagram showing the magnetic flux density distribution in Comparative Example 1.

[0077] Figure 7 This is an analysis diagram showing the velocity vector and oxygen concentration distribution in the melt in Comparative Example 1.

[0078] Figure 8 This is a schematic diagram showing an example of a conventional single crystal pulling apparatus.

[0079] Fig. 9 This is a schematic diagram showing an example of a conventional superconducting magnet.

[0080] Fig.10 This is an explanatory diagram showing an example of magnetic field distribution of a conventional superconducting magnet.

[0081] Fig.11A This is a perspective view showing an example of another conventional superconducting magnet.

[0082] Fig. 11B This is a cross-sectional view showing an example of another conventional superconducting magnet.

[0083] Fig. 12A This is a schematic diagram showing an example of another conventional single crystal pulling apparatus.

[0084] Fig. 12B This is a cross-sectional view showing an example of another conventional superconducting magnet.

[0085] Fig.13 This is a schematic diagram showing an example of a lifting device for a pulling furnace and a lifting device for a superconducting magnet.

[0086] Fig.14A This is a perspective view showing another example of the shape of the superconducting coil of the present invention.

[0087] Fig. 14B This is a cross-sectional view showing another example of the arrangement of the superconducting coil according to the present invention.

[0088] Fig.15 This is an analysis diagram showing the magnetic flux density distribution in Example 3.

[0089] Fig.16 This is an analysis diagram showing the velocity vector and oxygen concentration distribution in the melt in Example 3.

[0090] Fig.17 This is an analysis diagram showing the velocity vector and oxygen concentration distribution in the melt in Example 4.

[0091] Fig.18 This is a graph showing the relationship between the magnetic flux density component (B⊥) perpendicular to the inner wall of the crucible and the circumferential angle when four coils are arranged.

[0092] Fig.19 3 is an analysis diagram showing the magnetic flux density distribution in Example 5.

[0093] Fig. 20This is an analysis diagram showing the velocity vector and oxygen concentration distribution in the melt in Example 5. DETAILED DESCRIPTION

[0094] When a conductive fluid moves in a magnetic field, an induced current is generated in a direction perpendicular to the magnetic lines of force and the velocity component perpendicular to the magnetic lines of force. Since the crucible wall and the free surface of the molten semiconductor raw material form an insulating wall when an electrically insulating quartz crucible is used, the induced current in the direction perpendicular to these directions no longer flows. Therefore, even in the molten semiconductor raw material, the convection suppression force is insufficient near the cross section perpendicular to the X-axis.

[0095] However, when two pairs of superconducting coils are arranged opposite to each other around a pulling furnace, and the axes passing through the centers of the paired superconducting coils are taken as coil axes, if the two coil axes of the two pairs of superconducting coils are included in the same horizontal plane, and the center angle α between the two coil axes sandwiching the X-axis (the direction of the magnetic field lines of the central axis of the pulling furnace in the horizontal plane) is 100 degrees or more and 120 degrees or less, a magnetic field distribution as described in Patent Document 2 can be generated, and even in a cross section perpendicular to the X-axis where the convection suppression force based on the electromagnetic force is insufficient, the flow rate of the molten semiconductor raw material can be reduced, and the flow rate of the cross section parallel to the X-axis of the molten semiconductor raw material can be balanced with the flow rate of the cross section perpendicular to the X-axis of the molten semiconductor raw material. And, as a result, as described above, the oxygen concentration taken into the single crystal can be greatly reduced, and the growth streaks in the grown single crystal can be suppressed.

[0096] In addition, if a saddle-shaped coil is used as a superconducting coil, the efficiency of generating a magnetic field can be improved, and the total height of the coil can be easily reduced compared to a circular coil, thereby increasing the center height position of the coil, setting the center position of the magnetic field to a higher position, and obtaining a single crystal with a lower oxygen concentration.

[0097] In addition, since the saddle-shaped coil is bent with a curvature greater than the shape along the outer shape of the pulling furnace, the magnetic flux density in the coil axis angle region where oxygen is more easily dissolved from the crucible is reduced, thereby seeking to suppress the dissolution of oxygen from the crucible in this angle region, thereby obtaining a single crystal with a lower oxygen concentration.

[0098] The inventors of this case discovered these matters and completed the present invention.

[0099] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.

[0100] Figure 1 An example of a single crystal pulling apparatus according to the present invention is shown.

[0101] Figure 1The single crystal pulling device 11 is based on the CZ method and comprises: a pulling furnace 1, which is equipped with a heater 3 and a crucible 2 for accommodating molten semiconductor raw material 6 and has a central axis 10; and a superconducting magnet (magnetic field generating device 30), which is arranged around the pulling furnace 1 and has a superconducting coil, and is configured to apply a horizontal magnetic field to the molten liquid (molten semiconductor raw material, also called melt) 6 by energizing the superconducting coil, thereby suppressing the convection of the molten liquid 6 in the crucible 2 while pulling the single crystal 9 in the pulling direction 8.

[0102] (First Embodiment of Superconducting Coil)

[0103] Here, refer to Figure 2A , Figure 2B , the shape and arrangement of the superconducting coils in the magnetic field generating device 30 are described in detail. Figure 2A is a perspective view showing an example of the shape of a superconducting coil. Figure 2B This is a cross-sectional view showing an example of its configuration.

[0104] There are four superconducting coils (also simply referred to as coils) 4 (4a-4d) in total, each of which has a saddle shape bent along the outer shape of the cylindrical pulling furnace 1. Two pairs of coils are arranged opposite to each other around the pulling furnace 1. Here, they are a combination of 4a and 4c, and 4b and 4d.

[0105] Since the coil 4 is saddle-shaped instead of circular like the conventional ones, the circumference of the coil can be lengthened, a magnetic field with a higher magnetic flux density can be generated, and the efficiency of magnetic field generation can be improved.

[0106] Moreover, compared with a circular coil, it is easy to further reduce the total height of the coil, so the center height position of the coil can be raised to a higher position than that of a circular coil. That is, the magnetic field center can be set at a higher position relative to the melt 6, and the single crystal 9 with a lower oxygen concentration can be manufactured.

[0107] In addition, the vertical width of the coil 4 may be shorter than the horizontal width. In this case, the total height of the coil can be more reliably reduced, and the single crystal 9 with a low oxygen concentration can be obtained more easily.

[0108] In addition, when the axis passing through the centers of the paired coils 4 arranged opposite to each other is taken as the coil axis, the two coil axes 13 and 14 in the two pairs of coils 4 (the pair of 4a and 4c, the pair of 4b and 4d) are included in the same horizontal plane 12 (see Figure 1 ). In addition, regarding the magnetic force lines 7, in the horizontal plane 12, when the direction of the magnetic force lines of the central axis 10 of the pulling furnace 1 is the X-axis, the angle formed by the two coil axes 13 and 14 sandwiching the X-axis (center angle α) is greater than 100 degrees and less than 120 degrees.

[0109] Thus, if the central angle α is arranged to be 100 degrees or more, a magnetic field distribution can be generated as in Patent Document 2. In addition, the flow velocity of the cross section of the melt 6 parallel to the X axis and the flow velocity of the cross section perpendicular to the X axis can be balanced.

[0110] By achieving this balance, even in the cross section perpendicular to the X-axis, the time it takes for oxygen dissolved from the inner wall of crucible 2 to reach single crystal 9 is increased, and the amount of oxygen evaporated from the free surface of melt 6 is increased, thereby significantly reducing the oxygen concentration taken into single crystal 9.

[0111] Furthermore, by achieving the above-mentioned balance, growth streaks in single crystal 9 can be suppressed.

[0112] Furthermore, if the angle is 120 degrees or less, the adjacent coils 4 can be appropriately arranged without colliding with each other.

[0113] (Second Embodiment of Superconducting Coil)

[0114] Here, refer to Fig.14A , Fig. 14B Regarding the shape and arrangement of the superconducting coils in the magnetic field generating device 30, other embodiments are described in detail. Fig.14A is a perspective view showing an example of the shape of a superconducting coil. Fig. 14B This is a cross-sectional view showing an example of its configuration.

[0115] There are four superconducting coils (also simply referred to as coils) 4 (4a to 4d) in total, each of which has a saddle shape that is curved with a curvature greater than the shape along the outer shape of the cylindrical pulling furnace 1. Two pairs of coils are provided around the pulling furnace 1. Here, they are a combination of 4a and 4c, and 4b and 4d.

[0116] Since the coil 4 is saddle-shaped instead of circular like the conventional ones, the circumference of the coil can be lengthened, a magnetic field with a higher magnetic flux density can be generated, and the efficiency of magnetic field generation can be improved.

[0117] Moreover, compared with a circular coil, it is easy to further reduce the total height of the coil, so the center height position of the coil can be raised to a higher position than that of a circular coil. That is, the magnetic field center can be set at a higher position relative to the melt 6, and the single crystal 9 with a lower oxygen concentration can be manufactured.

[0118] In addition, the vertical width of the coil 4 may be shorter than the horizontal width. In this case, the total height of the coil can be more reliably reduced, and the single crystal 9 with a low oxygen concentration can be obtained more easily.

[0119] In addition, when the axis passing through the centers of the paired coils 4 arranged opposite to each other is taken as the coil axis, the two coil axes 13 and 14 in the two pairs of coils 4 (the pair of 4a and 4c, the pair of 4b and 4d) are included in the same horizontal plane 12 (see Figure 1 ). In addition, regarding the magnetic force lines 7, in the horizontal plane 12, when the direction of the magnetic force lines of the central axis 10 of the pulling furnace 1 is the X-axis, the angle formed by the two coil axes 13 and 14 sandwiching the X-axis (center angle α) is greater than 100 degrees and less than 120 degrees.

[0120] Thus, if the central angle α is arranged to be 100 degrees or more, a magnetic field distribution can be generated as in Patent Document 2. In addition, the flow velocity of the cross section of the melt 6 parallel to the X axis and the flow velocity of the cross section perpendicular to the X axis can be balanced.

[0121] By achieving this balance, even in the cross section perpendicular to the X-axis, the time it takes for oxygen dissolved from the inner wall of crucible 2 to reach single crystal 9 is increased, and the amount of oxygen evaporated from the free surface of melt 6 is increased, thereby significantly reducing the oxygen concentration taken into single crystal 9.

[0122] Furthermore, by achieving the above-mentioned balance, growth streaks in single crystal 9 can be suppressed.

[0123] Furthermore, if the angle is 120 degrees or less, the adjacent coils 4 can be appropriately arranged without colliding with each other.

[0124] Here, the curvature of the coil 4 will be described in detail. As described above, the coil 4 is curved with a curvature greater than the shape following the outer shape of the pulling furnace 1, and the process by which the inventors discovered the reason for such curvature will be described.

[0125] Fig.18 is a graph in which the magnetic flux density component (B⊥) perpendicular to the inner wall of the quartz crucible 2 is plotted against the circumferential angle. Fig. 14B As shown, the circumferential angle refers to the angle of counterclockwise rotation with the space between coils 4a and 4b as the reference (0°). In addition, here, the case where the four coils 4a-4d are arranged with a center angle α of 120 degrees is taken as an example. Taking the shape along the outer shape of the pulling furnace 1 as the reference, when the curvature ratio (the ratio of the curvature of the coil 4 to the curvature of the shape along the outer shape of the pulling furnace 1) is increased from 1.0 to 1.5 and then to 2.0 from this reference, B⊥ near 35° and 145° of the center area of ​​each coil (that is, the angle area near the position of the aforementioned coil axes 13 and 14, which is the coil axis angle area) is relaxed.

[0126] If the magnetic field distribution is formed by the arrangement of the coil 4 with the center angle α being 100 degrees or more and 120 degrees or less as in the present invention, the difference in the convection suppression force in the cross section parallel to the X-axis and the cross section perpendicular to the X-axis is smaller than that of the conventional horizontal magnetic field, even so, since there are four coil axis angle regions in the entire circumference, especially the magnetic flux density component orthogonal to the crucible 2 is strong, the diffusion boundary layer of oxygen in the melt 6 near the inner wall of the crucible 2 becomes thinner, and oxygen is more easily dissolved from the quartz crucible 2 than in other angle regions. Since the magnetic flux density at a place far from the coil 4 is inversely proportional to the square of the distance from the coil 4, the magnetic flux density in these coil axis angle regions can be reduced by increasing the curvature of the coil 4 (by making the curvature ratio greater than 1). As a result, the dissolution of oxygen from the crucible 2 in the coil axis angle region can be suppressed, and thus, a single crystal 9 with a lower oxygen concentration can be obtained.

[0127] The curvature of the coil 4 is not particularly limited as long as it is greater than the curvature of the shape along the outer shape of the pulling furnace 1. When the curvature ratio of the shape along the outer shape of the pulling furnace 1 is set to 1.0 (in Fig. 14B The curvature ratio is preferably in the range of 1.2 or more and 2.0 or less. In addition, the curvature ratio can be set to a value at the center of the wall thickness of the coil 4, for example. When it is set to 1.2 or more, the above-mentioned suppression of oxygen dissolution can be performed more effectively. In addition, if it is 2.0 or less, the outer shape of the shell storing the coil 4 can be prevented from being too large, and the reduction in the maximum magnetic field strength caused by the reduction in the central magnetic field strength can be suppressed.

[0128] In addition, if Figure 1 As shown, the single crystal pulling device 11 includes a lifting device 22 for the pulling furnace 1, and can lift and rotate the pulling furnace 1 in the vertical direction.

[0129] There is also a lifting device 23 for the magnetic field generating device 30, and the magnetic field generating device 30 installed on the lifting device 23 can be lifted and lowered in the vertical direction (moved up and down). Therefore, after the operation is completed, the hot area of ​​the pulling furnace 1 can be easily disassembled and cleaned, and by adjusting the height of the magnetic field generating device 30, the oxygen concentration of the grown single crystal 9 can be easily adjusted.

[0130] Next, a single crystal pulling method of the present invention using the single crystal pulling apparatus 11 of the present invention as described above will be described. Here, a method of pulling a semiconductor single crystal, that is, a silicon single crystal will be described.

[0131] First, in the single crystal pulling apparatus 11 , a semiconductor raw material (polycrystalline silicon) is placed in the crucible 2 and heated by the heater 3 to melt the semiconductor raw material (melt 6 ).

[0132] Next, by energizing superconducting coil 4 , a horizontal magnetic field generated by magnetic field generator 30 is applied to melt 6 , thereby suppressing convection of melt 6 in crucible 2 .

[0133] Then, a seed crystal (not shown) is lowered from, for example, the center of the crucible 2 to contact the melt 6, and the seed crystal is pulled while being rotated at a predetermined speed in the pulling direction 8 by a pulling mechanism (not shown). As a result, a crystal grows at the solid-liquid interface, and a semiconductor single crystal (silicon single crystal) 9 is generated.

[0134] Such a single crystal pulling method can produce a semiconductor single crystal with greatly reduced oxygen concentration and suppressed growth streaks. The oxygen concentration in the pulled single crystal is not particularly limited, and in particular, a single crystal with an oxygen concentration of 5 ppma-JEIDA or less, preferably 3 ppma-JEIDA or less, and further 1 ppma-JEIDA or less can be produced.

[0135] Furthermore, when the semiconductor single crystal is pulled up, the height position of the magnetic field generating device 30 can be adjusted using the lifting device 23 according to the target value of the oxygen concentration contained in the semiconductor single crystal.

[0136] Specifically, the relationship between the height position of the magnetic field generating device 30 and the oxygen concentration in the single crystal 9 is obtained in advance through experiments, and the height position of the magnetic field generating device 30 is set to a desired height position before the pulling starts. During the pulling of the single crystal 9, the oxygen concentration in the single crystal can be controlled by using other parameters without changing the magnetic field height. Representative parameters include the crucible rotation speed and the heater position.

[0137] Furthermore, during the pulling of one single crystal 9, the oxygen concentration can be finely controlled by pattern-controlling the height position of the magnetic field generating device 30.

[0138] Example

[0139] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.

[0140] (Example 1)

[0141] use Figure 1 , Figure 2A , Figure 2B The single crystal pulling apparatus 11 of the present invention shown in the figure pulled a single crystal.

[0142] After performing magnetic field analysis and 3D melt convection analysis on the following magnetic field generating device, a silicon single crystal was pulled using the device. In the magnetic field generating device, four superconducting coils with a longitudinal width of 620 mm and a lateral width (length along the outermost circumference of the bend) of about 985 mm are arranged in the same horizontal plane (there are two pairs of opposing coils). The coils are saddle-shaped coils in the shape of a circle with a radius of 900 mm with the central axis of the pulling furnace as the center line. When the direction of the magnetic field lines of the central axis is the X-axis, the center angle α between the two coil axes sandwiching the X-axis is arranged to be 120 degrees.

[0143] The calculation conditions for the analysis were 400 kg of feed, 32-inch (80 cm) crucible, 306 mm diameter silicon single crystal, 9 rpm crystallization speed, 0.4 rpm crucible speed, and 0.4 mm / min pulling speed.

[0144] Figure 3 This is a magnetic field analysis result based on ANSYS-Maxwell3D. It is a distribution diagram of the magnetic flux density after adjusting the coil current × number of turns to a magnetic flux density of 1000 Gauss on the central axis.

[0145] Based on the results of the magnetic field analysis, the magnetic flux density in the space including the crystal and melt regions was extracted, and a 3D melt convection analysis taking into account the magnetic field distribution was performed. The height position of the coil axis was set at 140 mm below the melt surface. Figure 4 The left side of shows the velocity vector in the melt obtained based on the result. Figure 4 The right side of shows the oxygen concentration distribution in the melt. ⊥B shows the cross section perpendicular to the magnetic field lines, and ∥B shows the cross section parallel to the magnetic field lines.

[0146] As in Comparative Example 1 described later, the convection suppression force was strong even in the cross section perpendicular to the magnetic field lines, and relatively active flow was observed only below the crystal end, and the oxygen concentration in the melt was also low.

[0147] Even with such a coil shape and arrangement in the present invention, it is possible to obtain an extremely low oxygen crystal having an a-JEIDA of about 3 to 5 ppm over the entire surface and excellent in-plane distribution.

[0148] In addition, since the longitudinal width of the coil is smaller than that of Comparative Example 1, there is room for increasing the center height position of the coil axis in order to further reduce the oxygen concentration. This will be described later as Example 2.

[0149] In Example 1, the center angle α between the coil axes is set to 120 degrees. However, even if the angle between the coil axes is reduced to 100 degrees, the effect obtained in Example 1 (low oxygen concentration and excellent in-plane distribution) can be obtained.

[0150] (Example 2)

[0151] In Example 1, by using a saddle-shaped coil, the coil height can be reduced by 280 mm compared to Comparative Example 1 (total coil height: 900 mm). Therefore, in Example 2, the height position of the coil axis 2 was set at the melt surface, and after performing 3D melt convection analysis, the device was used to pull a silicon single crystal.

[0152] Figure 5 The velocity vector in the melt and the oxygen concentration distribution in the melt obtained by numerical analysis are shown. It can be seen that the oxygen concentration in the melt is lower than that in Example 1.

[0153] In fact, with this coil configuration, the height position of the coil axis can be set at the surface of the melt, and an extremely low oxygen crystal with less than 1 ppma-JEIDA over the entire surface of the wafer and excellent in-plane distribution can be obtained.

[0154] (Comparative Example 1)

[0155] use Fig. 12A , Fig. 12B The single crystal was pulled by the single crystal pulling device using the conventional superconducting magnet (magnetic field generating device) shown.

[0156] After performing magnetic field analysis and 3D melt convection analysis on the following magnetic field generating device, a silicon single crystal was pulled using the device. The magnetic field generating device is arranged in a cylindrical vacuum container with two pairs of coils with a diameter of 900 mm arranged opposite to each other in a horizontal plane including the coil axis, when the direction of the magnetic field lines of the central axis of the pulling machine is set to the X-axis, so that the respective coil axes are included in the same horizontal plane, and the center angle α between the coil axes sandwiching the X-axis is set to 120 degrees.

[0157] The calculation conditions for the analysis were 400 kg of feed, 32-inch (80 cm) crucible, 306 mm diameter silicon single crystal, 9 rpm crystallization speed, 0.4 rpm crucible speed, and 0.4 mm / min pulling speed.

[0158] Figure 6 This is a magnetic field analysis result based on ANSYS-Maxwell3D. It is a distribution diagram of the magnetic flux density after adjusting the coil current × number of turns to a magnetic flux density of 1000 Gauss on the central axis.

[0159] Based on the results of the magnetic field analysis, the magnetic flux density of the space including the crystal and melt regions was extracted, and a 3D melt convection analysis considering the magnetic field distribution was performed. The height position of the coil axis was set 140 mm below the melt surface, which was the upper limit position in Comparative Example 1. Figure 7 The velocity vector in the melt obtained based on the result is shown, and the oxygen concentration distribution in the melt is shown on the right.

[0160] In the magnetic field of Comparative Example 1, the convection suppression force was strong even in the cross section perpendicular to the magnetic field lines, and relatively active flow was observed only below the crystal end, and the oxygen concentration in the melt was also low.

[0161] With this coil configuration, it is possible to obtain an extremely low oxygen crystal with about 3-5 ppma-JEIDA on the entire surface and excellent in-plane distribution, but in order to improve the efficiency of magnetic field generation, the coil diameter needs to be increased. In addition, in order to reduce the oxygen concentration, when the center height of the coil is increased, interference with the puller is likely to occur. Therefore, in the device of Comparative Example 1, it is difficult to further reduce the oxygen concentration.

[0162] (Comparative Example 2)

[0163] After performing magnetic field analysis and 3D melt convection analysis on a magnetic field generating device that was the same as Example 1 except that the center angle α between the two coil axes was set to 90 degrees, a silicon single crystal was pulled using the device.

[0164] However, since the convection suppression force in the cross section perpendicular to the X-axis is reduced, the oxygen concentration increases and the in-plane distribution also deteriorates, and a silicon single crystal having a desired low oxygen concentration and excellent in-plane distribution cannot be obtained.

[0165] (Comparative Example 3)

[0166] An attempt was made to assemble a magnetic field generating device which was the same as that of Example 1 except that the center angle α between the axes of the two coils was set to 130 degrees. However, the assembly could not be performed because the adjacent coils collided with each other.

[0167] (Example 3)

[0168] use Figure 1 , Fig.14A , Fig. 14B The single crystal pulling apparatus 11 of the present invention shown in the figure pulled a single crystal.

[0169] After performing magnetic field analysis and 3D melt convection analysis on the following magnetic field generating device, a silicon single crystal was pulled using the device. In the magnetic field generating device, four superconducting coils with a longitudinal width of 620 mm and a lateral width (the length along the outermost circumference of the bend) of about 980 mm are arranged in the same horizontal plane (there are two pairs of opposing coils). The coils are saddle-shaped coils bent with a curvature ratio of 1.8 relative to a circle with a radius of 900 mm along the central axis of the pulling furnace as the center line (a shape along the outer shape of the pulling furnace). When the direction of the magnetic field lines of the central axis is the X-axis, the center angle α between the two coil axes sandwiching the X-axis is arranged to be 120 degrees.

[0170] The calculation conditions for the analysis were 400 kg of feed, 32-inch (80 cm) crucible, 306 mm diameter silicon single crystal, 9 rpm crystallization speed, 0.4 rpm crucible speed, and 0.4 mm / min pulling speed.

[0171] Fig.15 This is a magnetic field analysis result based on ANSYS-Maxwell3D. It is a distribution diagram of the magnetic flux density after adjusting the coil current × number of turns to a magnetic flux density of 1000 Gauss on the central axis.

[0172] Based on the results of the magnetic field analysis, the magnetic flux density in the space including the crystal and melt regions was extracted, and a 3D melt convection analysis taking into account the magnetic field distribution was performed. The height position of the coil axis was set at 140 mm below the melt surface. Fig.16 The left side of shows the velocity vector in the melt obtained based on the result. Fig.16 The right side of shows the oxygen concentration distribution in the melt. ⊥B shows the cross section perpendicular to the magnetic field lines, and ∥B shows the cross section parallel to the magnetic field lines.

[0173] As in the above-mentioned Comparative Example 1, the convection suppression force is strong even in the cross section perpendicular to the magnetic field lines, and relatively active flow is observed only below the crystal end, and the oxygen concentration in the melt is also low.

[0174] Due to the coil shape and configuration of the present invention, and the curvature ratio of the coil shape being as large as 1.8, the magnetic flux density component (B⊥) orthogonal to the inner wall of the crucible is more uniform in the circumferential direction, so that extremely low oxygen crystals with an excellent in-plane distribution of about 1-3 ppma-JEIDA on the entire surface can be obtained.

[0175] In addition, since the longitudinal width of the coil is smaller than that of Comparative Example 1, there is room for raising the height position of the coil axis in order to further reduce the oxygen concentration. This will be described later as Example 4.

[0176] In Example 3, the center angle α between the coil axes is set to 120 degrees. However, even if the angle between the coil axes is reduced to 100 degrees, the effect obtained in Example 3 (low oxygen concentration and excellent in-plane distribution) can be obtained.

[0177] (Example 4)

[0178] In Example 3, by using a saddle-shaped coil, the coil height can be reduced by 280 mm compared to Comparative Example 1 (total coil height: 900 mm). Therefore, in Example 4, the height position of the coil axis was set at the melt surface, and after performing 3D melt convection analysis, the device was used to pull a silicon single crystal.

[0179] Fig.17 The velocity vector in the melt and the oxygen concentration distribution in the melt obtained by numerical analysis are shown. It can be seen that the oxygen concentration in the melt is lower than that in Example 3.

[0180] In fact, with this coil configuration, the height position of the coil axis can be set at the surface of the melt, and an extremely low oxygen crystal with less than 0.5 ppma-JEIDA over the entire surface of the wafer and excellent in-plane distribution can be obtained.

[0181] (Comparative Example 4)

[0182] After performing magnetic field analysis and 3D melt convection analysis on a magnetic field generating device that was the same as Example 3 except that the center angle α between the two coil axes was set to 90 degrees, a silicon single crystal was pulled using the device.

[0183] However, since the convection suppression force in the cross section perpendicular to the X-axis is reduced, the oxygen concentration increases and the in-plane distribution also deteriorates, and a silicon single crystal having a desired low oxygen concentration and excellent in-plane distribution cannot be obtained.

[0184] (Comparative Example 5)

[0185] An attempt was made to assemble a magnetic field generating device which was the same as that of Example 3 except that the center angle α between the axes of the two coils was set to 130 degrees. However, the assembly could not be performed because the adjacent coils collided with each other.

[0186] (Example 5)

[0187] Except for using a saddle-shaped coil that is bent with a curvature ratio of 1.1 and has a longitudinal width of 620 mm and a lateral width (length along the outermost circumference of the bend) of approximately 890 mm, the magnetic field generating device was subjected to magnetic field analysis and 3D melt convection analysis in the same manner as in Example 3, and then the device was used to pull a silicon single crystal.

[0188] Fig.19This is a magnetic field analysis result based on ANSYS-Maxwell3D. It is a distribution diagram of the magnetic flux density after adjusting the coil current × number of turns to a magnetic flux density of 1000 Gauss on the central axis.

[0189] Based on the results of the magnetic field analysis, the magnetic flux density of the space including the crystal and melt regions was extracted, and a 3D melt convection analysis considering the magnetic field distribution was performed. The height position of the coil axis was set at 140 mm below the melt surface, the same as in Example 3 and Comparative Example 1. Fig. 20 The left side of shows the velocity vector in the melt obtained based on the result. Fig. 20 The right side of shows the oxygen concentration distribution in the melt.

[0190] In the magnetic field of Example 5, as in Comparative Example 1, the convection suppression force was strong even in the cross section perpendicular to the magnetic field lines, and relatively active flow was observed only below the crystal end, and the oxygen concentration in the melt was also low.

[0191] Even with such a saddle shape and curvature ratio coil shape and configuration, it is possible to obtain an extremely low oxygen crystal with an oxygen concentration of about 3-5 ppma-JEIDA on the entire surface and excellent in-plane distribution. In addition, as for the oxygen concentration, as described above, it is about 3-5 ppma-JEIDA on the entire surface, which is the same as that of Comparative Example 1, but can be a value lower than that of Comparative Example 1 as an average.

[0192] In addition, since the longitudinal width of the coil is smaller than that of Comparative Example 1, there is room for raising the height position of the coil axis as in Example 4 in order to further reduce the oxygen concentration.

[0193] The present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are illustrative, and any scheme having substantially the same structure and achieving the same function and effect as the technical idea described in the claims of the present invention is included in the technical scope of the present invention.

Claims

1. A single crystal pulling device, comprising: a pulling furnace, which is equipped with a heater and a crucible for accommodating molten semiconductor raw materials and has a central axis; and a magnetic field generating device, which is arranged around the pulling furnace and has a superconducting coil, and applies a horizontal magnetic field to the molten semiconductor raw materials by energizing the superconducting coil, thereby suppressing convection of the molten semiconductor raw materials in the crucible, characterized in that: The superconducting coil of the magnetic field generating device is saddle-shaped and curved with a curvature greater than the curvature along the outer shape of the pulling furnace, and two pairs of the saddle-shaped superconducting coils are arranged opposite to each other around the pulling furnace. The ratio of the curvature of the saddle-shaped superconducting coil to the curvature of the shape along the outer shape of the pulling furnace is 1.2 or more and 2.0 or less. When the axis passing through the centers of the pair of superconducting coils arranged opposite to each other is defined as the coil axis, The two coil axes of the two sets of superconducting coils are contained in the same horizontal plane, In the horizontal plane, when the direction of the magnetic force lines on the central axis of the pulling furnace is defined as an X-axis, a center angle α between the two coil axes sandwiching the X-axis is not less than 100 degrees and not more than 120 degrees.

2. The single crystal pulling device according to claim 1, characterized in that: The magnetic field generating device is arranged on a lifting device which can move up and down in a vertical direction.

3. The single crystal pulling device according to claim 1 or 2, characterized in that: The saddle-shaped superconducting coil has a longitudinal width shorter than a lateral width.

4. A single crystal pulling method, characterized in that: A semiconductor single crystal is pulled using the single crystal pulling device according to any one of claims 1 to 3.

5. The single crystal pulling method according to claim 4, characterized in that: When the semiconductor single crystal is pulled up, the height position of the magnetic field generating device is adjusted according to a target value of the oxygen concentration contained in the semiconductor single crystal.

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