阅读说明：本技术 单晶提拉装置及单晶提拉方法 (Single crystal pulling apparatus and single crystal pulling method ) 是由 高野清隆 矢岛涉 菅原孝世 鎌田洋之 太田友彦 于 2020-03-19 设计创作，主要内容包括：本发明是一种单晶提拉装置,具备：提拉炉,其配置有加热器和坩埚并具有中心轴；以及磁场产生装置,其具有超导线圈,磁场产生装置具有四个超导线圈,在由包含X轴和提拉炉的中心轴的剖面划分的两个区域的每一个中,各两个超导线圈配置为相对于剖面线对称,其中,该X轴是包含四个超导线圈的所有线圈轴的水平面内的中心轴上的磁力线方向,四个超导线圈都配置为,线圈轴相对于Y轴成大于-30°小于30°的角度范围,该磁力线的方向相对于剖面线对称,在每一个区域中,两个超导线圈产生的磁力线的方向相反。由此,提供一种在单晶提拉装置的解体·安装时不需要使磁场产生装置移动,能够降低培育的单晶中的氧浓度,并且能够抑制培育的单晶中的生长条纹的单晶提拉装置。(The present invention is a single crystal pulling apparatus including: a pulling furnace provided with a heater and a crucible and having a central axis; and a magnetic field generating device having superconducting coils, the magnetic field generating device having four superconducting coils, each of the two superconducting coils being disposed symmetrically with respect to a cross-sectional line in each of two regions divided by the cross-sectional plane including an X-axis and a central axis of the pulling furnace, wherein the X-axis is a direction of magnetic lines of force on the central axis in a horizontal plane including all of the coil axes of the four superconducting coils, the four superconducting coils being disposed such that the coil axes are in an angular range of more than-30 ° and less than 30 ° with respect to a Y-axis, the direction of the magnetic lines of force being symmetric with respect to the cross-sectional line, and the directions of the magnetic lines of force generated by the two superconducting coils being opposite in each of the regions. Thus, there is provided a single crystal pulling apparatus which does not require movement of a magnetic field generating device at the time of disassembly and assembly of the single crystal pulling apparatus, can reduce the oxygen concentration in the grown single crystal, and can suppress growth streaks in the grown single crystal.)

1. A single crystal pulling apparatus includes:

a pulling furnace provided with a heater and a crucible containing a molten single crystal material and having a central axis; and

a magnetic field generating device provided around the pulling furnace and having a superconducting coil and a cryostat in which the superconducting coil is built,

suppressing convection of the molten single crystal material in the crucible by applying a horizontal magnetic field to the molten single crystal material by energizing the superconducting coil,

it is characterized in that the preparation method is characterized in that,

the magnetic field generating device has four superconducting coils and is configured such that all coil axes of the four superconducting coils are contained in a single horizontal plane,

two superconducting coils are disposed in a first region and a second region defined by a cross section including the X axis and a central axis of the pulling furnace, respectively, with a direction of magnetic lines of force on the central axis in the horizontal plane being defined as the X axis,

the four superconducting coils are arranged symmetrically with respect to the sectional line,

the four superconducting coils are each configured such that a coil axis is in an angular range of more than-30 DEG and less than 30 DEG in the horizontal plane with respect to a Y axis perpendicular to the X axis,

the directions of the magnetic lines of force generated by the four superconducting coils are symmetrical relative to the section line,

in each of the first region and the second region, the directions of magnetic lines of force generated by the two superconducting coils are opposite.

2. The single crystal pulling apparatus according to claim 1,

as the cryostat, the magnetic field generating device may be provided with an コ -shaped cryostat having all of the four superconducting coils built therein, or may be provided with a cryostat having two superconducting coils built therein in the first region and the second region, respectively, and the two cryostats may be structurally connected to each other.

3. The single crystal pulling apparatus according to claim 1 or 2,

the superconducting coil has a vertical height that is greater than a width of the superconducting coil as viewed from above in the vertical direction.

4. A method of pulling a single crystal,

pulling up single-crystal silicon using the single-crystal pulling apparatus according to claims 1 to 3.

Technical Field

The present invention relates to a single crystal pulling apparatus and a single crystal pulling method using the same.

Background

Semiconductors such as silicon and gallium arsenide are made of single crystals, and are used for memories of computers ranging from small to large, and there is a demand for larger capacity, lower cost, and higher quality of memory devices.

Conventionally, as one of single crystal pulling methods for producing a single crystal satisfying these semiconductor requirements, the following methods are known: a magnetic field is applied to a molten semiconductor material (melt ) contained in a crucible, thereby suppressing thermal convection generated in the melt, and producing a large-diameter and high-quality semiconductor (generally referred to as a magnetic field applied czochralski (MCZ) method).

An example of a conventional single crystal pulling apparatus by the CZ method will be described with reference to FIG. 11. The single crystal pulling apparatus 100 shown in FIG. 11 includes a pulling furnace 101 having an openable/closable upper surface, and is configured such that a crucible 102 is built into the pulling furnace 101. Further, inside the pulling furnace 101, a heater 103 for heating and melting the semiconductor material in the crucible 102 is provided around the crucible 102, and outside the pulling furnace 101, a superconducting magnet 130 in which a pair of (two) superconducting coils 104(104a, 104b) are built in a refrigerant container (hereinafter referred to as a cylindrical refrigerant container) 105 as a cylindrical container is arranged.

In the production of a single crystal, a semiconductor material 106 is placed in a crucible 102 and heated by a heater 103, whereby the semiconductor material 106 is melted. A seed crystal, not shown, is lowered from above the central portion of the crucible 102, for example, and inserted into the melt, and the seed crystal is pulled in the direction of the pulling direction 108 at a predetermined speed by a pulling mechanism, not shown. Thereby, crystals grow at the solid-liquid boundary layer, and single crystals are produced. At this time, if thermal convection, which is the movement of the melt due to the heating by the heater 103, occurs, the pulled single crystal is likely to be dislocated, and the yield of the single crystal generation decreases.

Therefore, as a countermeasure, superconducting coil 104 of superconducting magnet 130 is used. That is, the semiconductor material 106 in the molten liquid is subjected to the operation suppressing force by the magnetic lines of force 107 generated by the energization of the superconducting coil 104, convection does not occur in the crucible 102, and the grown single crystal is gradually pulled upward along with the pulling of the seed crystal, and is produced as a solid single crystal 109. Although not shown, a pulling mechanism for pulling the single crystal 109 along the central axis 110 of the crucible is provided above the pulling furnace 101.

Next, an example of superconducting magnet 130 used in single crystal pulling apparatus 100 shown in fig. 11 will be described with reference to fig. 12. The superconducting magnet 130 has a structure in which: the superconducting coils 104(104a, 104b) are accommodated in a cylindrical vacuum container 119 via a cylindrical refrigerant container. Superconducting magnet 130 accommodates a pair of superconducting coils 104a and 104b facing each other via a central portion in vacuum chamber 119. The pair of superconducting coils 104a and 104b are helmholtz type field coils that generate magnetic fields in the same lateral direction, and generate magnetic lines of force 107 that are bilaterally symmetric with respect to the central axis 110 of the pulling furnace 101 and the vacuum chamber 119 (the position of the central axis 110 is referred to as a magnetic field center), as shown in fig. 11.

As shown in fig. 11 and 12, the superconducting magnet 130 includes: a current lead 111 for introducing a current to the two superconducting coils 104a and 104b, a compact helium refrigerator 112 for cooling the first radiation shield 117 and the second radiation shield 118 housed inside the cylindrical refrigerant container 105, a gas discharge pipe 113 for discharging helium gas in the cylindrical refrigerant container 105, and a maintenance port (japanese: サービスポート)114 having a supply port for supplying liquid helium. The pulling furnace 101 shown in fig. 11 is disposed in the hole 115 (the inner diameter of the hole is indicated by D) of the superconducting magnet 130.

Fig. 13 shows the magnetic field distribution of the above-described conventional superconducting magnet 130. As shown in fig. 13, in conventional superconducting magnet 130, since a pair of superconducting coils 104a and 104b are arranged to face each other, the magnetic field gradually increases toward both sides in the coil arrangement direction (X direction in fig. 13) and gradually decreases toward the top and bottom in the direction perpendicular thereto (Y direction in fig. 13). In such a conventional structure, as shown in fig. 12 and 13, since the magnetic field gradient in the range inside the hole 115 is excessively large, suppression of thermal convection generated in the molten single crystal material (melt) becomes uneven, and the magnetic field efficiency is poor. That is, as shown by the hatched lines in fig. 13, in the region near the central magnetic field, the magnetic field uniformity is poor (that is, in fig. 13, the magnetic field has a shape of a long and narrow cross in the upper and lower directions, and the left and right directions), and therefore, there is a problem that the effect of suppressing the thermal convection is low, and the single crystal of high quality cannot be pulled.

Patent document 1 discloses a technique for solving the above problem. The technique disclosed in patent document 1 is explained with reference to fig. 14. Fig. 14 (b) shows a section a-a of fig. 14 (a). In order to solve the above-described problem, as shown in fig. 14a and 14b, patent document 1 sets the number of superconducting coils 104 to four or more (for example, four of 104a, 104b, 104c, and 104 d), arranges the coils on a plane in a cylindrical container coaxially provided around a pulling furnace, sets the orientation of each of the arranged superconducting coils to face each other with the axis of the cylindrical container interposed therebetween, and sets an arrangement angle θ (see fig. 14 b) at which each pair of adjacent superconducting coils of the superconducting coils face the inside of the cylindrical container to a range of 100 ° to 130 ° (that is, a central angle α (see fig. 14 b) between the axes of the coils adjacent to each other with the X axis interposed therebetween to a range of 50 ° to 80 °). As a result, a transverse magnetic field having a small magnetic field gradient and good uniformity can be generated inside the hole 105, a concentric or square magnetic field distribution can be generated on a plane, and unbalanced electromagnetic force can be greatly suppressed, and as a result, a high-quality single crystal can be produced by suppressing unbalanced electromagnetic force in a uniform magnetic field enhancement region in the pulling direction and with the magnetic field in the transverse magnetic field direction being substantially horizontal, and further, according to this single crystal pulling method, a high-quality single crystal can be pulled up with good yield. In fig. 14, d is the diameter (inner diameter) of the superconducting coil, and l is the distance between the pair of coils.

According to this method, since the magnetic field distribution applied to the molten single crystal material is uniformized and the unbalanced electromagnetic force is suppressed, the thermal convection can be suppressed even if the magnetic flux density is lower than that of the conventional technique using two coils.

However, even with such a uniform magnetic field distribution, comprehensive heat transfer analysis including three-dimensional melt convection in a transverse magnetic field with magnetic lines of force oriented in the X-axis direction revealed that: there is a difference in thermal convection between a cross section parallel to the X axis and a cross section parallel to the Y axis (see patent document 2).

When the conductive fluid moves in the magnetic field, an induced current is generated in a direction orthogonal to the magnetic lines of force and the fluid component perpendicular to the magnetic lines of force, but in the case of using a quartz crucible having electrical insulation, since the crucible wall and the free surface of the molten semiconductor material are insulating walls, the induced current in the direction orthogonal to them does not flow. Therefore, the convection suppression force by the electromagnetic force is weakened in the upper portion of the molten semiconductor material, and if a cross section parallel to the X axis (cross section parallel to the magnetic field lines) is compared with a cross section perpendicular to the X axis (cross section perpendicular to the magnetic field lines), convection in the cross section perpendicular to the X axis (in the cross section perpendicular to the magnetic field lines) becomes stronger.

In this way, when a uniform magnetic field distribution is formed by the four coils, the difference in the convective velocity is slightly reduced, but even then, a flow velocity distribution is not uniform in the circumferential direction. In particular, since a flow field connecting a growth interface from a crucible wall remains in a cross section perpendicular to magnetic lines of force, oxygen eluted from a quartz crucible reaches a crystal, and thus the effect of reducing the oxygen concentration by applying a horizontal magnetic field is limited, and there is a problem as follows: it is difficult to satisfy the oxygen concentration requirement of extremely low concentration in semiconductor crystals for power devices or image sensors, which has been increasing recently. Further, the presence of a flow field that is not uniform in the circumferential direction of the crucible is a cause of growth streaks occurring in the single crystal pulled up while rotating the single crystal, and if the cross section parallel to the growth direction is evaluated, the resistivity and the oxygen concentration of the crystal rotation period are observed to vary, and therefore, the distribution is ring-shaped in the wafer plane sliced perpendicular to the growth direction.

In patent document 2, in order to solve this problem, magnetic field distribution is generated in a horizontal plane including a coil axis of a superconducting coil such that: when the direction of the magnetic force line of the central axis of the pulling furnace is set as the X axis, the magnetic flux density distribution on the X axis is in a convex distribution, when the magnetic flux density of the central axis in the horizontal plane is set to a set value of magnetic flux density, the magnetic flux density on the X axis is 80% or less of the set value of the magnetic flux density in the crucible wall, and a magnetic flux density distribution in the horizontal plane on the Y axis orthogonal to the X axis and passing through the central axis is a downward convex distribution, the magnetic flux density on the Y axis is 140% or more of the set value of the magnetic flux density in the crucible wall, in the above-described magnetic field generating device, two pairs of superconducting coils are arranged so that respective coil axes of the superconducting coils are included in the same horizontal plane, and the central angle alpha between the coil axes and the X axis is set to be more than 100 degrees and less than 120 degrees. Thus, the technique disclosed in patent document 2 can provide the following effects. That is, even in a cross section perpendicular to the X axis where the convection suppression force by the electromagnetic force is insufficient, the flow velocity of the molten single crystal material can be reduced, and the flow velocity of the molten single crystal material in the cross section parallel to the X axis and the flow velocity of the molten single crystal material in the cross section perpendicular to the X axis can be balanced. Further, even in the cross section perpendicular to the X axis, by reducing the flow rate of the molten single crystal material, the time taken for the oxygen eluted from the crucible wall to reach the single crystal becomes longer, the amount of oxygen evaporated from the free surface of the molten single crystal material increases, and a single crystal pulling apparatus capable of greatly reducing the concentration of oxygen taken into the single crystal can be obtained. Further, by balancing the flow rate of the molten single crystal material in the cross section parallel to the X axis and the flow rate of the molten single crystal material in the cross section perpendicular to the X axis, a single crystal pulling apparatus capable of suppressing growth streaks in the grown single crystal can be obtained.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2004-51475

Patent document 2: japanese patent laid-open publication No. 2017-57127

Disclosure of Invention

Technical problem to be solved

However, the present inventors have analyzed the magnetic field distribution in various coil arrangements, and as a result, it has been clarified that the magnetic field distribution described in patent document 2 can be realized in addition to the coil arrangement described in patent document 2. In the coil arrangement described in patent document 2, all superconducting coils are located as close to the pulling furnace 101 (chamber) as possible in order to improve the magnetic field efficiency, and therefore the spacing between the superconducting coils 104a and 104b, or 104c and 104d is narrower than the chamber of the pulling furnace 101 and the graphite member inside (see fig. 15 (a)).

As shown in fig. 15 (b), even if the notches 131 are provided in the cylindrical container 105 on both sides or one side of the cylindrical container and the chamber of the pulling furnace 101 can be raised and rotated, the chamber of the pulling furnace 101 and the large graphite member need to be raised and removed so as to avoid the superconducting magnet 130 (magnet) temporarily, and therefore, the work efficiency is low, and it takes time and ensures safety when the high-weight object is lifted up (using the arm 150, see fig. 16), and therefore, the magnetic field generating device needs to be lowered and then mounted when the superconducting coils 104a and 104b or 104c and 104d are disassembled.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a single crystal pulling apparatus which does not require a traveling magnetic field generating device at the time of disassembling and assembling the single crystal pulling apparatus, can reduce the oxygen concentration in the grown single crystal, and can suppress growth streaks in the grown single crystal. Further, an object of the present invention is to provide a single crystal pulling method using such a single crystal pulling apparatus.

(II) technical scheme

In order to achieve the above object, the present invention provides a single crystal pulling apparatus comprising: a pulling furnace provided with a heater and a crucible containing a molten single crystal material and having a central axis; and a magnetic field generating device provided around the pulling furnace, the magnetic field generating device including a superconducting coil and a cryostat in which the superconducting coil is built, the superconducting coil being energized to apply a horizontal magnetic field to the molten single crystal material, thereby suppressing convection of the molten single crystal material in the crucible, wherein the magnetic field generating device includes four superconducting coils, and is arranged such that all coil axes of the four superconducting coils are included in a single horizontal plane, and when a direction of a magnetic force line on the central axis in the horizontal plane is taken as an X axis, two superconducting coils are arranged in a first region and a second region divided by a cross section including the X axis and a central axis of the pulling furnace, the four superconducting coils are arranged symmetrically with respect to the cross section line, and the four superconducting coils are all arranged, the coil axis forms an angle range of more than-30 degrees and less than 30 degrees relative to a Y axis vertical to the X axis in the horizontal plane, the directions of magnetic lines generated by the four superconducting coils are symmetrical relative to the section line, and the directions of the magnetic lines generated by the two superconducting coils are opposite in each of the first region and the second region.

If the single crystal pulling apparatus is provided with the magnetic field generating device having such a configuration of the superconducting coil, it is possible to provide a configuration of the superconducting coil that does not require moving the magnetic field generating device when the single crystal pulling apparatus is disassembled and mounted. Further, if the single crystal pulling apparatus is provided with the magnetic field generating device having the arrangement of the superconducting coils, even in a cross section perpendicular to the X axis where the convection suppression force by the electromagnetic force is insufficient, the flow velocity of the molten single crystal material can be reduced, and the flow velocity of the molten single crystal material in the cross section parallel to the X axis and the flow velocity of the molten single crystal material in the cross section perpendicular to the X axis can be balanced. Even in the cross section perpendicular to the X axis, by reducing the flow rate of the molten single crystal material, the time taken for oxygen eluted from the crucible wall to reach the single crystal becomes longer, and the amount of oxygen evaporated from the free surface of the molten single crystal material increases, whereby a single crystal pulling apparatus capable of greatly reducing the concentration of oxygen entering the single crystal can be obtained. Further, by balancing the flow rate of the molten single crystal material in the cross section parallel to the X axis and the flow rate of the molten single crystal material in the cross section perpendicular to the X axis, a single crystal pulling apparatus capable of suppressing growth streaks in the grown single crystal can be obtained.

In the single crystal pulling apparatus according to the present invention, it is preferable that the magnetic field generating device includes, as the cryostat, an コ -shaped cryostat in which all of the four superconducting coils are built, or a cryostat in which two superconducting coils are built in the first region and the second region, respectively, and the two cryostats have a structure of being structurally connected to each other.

In such a magnetic field generating device, since a space having nothing is formed on the front side or the back side in the direction of the magnetic field lines, the components constituting the pulling furnace can be operated without raising and lowering the magnetic field generating device, and the raising and lowering device is not required.

Further, the height of the superconducting coil in the vertical direction is longer than the width of the superconducting coil as viewed from above in the vertical direction.

By providing the superconducting coil of the magnetic field generating device in such a shape, even if the width of the coil as viewed from above is narrow, the magnetic flux density on the central axis of the pulling furnace can be increased in the horizontal plane including the coil axis.

Further, the present invention provides a single crystal pulling method for pulling a single crystal silicon by using any one of the single crystal pulling apparatuses described above.

By such a single crystal pulling method, a silicon single crystal in which the concentration of the oxygen taken in is greatly reduced and growth streaks are suppressed can be grown.

(III) advantageous effects

In the single crystal pulling apparatus of the present invention, it is possible to provide an arrangement of the superconducting coil that does not require moving the magnetic field generating device when the single crystal pulling apparatus is disassembled and mounted. Further, the single crystal pulling apparatus of the present invention can provide a single crystal pulling apparatus capable of significantly reducing the concentration of oxygen entering the single crystal and suppressing growth streaks in the grown single crystal. Further, according to the single crystal pulling method of the present invention, it is possible to grow a single crystal in which the concentration of the oxygen taken in is greatly reduced and growth streaks are suppressed.

Drawings

FIG. 1 is a schematic diagram showing an example of a single crystal pulling apparatus according to the present invention, wherein (a) is a schematic cross-sectional view of the single crystal pulling apparatus, and (b) is a schematic diagram showing the arrangement (viewed from above) of a superconducting coil in a superconducting generator.

FIG. 2 is a schematic view showing an example of a coil arrangement (a view seen from above) of the single crystal pulling apparatus of the present invention.

FIG. 3 is a schematic view showing an example of a cryostat incorporated in a magnetic field generating apparatus of a single crystal pulling apparatus according to the present invention.

Fig. 4 is a schematic diagram showing the shape of a superconducting coil that can be used in the present invention.

Fig. 5 (a) is a diagram showing the result of magnetic field analysis based on the simulation in example 1, and (b) is a diagram showing the configuration of the superconducting coil in example 1.

Fig. 6 is a diagram showing the results of 3D melt convection analysis in consideration of the magnetic field distribution simulated in example 1, where (a) shows the velocity vector of the melt in a cross section perpendicular to the magnetic field, (b) shows the oxygen concentration of the melt in a cross section perpendicular to the magnetic field, (c) shows the velocity vector of the melt in a cross section parallel to the magnetic field, and (D) shows the oxygen concentration of the melt in a cross section parallel to the magnetic field.

Fig. 7 (a) is a diagram showing the result of magnetic field analysis based on the simulation in comparative example 1, and (b) is a diagram showing the arrangement of the superconducting coils in comparative example 1.

Fig. 8 is a graph showing the results of 3D melt convection analysis in consideration of the magnetic field distribution simulated in comparative example 1, where (a) shows the velocity vector of the melt in the cross section perpendicular to the magnetic field, (b) shows the oxygen concentration of the melt in the cross section perpendicular to the magnetic field, (c) shows the velocity vector of the melt in the cross section parallel to the magnetic field, and (D) shows the oxygen concentration of the melt in the cross section parallel to the magnetic field.

Fig. 9 (a) is a diagram showing the result of magnetic field analysis based on the simulation in comparative example 2, and (b) is a diagram showing the arrangement of the superconducting coils in comparative example 2.

Fig. 10 is a graph showing the results of 3D melt convection analysis in consideration of the magnetic field distribution simulated in comparative example 2, where (a) shows the velocity vector of the melt in the cross section perpendicular to the magnetic field, (b) shows the oxygen concentration of the melt in the cross section perpendicular to the magnetic field, (c) shows the velocity vector of the melt in the cross section parallel to the magnetic field, and (D) shows the oxygen concentration of the melt in the cross section parallel to the magnetic field.

FIG. 11 is a schematic cross-sectional view showing an example of a conventional single crystal pulling apparatus.

Fig. 12 is a schematic perspective view showing an example of a superconducting magnet in a conventional single crystal pulling apparatus.

Fig. 13 is a diagram showing a conventional magnetic flux density distribution.

Fig. 14 is a schematic perspective view and a schematic cross-sectional view showing the superconducting magnet of patent document 1.

Fig. 15 is a schematic cross-sectional view showing the superconducting magnet of patent document 2, wherein (a) shows a case of a cylindrical container, and (b) shows a case where a notch is provided in a part of the cylindrical container.

Fig. 16 is a schematic diagram showing a process of raising and rotating a pulling furnace (chamber) when the superconducting magnet of patent document 2 is used.

Detailed Description

The present invention will be described in detail below with reference to the accompanying drawings as an example of an embodiment, but the present invention is not limited thereto.

First, an example of an embodiment of a single crystal pulling apparatus according to the present invention will be described with reference to fig. 1. The single crystal pulling apparatus 21 shown in fig. 1 (a) includes: a heater 13, a pulling furnace 11 having a central axis 20 and provided with a crucible 12 for containing a molten single crystal material (hereinafter also simply referred to as "melt") 16, and a magnetic field generating device 30 provided around the pulling furnace 11 and having a superconducting coil and a cryostat in which the superconducting coil is built, wherein a horizontal magnetic field is applied to the melt 16 by energization of the superconducting coil, thereby pulling a single crystal 19 in a pulling direction 18 while suppressing convection of the melt 16 in the crucible 12.

In the magnetic field generating device 30, a superconducting coil is disposed as shown in fig. 1 (b). As shown in fig. 1 (b), the magnetic field generating device 30 has four superconducting coils. Further, the coil axes of all of the four superconducting coils 14a, 14b, 14c, and 14d are arranged to be contained in a single horizontal plane (a horizontal plane 22 including the coil axes shown in fig. 1 (a)). Further, when the direction of the magnetic flux lines 17 on the central axis 20 in the horizontal plane 22 is defined as the X axis, two superconducting coils are disposed in a first region and a second region defined by a cross section including the X axis and the central axis 20 of the pulling furnace, respectively. In fig. 1 (b), if the left side of the X axis on the paper is set as a first region and the right side of the X axis is set as a second region, superconducting coils 14a and 14d are arranged in the first region. In the second region, superconducting coils 14b and 14c are arranged. In the present invention, as shown in fig. 1 (b), four superconducting coils 14a, 14b, 14c, and 14d are arranged in line symmetry with respect to the cross section. Furthermore, the four superconducting coils 14a, 14b, 14c, 14d are all arranged with the coil axes in the horizontal plane 22 in an angular range of more than-30 ° and less than 30 ° with respect to the Y axis perpendicular to the X axis. Fig. 1 (b) shows a state in which two superconducting coils disposed in the first region and the second region, respectively, are disposed parallel to the X axis. In the present invention, as shown in fig. 1 (b), the directions of the magnetic lines of force generated by the four superconducting coils 14a, 14b, 14c, and 14d are symmetrical with respect to the cross-sectional line. Further, in the present invention, the directions of the magnetic lines of force generated by the two superconducting coils are opposite in each of the first region and the second region.

As described above, in the present invention, it is necessary to arrange all of the four superconducting coils 14a, 14b, 14c and 14d such that the coil axes are in the horizontal plane 22 in an angular range of more than-30 ° and less than 30 ° with respect to the Y axis perpendicular to the X axis. Fig. 2 shows an example of a coil arrangement (a view seen from above) of the single crystal pulling apparatus of the present invention. Fig. 2 (a) shows a case where the coil axis is 0 ° with respect to the Y axis in the horizontal plane 22. In this case, the four superconducting coils 14a, 14b, 14c, and 14d are parallel to the X axis, and the coil axis is parallel to the Y axis. Fig. 2 (b) shows a case where the coil axis is 25 ° with respect to the Y axis in the horizontal plane 22. Fig. 2 (c) also shows the coil axis at-25 deg. relative to the Y axis in the horizontal plane 22. As shown in fig. 2 (c), when the coil axis intersects the Y axis on the opposite side of the superconducting coil from the X axis, a negative angle is defined.

A defined magnetic field distribution can be generated if the coil axis is arranged in an angular range of more than-30 deg. and less than 30 deg. with respect to the Y-axis. In the case of the magnetic field distribution generated by the arrangement of the superconducting coils according to the present invention, even in the cross section perpendicular to the X axis where the convection suppression force by the conventional electromagnetic force is insufficient, the flow velocity of the molten single crystal material can be reduced, and the flow velocity of the molten single crystal material in the cross section parallel to the X axis and the flow velocity of the molten single crystal material in the cross section perpendicular to the X axis can be balanced. Further, even in the cross section perpendicular to the X axis, by reducing the flow rate of the molten single crystal material, the time taken for oxygen eluted from the crucible wall to reach the single crystal becomes longer, and the amount of oxygen evaporated from the free surface of the molten single crystal material increases, whereby a single crystal pulling apparatus capable of greatly reducing the concentration of oxygen taken into the single crystal can be obtained. Further, by balancing the flow rate of the molten single crystal material in the cross section parallel to the X axis and the flow rate of the molten single crystal material in the cross section perpendicular to the X axis, a single crystal pulling apparatus capable of suppressing growth streaks in the grown single crystal can be obtained.

Further, if the coil axis is disposed in an angular range of more than-30 ° and less than 30 ° with respect to the Y axis, it is possible to provide a configuration of the superconducting coil that does not require moving the magnetic field generating device when the single crystal pulling device is disassembled and mounted. If the coil axis is disposed in the range of an angle of-30 ° or less or 30 ° or more with respect to the Y axis, the width of the cryostat incorporating the superconducting coils becomes large or the distance between the superconducting coils becomes short, and it is necessary to raise and lower the magnetic field generating device in order to disassemble and attach the graphite member as in the conventional art, which is problematic.

The angle of the coil axis is particularly preferably-5 ° or less with respect to the Y axis. By providing such an angle, the magnetic flux density on the central axis can be maintained even if the number of turns of the superconducting wire or the current value is reduced, and therefore, the force applied to the coil can be reduced, and the magnetic field generating device which is less likely to quench can be obtained.

Further, in the magnetic field generating device, as shown in fig. 3 (a), the cryostat for generating the superconducting state may be provided with an コ -shaped cryostat 31 in which all four superconducting coils 14a, 14b, 14c, and 14d are built. In addition, a cryostat having two superconducting coils built therein may be provided in each of the first region and the second region, and the two cryostats may be structurally connected to each other. Fig. 3 (b) shows an example of a cryostat of this type. In this mode, in the first region, two superconducting coils 14a and 14d are built in the first cryostat 32, and in the second region, two superconducting coils 14b and 14c are built in the second cryostat 33. Further, the first cryostat 32 and the second cryostat 33 are structurally connected by a structural member 34.

In the case of such a magnetic field generating device, since a space having nothing is formed on the near side or the far side in the direction of the magnetic field lines, the rotation of the chamber of the pulling furnace 11, the disassembly and attachment of the graphite member, and the lifting and lowering of the magnetic field generating device are enabled without lifting and lowering the magnetic field generating device.

In the superconducting coil used in the single crystal pulling apparatus according to the present invention, the height of the superconducting coil in the vertical direction is longer than the width of the superconducting coil as viewed from above in the vertical direction. Fig. 4 (a) and (b) show the superconducting coil. Fig. 4 (a) shows a cross section of the superconducting coil, fig. 4 (b) shows a state in which fig. 4 (a) is laid out horizontally, and the height of the superconducting coil is indicated by H. The direction H is vertical. In fig. 4 (b), R is a curvature radius of a curved portion (arc) of the superconducting coil. By providing the superconducting coil of the magnetic field generating device in such a shape, even if the width of the coil as viewed from above is narrow, the magnetic flux density on the central axis of the pulling furnace can be increased in the horizontal plane including the coil axis.

Further, a silicon single crystal can be pulled by using the single crystal pulling apparatus of the present invention. In the case of such a single crystal pulling method, it is possible to grow a silicon single crystal in which the concentration of the oxygen taken in is greatly reduced and growth streaks are suppressed.

Examples

The present invention is further illustrated below based on examples and comparative examples, but these examples are illustrative and should not be construed as limiting.

(example 1)

When two pairs (four) of coils having vertical arcs of 250mm in radius and 1000mm in height are provided, and the direction of the magnetic force line of the central axis in the horizontal plane including the coil axes of the two pairs (four) of superconducting coils is set to the X axis, a pair of two superconducting coils are arranged in parallel to the X axis on the left and right (first and second regions) with respect to the cross section including the X axis and the central axis of the pulling furnace, respectively, and a magnetic field generating device disposed in line symmetry with respect to the cross section performs magnetic field analysis and 3D melt convection analysis, and then silicon single crystal is pulled using the device.

Fig. 5 (a) shows the distribution of the magnetic flux density after the magnetic field analysis result by ANSYS-Maxwell3D was analyzed by adjusting the current × the number of turns of the coil so that the magnetic flux density at the center axis was 1000 gauss (0.1 tesla). Fig. 5 (b) is a schematic diagram showing the arrangement of the four superconducting coils 14a, 14b, 14c, and 14d at this time.

From the results of the above-described magnetic field analysis, the magnetic flux density of the space including the crystal and the melt (melt) region was extracted, and 3D melt convection analysis in consideration of the magnetic field distribution was performed. Fig. 6 (a) and (c) show velocity vectors in the melt obtained from the results (fig. 6 (a) is a cross section perpendicular to the magnetic field, fig. 6 (c) is a cross section parallel to the magnetic field), and fig. 6 (b) and (d) show oxygen concentration distributions in the melt (fig. 6 (b) is a cross section perpendicular to the magnetic field, and fig. 6 (d) is a cross section parallel to the magnetic field).

The calculation conditions at this time are set as: the amount of the silicon crystal fed was calculated from a crucible having a feed rate of 400kg and a diameter of 32 inches (1 inch: 25.4mm), a silicon crystal having a diameter of 306mm, a crystal rotation rate of 9rpm, a crucible rotation rate of 0.4rpm, and a pulling rate of 0.4 mm/min.

In the magnetic field of example 1, similarly to comparative example 2 described later, even if the convection suppression force is strong in the cross section perpendicular to the magnetic field lines, a relatively active flow is observed only below the crystal edge, and the oxygen concentration in the melt is also low.

In the case of this coil arrangement (see FIG. 5 (b)), the magnetic field generator does not need to be moved up and down before the graphite member is disassembled and mounted, and the entire surface of the wafer can be cut by 5ppma-JEIDA to obtain an extremely low oxygen crystal having excellent in-plane distribution.

Comparative example 1

A magnetic field generating device in which a pair of (two) coils having an outer diameter of 1100mm were arranged in bilateral symmetry with respect to the central axis of a pulling machine was used to perform magnetic field analysis and 3D melt convection analysis, and then silicon single crystal pulling was performed using the device.

Fig. 7 (a) shows the distribution of the magnetic flux density after the magnetic field analysis result by ANSYS-Maxwell3D was analyzed by adjusting the current × the number of turns of the coil so that the magnetic flux density at the center axis was 1000 gauss (0.1 tesla). Fig. 7 (b) is a schematic diagram showing the arrangement of the two superconducting coils 104a and 104b at this time.

From the results of the magnetic field analysis, the magnetic flux density of the space including the crystal and the melt region was extracted, and 3D melt convection analysis was performed in consideration of the magnetic field distribution. Fig. 8 (a) and (c) show velocity vectors in the melt obtained from the results (fig. 8 (a) is a cross section perpendicular to the magnetic field, fig. 8 (c) is a cross section parallel to the magnetic field), and fig. 8 (b) and (d) show oxygen concentration distributions in the melt (fig. 8 (b) is a cross section perpendicular to the magnetic field, and fig. 8 (d) is a cross section parallel to the magnetic field). In the magnetic field of comparative example 1, the convection suppression force is weak in the cross section perpendicular to the magnetic field lines, an active eddy current is generated, and the oxygen concentration in the melt is also high.

The calculation conditions at this time were set as in example 1: the amount of the silicon crystal fed was calculated from a crucible having a feed rate of 400kg and a diameter of 32 inches (1 inch: 25.4mm), a silicon crystal having a diameter of 306mm, a crystal rotation rate of 9rpm, a crucible rotation rate of 0.4rpm, and a pulling rate of 0.4 mm/min.

In the case of this coil arrangement (see FIG. 7 (b)), the magnetic field generator does not need to be moved up and down before the graphite member is disassembled and mounted, but it is impossible to obtain an extremely low oxygen crystal having an excellent in-plane distribution by cutting 5ppma-JEIDA over the entire surface of the wafer.

Comparative example 2

When the direction of magnetic force lines on the central axis of the pulling machine is set to the X axis in a horizontal plane including the coil axis, two (four) pairs of coils having a diameter of 900mm, which are arranged to face each other, are provided so that the respective coil axes are included in the same horizontal plane, and are arranged in a cylindrical container with an inter-coil-axis angle α sandwiching the X axis set to 120 degrees, the magnetic field generating device is subjected to magnetic field analysis and 3D melt convection analysis, and then the silicon single crystal is pulled using the device.

Fig. 9 (a) shows the distribution of the magnetic flux density after the magnetic field analysis result by ANSYS-Maxwell3D was analyzed by adjusting the current × the number of turns of the coil so that the magnetic flux density at the center axis was 1000 gauss (0.1 tesla). Fig. 9 (b) is a schematic diagram showing the arrangement of the four superconducting coils 104a, 104b, 104c, and 104 d.

The magnetic flux density of the space including the crystal and the melt region is extracted from the results of the magnetic field analysis, and 3D melt convection analysis is performed in consideration of the magnetic field distribution. Fig. 10 (a) and (c) show velocity vectors in the melt obtained from the results (fig. 10 (a) is a cross section perpendicular to the magnetic field, fig. 10 (c) is a cross section parallel to the magnetic field), and fig. 10 (b) and (d) show oxygen concentration distributions in the melt (fig. 10 (b) is a cross section perpendicular to the magnetic field, and fig. 10 (d) is a cross section parallel to the magnetic field).

In the magnetic field of comparative example 2, even if the convection suppression force is strong in the cross section perpendicular to the magnetic field lines, a relatively active flow is observed only below the crystal end, and the oxygen concentration in the melt is also low.

The calculation conditions at this time were set as in example 1 and comparative example 1: the amount of the silicon crystal fed was calculated from a crucible having a feed rate of 400kg and a diameter of 32 inches (1 inch: 25.4mm), a silicon crystal having a diameter of 306mm, a crystal rotation rate of 9rpm, a crucible rotation rate of 0.4rpm, and a pulling rate of 0.4 mm/min.

In the case of this coil arrangement (see fig. 9 (b)), the entire surface of the graphite member can be cut by 5ppma-JEIDA, and extremely low oxygen crystal having excellent in-plane distribution can be obtained.

The present invention is not limited to the above embodiments. The above embodiments are merely illustrative, and any configuration having substantially the same configuration as the technical idea described in the claims of the present invention and producing the same operation and effect is included in the technical scope of the present invention.