Apparatus and method for manufacturing single crystal

Abstract

To provide an apparatus for manufacturing a single crystal, capable of manufacturing a large-sized single crystal without using a crucible, and a method for manufacturing a single crystal using the apparatus.SOLUTION: An apparatus 1 for manufacturing a single crystal, capable of growing a single crystal 21 upward from a seed crystal 20 includes: a thermal insulation space 10 insulated from a space outside the apparatus; a thermal insulation plate 12 dividing the thermal insulation space 10 into a first space 101 including a crystal growth area 103 for growing the single crystal 21 and a second space 102 thereon and having a hole 121 above the crystal growth area 103; a heating body 13 capable of heating the inside of the thermal insulation space 10 and installed on the outside of the second space 102 from the hole 121; and a support shaft 19 for movably supporting the seed crystal 20 from the bottom in the vertical direction. The heating body 13 is arranged at a position without contacting a raw material melt supplied to the top surface of the seed crystal 21 when growing the single crystal 21.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Conventionally, there is known an apparatus for producing a single crystal without using a crucible (see Patent Document 1). In the single crystal production apparatus described in Patent Document 1, a raw material melt is supplied into a melt formed on the upper surface of a seed crystal to form a mixed melt, and a solid is precipitated from the mixed melt as a single crystal to produce a single crystal. The melt on the upper surface of the seed crystal is formed by irradiating the upper surface of the seed crystal with infrared rays from an infrared irradiation device.

[0003] According to the single crystal manufacturing apparatus that does not use a crucible, there is no risk of the purity of the single crystal being reduced due to the mixing of components contained in the crucible. In addition, when using a crucible, depending on the type of single crystal to be manufactured, the material of the crucible is often very expensive, so by using an apparatus that does not use a crucible, the equipment cost can be significantly reduced. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6607651 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the single crystal manufacturing apparatus described in Patent Document 1, the space around the top surface of the growing single crystal is widely open, presumably to ensure an entry path for infrared rays. For this reason, if the melting point of the material is high, the amount of heat dissipated from the crystal growth surface increases to the extent that it adversely affects crystal growth (radiant energy is proportional to the difference between the fourth power of the object temperature and the fourth power of the ambient temperature), making it difficult to manufacture large single crystals. Specifically, it is considered difficult to manufacture materials with a melting point higher than that of silicon, for example, a melting point of 1500°C or higher.

[0006] An object of the present invention is to provide a single crystal production apparatus capable of producing a large single crystal without using a crucible, and a single crystal production method using the apparatus. [Means for solving the problem]

[0007] In order to achieve the above object, one aspect of the present invention provides the following single crystal production apparatus and single crystal production method.

[0008] [1] A single crystal manufacturing apparatus for growing a single crystal upward from a seed crystal, comprising: an insulating space insulated from a space outside the single crystal manufacturing apparatus; a first space including a crystal growth region for growing the single crystal; and a second space above the first space, the insulating space being divided into an insulating plate having a hole above the crystal growth region; a heating body for heating the inside of the insulating space, the heating body being installed outside the hole in the second space; and a support shaft for supporting the seed crystal from below so that the seed crystal can be moved in the vertical direction, the heating body being positioned so as not to come into contact with a raw material molten liquid supplied to an upper surface of the seed crystal when the single crystal is grown. [2] The single crystal manufacturing apparatus described in [1] above, further comprising an annular member having an annular bottom surface that is installed inside the hole in the insulating plate and whose outer edge planar shape can control the cross-sectional shape of the single crystal. [3] The single crystal manufacturing apparatus described in [2] above, wherein the annular bottom surface has a width that allows a portion of the inner edge side to contact the upper surface of the seed crystal. [4] A single crystal manufacturing apparatus described in any one of [1] to [3] above, wherein the insulating space is surrounded by a first insulating material that forms the side walls of the first space and the second space, a second insulating material that forms the upper wall of the second space, and a base that supports the first insulating material and the second insulating material from the bottom of the first space, the second insulating material has a through hole that penetrates the second insulating material from above to below for supplying the single crystal raw material to the second space, and the base has an axial hole through which the support shaft can move up and down. [5] A single crystal manufacturing apparatus as described in [4] above, wherein a third insulating material is installed on top of the second insulating material as an upper wall, and the third insulating material has a through hole that penetrates the third insulating material vertically so as to connect to the through hole of the second insulating material, and the diameters of the through hole of the second insulating material and the through hole of the third insulating material are smaller than the diameter of the crystal growth region. [6] The single crystal manufacturing apparatus described in [4] above, wherein a fourth annular insulating material surrounding the crystal growth region is installed in the first space. [7] A method for producing a single crystal, comprising the steps of: placing a seed crystal below the hole in a first space of an insulating space partitioned by an insulating plate having a hole into a first space and a second space above the first space; melting an upper surface of the seed crystal by radiant heat from a heating body installed outside the hole in the second space; supplying a raw material melt of a single crystal onto an upper surface of the molten seed crystal through the second space and the hole in the insulating plate; and moving the seed crystal downward while continuing to supply the raw material melt, thereby growing the single crystal upward from the seed crystal, wherein the heating body does not come into contact with the raw material melt in the step of supplying the raw material melt of the single crystal and the step of growing the single crystal. [8] The method for producing a single crystal described in [7] above, wherein an annular member is installed inside the hole in the insulating plate so that a portion of the inner edge side of the annular bottom surface is in contact with the upper surface of the seed crystal, and in the process of growing the single crystal, the raw material melt is supplied to the upper surface of the seed crystal or to the interface between the upper surface of the single crystal and the annular bottom surface of the annular member. [9] The method for producing a single crystal described in [8] above, wherein in the step of growing the single crystal, while the single crystal is grown upward from the seed crystal, the raw material melt is spread toward the outer edge of the annular bottom surface at the interface between an upper surface of the seed crystal or an upper surface of the single crystal and the annular bottom surface of the annular member, thereby broadening the shoulders of the single crystal.

[10] The method for producing a single crystal described in [8] above, wherein in the step of growing the single crystal, the single crystal is grown in a region inside the outer edge of the annular bottom surface, and the cross-sectional shape of the single crystal is controlled by the planar shape of the outer edge of the annular bottom surface.

[11] A method for producing a single crystal, comprising: a step of supplying a raw material melt of a single crystal onto an upper surface of a single crystal grown on a seed crystal; and a step of moving the seed crystal downward while continuing to supply the raw material melt, thereby growing the single crystal upward from the seed crystal, wherein, in the step of supplying the raw material melt, the raw material melt on the outer periphery of the upper surface of the single crystal comes into contact with an annular bottom surface of an annular member placed on the single crystal, and, in the step of growing the single crystal, the single crystal is grown in a region inside an outer edge of the annular bottom surface, and a cross-sectional shape of the single crystal is controlled by the planar shape of the outer edge of the annular bottom surface.

[12] The method for producing a single crystal according to any one of the above [7] to

[11] , wherein all of the steps are carried out in an insulated space that is insulated from an outside space.

[13] The method for producing a single crystal according to any one of the above [7] to

[12] , wherein the single crystal is an oxide.

[14] The method for producing a single crystal according to any one of the above [7] to

[13] , wherein in the step of supplying the raw material melt, droplets of the raw material melt are supplied onto an upper surface of the molten seed crystal, and in the step of growing the single crystal, droplets of the raw material melt are supplied onto an upper surface of the single crystal. Effect of the Invention

[0009] According to the present invention, it is possible to provide a single crystal production apparatus capable of producing a large single crystal without using a crucible, and a single crystal production method using the apparatus. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a vertical sectional view of a single crystal manufacturing apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged vertical cross-sectional view of the periphery of the heat insulating space of the single crystal production apparatus. [Diagram 3] 3(a) to (c) are vertical cross-sectional views showing the growth process of a single crystal. [Figure 4]FIG. 4(a) is a vertical cross-sectional view showing the shape of a single crystal during the growth process when only shoulder broadening is performed without necking, and FIG. 4(b) is a vertical cross-sectional view showing the shape of a single crystal during the growth process when neither necking nor shoulder broadening is performed. [Diagram 5] 5(a) and (b) are vertical cross-sectional views showing a structure in which an annular heat insulating material is provided around the crystal growth region in the first space, and FIG. 5(c) is a vertical cross-sectional view showing a structure in which a heater is provided around the crystal growth region in the first space. [Figure 6] 6(a) and (b) are vertical cross-sectional views showing a structure in which a heat insulating plate having a thickness distribution is installed, and Fig. 6(c) is a vertical cross-sectional view showing a structure in which the diameter of the annular heating element is reduced. [Figure 7] Fig. 7(a) is a vertical cross-sectional view showing a structure in which a shape-controlling member for controlling the shape of a single crystal is installed, and Fig. 7(b) is a vertical cross-sectional view showing a structure in which a shape-controlling member with an increased width of the annular bottom surface is installed. [Figure 8] Fig. 8(a) is a vertical cross-sectional view showing a schematic diagram of supplying the raw material melt using a raw material rod, Fig. 8(b) is a vertical cross-sectional view showing a schematic diagram of supplying the raw material melt using a hollow raw material rod, and Fig. 8(c) is a vertical cross-sectional view showing a schematic diagram of supplying the raw material melt using a funnel. [Figure 9] FIG. 9 is a vertical cross-sectional view that shows a schematic process of reacting a powder, granule, or liquid metal with oxygen gas to obtain a raw material oxide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Embodiment] (Configuration of manufacturing equipment) Fig. 1 is a vertical cross-sectional view of a single crystal manufacturing apparatus 1 according to an embodiment of the present invention. Fig. 2 is a vertical cross-sectional view enlarging the periphery of a thermal insulation space 10 of the single crystal manufacturing apparatus 1. The single crystal manufacturing apparatus 1 is an apparatus that does not use a crucible, but supplies raw material to the upper surface of a seed crystal 20 and grows a single crystal 21 upward from the seed crystal 20.

[0012] The single crystal manufacturing apparatus 1 includes an insulating space 10 insulated from a space outside the apparatus, an induction heating coil 11 installed outside the insulating space 10, an insulating plate 12 dividing the insulating space 10 into a first space 101 and a second space 102 above the first space 101, a heater 13 installed in the second space 102 that generates heat by an induced current caused by electromagnetic induction using the induction heating coil 11 and heats the insulating space 10, and a support shaft 19 for supporting the seed crystal 20 from below so as to be movable up and down. Note that the up and down direction in this embodiment refers to a direction along or approximately along the vertical direction.

[0013] The first space 101 of the insulating space 10 includes a crystal growth region 103 which is a region for growing the single crystal 21. The crystal growth region 103 is included in a region directly above a hole 181 in the base 18 which will be described later. The insulating plate 12 has a hole 121 located above the crystal growth region 103. Therefore, the raw material of the single crystal 21 can be supplied to the upper surface of the seed crystal 20 or the upper surface of the single crystal 21 grown on the seed crystal 20 through the second space 102 and the hole 121 in the insulating plate 12.

[0014] The single crystal production apparatus 1 also includes a heat insulating material 14 which forms the side wall of the heat insulating space 10, a heat insulating material 15 which forms the upper wall of the heat insulating space 10, a heat insulating material 16 installed on the heat insulating material 15, an outer wall 17 which surrounds the heat insulating materials 14, 15, and 16, and a base 18 which forms the base of the heat insulating materials 14, 15, and 16 and the outer wall 17. These members are made of a material having heat resistance that can withstand temperatures near the melting point of the single crystal 21.

[0015] For example, when the single crystal 21 is a gallium oxide-based single crystal, the heat insulating material 14 is made of, for example, porous zirconia or zirconia fiberboard. The heat insulating material 15 is made of, for example, porous zirconia or zirconia fiberboard. The heat insulating material 16 is made of, for example, an alumina fiberboard. The outer wall 17 is made of, for example, an alumina fiberboard. The base 18 is made of, for example, an alumina board.

[0016] Since the heat insulating material 15 is most susceptible to deformation due to its shape and arrangement position, it is preferable to use a hardened zirconia fiberboard, hardened porous alumina, hardened dense zirconia, hardened dense alumina, or a zirconia fiberboard coated with zirconia cement as the heat insulating material 15. The hardening treatment of the above-mentioned zirconia fiberboard, etc., is performed by high-temperature annealing before use, for example, high-temperature annealing at 1700 to 1900°C. The fact that such prior high-temperature annealing hardens the zirconia fiberboard, etc., and suppresses deformation in a high-temperature environment, was discovered for the first time by the present inventors.

[0017] In addition to the single crystal manufacturing apparatus 1, the heat insulating material 15 can be used as a heat insulating material around the heating element where the temperature becomes highest in various high-temperature heating devices such as a crystal growth furnace, a firing furnace, and an annealing furnace. In any case, deformation and cracks due to deformation can be prevented, so that the temperature inside the furnace can be stabilized. In addition, since the heat insulating material 15 has a long life, the maintenance costs of the device can be reduced.

[0018] In addition, it is preferable to use an alumina fiber board with an alumina blanket attached to the inner surface of the outer wall 17. In this case, the cushioning property of the alumina blanket can be utilized to suppress cracking of the outer wall 17 when the heat insulating material 16 expands. The alumina blanket attached to the inner surface of the alumina fiber board is required to have a thickness that can cushion the expansion of the heat insulating material 16 installed on the alumina blanket side. However, since it is difficult to measure the expansion amount of the heat insulating material in a high temperature environment, it is preferable to use an alumina blanket with a thickness that is estimated to be sufficient to obtain an effect, for example, 5 mm or more, preferably 10 mm or more. In addition, the alumina fiber board to which the alumina blanket is attached is preferably 10 mm or more thick, taking into consideration ease of handling. The outer wall 17 can be used in various high-temperature heating devices such as a crystal growth furnace, a firing furnace, and an annealing furnace, in addition to the single crystal manufacturing device 1. The method of absorbing the expansion of adjacent members by attaching an alumina blanket to the inner surface of the alumina fiber board was first discovered by the present inventor.

[0019] The zirconia fiberboard is a fibrous insulation material obtained by vacuum molding zirconia fiber. The alumina fiberboard is a fibrous insulation material obtained by adding inorganic and organic binders to alumina fiber and molding the mixture. The alumina blanket is a fibrous insulation material obtained by needle processing alumina fiber into a mat shape.

[0020] Induction heating coil 11 is installed at a position surrounding heating element 13 from the outside of outer wall 17. When a magnetic field generated around induction heating coil 11 by passing a current through induction heating coil 11 passes inside annular heating element 13, an induced current flows through heating element 13, and heating element 13 generates heat due to the electrical resistance of heating element 13.

[0021] The heater 13 is made of a heat-resistant conductor capable of withstanding temperatures near the melting point of the single crystal 21. For example, when the single crystal 21 is a gallium oxide-based single crystal, the material of the heater 13 is iridium, platinum-rhodium, or zirconia-coated iridium or platinum-rhodium. The heater 13 has an annular shape, typically a cylindrical shape as shown in FIG. 1. The heater 13 is placed on the insulating plate 12 so as to surround the space directly above the crystal growth region 103.

[0022] The insulating plate 12 is made of a material, such as porous zirconia, that has heat resistance that can withstand temperatures near the melting point of the single crystal 21. In order to suppress deformation, it is preferable to use the material used for the above-mentioned insulating material 15, such as a hardened zirconia fiberboard, as the material for the insulating plate 12. The insulating plate 12 is used to selectively melt the upper surface of the seed crystal 20 or the upper surface of the single crystal 21, which will be the growth surface of the single crystal 21.

[0023] Radiation emitted from the heater 13 reaches the crystal growth region 103 in the first space 101 directly through the holes 121 in the heat insulating plate 12. On the other hand, the radiation emitted from the heater 13 reaches the region 104 around the crystal growth region 103 in the first space 101 after being weakened by the heat insulating plate 12. Therefore, the seed crystal 20 and the single crystal 21 in the crystal growth region 103 are heated more strongly from above than from the sides. This makes it possible to selectively melt the top surface of the seed crystal 20 or the top surface of the single crystal 21, which is the growth surface of the single crystal 21.

[0024] 1, in order to ensure symmetry of the temperature distribution in the first space 101. Also, in order to suppress a drop in temperature at the outer periphery of the crystal growth surface, it is preferable that the contour of the hole 121 be outside the contour of the single crystal 21 so that the insulating plate 12 does not cover the outer periphery of the crystal growth surface. The diameter of the hole 121 is set to a value obtained by adding 10 mm to the diameter of the single crystal 21, for example.

[0025] The support shaft 19 can be moved up and down in an axial hole 181 that penetrates the base 18 in the up-down direction by a driving mechanism (not shown). The support shaft 19 can be moved up and down in the crystal growth region 103 of the first space 101 and in the axial hole 181 below it. The support shaft 19 may also be rotatable about its central axis as a rotation axis by the driving mechanism. In this case, the seed crystal 20 supported by the support shaft 19 and the single crystal 21 grown from the seed crystal 20 can be rotated.

[0026] The support shaft 19 may have a hole 191 penetrating the support shaft 19 in the vertical direction. The temperatures of the seed crystal 20 and the single crystal 21 can be measured through the hole 191 by a thermocouple or a radiation thermometer. The support shaft 19 is made of a material having heat resistance capable of withstanding a temperature near the melting point of the single crystal 21. For example, when the single crystal 21 is a gallium oxide-based single crystal, the support shaft 19 is made of a zirconia fiber board, an alumina fiber board, a porous zirconia, a porous alumina, or a combination thereof. The portion 192 of the support shaft 19 in contact with the single crystal 21 is made of a material having heat resistance capable of withstanding a temperature near the melting point of the single crystal 21 and not reacting with the material of the single crystal 21, for example, porous alumina, dense alumina, sapphire, or iridium. The support shaft 19 is made of a plurality of blocks connected in the vertical direction, for example, as shown in FIG. 1.

[0027] The insulating material 15, which is the upper wall of the insulating space 10, has a through hole 151 that passes through the insulating material 15 in the vertical direction. Moreover, the insulating material 16 above the insulating material 15 has a through hole 161 that passes through the insulating material 16 in the vertical direction. The through hole 151 and the through hole 161 are continuous and connect the insulating space 10 to the space outside the single crystal production apparatus 1. Therefore, the raw material of the single crystal 21 can be supplied into the insulating space 10 through the through holes 151, 161. The diameter of the through holes 151, 161 is, for example, 5 to 30 mm.

[0028] (Method of manufacturing single crystal) An example of a method for producing a single crystal 21 using the single crystal production apparatus 1 will be described below.

[0029] First, the seed crystal 20 is placed on the support shaft 19 below the hole 121, and the vertical position of the support shaft 19 is adjusted to place the seed crystal 20 in the first space 101 of the thermal insulation space 10. At this time, in order to efficiently heat the upper surface of the seed crystal 20, it is preferable to place the seed crystal 20 in a position as high as possible in the first space 101, for example, a position where the height of the upper surface of the seed crystal 20 coincides with the height of the lower surface of the thermal insulation plate 12.

[0030] Next, a current is applied to the induction heating coil 11 to inductively heat the heater 13 installed in the second space 102, and the upper surface of the seed crystal 20 is melted by the heat generated from the heater 13. At this time, as described above, the upper surface of the seed crystal 20 can be selectively melted by the heat insulating plate 12.

[0031] Next, the raw material melt of the single crystal 21 is supplied onto the upper surface of the molten seed crystal 20 through the second space 102 and the hole 121 of the heat insulating plate 12. The method of supplying the raw material melt of the single crystal 21 will be described later.

[0032] 3(a) to 3(c), while continuing to supply the raw material melt of the single crystal 21, the support shaft 19 is lowered to move the seed crystal 20 downward, and the melt is gradually crystallized from below. This causes the single crystal 21 to grow upward from the seed crystal 20. The growth speed of the single crystal 21 is set to, for example, 2 to 8 mm / h. When the single crystal 21 is grown while rotating, the rotation speed is set to, for example, 3 to 12 rpm.

[0033] 3(a) to (c), necking is performed during the growth of the single crystal 21, and the diameter of the single crystal 21 is increased by shoulder broadening (diameter increase). By performing necking, the quality of the single crystal 21 can be improved when the quality of the seed crystal 20 is not high. Furthermore, by shoulder broadening, the diameter of the single crystal 21, which has become smaller at the necking portion, can be increased.

[0034] However, if the seed crystal 20 has sufficient quality, necking may not be performed. If the diameter of the necking portion is small, it may not be able to support the weight of the grown single crystal 21, and may break at the necking portion. In order to prevent the crystal from breaking at the necking portion, a mechanism for supporting the crystal at a shoulder expansion portion may be provided in the single crystal production apparatus 1, but this would make the structure of the single crystal production apparatus 1 more complicated. If necking is not performed, such problems can be avoided.

[0035] Furthermore, when using a seed crystal 20 that is not necked and has a diameter that is almost the same as the diameter of the desired single crystal 21 (for example, a difference within ±10%), shoulder broadening is not necessary. In this case, problems such as twinning caused by shoulder broadening can be avoided, and a higher quality single crystal 21 can be obtained.

[0036] FIG. 4(a) shows the shape of a single crystal 21 during the growth process when only shoulder broadening is performed without necking, and FIG. 4(b) shows the shape of a single crystal 21 during the growth process when neither necking nor shoulder broadening is performed.

[0037] In the single crystal production apparatus 1, the upper surface of the seed crystal 20 or the upper surface of the single crystal 21, which is the crystal growth surface, is located immediately below the high-temperature second space 102 in which the heater 13 is installed. This suppresses heat radiation from the crystal growth surface, and allows the production of a large single crystal 21.

[0038] The atmosphere during growth of the single crystal 21 can be selected depending on the material of the heater 13. For example, if the heater 13 is made of a material that does not oxidize, an oxygen atmosphere can be used. If the single crystal 21 is a gallium oxide single crystal, iridium is usually used as the material of the heater 13. In this case, in order to suppress oxidation of the iridium, the oxygen concentration in the atmosphere is preferably less than 10% (e.g., 4%). If the surface of the iridium is coated with zirconia, the oxygen concentration in the atmosphere is preferably less than 50%.

[0039] (Temperature distribution control method) A method for controlling the temperature distribution on the growth surface of the single crystal 21 (the upper surface of the seed crystal 20 or the upper surface of the single crystal 21) will be described below. The temperature distribution on the growth surface of the single crystal 21 is preferably a distribution in which the temperature at the center and the periphery are approximately equal (flat distribution), or a distribution in which the temperature is lower at the center and higher at the periphery (convex downward distribution). This allows the interface between the single crystal 21 and the melt thereon (solid-liquid interface) to be flat or convex upward, and the occurrence of crystal defects due to the concentration of crystal distortion at the center can be suppressed.

[0040] 5(a) and (b) are vertical cross-sectional views showing a structure in which annular heat insulating materials 31 and 32 are respectively provided in a region 104 around the crystal growth region 103 in the first space 101 so as to surround the crystal growth region 103. FIG.

[0041] 5(a) is a thermal insulator provided over the entire region 104, and the thermal insulator 32 shown in Fig. 5(b) is a thermal insulator provided in a portion of the region 104 near the crystal growth region 103. The thermal insulators 31 and 32 are made of a material having heat resistance capable of withstanding temperatures near the melting point of the single crystal 21, and are made of, for example, porous zirconia.

[0042] By using the heat insulating materials 31, 32 surrounding the crystal growth region 103, it is possible to suppress heat radiation from the side surface of the single crystal 21 and to increase the temperature of the outer periphery of the crystal growth surface. This makes it easy to make the temperature distribution of the growth surface of the single crystal 21 flat or downwardly convex.

[0043] Furthermore, by using the heat insulating materials 31 and 32, it is possible to reduce the variation in temperature distribution in the crystal growth direction (vertical direction) of the single crystal 21, thereby improving the quality of the single crystal 21. These effects can be obtained in the same way whether the heat insulating material 31 or the heat insulating material 32 is used.

[0044] 5(c) is a vertical cross-sectional view showing a structure in which a heating element 33, which is a member similar to the heating element 13, is installed in a region 104 around the crystal growth region 103 in the first space 101. Like the heating element 13, the heating element 33 is induction heated by passing a current through the induction heating coil 11, and generates heat.

[0045] The heater 33 heats the single crystal 21 from the side, and therefore can increase the temperature of the outer periphery of the growth surface of the single crystal 21. This makes it easy to make the temperature distribution of the growth surface of the single crystal 21 flat or downwardly convex.

[0046] However, in order to suppress melting of portions other than the top surface of the single crystal 21, it is necessary to make the heating by the heating element 33 weaker than the heating by the heating element 13. For this purpose, for example, measures can be taken such as using the heating element 33 in combination with the heat insulating material 32 shown in Fig. 5(b) to weaken the radiation emitted from the heating element 33 by the heat insulating material 32, or providing the induction heating coil 11 only on the side of the heating element 13 to reduce the amount of heat generated by the heating element 33.

[0047] 6(a) and (b) are vertical cross-sectional views showing a structure in which an insulating plate 34 having a thickness distribution is installed instead of the insulating plate 12. In the insulating material 34, a portion 342 located above the region 104 around the crystal growth region 103 is the thickest, a portion 344 located above the outer periphery of the growth surface of the single crystal 21 is the thinnest, and a portion 343 inside portion 342 is thinner than portion 342 and thicker than portion 344.

[0048] The thicker the portion of the heat insulating material 34 is, the more the radiation emitted from the heater 13 is weakened, so that the temperature of the outer periphery of the growth surface of the single crystal 21 can be made higher than the temperature of the inner region, and the temperature of the side surface of the single crystal 21 can be made lower than the temperature of the growth surface. This makes it easy to make the temperature distribution of the growth surface of the single crystal 21 flat or downwardly convex.

[0049] The insulation material 34 shown in FIG. 6(a) has parts 342 to 344 formed as an integral unit, while the insulation material 34 shown in FIG. 6(b) has a member including part 342 and a member including parts 343 and 344 formed separately, but the same effect can be obtained in either form.

[0050] The insulating plate 34 has holes 341 necessary for supplying the raw material melt to the single crystal 21, but in order to suppress a rise in temperature in the central part of the crystal growth surface, it is preferable to make the diameter of the holes 341 as small as possible without interfering with the supply of the raw material melt.

[0051] Furthermore, when a transparent member that can be used at high temperatures, such as sapphire, is used as the material for the heat insulating plate 34, a similar effect can be obtained by forming a distribution of surface roughness instead of forming a distribution of thickness, thereby distributing the amount of transmission of radiation emitted from the heater 13. Specifically, for example, the surface of portion 344 is made smooth, the surface roughness of portion 342 is made the greatest, and the surface roughness of portion 343 is made smaller than the surface roughness of portion 342.

[0052] Fig. 6(c) is a vertical cross-sectional view showing a structure in which the diameter of the annular heating element 13 is made smaller than that shown in Fig. 2 etc. By making the diameter of the heating element 13 smaller, the ratio of the distance between the heating element 13 and the outer periphery of the crystal growth surface to the distance between the heating element 13 and the center of the crystal growth surface increases, so that the temperature of the outer periphery of the crystal growth surface can be relatively increased. As a result, even if the temperature distribution of the crystal growth surface is upwardly convex when the diameter of the heating element 13 is large, it can be made flat or downwardly convex by making the diameter of the heating element 13 smaller.

[0053] Furthermore, by providing the through holes 151, 161 for supplying raw material directly above the center of the growth surface of the single crystal 21, i.e., directly above the center of the support shaft 19, the temperature at the center of the growth surface can be lowered. This makes it easy to make the temperature distribution at the growth surface of the single crystal 21 flat or downwardly convex. Furthermore, in order to effectively lower the temperature at the center of the growth surface, it is preferable to make the diameters of the through holes 151, 161 somewhat large (for example, 10 to 60% of the diameter of the single crystal 21).

[0054] Furthermore, in addition to the through holes 151, 161 for supplying raw material, holes for lowering the temperature at the center of the growth surface of the single crystal 21 may be provided directly above the center of the growth surface. In this case, the through holes 151, 161 for supplying raw material are provided at a position off-center of the growth surface of the single crystal 21, so that the raw material melt is dripped at a position off-center of the growth surface of the single crystal 21, but this does not pose a problem if the single crystal 21 is grown while rotating. In addition, this has the advantage that the distribution of impurities in the single crystal 21 is more gradual than when the raw material is dripped at the center of the growth surface of the single crystal 21.

[0055] (Method of controlling the cross-sectional shape of a single crystal) The following describes a method for controlling the cross-sectional shape of the single crystal 21. Here, the cross-sectional shape refers to the shape of a cross section in the radial direction, and for example, the cross-sectional shape of a cylindrical single crystal 21 is circular, and the cross-sectional shape of a polygonal columnar single crystal 21 is polygonal.

[0056] The cross-sectional shape of single crystal 21 depends on the shape of hole 121 in insulating plate 12. This is because the temperature distribution on the upper surface of single crystal 21 depends on the shape of hole 121, and an area on the upper surface of single crystal 21 having a shape similar to that of hole 121 melts, causing crystal growth. For example, if hole 121 is circular, the cross-sectional shape of single crystal 21 will be circular, and if hole 121 is polygonal, the cross-sectional shape of single crystal 21 will be polygonal with rounded corners.

[0057] However, when using an insulating plate 12 with polygonal holes 121 to make the cross-sectional shape of single crystal 21 polygonal, and when single crystal 21 is grown while being rotated around its central axis, insulating plate 12 must also be rotated in accordance with the rotation of single crystal 21.

[0058] 7(a) is a vertical cross-sectional view showing a structure in which a shape-controlling member 35 for controlling the shape of the single crystal 21 is installed. The shape-controlling member 35 is an annular member that is installed inside the hole 121 of the heat insulating plate 12 and comes into contact with the melt on the outer periphery of the upper surface of the single crystal 21, and the crystal grows mainly in the inner region of the outer edge of the annular bottom surface 351 that comes into contact with the melt. Therefore, the cross-sectional shape of the single crystal 21 can be controlled by the planar shape of the outer edge of the bottom surface 351 of the annular shape-controlling member 35.

[0059] The shape control member 35 is made of a material that does not react with the single crystal 21 and the melt, since it comes into contact with them. For example, when the single crystal 21 is a gallium oxide single crystal, iridium or sapphire is used as the material for the shape control member 35. Nevertheless, since the shape control member 35 comes into contact with the melt, impurity contamination from the shape control member 35 may occur in the melt depending on the composition of the single crystal 21 (melt) and the material of the shape control member 35. However, since the melt flows from the non-contact area with the shape control member 35 toward the contact area, impurity contamination is limited to the vicinity of the contact area. Therefore, even when the shape control member 35 is used, a high-purity single crystal 21 can be obtained. For example, when processing the single crystal 21 into a wafer, the contaminated part can be removed by scraping off the outer peripheral part that was in contact with the shape control member 35.

[0060] 7(b) is a vertical cross-sectional view showing a structure in which a shape-controlling member 35 with an increased width of the annular bottom surface 351 is installed. By increasing the width of the annular bottom surface 351 until a part of the inner edge side of the bottom surface 351 comes into contact with the upper surface of the seed crystal 20, the shape-controlling member 35 can be used not only for shape control of the single crystal 21 but also as a member for facilitating shoulder expansion (diameter increase). The melt on the upper surface of the single crystal 21 (seed crystal 20) expands the interface between the single crystal 21 (seed crystal 20) and the bottom surface 351 toward the outer edge of the annular bottom surface 351, so that the diameter of the single crystal 21 can be expanded from approximately the diameter of the seed crystal 20 to the diameter of the outer edge of the bottom surface 351 while it is growing.

[0061] 7(b), the contact area between the bottom surface 351 and the melt is wide, and therefore the single crystal 21 is relatively susceptible to impurity contamination from the shape control member 35. For this reason, a single crystal 21 with a large diameter is grown by spreading the shoulders using a shape control member 35 with a large bottom surface 351, and then a large-diameter seed crystal 20 cut from this single crystal 21 is used to grow a new single crystal 21 without using a shape control member 35 with a large bottom surface 351, thereby obtaining a single crystal 21 with a large diameter and high purity.

[0062] (Method of Supplying Raw Material Melt) A method for supplying the raw material melt to the upper surface of the seed crystal 20 or the single crystal 21 will be described below.

[0063] 8(a) is a vertical cross-sectional view showing a schematic view of supplying a raw material melt using a raw material rod 40. The raw material rod 40 is a rod-shaped sintered body of the material that constitutes the single crystal 21. For example, when producing a single crystal of a gallium oxide-based semiconductor as the single crystal 21, a sintered body of a gallium oxide-based semiconductor is used as the raw material rod 40.

[0064] The raw material rod 40 is inserted into the through holes 151, 161, which are raw material supply ports, and its lower end is positioned inside or near the second space 102, and melted by the heat of the second space 102 to enlarge the pool of melt 41 and allow it to drip. At this time, it is possible to wait for the melt 41 to drip by its own weight, or to vibrate the raw material rod 40 to encourage the dripping. The dripped melt 41 passes through the second space 102 and the hole 121 of the heat insulating plate 12 and is supplied to the upper surface of the seed crystal 20 or the single crystal 21.

[0065] If the droplets of melt 41 are too large, they may scatter when they reach the upper surface of single crystal 21 or may destabilize the shape of the solid-liquid interface. For this reason, it is preferable to adjust the size of the droplets according to the diameter of feed rod 40. The relationship between the diameter of feed rod 40 and the size of the droplets of melt 41 varies depending on the specific gravity of melt 41, but for example, when feed rod 40 is a sintered body of a gallium oxide-based semiconductor, it is preferable to set the diameter to 5 mm or less.

[0066] 8(b) is a vertical sectional view showing a schematic view of supplying the raw material melt using a hollow raw material rod 42. The hollow raw material rod 42 is a hollow rod made of a sintered body of the material that constitutes the single crystal 21.

[0067] A hollow raw material rod 42 is inserted into the through-holes 151, 161, which are raw material supply ports, and its tip is positioned inside or near the second space 102, where it is melted by the heat of the second space 102 to form a pool of melt 41. Furthermore, powder or granular raw material 43 is dropped through the inside of the hollow raw material rod 42, and is melted by the heat of the second space at the lower end of the hollow raw material rod 42 to enlarge the pool of melt. The raw material 43, like the hollow raw material rod 42, is made of a sintered body of the material that constitutes the single crystal 21.

[0068] The melt 41 may be waited for to drip from the liquid pool under its own weight, or the dripping may be promoted by vibrating the feed rod 40, or the dripping may be promoted by feeding gas through the inside of the hollow feed rod 42. The dripped melt 41 passes through the second space 102 and the hole 121 of the heat insulating plate 12 and is supplied to the upper surface of the seed crystal 20 or the single crystal 21.

[0069] Instead of the hollow raw material rod 42, a hollow tube made of a material that is not the raw material of the single crystal 21 and does not react with the raw material 43 or the melt 41 may be used. In this case, too, by making the inner diameter of the hollow tube sufficiently small, the raw material 43 dropped into the hollow tube can be melted at the bottom end of the hollow tube to form a liquid pool.

[0070] 8(c) is a vertical cross-sectional view showing a schematic view of supplying the raw material melt using a funnel 44. The funnel 44 is made of a material that does not react with the raw material 43 or the melt 41. For example, when producing a single crystal 21 made of a gallium oxide-based semiconductor, the funnel 44 is made of iridium or sapphire.

[0071] The funnel 44 is installed so that its lower end is located within the second space 102. When raw material 43 is introduced into the funnel 44 through the through holes 151 and 161, which are raw material supply ports, the raw material 43 melts in the funnel 44 due to the heat of the second space 102 to become a melt 41. The melt 41 dripping from the funnel 44 passes through the second space 102 and the hole 121 of the heat insulating plate 12 and is supplied to the upper surface of the seed crystal 20 or the single crystal 21.

[0072] The raw material 43 may be dropped into the through-holes 151, 161 without using the hollow raw material rod 42 or the funnel 44. In this case, it is ideal that the raw material 43 melts while falling due to the heat of the second space 102 and is supplied to the upper surface of the single crystal 21 in the form of melt 41. However, even if the raw material 43 does not melt but reaches the upper surface of the single crystal 21 in the form of powder or granules and melts on the upper surface of the single crystal 21, this does not cause a problem if the growth speed of the single crystal 21 is slowed down.

[0073] 9 is a vertical cross-sectional view showing a schematic state in which metal 47 is reacted with oxygen gas to obtain raw material 43, which is an oxide. Metal 47 is a metal that is a raw material of the metal component of single crystal 21. For example, when a single crystal of gallium oxide is produced as single crystal 21, Ga metal is used as metal 47 to obtain raw material 43, which is a sintered body of gallium oxide.

[0074] Metal 47 is dropped into hollow tube 46 installed on insulation material 16 so as to be connected to through hole 161. At the same time as dropping metal 47, oxygen gas is caused to flow into hollow tube 46. An induction heating coil 45 for induction heating metal 47 is wound around hollow tube 46, and heated metal 47 reacts with oxygen gas while descending inside hollow tube 46, producing raw material 43 which is an oxide.

[0075] According to the method of forming the raw material 43 by reacting this metal 47 with oxygen gas, it is possible to obtain a powder or granular raw material 43 with a very high purity. For example, when forming the raw material 43 which is a sintered body of gallium oxide, the raw material 43 obtained has a purity of about 7N. According to this method, for example, the raw material 43 shown in FIG. 8(b) or FIG. 8(c) can be formed.

[0076] When Ga metal is used as the metal 47, the frequency of induction heating (the frequency of the AC current flowing through the induction heating coil 45) is preferably 100 kHz or more if the amount is small. Here, a small amount means, for example, that the total volume of the Ga metal added at one time is 550 mm 3 This means that:

[0077] Moreover, since only the surface of the Ga metal is oxidized at about 1000°C, it is preferable to heat the Ga metal to a temperature of 1400°C or higher in order to oxidize the entire Ga metal. When the heating temperature is 1400°C or higher, the Ga metal may be in any form such as powder, granules, liquid, etc. When mist-like Ga metal made of nanoparticles is used as the metal 47, the entire Ga metal can be oxidized even if the heating temperature is less than 1400°C. Here, the Ga metal nanoparticles can be formed, for example, by irradiating the Ga metal with sound waves. Also, since it is difficult to directly inductively heat the Ga metal nanoparticles, a means for indirectly heating the Ga metal nanoparticles is required, such as placing a heated body for induction heating inside the hollow tube 46 and utilizing the radiant heat.

[0078] Based on the above-mentioned method for obtaining the high-purity powder or granular raw material 43, the following methods [1] to [3] for producing gallium oxide can be provided. [1] A process of introducing oxygen gas into a hollow tube around which an induction heating coil is wound, and dropping Ga metal into the tube; a step of inductively heating the Ga metal inside the hollow tube by a magnetic field generated by passing an AC current through the induction heating coil, and reacting the Ga metal with the oxygen gas to obtain gallium oxide; A method for producing gallium oxide, comprising: [2] The Ga metal is heated to a temperature of 1400°C or higher by the induction heating. The method for producing gallium oxide described in [1] above. [3] The frequency of the induction heating is 100 kHz or more; The method for producing gallium oxide according to [1] or [2] above.

[0079] (Effects of the embodiment) According to the single crystal manufacturing apparatus 1 of the above embodiment, since a crucible is not used, the amount of metal used is small, and the equipment cost can be significantly reduced. Also, since a crucible is not used, there is no risk of the purity of the single crystal 21 being reduced due to the inclusion of components contained in the crucible. Furthermore, since heat radiation from the growth surface of the single crystal 21 is suppressed, a large single crystal 21 can be manufactured.

[0080] For example, when a single crystal 21 made of gallium oxide is manufactured using a raw material with a purity of 6N by the single crystal manufacturing apparatus 1 (excluding the form using the shape control member 35 with a large bottom surface 351 shown in FIG. 7(b) and the form using the funnel 44 shown in FIG. 8(c)), the carrier concentration without hole compensation is 1×10 16 cm -3 Wafers of less than 1×10 can be cut from the single crystal 21. In addition, when the single crystal 21 made of gallium oxide is produced by the single crystal production apparatus 1 using a raw material with a purity of 7N, the carrier concentration without hole compensation is 1×10 15 cm -3 Wafers of less than 100 mm can be cut from the single crystal 21. By using these wafers, a high-voltage device can be fabricated without providing an epitaxial layer for ensuring the voltage resistance. The reason why the form using the shape control member 35 having a large bottom surface 351 shown in FIG. 7(b) and the form using the funnel 44 shown in FIG. 8(c) are excluded is that the single crystal 21 may be contaminated with impurities from the shape control member 35 or the funnel 44.

[0081] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the invention. Furthermore, the components of the above embodiment can be combined in any manner without departing from the spirit of the invention.

[0082] In addition, the above-described embodiments do not limit the scope of the invention according to the claims. Also, it should be noted that not all of the combinations of features described in the embodiments are essential to the means for solving the problems of the invention. [Explanation of symbols]

[0083] 1...single crystal manufacturing apparatus, 10...insulating space, 101...first space, 102...second space, 103...crystal growth area, 11...induction heating coil, 12...insulating plate, 121...hole, 13...heater, 19...support shaft, 20...seed crystal, 21...single crystal, 31, 32...insulating material, 33...heater, 34...insulating plate, 35...shape control member, 40...feedstock rod, 41...melt, 42...hollow feedstock rod, 43...feedstock, 44...funnel

Claims

1. A single crystal manufacturing apparatus for growing a single crystal upward from a seed crystal, comprising: a thermally insulated space insulated from a space outside the single crystal production apparatus; an insulating plate that divides the insulating space into a first space including a crystal growth region for growing the single crystal and a second space above the first space, the insulating plate having a hole above the crystal growth region; A heating body that heats the inside of the insulating space and is installed outside the hole of the second space; a support shaft for supporting the seed crystal from below so as to be movable in a vertical direction; Equipped with the heater is disposed at a position where it does not come into contact with the raw material melt supplied to the upper surface of the seed crystal when the single crystal is grown. Single crystal manufacturing equipment.

2. The insulating plate further includes an annular member having a bottom surface and a planar shape of an outer edge of the annular member, the bottom surface being disposed inside the hole of the insulating plate and capable of controlling a cross-sectional shape of the single crystal. The apparatus for producing a single crystal according to claim 1.

3. the annular bottom surface has a width that allows a part of an inner edge side to contact an upper surface of the seed crystal; The apparatus for producing a single crystal according to claim 2.

4. the heat-insulating space is surrounded by a first heat-insulating material that forms side walls of the first space and the second space, a second heat-insulating material that forms an upper wall of the second space, and a base that supports the first heat-insulating material and the second heat-insulating material from a bottom of the first space; the second heat insulating material has a through hole that vertically passes through the second heat insulating material for supplying the raw material of the single crystal to the second space, The base body has a shaft hole through which the support shaft can move up and down. The single crystal manufacturing apparatus according to any one of claims 1 to 3.

5. A third insulating material is installed on the second insulating material as an upper wall, The third insulating material is provided with a through hole that vertically penetrates the third insulating material so as to connect to the through hole of the second insulating material, the diameter of the through hole of the second insulating material and the diameter of the through hole of the third insulating material are smaller than the diameter of the crystal growth region; The apparatus for producing a single crystal according to claim 4.

6. A ring-shaped fourth insulating material surrounding the crystal growth region is installed in the first space. The apparatus for producing a single crystal according to claim 4.

7. A step of placing a seed crystal below the hole in a first space of an insulating space partitioned into a first space and a second space above the first space by an insulating plate having a hole; melting an upper surface of the seed crystal by radiant heat from a heater installed outside the hole in the second space; supplying a single crystal raw material melt onto an upper surface of the molten seed crystal through the second space and the hole in the insulating plate; a step of moving the seed crystal downward while continuing to supply the raw material melt, and growing the single crystal upward from the seed crystal; Including, the heating body does not come into contact with the raw material melt during the step of supplying the raw material melt for the single crystal and the step of growing the single crystal; A method for producing single crystals.

8. an annular member is installed inside the hole of the insulating plate such that a part of an inner edge side of a bottom surface of the annular member contacts an upper surface of the seed crystal; In the step of growing the single crystal, the raw material melt is supplied to an upper surface of the seed crystal or to an interface between an upper surface of the single crystal and the annular bottom surface of the annular member. The method for producing the single crystal according to claim 7.

9. In the step of growing the single crystal, while the single crystal is being grown upward from the seed crystal, the raw material melt is spread toward an outer edge of the annular bottom surface at an interface between an upper surface of the seed crystal or an upper surface of the single crystal and the annular bottom surface of the annular member, thereby broadening the shoulders of the single crystal. The method for producing the single crystal according to claim 8 .

10. In the step of growing the single crystal, the single crystal is grown in a region inside an outer edge of the annular bottom surface, and a cross-sectional shape of the single crystal is controlled by a planar shape of the outer edge of the annular bottom surface. The method for producing the single crystal according to claim 8 .

11. supplying a single crystal raw material melt onto an upper surface of the single crystal grown on the seed crystal; a step of moving the seed crystal downward while continuing to supply the raw material melt, and growing the single crystal upward from the seed crystal; Including, In the step of supplying the raw material melt, the raw material melt on the outer periphery of the upper surface of the single crystal comes into contact with an annular bottom surface of an annular member placed on the single crystal, In the step of growing the single crystal, the single crystal is grown in a region inside an outer edge of the annular bottom surface, and a cross-sectional shape of the single crystal is controlled by a planar shape of the outer edge of the annular bottom surface. A method for producing single crystals.

12. All of the above steps are carried out in an insulated space that is insulated from the outside space. The method for producing a single crystal according to any one of claims 7 to 11.

13. The single crystal is an oxide. The method for producing a single crystal according to any one of claims 7 to 12.

14. In the step of supplying the raw material melt, droplets of the raw material melt are supplied onto an upper surface of the molten seed crystal; In the step of growing the single crystal, droplets of the raw material melt are supplied onto an upper surface of the single crystal. The method for producing a single crystal according to any one of claims 7 to 13.

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