Induction heating coil and single crystal manufacturing device using the same

Abstract

[Problem] To provide: an induction heating coil that is capable of suppressing variation in the height of the melting surface of a source material rod and stably growing a single crystal; and a single crystal production device using the same. [Solution] An induction heating coil 20 comprises an annular coil body 21 that has an opening 22 in the center thereof and that has a first end 21e1 and a second end 21e2 which are separated from each other by a slit 23 extending in a substantially radial direction from the opening 22. The slit 23 is a diagonal slit cut in the coil body 21 in a diagonal direction from the upper surface 21a side to the lower surface 21b such that a corner part at the upper surface 21a side of the first end 21e1 forms an acute angle, and a corner part at the upper surface 21a side of the second end 21e2 forms an obtuse angle. The upper surface 21a of the coil body 21 has a lower step surface 21a1 and an upper step surface 21a2. The lower step surface 21a1 is provided at least in a region near the slit on the first end 21e1 side. The upper step surface 21a2 is provided in a region excluding the region where the lower step surface 21a1 is formed.

Description

[Technical Field]

[0001] The present invention relates to an induction heating coil used in producing a single crystal by the FZ method (Floating Zone method) and a single crystal production apparatus using the same. [Background technology]

[0002] The FZ method is known as a method for producing silicon single crystals. In the FZ method, a portion of a raw material rod made of polycrystalline silicon is heated to create a molten zone, and the raw material rod and seed crystal, positioned above and below the molten zone, are gradually lowered to grow a large single crystal above the seed crystal. The FZ method does not use a quartz crucible like the CZ method (Czochralski method), and therefore can produce single crystals with a low oxygen concentration.

[0003] In the FZ method, induction heating is used to heat the polycrystalline silicon raw material. When a magnetic field generated by passing a high-frequency current through an induction heating coil is applied to the silicon raw material, eddy currents flow in the silicon raw material due to electromagnetic induction, and Joule heat is generated by the eddy currents. In the induction heating method, this Joule heat is used to heat the silicon raw material.

[0004] Regarding induction heating coils, for example, Patent Document 1 describes a method of uniformly distributing heating on the single crystal side by locally providing grooves on the surface of the induction heating coil on the single crystal side in order to reduce resistance fluctuations in the single crystal. Patent Document 2 also discloses a method of movably inserting an insulating member into a slit in an induction heating coil. Examples of cross-sectional shapes of the slit include vertical, oblique, and crank types. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2914077 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-232859 Summary of the Invention [Problem to be solved by the invention]

[0006] The FZ method requires larger diameter feed rods to improve single crystal yields. However, as the diameter of the feed rod increases, it becomes difficult to uniformly heat the entire circumferential direction of the feed rod. This causes the amount of melted material to increase locally, resulting in greater circumferential height variation in the molten surface of the feed rod. This uneven molten surface eventually comes into contact with the coil surface, forcing the manufacturing process to be halted.

[0007] Therefore, an object of the present invention is to provide an induction heating coil that can suppress variations in the height of the melting surface of a raw material rod and enable stable growth of a single crystal, and a single crystal manufacturing apparatus using the same. [Means for solving the problem]

[0008] In order to solve the above problems, the induction heating coil of the present invention is used for producing single crystals by the FZ method, and comprises an annular coil body having an opening in the center and a first end and a second end separated from each other by a slit extending approximately radially from the opening, wherein the slit is an oblique slit that cuts the coil body obliquely from the top surface side to the bottom surface side so that the corner portion on the top surface side of the first end forms an acute angle and the corner portion on the top surface side of the second end forms an obtuse angle, and the top surface of the coil body has an upper step surface and a lower step surface, the lower step surface is provided in the region near the slit on the first end side, and the upper step surface is provided in the region excluding the region where the lower step surface is formed.

[0009] When the slit in the induction heating coil is formed at an angle, one corner of the slit is acute and the other corner is obtuse. This means that current tends to concentrate at the acute corner, resulting in a significant increase in heat generation in the area near the slit. However, if the height of the top surface on the first end side where the acute corner is provided is lowered, the bias in the heat generation distribution in the circumferential direction of the melting surface due to current concentration near the slit can be reduced. This allows for stable growth of single crystals by suppressing variations in the height of the melting surface of the raw material rod.

[0010] The difference in height between the upper and lower surfaces is preferably 2 mm or more. In this case, the thickness of the coil body in the region where the lower surface is formed is preferably thinner than the thickness of the coil body in the region where the upper surface is formed. The effect of providing a height difference on the upper surface of the coil body can be exerted, and the bias in the circumferential heat distribution caused by current concentration near the slits can be reduced.

[0011] The formation region of the upper surface preferably includes a region near the slit on the second end side, thereby reducing the difference in heating distribution between the left and right sides of the slit and reducing bias in the heat generation distribution in the circumferential direction.

[0012] When the direction of the center line of the slit extending substantially radially from the center of the opening is taken as 0°, the lower stage surface is preferably provided in a range of at least 0° to 30°. In this case, it is preferable that the lower stage surface is provided in a range of 0° to 90°, and the upper stage surface is provided in a range of at least 180° to 360°. Alternatively, the lower stage surface may be provided in a range of 0° to 180°, and the upper stage surface may be provided in a range of 180° to 360°. This can suppress the difference in heating distribution in the circumferential direction, thereby reducing the circumferential height variation of the melting surface of the raw material rod.

[0013] Furthermore, the single crystal manufacturing apparatus according to the present invention is a single crystal manufacturing apparatus used for manufacturing single crystals by the FZ method, and is characterized by comprising an upper shaft that supports a raw material rod so that it can rotate and rise and fall, a lower shaft that is positioned below the upper shaft and supports a seed crystal so that it can rotate and rise and fall, and the induction heating coil according to the present invention described above that heats the raw material rod.

[0014] According to the present invention, it is possible to provide a single crystal manufacturing apparatus that can suppress variations in the height of the melting surface of the raw material rod in the circumferential direction and stably grow a single crystal. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide an induction heating coil that can suppress the circumferential height variation of the melting surface of the raw material rod and stably grow a single crystal, and a method and apparatus for manufacturing a single crystal using the same. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic perspective view showing the configuration of the induction heating coil according to the first embodiment of the present invention. [Figure 3] 3(a) and (b) are diagrams showing the configuration of the induction heating coil shown in FIG. 2, with FIG. 3(a) being a plan view and FIG. 3(b) being a cross-sectional view taken along line XX' in FIG. 3(a). [Figure 4] FIG. 4(a) is a diagram showing the height profile of the upper surface of the coil body, and FIG. 4(b) is a cross-sectional view of the slit. [Figure 5] FIG. 5 is a schematic diagram showing the flow of current inside the coil body. [Figure 6] 6(a) and (b) are schematic diagrams for explaining the coil shape of the present invention, where (a) shows a conventional coil shape and (b) shows the coil shape of the present invention. [Figure 7]7(a) and (b) are diagrams showing the configuration of an induction heating coil according to a second embodiment of the present invention, where FIG. 7(a) is a plan view and FIG. 7(b) is a diagram showing the height profile of the upper surface of the coil body. [Figure 8] 8(a) and (b) are diagrams showing the configuration of an induction heating coil according to a third embodiment of the present invention, where FIG. 8(a) is a plan view and FIG. 8(b) is a diagram showing the height profile of the upper surface of the coil body. [Figure 9] 9(a) and 9(b) are diagrams showing the configuration of an induction heating coil according to a fourth embodiment of the present invention, where FIG. 9(a) is a plan view and FIG. 9(b) is a diagram showing the height profile of the upper surface of the coil body. [Figure 10] 10(a) and (b) are diagrams showing the configuration of an induction heating coil 20 according to a fifth embodiment of the present invention, where FIG. 10(a) is a plan view and FIG. 10(b) is a diagram showing the height profile of the upper surface of the coil body. [Figure 11] Figures 11(a) and (b) are diagrams for explaining the operation (problems) of a conventional induction heating coil, with Figure 11(a) showing the molten state when heated at the right side of the slit, and Figure 11(b) showing the molten state when heated at the left side of the slit. [Figure 12] Figures 12(a) and (b) are diagrams for explaining the action (effect) of the induction heating coil according to this embodiment, where Figure 12(a) shows the molten state when heated at the right side of the slit, and Figure 12(b) shows the molten state when heated at the left side of the slit. [Figure 13] FIG. 13 is a graph showing the measurement results of the distance between the raw material melting surface and the coil when growing a single crystal using an induction heating coil according to a comparative example. [Figure 14] FIG. 14 is a graph showing the measurement results of the distance between the raw material melting surface and the coil when growing a single crystal using the induction heating coil according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0018] FIG. 1 is a schematic diagram showing the configuration of a single crystal manufacturing apparatus according to an embodiment of the present invention.

[0019] As shown in FIG. 1, this single crystal manufacturing apparatus 1 is an apparatus for growing silicon single crystals by the FZ method, and is equipped with a reactor 10 that accommodates a raw material rod 2, a seed crystal 3, and a silicon single crystal 4 grown on the seed crystal 3, an upper shaft 11 that supports the raw material rod 2 so that it can rotate and move up and down, a lower shaft 12 that supports the seed crystal 3 and the silicon single crystal 4 so that they can rotate and move up and down, an induction heating coil 20 that heats the lower end of the raw material rod 2, a single crystal weight holder 14 that supports the weight of the silicon single crystal 4 that has become larger as the crystal growth progresses, and a gas doping device 15 that supplies a doping gas to a molten zone 5 (molten silicon) between the raw material rod 2 and the silicon single crystal 4.

[0020] The source rod 2 is made of high-purity polycrystalline silicon obtained by refining a silicon source such as monosilane or trichlorosilane, and the upper end of the source rod 2 is attached to the lower end of the upper shaft 11 via a source holder 16. The lower end of the seed crystal 3 is attached to the upper end of the lower shaft 12 via a seed crystal holder 17. The upper shaft 11 and the lower shaft 12 are rotated and raised and lowered, respectively, by a drive mechanism (not shown).

[0021] The induction heating coil 20 is a high-frequency coil with approximately one turn that surrounds the molten zone 5 or the raw material rod 2, and is connected to a high-frequency oscillator (not shown). The induction heating coil 20 is preferably made mainly of copper or silver. By passing a high-frequency current through the induction heating coil 20, the lower end of the raw material rod 2 is induction heated, and a molten zone 5 is generated. After the seed crystal 3 is fused to the molten zone 5 thus generated, the raw material rod 2 and the seed crystal 3 are lowered while being rotated, whereby a silicon single crystal 4 can be grown from the molten zone 5.

[0022] Fig. 2 is a schematic perspective view showing the configuration of induction heating coil 20 according to the first embodiment of the present invention. Fig. 3(a) and (b) are configuration diagrams of induction heating coil 20 shown in Fig. 2, with Fig. 3(a) being a plan view and Fig. 3(b) being a cross-sectional view taken along line X-X' in Fig. 3(a). Fig. 4(a) is a diagram showing the height profile of the upper surface of the coil body, and Fig. 4(b) is a cross-sectional view of the slits.

[0023] 2, 3(a), 3(b), 4(a), and 4(b), induction heating coil 20 includes a coil body 21 made of a substantially flattened, annular coil conductor, an opening 22 provided at the center of coil body 21 in plan view, a slit 23 extending substantially radially from opening 22 toward the outer circumferential end to separate one circumferential end (first end) 21e1 from the other circumferential end (second end) 21e2 of coil body 21, and a pair of terminal electrodes 24A and 24B connected to first end 21e1 and second end 21e2, respectively, of coil body 21. Coil body 21 is connected to a high-frequency oscillator via the pair of terminal electrodes 24A and 24B.

[0024] Typically, the outer diameter of the coil body 21 is larger than the diameter of the raw material rod 2, and the inner diameter of the coil body 21 (the diameter of the opening 22) is smaller than the diameter of the raw material rod 2. The upper surface 21a of the coil body 21 may be a surface that slopes upward from the inner periphery toward the outer periphery, or may be a horizontal surface. The lower surface 21b of the coil body 21 may be a surface that slopes downward from the inner periphery toward the outer periphery, or may be a horizontal surface.

[0025] As shown in Figures 2 and 3(a), the slit 23 penetrates from the upper surface 21a to the lower surface 21b of the coil body 21, cutting the coil body 21 at one point in the circumferential direction. The slit 23 is formed obliquely, not vertically, and in particular, is formed so as to approach the first end 21e1 side from the upper surface 21a to the lower surface 21b. Therefore, as shown in Figure 4(b), the corner C on the upper surface 21a side of the first end 21e1 of the coil body 21 located to the right of the slit 23 a1 The corner C of the second end 21e2 on the upper surface 21a side, which is located on the left side of the slit 23, forms an acute angle.a2 On the other hand, the corner C of the first end 21e1 on the lower surface 21b side is b1 The corner C of the second end 21e2 on the lower surface 21b side forms an obtuse angle. b2 forms an acute angle.

[0026] If slits 23 are formed vertically, the magnetic field generated by current flowing along slits 23 to first end 21e1 of coil body 21 and the magnetic field generated by current flowing along slits 23 to second end 21e2 will have the same direction, so the magnetic field will be emphasized at the position of slits 23, resulting in a significant circumferential deviation in the magnetic field distribution of induction heating coil 20. However, if slits 23 are formed obliquely, the concentration of the magnetic field at the position of slits 23 can be alleviated.

[0027] The height of upper surface 21a of coil body 21 is different on the right and left sides across slit 23. Upper surface 21a of coil body 21 is composed of two surfaces of different heights with a step between them, and when viewed from the opening 22 side, the area to the right of slit 23 is lower step surface 21a1, and the area to the left of slit 23 is upper step surface 21a2.

[0028] The height difference d (see FIG. 3(b)) between the lower surface 21a1 and the upper surface 21a2 is preferably 2 mm or more and 10 mm or less, although it varies depending on the diameter of the raw material rod 2. If the height difference d is less than 2 mm, the effect of suppressing the height variation of the melting surface of the raw material is insufficient, and if the height difference d is more than 10 mm, the height variation of the melting surface may actually worsen.

[0029] When the orientation of the centerline of slit 23, which extends substantially radially from the center of opening 22, is taken as 0° (reference position), lower surface 21a1 is provided in a circumferential region ranging from 0° to 180° clockwise from the reference position. On the other hand, upper surface 21a2 is provided in a circumferential region ranging from 180° to 360° clockwise from the reference position. The formation region of lower surface 21a1 is adjacent to first end 21e1 on the right side of slit 23, and extends in the circumferential direction clockwise from first end 21e1. The formation region of upper surface 21a2 is adjacent to second end 21e2 on the left side of slit 23, and extends in the circumferential direction counterclockwise from second end 21e2.

[0030] Boundary 21a between lower surface 21a1 and upper surface 21a2 x is provided at a position 180° clockwise (or counterclockwise) from the reference position. Therefore, about half of the area of the upper surface 21a of the coil body 21 is the lower surface 21a1, and the other half is the upper surface 21a2.

[0031] Thus, the formation region of lower surface 21a1 includes slit neighborhood 25 on the first end 21e1 side, and the formation region of upper surface 21a2 includes slit neighborhood 25 on the second end 21e2 side. Here, the "slit neighborhood" refers to a circumferential region that spreads out on both sides of slit 23 as the center, and can be defined as, for example, a sector-shaped region of ±30° around slit 23. Slit neighborhood 25 on the first end 21e1 side is a region of 0° to 30° extending in the circumferential direction clockwise from the center line of slit 23, and slit neighborhood 25 on the second end 21e2 side is a region of 0° to 30° extending in the circumferential direction counterclockwise from the center line of slit 23 (a region of 330° to 360° clockwise).

[0032] Boundary 21a between lower surface 21a1 and upper surface 21a2 x The step surface of the boundary portion 21a is preferably a gently inclined surface, and the inclination angle is preferably 60 degrees or less, and more preferably 45 degrees or less. x This is because, when the inclination angle is 60 degrees or less, it is easy to perform the step processing and mirror finishing on the upper surface 21a of the coil body 21.

[0033] As described above, in order to make the height of the lower surface 21a1 lower than that of the upper surface 21a2, the thickness of the coil body 21 in the region where the upper surface 21a2 is formed is set to be smaller than the thickness of the coil body 21 in the region where the lower surface 21a1 is formed. Thick It is preferable to do so.

[0034] FIG. 5 is a schematic diagram showing the flow of current inside the coil body 21. As shown in FIG.

[0035] As shown by the arrows in Figure 5, the current flowing through the induction heating coil 20 follows a path that minimizes the distance between the pair of terminal electrodes 24A, 24B, and is concentrated near the edge of the coil body 21. As a result, the current flowing through the coil body 21 is concentrated in the slit vicinity region 25, and the amount of heat generated in the slit vicinity region 25 is large. On the other hand, the current does not concentrate in the region far from the slit 23 (the slit distant region), and therefore the amount of heat generated is small. As a result, the heating in the circumferential direction becomes uneven at the outer periphery of the raw material rod 2, making it difficult to melt the raw material rod 2 uniformly in the circumferential direction. Furthermore, when the slit 23 is an oblique slit, the two corner portions C on both sides of the slit 23 a1 ,C a2 Among them, acute corner part C a1 Since the current is concentrated at the sharp corner C a1 The amount of heat generated at the first end 21e1 where the heat generating portion is provided is greater.

[0036] When the raw material rod 2 placed above the induction heating coil 20 rotates, for example, clockwise, any one point on the circumferential direction of the raw material rod 2 is strongly heated near the slit, and a large amount of molten silicon is produced. Thereafter, the raw material rod 2 gradually moves away from the slit 23, and the amount of heat generated by the raw material rod 2 also gradually decreases. Normally, there is a slight error in the position and inclination of the central axis of the raw material rod 2, so the circumferential variation in the melting surface of the raw material is thought to be due to the influence of slight eccentric rotation of the raw material rod 2, etc.

[0037] 6(a) and (b) are schematic diagrams for explaining the coil shape of the present invention, where FIG. 6(a) shows a conventional coil shape and FIG. 6(b) shows the coil shape of the present invention.

[0038] As shown in FIG. 6(a), in the conventional induction heating coil 20, the height of the upper surface 21a of the coil body 21 on both sides of the slit 23 is the same. Therefore, when the conventional induction heating coil 20 is used to heat the raw material rod 2, the amount of melted raw material increases in the region near the slit on the first end 21e1 side within a certain circumferential range from the position of the slit 23 (reference position), resulting in a large melting of the melted surface of the raw material rod 2, as shown in FIG. 11(a). Conversely, the amount of melted raw material decreases in the region excluding the region near the slit on the first end 21e1 side, resulting in a lowered position of the melted surface of the raw material rod 2, as shown in FIG. 11(b). As a result, the height of the melted surface of the raw material rod 2 facing the upper surface 21a of the induction heating coil 20 becomes nonuniform in the circumferential direction. In particular, when the height of the upper surface near the slit 23 with an acute-angled corner on the upper surface 21a side is the same as the height of the surrounding area, the amount of heat generated at the acute-angled corner is very large, resulting in a significant variation in the circumferential heating distribution of the raw material.

[0039] The variation in height of the melting surface of the raw material rod 2 gradually increases as the crystal growth process progresses, and if the melting surface comes into contact with the coil surface, the crystal growth process cannot be continued. This phenomenon is more pronounced the larger the diameter of the raw material rod 2. This is thought to be because the larger the raw material diameter, the more difficult it is for heat to be dissipated from the bottom end of the raw material rod 2, and the higher the temperature of the melting surface, the more likely it is that the interface shape will change.

[0040] On the other hand, as shown in Figure 6(b), in the induction heating coil 20 according to this embodiment, the height of the upper surface 21a of the slit vicinity region 25 on the right side of the slit 23 is different from the height of the upper surface 21a of the slit vicinity region 25 on the left side of the slit 23, and in particular, the height of the upper surface 21a on the first end 21e1 side, which has a sharp corner portion, is lower than the height of the upper surface 21a in other regions, particularly the second end 21e2 side.

[0041] Therefore, the upper surface 21a on the first end 21e1 side of the slit 23, where the amount of heat generated by the raw material increases, can be kept away from the melting surface 2s of the raw material rod 2, and the amount of raw material melted can be reduced by suppressing the heat generated by the raw material on the right side of the slit 23, regardless of the rotation direction of the raw material rod 2. That is, as shown in FIG. 12(a), in the region near the slit on the right side of the slit 23, excessive melting of the melting surface of the raw material rod 2 can be suppressed. Also, as shown in FIG. 12(b), Slit 23 In the area near the slit on the left side of the figure, excessive lowering of the melting surface of the raw material can be suppressed. This makes it possible to make the heat generation amount of the raw material as uniform as possible in the circumferential direction, reduce the circumferential height variation of the melting surface, and prevent contact between the melting surface and the coil surface.

[0042] As described above, in the induction heating coil 20 according to this embodiment, the slits 23 extending substantially radially from the opening 22 of the coil body 21 are formed obliquely rather than vertically in a cross-sectional view, and the height of the upper surface of the slit vicinity region 25 on the side of the first end 21e1, where the corners of the slits 23 form acute angles, is lower than the upper surface of the slit distant region that is further from the slit 23 than the slit vicinity region 25. Therefore, the portion near the slit that generates a large amount of heat can be moved slightly away from the raw material, thereby suppressing its influence and reducing variations in the heating distribution of the raw material in the circumferential direction.

[0043] 7(a) and (b) are diagrams showing the configuration of an induction heating coil 20 according to a second embodiment of the present invention, where FIG. 7(a) is a plan view and FIG. 7(b) is a diagram showing the height profile of the upper surface of the coil body.

[0044] As shown in Fig. 7, the induction heating coil 20 according to this embodiment is characterized in that the lower surface 21a1 is provided in a circumferential region of 0° to 30° clockwise from the position of the slit 23, and the upper surface 21a2 is provided in a circumferential region of 30° to 360°. In other words, the lower surface is provided only in the slit vicinity region 25 on the first end portion 21e1 side. The boundary 21a between the lower surface 21a1 and the upper surface 21a2 xis provided at a position 30° clockwise from the position of the slit 23. The other configurations are the same as those of the first embodiment.

[0045] As described above, if the circumferential end position of the formation region of lower surface 21a1 is less than 30°, the effect of uniforming the melting surface by lowering the height of upper surface 21a on the first end 21e1 side of slit 23 becomes insufficient, and the probability of the melting surface of the raw material coming into contact with the coil surface increases. However, in this embodiment, lower surface 21a1 is provided in a circumferential region 0° to 30° clockwise from the position of slit 23, so it is possible to uniform the melting surface.

[0046] 8(a) and (b) are diagrams showing the configuration of an induction heating coil 20 according to a third embodiment of the present invention, where FIG. 8(a) is a plan view and FIG. 8(b) is a diagram showing the height profile of the upper surface of the coil body.

[0047] As shown in Fig. 8, the induction heating coil 20 according to this embodiment is characterized in that the lower surface 21a1 is provided in a circumferential region of 0° to 90° clockwise from the position of the slit 23, and the upper surface 21a2 is provided in a circumferential region of 90° to 360°. x is provided at a position 90° clockwise from the position of the slit 23. The other configurations are the same as those of the first embodiment.

[0048] According to this embodiment, the heating distribution in the circumferential direction of the raw material rod can be made as uniform as possible, as in the first embodiment, and therefore the circumferential height variation of the melting surface of the raw material rod can be reduced, and contact between the melting surface and the coil surface can be prevented.

[0049] 9(a) and 9(b) are diagrams showing the configuration of an induction heating coil 20 according to a fourth embodiment of the present invention, where FIG. 9(a) is a plan view and FIG. 9(b) is a diagram showing the height profile of the upper surface of the coil body.

[0050] 9, the induction heating coil 20 according to this embodiment is characterized in that the upper surface 21a of the coil body 21 is composed of three surfaces at different heights. In detail, a lower surface 21a1 is provided in a circumferential region of 0° to 90° clockwise from the position of the slit 23, a middle surface 21a3 is provided in a circumferential region of 90° to 180°, and an upper surface 21a2 is provided in a circumferential region of 180° to 360°. Lower surface 21a 1 and the middle surface 21a3 X1 is clockwise from the position of slit 23 90° The intermediate surface 21a3 is provided at the position Upper surface 21a Boundary 21a with 2 X2 is clockwise from the position of slit 23 180° It is located at the position.

[0051] The height difference d between the lower surface 21a1 and the upper surface 21a2 is, for example, 2 mm, and the lower surface 21a1 is 1 mm higher than the middle surface 21a3. Low The middle surface 21a3 is 1 mm larger than the upper surface 21a2. low In this way, by providing the middle surface 21a3 between the lower surface 21a1 and the upper surface 21a2 and setting the circumferential change in the height of the upper surface 21a of the coil body 21 more finely, it is possible to make the circumferential change in the heating temperature of the raw material rod 2 more gradual.

[0052] 10(a) and (b) are diagrams showing the configuration of an induction heating coil 20 according to a fifth embodiment of the present invention, where FIG. 10(a) is a plan view and FIG. 10(b) is a diagram showing the height profile of the upper surface of the coil body.

[0053] As shown in Fig. 10, the induction heating coil 20 according to this embodiment is characterized in that the height of the upper surface 21a of the coil body 21 changes linearly from a first end 21e1 on the right side of the slit 23 to a second end 21e2 on the left side. This corresponds to the case where the number of steps for gradually changing the height of the upper surface 21a shown in Fig. 9 is infinite. Therefore, when viewed from the opening 22 side, the area to the right of the slit 23 is the lower surface 21a1, and the area to the left of the slit 23 is the upper surface 21a2. According to this embodiment, the change in the heating temperature of the raw material rod 2 in the circumferential direction can be made even more gradual.

[0054] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention.

[0055] For example, in the above embodiment, the acute corner portion C a1 The upper surface 21a in the vicinity is the lower surface, and the obtuse corner portion C a2 The upper surface 21a in the vicinity of the slit is the upper surface, but the temperature of the upper surface 21a in the region 25 near the slit is a1 Not only the vicinity but also the obtuse corner C a2 Therefore, the height of the upper surface 21a on both sides of the slit 23 may be lowered. a1 Not only in the vicinity but also at sharp corners C a1 Obtuse corner C with neighboring a2 In this case, the lower surface 21a1 may be provided on both sides of the acute corner portion C. a1 It is desirable to make the wall thickness of the coil body 21 in the vicinity thinner. [Example]

[0056] (Comparative Example) An induction heating coil with a conventional structure (see Figure 6(a)) was prepared, with the entire top surface flat and no height difference between the left and right upper surfaces of the slit in between. Using this, silicon single crystals with a diameter of approximately 200 mm were produced by the FZ method. A polycrystalline silicon rod with a diameter of 160 mm produced by the monosilane method was used as the raw material rod. The slit 23 in the induction heating coil was an oblique slit, formed so that it approached one end on the right side as it moved from the top to the bottom. As a result, the corner on the top surface of the first end formed an acute angle, and the corner on the top surface of the second end, which faces the acute corner on the first end across the slit, formed an obtuse angle.

[0057] Figure 13 shows the results of measuring the distance (gap) between the raw material melting surface and the upper surface of the coil. As is clear from Figure 13, the fluctuation in the height of the molten zone on the raw material side was large, and the variation in the height of the lower surface of the molten zone on the raw material side increased during the crystal growth process, resulting in the gap falling below 1 mm when the length of the straight body portion reached 200 mm or more. Although silicon single crystals were successfully grown in this process, dangerous operation continued, as it was possible that the melting surface could come into contact with the coil surface at any time.

[0058] (Example) An induction heating coil according to Example 1 (see FIGS. 3 and 4) was prepared, in which the region from 0° to 180° clockwise from the slit position was the lower surface, and the region from 180° to 360° was the upper surface, with a height difference between the lower and upper surfaces of 2 mm. Using this, a silicon single crystal with a diameter of approximately 200 mm was produced under the same conditions as in the comparative example. As a result, as shown in the graph in FIG. 14, the amount of fluctuation in the height of the molten zone on the raw material side was reduced. In this example, a clearance of 3 mm or more could be secured between the molten surface and the coil surface even in the latter half of the crystal growth process, enabling the single crystal to be grown safely. [Explanation of symbols]

[0059] 1. Single crystal manufacturing equipment 2 Raw material rod 2s Melting surface of raw material rod 3 seed crystals 4. Silicon single crystal 5. Melting Zone 10 Reactor 11 Upper shaft 12 Lower axis 14 Single crystal weight holder 15 Gas doping device 16 Raw material holder 17 Seed crystal holder 20 induction heating coil 21 Coil body 21a Top surface of coil body 21a1 lower surface 21a2 upper surface 21a3 middle surface 21a x ,21a X1 ,21a X2 Boundary (step) 21b Underside of coil body 21e1 first end of coil body 21e2 second end of coil body 22 Opening 23 Slit 24A,24B terminal electrode 25 Slit Neighborhood Area C a1 ,C a2 Corner part C b1 ,C b2 Corner part

Claims

1. An induction heating coil used for producing a single crystal by the FZ method, an annular coil body having a central opening and first and second ends separated from each other by a slit extending generally radially from the opening; the slit is an oblique slit that cuts the coil body obliquely from the upper surface side toward the lower surface side so that a corner portion on the upper surface side of the first end portion forms an acute angle and a corner portion on the upper surface side of the second end portion forms an obtuse angle, the upper surface of the coil body has an upper surface and a lower surface, the lower surface is provided at least in a region near the slit on the first end side, An induction heating coil, characterized in that the upper surface is provided in an area excluding an area where the lower surface is formed.

2. 2. The induction heating coil according to claim 1, wherein the difference in height between the upper surface and the lower surface is 2 mm or more.

3. The induction heating coil according to claim 1 , wherein the thickness of the coil body in the region where the lower surface is formed is thinner than the thickness of the coil body in the region where the upper surface is formed.

4. The induction heating coil according to claim 1 , wherein the formation region of the upper surface includes a region near the slit on the second end side.

5. 2. The induction heating coil according to claim 1, wherein when the orientation of the center line of the slit extending approximately radially from the center of the opening is 0°, the lower surface is provided in a region of at least 0° to 30°.

6. The lower surface is provided in a region of 0° to 90°, The induction heating coil according to claim 5, wherein the upper surface is provided in an area of at least 180° to 360°.

7. The lower surface is provided in a region of 0° to 180°, 6. The induction heating coil according to claim 5, wherein the upper surface is provided in a region of 180° to 360°.

8. A single crystal manufacturing apparatus used to manufacture a single crystal by the FZ method, an upper shaft that supports the raw material rod rotatably and vertically; a lower shaft disposed below the upper shaft and supporting the seed crystal rotatably and vertically; 2. A single crystal manufacturing apparatus comprising: an induction heating coil according to claim 1 for heating the raw material rod.

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