Single crystal pulling device and single crystal pulling process

Abstract

Single crystal drawing device, comprising: a drawing furnace with a heater and a crucible in which a molten single-crystal material is arranged, and which has a central axis; and a magnetic field generating device arranged around the drawing furnace and comprising superconducting coils and a cryostat containing the superconducting coils, wherein the single-crystal pulling device applies a horizontal magnetic field to the molten single-crystal material by exciting the superconducting coils in order to suppress the convection of the molten single-crystal material in the crucible, wherein the magnetic field generating device comprises four of the superconducting coils, wherein all coil axes of the four superconducting coils are arranged such that they are contained in a single horizontal plane, If a direction of magnetic force lines on the central axis in the horizontal plane is determined as the X-axis, two of the superconducting coils are arranged in each of a first region and a second region, which are divided by a cross-section that includes the X-axis and the central axis of the drawing furnace. The four superconducting coils are arranged such that they have line symmetry around the cross-section; the four superconducting coils are all arranged such that the coil axes have an angle within a range of more than -30° and less than 30° in the horizontal plane relative to a Y-axis, the Y-axis being perpendicular to the X-axis. the direction of the magnetic field lines generated by the four superconducting coils exhibits a line symmetry around the cross-section, and The two superconducting coils in each of the first and second regions generate magnetic field lines in opposite directions.

Description

TECHNICAL AREA

[0001] The present invention relates to a device for growing single crystals and a method for growing single crystals using this device. STATE OF THE ART

[0002] Each semiconductor, such as silicon or gallium arsenide, consists of a single crystal and is used for memory and the like in small and large computers, and there have been demands for an increase in capacity, a reduction in cost, and an improvement in the quality of storage devices.

[0003] One of the single-crystal pulling processes for producing single crystals that meet these semiconductor requirements is a method for producing a large-diameter, high-quality semiconductor in which a magnetic field is applied to a molten semiconductor material (melt) located in a crucible, thereby inhibiting the heat convection occurring in the melt (generally referred to as the magnetic Czochralski process (MCZ)).

[0004] An example of a single-crystal pulling device that uses the conventional CZ process is now given with reference to Fig. described. A single-crystal pulling device 100 in Fig. The drawing furnace 101 comprises a drawing furnace 101 with an opening / closing top and includes a crucible 102 within this drawing furnace 101. Furthermore, a heating element 103 for heating and melting a semiconductor material in the crucible 102 is provided around the crucible 102 within the drawing furnace 101, and a superconducting magnet 130 with a pair (two) of superconducting coils 104 (104a and 104b) inserted in a coolant reservoir 105 as a cylindrical container (hereinafter referred to as the cylindrical coolant reservoir) is arranged on an outside of the drawing furnace 101.

[0005] In the production of single crystals, a semiconductor material 106 is placed in the crucible 102 and heated by the heater 103 to melt the semiconductor material 106. A seed crystal (not shown) is moved downwards and inserted from above into this melt, e.g., into a central region of the crucible 102, and the seed crystal is drawn in a direction 108 at a predetermined speed by a drawing mechanism (not shown). As a result, a crystal grows in a solid-liquid interface, and a single crystal is produced. If, at this point, fluid motion of the melt is generated by the heating of the heating element 103, i.e., thermal convection, dislocation of the single crystal being grown can occur, and the yield of single crystal production is reduced.

[0006] As a countermeasure, the superconducting coils 104 of the superconducting magnet 130 are used. That is, the semiconductor material 106, which is the melt, receives a motion-suppressing force from the lines of magnetic force 107, which is generated by the excitation of the superconducting coils 104. The growing single crystal is slowly pulled upwards by drawing the seed crystal without generating convection in the crucible 102, and the single crystal is produced as a solid single crystal 109. It should be noted that the drawing mechanism for drawing the single crystal 109 along a crucible central axis 110 above the drawing furnace 101 is provided, although it is not shown.

[0007] Next, an example of the superconducting magnet 130, which is used in the Fig. the illustrated single-crystal drawing device 100 is used, with reference to Fig. described. In this superconducting magnet 130, the superconducting coils 104 (104a and 104b) are contained within a cylindrical vacuum vessel 119, extending through the cylindrical coolant reservoir. This superconducting magnet 130 houses the pair of superconducting coils 104a and 104b, which face each other through a central part of the vacuum vessel 119. The pair of superconducting coils 104a and 104b are magnetic coils that generate magnetic fields parallel to the same transverse direction, and as described in Fig. As shown, the lines of magnetic force 107 are generated bisymmetrically to the central axis 110 of the drawing furnace 101 and the vacuum vessel 119 (one position of this central axis 110 is called the magnetic field center).

[0008] It should be noted that this superconducting magnet 130, as in the Fig. The figure shows a current line 111 through which a current is introduced into the two superconducting coils 104a and 104b, a small helium cooler 112 for cooling a first radiation shield 117 and a second radiation shield 118 contained in the cylindrical coolant container 105, a gas drain tube 113 through which helium gas is drained from the cylindrical coolant container 105, a maintenance opening 114 with a refill opening from which liquid helium is added, and other components. Fig. The illustrated drawing furnace 101 is arranged in a bore 115 (the inner diameter of the bore is designated by D) of such a superconducting magnet 130.

[0009] Fig. shows a magnetic field distribution of the conventional superconducting magnet 130 described above. As in this Fig. As shown, in the conventional superconducting magnet 130 a magnetic field gradually assumes both sides in each coil arrangement direction (an X-direction in Fig. ) and the magnetic field gradually increases in an upward and downward direction in a direction orthogonal to the former (a Y-direction in Fig. ) because the pair of superconducting coils 104a and 104b are arranged opposite each other. In such a conventional configuration, the suppression of heat convection generated in the molten single-crystal material (melt) is unbalanced, and the magnetic field efficiency is poor because the magnetic field gradient in the region of bore 115 is too large, as shown in the Fig. shown. That is, as shown by the hatched lines, which represent an area with the same magnetic flux density in Fig. As indicated, the uniformity of the magnetic field in an area near the central magnetic field and its surroundings is not good (i.e., a cross shape extending from right to left and top to bottom is formed in Fig. formed), and therefore the problem arises that the heat convection suppression effect is low and a high-quality single crystal cannot be grown.

[0010] A technique for solving the problem described above is disclosed in patent document 1. The technique disclosed in patent document 1 is described with reference to Fig. described. Fig. shows an AA cross-section of Fig. To do that in Fig. and Fig. To solve the problem shown, patent document 1 discloses that the number of superconducting coils 104 is four or more (e.g., 104a, 104b, 104c and 104d), these coils are arranged on planes in a cylindrical container provided concentrically around a drawing furnace, the superconducting coils arranged in each direction are oriented towards each other through an axial center of the cylindrical container, and an arrangement angle θ (see Fig. ), in which each pair of superconducting coils that are adjacent to each other faces the inside of the cylindrical container, is set to a range of 100° to 130° (i.e., a central angle α (see Fig. ) between the axes of the adjacent coils with the X-axis in the middle is 50° to 80°). As a result, a lateral magnetic field can be generated in a bore 105, exhibiting a reduced magnetic field gradient and excellent uniformity; a magnetic field distribution with a concentric or square shape can be generated in a plane; an unbalanced electromagnetic force can be strongly suppressed, thereby improving a uniform magnetic field area in the pull direction; a magnetic field in the lateral magnetic field direction becomes essentially horizontal; the production of a high-quality single crystal can be achieved by suppressing the unbalanced electromagnetic force; and this patent document also discloses that a high-quality single crystal can be pulled with a good yield by this single-crystal pulling process. Note that in Fig. “d” is the diameter (inner diameter) of the superconducting coils and “l” is the distance between the coil pair.

[0011] This method makes the distribution of the magnetic field acting on the molten single crystal material uniform and suppresses an unbalanced electromagnetic force, making it possible to suppress heat convection even at a lower magnetic flux density than with the conventional technique using two coils.

[0012] However, a comprehensive heat transfer analysis, which also includes three-dimensional melt convection, has shown that the heat convection differs between a cross-section parallel to the X-axis and a cross-section parallel to the Y-axis when the lines of magnetic force form a lateral magnetic field extending in the direction of the X-axis, even with such a uniform magnetic field distribution (see patent specification 2).

[0013] When a conducting fluid moves in a magnetic field, an induced current is generated in a direction orthogonal to the lines of magnetic force and in a fluid component perpendicular to the lines of magnetic force. However, if a quartz crucible with electrically insulating properties is used, the crucible wall and the free surface of the molten semiconductor material form an insulating barrier. Therefore, the induced current does not flow orthogonally to these elements. Consequently, the convection-suppressing force generated by the electromagnetic force is weak in the upper part of the molten semiconductor material. Furthermore, comparing the cross-section parallel to the x-axis (the cross-section parallel to the lines of magnetic force) with the cross-section perpendicular to the x-axis (the cross-section perpendicular to the lines of magnetic force), convection is stronger in the cross-section perpendicular to the x-axis (the cross-section perpendicular to the lines of magnetic force).

[0014] As described, the velocity difference during convection is somewhat smaller when the four coils form a uniform magnetic field distribution, but there is still a non-uniform flow velocity distribution in the circumferential direction. In particular, since the flow field connecting the crucible wall to a growth interface remains perpendicular to the lines of magnetic force in cross-section, oxygen eluted from the quartz crucible, in particular, enters the crystal. Therefore, the problem is that the reduction in oxygen concentration achieved by applying a horizontal magnetic field has a limit, and the demand for extremely low oxygen concentrations in semiconductor crystals for power devices or image sensors, which have recently seen a surge in demand, is difficult to meet.Furthermore, the presence of the flux field, which is non-uniform in the circumferential direction of the crucible, can cause growth lines in the single crystal being pulled while rotating, and a resistivity / oxygen concentration fluctuation in one crystal rotation period is observed when the cross-section is evaluated parallel to a growth direction, and therefore there is also a problem that a ring-shaped distribution is formed in a wafer plane that is cut in a direction perpendicular to the growth direction.

[0015] Patent document 2 describes how, to solve these problems, a magnetic field distribution is generated such that a magnetic flux density distribution on an X-axis is an upwardly convex distribution when a direction of magnetic force lines on the central axis of a drawing furnace in a horizontal plane, which includes the coil axes of the superconducting coils, is defined as the X-axis, and that a magnetic flux density on the X-axis becomes 80% or less of a target value for the magnetic flux density at a crucible wall, and that simultaneously a distribution of the magnetic flux density on a Y-axis, which is orthogonal to the X-axis and passes through the central axis in the horizontal plane, is a downwardly convex distribution, and a magnetic flux density on the Y-axis becomes 140% or more of the target value for the magnetic flux density at the crucible wall.when the magnetic flux density at the central axis in the horizontal plane is determined as the target value for the magnetic flux density. Furthermore, the device for generating a magnetic field comprises two pairs of superconducting coils arranged opposite each other, such that their respective coil axes lie in the same horizontal plane, and a central angle α, at which the X-axis lies between the coil axes, is set to 100 degrees or more and 120 degrees or less. In this way, the technology disclosed in patent document 2 can achieve the following effects. That is, a flow velocity of the molten single-crystal material can be reduced even in the cross-section perpendicular to the X-axis, which exhibits an insufficient convection suppression force provided by electromagnetic force.A flow velocity of the molten single-crystal material in the cross-section parallel to the X-axis can be balanced by a flow velocity of the molten single-crystal material in the cross-section perpendicular to the X-axis. Furthermore, if the flow velocity of the molten single-crystal material is also reduced in the cross-section perpendicular to the X-axis, the time required for the oxygen eluted from the crucible wall to reach the single crystal is increased. It is also possible to provide a single-crystal growing device that can significantly reduce the oxygen concentration absorbed into the single crystal by increasing the amount of oxygen evaporated from the free surface of the molten single-crystal material. Finally, it is found that it is possible to provide a single-crystal growing device that can suppress growth lines in the single crystal being grown.by balancing the flow velocity of the molten single-crystal material in the cross-section parallel to the X-axis with the flow velocity of the molten single-crystal material in the cross-section perpendicular to the X-axis. QUOTE LIST PATENT LITERATURE Patent document 1: JP 2004 - 51 475 A Patent document 2: JP 2017 - 57 127 A SUMMARY OF THE INVENTIONAL PROBLEM

[0016] However, the present inventors have analyzed the magnetic field distribution with different coil arrangements, and as a result, it has been shown that the magnetic field distribution disclosed in Patent 2 can also be realized with coil arrangements other than those disclosed in Patent 2. Furthermore, in the coil arrangement disclosed in Patent 2, all superconducting coils are positioned as close as possible to the drawing furnace 101 (chamber) in order to increase the efficiency of the magnetic field. Therefore, the space between the superconducting coils 104a and 104b or 104c and 104d is narrower than the chamber of the drawing furnace 101 and the graphite element located therein (see Fig. ).

[0017] Furthermore, as in Fig. As shown, it is necessary to temporarily lift the chamber of the drawing furnace 101 and the large graphite element to avoid the superconducting magnet 130 (magnet) and then remove it, even if a cutout 131 is provided in a cylindrical container 105 on both sides or one side of the superconducting coils 104a and 104b or 104c and 104d to allow the chamber of the drawing furnace 101 to be lifted and rotated. Therefore, the work efficiency is poor, and since a heavy object is being lifted to a high place (using an arm 150, see Fig. ), the process requires effort, and it is also necessary to ensure safety, so during dismantling and assembly it is necessary to lower the device for generating a magnetic field and then carry out the process.

[0018] The present invention was made with regard to the problems mentioned above, and one objective is to provide a single-crystal growing device that eliminates the need to move the magnetic field generation device when the single-crystal growing device is dismantled and set up, and that reduces the oxygen concentration in the single crystal being grown, while simultaneously suppressing growth lines in the single crystal being grown. A further objective of the present invention is to provide a single-crystal growing method using such a single-crystal growing device. SOLUTION TO THE PROBLEM

[0019] To achieve this goal, the present invention provides a single-crystal pulling device comprising the following: a drawing furnace with a heater and a crucible in which a molten single-crystal material is arranged, and which has a central axis; and a device for generating a magnetic field, arranged around the drawing furnace and comprising superconducting coils and a cryostat containing the superconducting coils, wherein the single-crystal pulling device applies a horizontal magnetic field to the molten single-crystal material by exciting the superconducting coils in order to suppress the convection of the molten single-crystal material in the crucible, wherein the device for generating a magnetic field comprises four of the superconducting coils, wherein all coil axes of the four superconducting coils are arranged such that they are contained in a single horizontal plane, If a direction of magnetic force lines on the central axis in the horizontal plane is determined as the X-axis, two of the superconducting coils are arranged in each of a first region and a second region, which are divided by a cross-section that includes the X-axis and the central axis of the drawing furnace. The four superconducting coils are arranged such that they have line symmetry around the cross-section; the four superconducting coils are all arranged such that the coil axes have an angle within a range of more than -30° and less than 30° in the horizontal plane relative to a Y-axis, the Y-axis being perpendicular to the X-axis. the direction of the magnetic field lines generated by the four superconducting coils exhibits a line symmetry around the cross-section, and The two superconducting coils in each of the first and second regions generate magnetic field lines in opposite directions.

[0020] A single-crystal growing device with a magnetic field generation device having such an arrangement of superconducting coils can achieve an arrangement of superconducting coils that does not require the magnetic field generation device to be moved during the dismantling and assembly of the single-crystal growing device.If the single-crystal pulling device includes a device for generating a magnetic field with such an arrangement of superconducting coils, the flow velocity of the molten single-crystal material can also be reduced even in the cross-section perpendicular to the X-axis, which has an insufficient convection suppression force provided by the electromagnetic force, and the flow velocity of the molten single-crystal material in the cross-section parallel to the X-axis can be balanced with the flow velocity of the molten single-crystal material in the cross-section perpendicular to the X-axis.If the flow velocity of the molten single-crystal material is also reduced in the cross-section perpendicular to the X-axis, the time required for the oxygen eluted from the crucible wall to reach the single crystal increases. It is then possible to provide a single-crystal growing device that can significantly reduce the oxygen concentration absorbed into the single crystal by increasing the amount of oxygen evaporated from a free surface of the molten single-crystal material. Furthermore, it is possible to provide a single-crystal growing device that can suppress growth lines in the single crystal being grown by balancing the flow velocity of the molten single-crystal material in the cross-section parallel to the X-axis with the flow velocity of the molten single-crystal material in the cross-section perpendicular to the X-axis.

[0021] In the single-crystal growing device according to the invention, the device for generating a magnetic field as a cryostat preferably comprises a U-shaped cryostat containing all four superconducting coils, or a cryostat containing two of the superconducting coils in the first and second regions, wherein the two cryostats have a structurally coupled structure.

[0022] With such a device for generating a magnetic field, a space in which there is nothing is created on a near or far side of the direction of the lines of magnetic force, so that it becomes possible to operate elements that configure the drawing furnace without raising and lowering the device for generating a magnetic field, and a device for raising and lowering also becomes unnecessary.

[0023] Furthermore, the height of the superconducting coils in the vertical direction can be greater than the width of the superconducting coils in the vertical direction as seen from above.

[0024] If the superconducting coils of the device for generating a magnetic field have such a shape, the magnetic flux density in the central axis of the drawing furnace in the horizontal plane containing the coil axes can be increased, even though the width of the coils is narrow when viewed from above.

[0025] Furthermore, the present invention provides a method for growing single crystals, wherein a silicon single crystal is grown using one of the single crystal growing devices described above.

[0026] In such a single-crystal growing process, the concentration of absorbed oxygen is greatly reduced, and a silicon single crystal with suppressed growth lines can be grown. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0027] The single-crystal growing device according to the invention can achieve an arrangement of superconducting coils that eliminates the need to move the device for generating a magnetic field during the dismantling and assembly of the single-crystal growing device. Furthermore, the single-crystal growing device according to the invention can be a single-crystal growing device that can significantly reduce the concentration of oxygen absorbed into the single crystal and also suppress growth lines in a single crystal being grown. Moreover, according to the single-crystal growing method according to the invention, the concentration of absorbed oxygen is significantly reduced, and a single crystal with suppressed growth lines can be grown. BRIEF DESCRIPTION OF THE DRAWINGS Fig. (a) is a schematic view showing an example of the single crystal growing device according to the invention, and (b) is a schematic cross-sectional view of the single crystal growing device and (c) is a schematic view showing an arrangement of superconducting coils in a superconductivity generation device (a top view). Fig. Figure 1 is a schematic view showing examples of the coil arrangement in the single crystal drawing device according to the invention (top view). Fig. Figure 1 is a schematic view showing examples of cryostats incorporated into a device for generating a magnetic field in the single-crystal growing device according to the invention. Fig. Figure 1 is a schematic view showing one form of superconducting coils that can be used in the present invention. In Fig. is (a) a schematic view showing a result of the magnetic field analysis by simulation in Example 1, and (b) a schematic view showing an arrangement of superconducting coils in Example 1. Fig. is a diagram that shows the results of the 3D melt convection analysis taking into account the magnetic field distribution by simulation in Example 1. shows, and (a) shows a velocity vector of a melt in a cross-section perpendicular to the magnetic field, (b) shows an oxygen concentration of the melt in the cross-section perpendicular to the magnetic field, (c) shows a velocity vector of the melt in a cross-section parallel to the magnetic field, and (d) shows an oxygen concentration of the melt in the cross-section parallel to the magnetic field. Fig. Figure (a) shows a diagram representing a result of the magnetic field analysis by simulation in Comparative Example 1, and Figure (b) shows a diagram showing the arrangement of the superconducting coils in Comparative Example 1. Fig. is a diagram showing the results of the 3D melt convection analysis taking into account the magnetic field distribution by simulation in Comparative Example 1, and (a) shows a velocity vector of a melt in a cross-section perpendicular to the magnetic field, (b) shows an oxygen concentration of the melt in the cross-section perpendicular to the magnetic field, (c) shows a velocity vector of the melt in a cross-section parallel to the magnetic field, and (d) shows an oxygen concentration of the melt in the cross-section parallel to the magnetic field. Fig. Figure (a) shows a diagram showing a result of the magnetic field analysis by simulation in Comparative Example 2, and Figure (b) shows a diagram showing an arrangement of superconducting coils in Comparative Example 2. Fig. is a diagram showing the results of the 3D melt convection analysis taking into account the magnetic field distribution by simulation in Comparative Example 2, and (a) shows a velocity vector of a melt in a cross-section perpendicular to the magnetic field, (b) shows an oxygen concentration of the melt in the cross-section perpendicular to the magnetic field, (c) shows a velocity vector of the melt in a cross-section parallel to the magnetic field, and (d) shows an oxygen concentration of the melt in the cross-section parallel to the magnetic field. Fig. is a schematic cross-sectional view showing an example of a conventional single-crystal pulling device. Fig. is a schematic perspective view showing an example of a superconducting magnet in a conventional single-crystal pulling device. Fig. is a diagram showing a conventional magnetic flux density distribution. Fig. shows a schematic perspective view and a schematic transverse cross-sectional view of a superconducting magnet from patent document 1. Fig. Figure 2 shows schematic transverse cross-sectional views of superconducting magnets of patent document 2, and (a) shows a housing with a cylindrical container, and (b) shows a housing with a cutout in part of a cylindrical container. Fig. Figure 1 is a schematic view showing a method for lifting and rotating a drawing furnace (chamber) in a case where a superconducting magnet of patent document 2 is used. DESCRIPTION OF THE EXECUTION FORMS

[0028] The present invention is described in detail below as an exemplary embodiment with reference to the drawings, although the present invention is not limited thereto.

[0029] First, an embodiment of the single-crystal pulling device according to the invention is described with reference to Fig. described. The single-crystal pulling device 21 in Fig. The apparatus comprises a drawing furnace 11 in which a heater 13 and a crucible 12 containing a molten single-crystal material (hereinafter also referred to simply as "melt") 16 are arranged and which has a central axis 20, and a magnetic field generating device 30 provided around the drawing furnace 11 and comprising superconducting coils and a cryostat containing the superconducting coils, and the single-crystal drawing device 21 configured to apply a horizontal magnetic field to the melt 16 by exciting the superconducting coils in order to suppress the convection of the melt 16 in the crucible 12, and in the meantime draws a single crystal 19 in a drawing direction 18.

[0030] Furthermore, the magnetic field generating device 30 has superconducting coils, which, as in Fig. are shown arranged as in Fig. As shown, the magnetic field generating device 30 has four superconducting coils. Furthermore, the coil axes of all four superconducting coils 14a, 14b, 14c, and 14d are arranged such that they lie in a single horizontal plane (which is shown in Fig. The horizontal plane 22 shown includes the coil axes). If a direction of the lines 17 of the magnetic force at the central axis 20 in the horizontal plane 22 is determined as the X-axis, then furthermore, two of the superconducting coils are each arranged in a first region and a second region, which are subdivided by a cross-section that includes the X-axis and the central axis 20 of the drawing furnace. Fig. The superconducting coils 14a and 14d are arranged in the first region, where the left side of the x-axis is defined as the first region and the right side of the x-axis as the second region. The superconducting coils 14b and 14c are arranged in the second region. Furthermore, in the present invention, the four superconducting coils 14a, 14b, 14c, and 14d are arranged such that they exhibit line symmetry over the cross-section, as shown in Fig. shown. Furthermore, the four superconducting coils 14a, 14b, 14c and 14d are all arranged such that the coil axes have an angle within a range of more than -30° and less than 30° in the horizontal plane 22 relative to a Y-axis, the Y-axis being perpendicular to the X-axis. Fig. Figure 1 shows a state in which the two superconducting coils, located in the first region and the second region respectively, are arranged such that they are positioned parallel to the X-axis. Furthermore, in the present invention, the direction of the lines of magnetic force generated by the four superconducting coils 14a, 14b, 14c, and 14d has linear symmetry over the cross-section, as shown in Figure 2. Fig. shown. Furthermore, in the present invention, the two superconducting coils generate lines of magnetic force in opposite directions in the first region and the second region, respectively.

[0031] As described above, in the present invention the four superconducting coils 14a, 14b, 14c and 14d must all be arranged such that the coil axes in the horizontal plane 22 have an angle relative to the Y-axis in a range of more than -30° and less than 30°, wherein the Y-axis is perpendicular to the X-axis. Fig. shows an example of a coil arrangement (top view) in the single crystal drawing device according to the invention. Fig. Figure 2 shows a case in which the coil axes in the horizontal plane 22 are at 0° relative to the Y-axis. In this case, the four superconducting coils 14a, 14b, 14c and 14d are parallel to the X-axis, and the coil axes are parallel to the Y-axis. Fig. shows a case where the coil axes are at 25° in the horizontal plane 22 relative to the Y-axis. Similarly, shows Fig. A case in which the coil axes lie at -25° in the horizontal plane 22 relative to the Y-axis. If the coil axes and the Y-axis intersect on the side of the superconducting coils facing away from the X-axis, the angle is defined as a negative angle, as in Fig. shown.

[0032] If the coil axes are arranged such that they have an angle within a range of more than -30° and less than 30° relative to the Y-axis, a predetermined magnetic field distribution can be generated. With such a magnetic field distribution, formed by the arrangement of the superconducting coils of the present invention, the flow velocity of the molten single-crystal material can be reduced even in the cross-section perpendicular to the X-axis, which conventionally exhibits an insufficient convection suppression force provided by electromagnetic force, and the flow velocity of the molten single-crystal material in the cross-section parallel to the X-axis can be balanced against the flow velocity of the molten single-crystal material in the cross-section perpendicular to the X-axis.If the flow rate of the molten single-crystal material is reduced, even in the cross-section perpendicular to the X-axis, the time required for the oxygen eluted from the crucible wall to reach the single crystal is also increased. It is therefore possible to provide a single-crystal growing device that can significantly reduce the oxygen concentration absorbed into the single crystal by increasing the amount of oxygen evaporated from a free surface of the molten single-crystal material. Furthermore, it is possible to provide a single-crystal growing device that can suppress growth lines in the single crystal being grown by balancing the flow rate of the molten single-crystal material in the cross-section parallel to the X-axis with the flow rate of the molten single-crystal material in the cross-section perpendicular to the X-axis.

[0033] If the coil axes are arranged at an angle within a range of more than -30° and less than 30° relative to the Y-axis, it is also possible to achieve an arrangement of superconducting coils that does not require the magnetic field generation device to be moved during the dismantling and assembly of the single-crystal pulling device. However, if the coil axes are arranged at an angle in the range of -30° or less, or 30° or more relative to the Y-axis, the width of the cryostat containing the superconducting coils becomes large, or the spacing between the superconducting coils becomes short, and the problem arises that the magnetic field generation device must be raised and lowered as before to dismantle and assemble the graphite component.

[0034] The angle of the coil axes is particularly preferably -5° or less with respect to the Y-axis. At such an angle, the magnetic flux density at the central axis can be maintained even when the number of turns of the superconducting wire or the current value is reduced, thus reducing the force exerted on the coils and achieving a device for generating a magnetic field that is not easily quenched.

[0035] Furthermore, the device for generating a magnetic field as a cryostat for generating the superconducting state can comprise a U-shaped cryostat 31 containing all four superconducting coils 14a, 14b, 14c and 14d, as shown in Fig. shown. Alternatively, the device for generating a magnetic field can comprise a cryostat containing two of the superconducting coils each in the first region and in the second region, the two cryostats having a structurally coupled structure. An example of a cryostat of this embodiment is shown in Fig. As shown, in this embodiment, two superconducting coils 14a and 14d are housed in a first cryostat 32 in the first region, and two superconducting coils 14b and 14c are housed in a second cryostat 33 in the second region. Furthermore, the first cryostat 32 and the second cryostat 33 are structurally coupled by a structural element 34.

[0036] With such a device for generating a magnetic field, a space is created in which there is nothing, either near or far from the direction of the lines of magnetic force, so that it becomes possible to rotate a chamber of the drawing furnace 11 or to remove and assemble a graphite component without raising and lowering the device for generating a magnetic field, and a device for raising and lowering it also becomes unnecessary.

[0037] Note that in the superconducting coils used in the single crystal pulling device according to the invention, the height of the superconducting coils in the vertical direction can be greater than the width of the superconducting coils seen from above in the vertical direction. Fig. and (b) show such superconducting coils. Fig. shows a cross-section through the superconducting coils. Fig. shows Fig. The superconducting coils are rotated sideways, and the height of the superconducting coils is represented by H. The direction of H is the upward and downward direction of the vertical direction. Fig. R is the radius of curvature of a curved section (circular arc) of the superconducting coils. If the superconducting coils of the magnetic field generating device have such a shape, the magnetic flux density in the central axis of the drawing furnace in the horizontal plane, including the coil axes, can be increased, even if the width of the coils is narrow when viewed from above.

[0038] Furthermore, a silicon single crystal can be grown using the single-crystal growing device according to the invention. In such a single-crystal growing process, the concentration of absorbed oxygen is greatly reduced, and a silicon single crystal with suppressed growth lines can be grown. EXAMPLE

[0039] The present invention is described in more detail below with reference to examples and comparative examples. However, these examples are presented merely as examples and should not be understood as limiting. (Example 1)

[0040] A magnetic field generation device was used to perform a magnetic field analysis and a 3D melt convection analysis. A silicon single crystal was then grown using this device. The magnetic field generation device had two pairs of four coils with a radius of 250 mm in upper and lower circular arcs and a height of 1000 mm. Once the direction of the magnetic force lines on the central axis in a horizontal plane, including the coil axes of the two pairs of four superconducting coils as the X-axis, was determined, a pair of superconducting coils was placed and arranged parallel to the X-axis on the left and right sides (first region and second region) of the cross-section encompassing the X-axis and the central axis of the drawing furnace, to exhibit line symmetry around the cross-section.

[0041] Fig. This is the result of a magnetic field analysis using ANSYS-Maxwell 3D, and was obtained by adjusting the current × number of coil turns so that the magnetic flux density on the central axis was 1000 Gauss (0.1 Tesla), performing the analysis, and subsequently displaying the magnetic flux density distribution. It should be noted that Fig. A schematic view showing the arrangement of the four superconducting coils 14a, 14b, 14c and 14d in this case.

[0042] The magnetic flux density of the space encompassing the crystal and melt regions was extracted from the results of the magnetic field analysis described above, and the 3D melt convection analysis was performed taking into account the magnetic field distribution. Fig. and (c) show the velocity vector in the melt obtained from the results of the analysis ( Fig. is a cross-section perpendicular to the magnetic field, and Fig. (is a cross-section parallel to the magnetic field). Fig. and (d) show the oxygen concentration distribution in the melt ( Fig. is a cross-section perpendicular to the magnetic field and Fig. (is a cross-section parallel to the magnetic field).

[0043] In this case, the calculations were performed under the following conditions: a charge of 400 kg, an 812.8 mm crucible (32-inch crucible (1 inch equals 25.4 mm)), a silicon crystal with a diameter of 306 mm, a crystal rotation of 9 rpm, a crucible rotation of 0.4 rpm and a drawing speed of 0.4 mm / min.

[0044] In the magnetic field of Example 1, the convection-suppressing force in the cross-section perpendicular to the magnetic field lines was also strong, as in the comparative example 2 described below, and a comparatively active flux was observed only below the crystal end. Furthermore, the oxygen concentration in the melt was low.

[0045] With this coil arrangement (see Fig. It is not necessary to raise and lower the magnetic field generation device before degrading and building up the graphite component. Furthermore, a crystal with an extremely low oxygen concentration of less than 5 ppma-JEIDA across the entire wafer surface and excellent in-plane distribution was successfully produced. (Comparative example 1)

[0046] A magnetic field analysis and a 3D melt convection analysis were performed using a device for generating a magnetic field, consisting of a pair (two) coils with an outer diameter of 1100 mm, arranged bisymmetrically around the central axis of a drawing machine, and subsequently a silicon single crystal was drawn with this device.

[0047] Fig. This is the result of a magnetic field analysis using ANSYS-Maxwell 3D, and was obtained by adjusting the current × number of turns of the coils so that the magnetic flux density on the central axis is 1000 Gauss (0.1 Tesla), and performing the analysis and subsequently displaying the distribution of the magnetic flux density. Fig. is a schematic view showing the arrangement of the two superconducting coils 104a and 104b in this case.

[0048] The magnetic flux density of the space enclosing the crystal and melt regions was extracted from the results of the magnetic field analysis, and the 3D melt convection analysis was performed taking the magnetic field distribution into account. (a) and (c) of Fig. show the velocity vector in the melt, which was obtained from the results of the analysis ( Fig. is a cross-section perpendicular to the magnetic field, and Fig. ( is a cross-section parallel to the magnetic field). Simultaneously, (b) and (d) show of Fig. the oxygen concentration distribution in the melt ( Fig. is a cross-section perpendicular to the magnetic field and Fig. (is a cross-section parallel to the magnetic field). In the magnetic field of comparison example 1, the convection-suppressing force in the cross-section perpendicular to the magnetic field lines was weak, and an active eddy current developed. Furthermore, the oxygen concentration in the melt was high.

[0049] As in Example 1, the calculations were performed under the following conditions: a charge of 400 kg, an 812.8 mm crucible (32-inch crucible (1 inch equals 25.4 mm)), a silicon crystal with a diameter of 306 mm, a crystal rotation of 9 rpm, a crucible rotation of 0.4 rpm and a drawing speed of 0.4 mm / min.

[0050] In this coil arrangement (see Fig. It is not necessary to raise and lower the device for generating the magnetic field before the removal and build-up of the graphite component. However, it was not possible to obtain a crystal with an extremely low oxygen concentration of less than 5 ppma-JEIDA across the entire wafer surface and excellent in-plane distribution. (Comparative example 2)

[0051] A magnetic field generation device was used to perform a magnetic field analysis and a 3D melt convection analysis, followed by the pulling of a silicon single crystal using this device. The magnetic field generation device, defined as the X-axis with respect to the direction of the magnetic force lines in the horizontal plane encompassing the coil axes on the central axis of the pulling machine, comprised pairs of 900 mm diameter coils arranged opposite each other to form two pairs of four coils, with the coil axes lying in the same horizontal plane. Furthermore, the coils were arranged in a cylindrical container with an angle α of 120 degrees between the coil axes and the X-axis.

[0052] Fig. This is the result of a magnetic field analysis using ANSYS-Maxwell 3D, and was obtained by adjusting the current × number of coil turns so that the magnetic flux density on the central axis was 1000 Gauss (0.1 Tesla), performing the analysis, and subsequently displaying the magnetic flux density distribution. It should be noted that Fig. A schematic view showing the arrangement of the four superconducting coils 104a, 104b, 104c and 104d in this case.

[0053] The magnetic flux density of the space encompassing the crystal and melt regions was extracted from the results of the magnetic field analysis, and the 3D convection analysis of the melt was performed taking into account the magnetic field distribution. Fig. and (c) show the velocity vector in the melt obtained from the results of the analysis ( Fig. is a cross-section perpendicular to the magnetic field and Fig. (is a cross-section parallel to the magnetic field). Fig. and (d) show the oxygen concentration distribution in the melt ( Fig. is a cross-section perpendicular to the magnetic field and Fig. (is a cross-section parallel to the magnetic field).

[0054] In the magnetic field of comparison example 2, the convection-suppressing force was also strong in the cross-section perpendicular to the magnetic field lines, and a comparatively active flux was observed only below the crystal end. Furthermore, the oxygen concentration in the melt was low.

[0055] As in Example 1 and Comparative Example 1, the calculations in this case were performed under the following conditions: a charge of 400 kg; an 812.8 mm crucible (32-inch crucible (1 inch equals 25.4 mm)); a silicon crystal with a diameter of 306 mm; a crystal rotation of 9 rpm; a crucible rotation of 0.4 rpm; and a drawing speed of 0.4 mm / min.

[0056] With this coil arrangement (see Fig. It is possible to obtain a crystal with an extremely low oxygen concentration of less than 5 ppma-JEIDA across its entire surface and excellent in-plane distribution. However, it is necessary to raise and lower the device for generating the magnetic field before the graphite component is mined and built up.

[0057] It should be noted that the present invention is not limited to the embodiments described above but is defined in the claims.

Claims

[1] Single crystal pulling device comprising: a drawing furnace with a heater and a crucible in which a molten single-crystal material is arranged, and which has a central axis; and a magnetic field generating device arranged around the drawing furnace and comprising superconducting coils and a cryostat containing the superconducting coils, wherein the single-crystal pulling device applies a horizontal magnetic field to the molten single-crystal material by exciting the superconducting coils in order to suppress the convection of the molten single-crystal material in the crucible, wherein the magnetic field generating device comprises four of the superconducting coils, wherein all coil axes of the four superconducting coils are arranged such that they are contained in a single horizontal plane, If a direction of magnetic force lines on the central axis in the horizontal plane is determined as the X-axis, two of the superconducting coils are arranged in each of a first region and a second region, which are divided by a cross-section that includes the X-axis and the central axis of the drawing furnace. The four superconducting coils are arranged such that they have line symmetry around the cross-section; the four superconducting coils are all arranged such that the coil axes have an angle within a range of more than -30° and less than 30° in the horizontal plane relative to a Y-axis, the Y-axis being perpendicular to the X-axis. the direction of the magnetic field lines generated by the four superconducting coils exhibits a line symmetry around the cross-section, and The two superconducting coils in each of the first and second regions generate magnetic field lines in opposite directions. [2] Single crystal growing device according to claim 1, wherein the device for generating a magnetic field as a cryostat comprises: a U-shaped cryostat containing all four superconducting coils, or a cryostat containing two of the superconducting coils each in the first region and in the second region, wherein the two cryostats have a structurally coupled structure. [3] Single crystal pulling device according to claim 1 or 2, wherein the height of the superconducting coils in the vertical direction is greater than the width of the superconducting coils seen from above in the vertical direction. [4] Single crystal growing process in which a silicon single crystal is grown using the single crystal growing device according to one of claims 1 to 3.

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