Manufacturing apparatus and manufacturing method

Abstract

The present invention addresses the problem of providing a manufacturing device and a manufacturing method that make it possible to industrially advantageously manufacture a crystal. The solution is to produce a crystal using a device for producing a crystal, the device being provided with at least a high-frequency induction heating coil for forming a melting zone of a raw material solution using high-frequency induction heating and producing a crystal by growing a crystal in the longitudinal direction in the melting zone, the upper end of the high-frequency induction heating coil is disposed at a depth of 5 mm or less from the liquid surface of the raw material melt, and a positional relationship holding means for growing the crystal while holding the positional relationship between the depth position and the upper end is provided.

Description

Technical Field

[0001] This invention relates to a crystal manufacturing apparatus and a method for manufacturing crystals. Background Technology

[0002] To build the next generation of digital infrastructure, energy efficiency is required for electrical equipment that performs power conversion, including home appliances, electric vehicles, industrial machinery, and renewable energy sources. Previously, silicon-based electrical equipment was the mainstream, but there is a search for power semiconductor materials with lower energy conversion losses compared to silicon. Research and development have been conducted on silicon carbide (SiC), gallium nitride (GaN), and gallium oxide as such materials.

[0003] Currently, as a single crystal growth technique for, for example, gallium oxide, the finite-edge-fed growth (EFG) method is known, as disclosed in Patent Document 1 and Non-Patent Document 1. Stable crystals can be obtained using the EFG method, but its crystallinity and growth rate are still unsatisfactory.

[0004] Furthermore, research and development have been conducted on the cold crucible method, which involves directly applying an electromagnetic field to a substrate material used for crystal growth via an induction coil to grow a single crystal. Patent documents 2 and 3 disclose cold crucibles suitable for the cold crucible method and examples of single crystal manufacturing using these methods. Patent document 4 discloses a gallium oxide cold crucible and a method for manufacturing gallium oxide single crystals based on the cold crucible method using this method, while patent document 5 discloses the structure of an apparatus for manufacturing single crystals using the cold crucible method. However, the techniques described in patent document 1 and non-patent document 1 still have the following problems: increasing the size of the crystal requires increasing the size of the crucible, and since the crucible materials usable at the melting point of gallium oxide are high-cost materials such as iridium, it is difficult to reduce costs. Additionally, the specific manufacturing conditions for single crystals are not disclosed in patent documents 2 to 5. Furthermore, although research and development on crystal growth based on the cold crucible method is underway, industrial mass production and commercialization still face many challenges, thus a method strategy that can achieve good crystal growth in industrial applications is desired.

[0005] Existing technical documents

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2006-312571

[0008] Patent Document 2: U.S. Patent Application Publication No. 4049384

[0009] Patent Document 3: Japanese Patent Application Publication No. 60-2876

[0010] Patent Document 4: Japanese Patent Application Publication No. 2017-61396

[0011] Patent Document 5: Japanese Patent Application Publication No. 2018-191426

[0012] Non-patent literature

[0013] Non-patent document 1: Hideo Aida et al., Growth of β-Ga2O3 single crystals by theEdge-Defined, Film Fed Growth Method, Jpn. Journal of Applied Physics, Vol. 47, No. 11, 2008, pp. 8506-8509 Summary of the Invention

[0014] The technical problem that the invention aims to solve

[0015] The purpose of this invention is to provide an industrially advantageous manufacturing apparatus and method for producing crystals.

[0016] Solution for solving the problem

[0017] In order to achieve the above-mentioned objectives, the inventors conducted in-depth research and obtained the following insights: When using high-frequency induction heating based on a high-frequency induction heating coil to form a molten band of raw material solution and manufacturing crystals by crystal growth in the long side direction of the molten band, crystal growth can be carried out efficiently and well when the positional relationship between the depth position of the raw material molten liquid (less than 5 mm from the liquid surface) and the upper end of the high-frequency induction heating coil is controlled, and it was found that such a manufacturing method and manufacturing apparatus can solve the above-mentioned conventional problems in one fell swoop.

[0018] Furthermore, after obtaining the above insights, the inventors conducted further and repeated research, thereby completing this invention.

[0019] That is, the present invention relates to the following solutions.

[0020] [1] A crystal manufacturing apparatus, the apparatus comprising at least a high-frequency induction heating coil for forming a molten band of a raw material solution using high-frequency induction heating, and manufacturing a crystal by crystal growth along the long side direction in the molten band, characterized in that,

[0021] The upper end of the high-frequency induction heating coil is disposed at a depth of 5 mm or less from the surface of the raw material molten liquid, and the manufacturing apparatus has a position relationship maintaining unit that maintains the position relationship between the depth position and the upper end while performing the crystal growth.

[0022] [2] According to the manufacturing apparatus described in [1] above, the position relationship maintaining unit includes a movable unit of the high-frequency induction heating coil or a movable unit of the molten strip.

[0023] [3] According to the manufacturing apparatus described in [1] above, wherein the manufacturing apparatus is configured such that the width of the molten zone satisfies the following formula (1):

[0024] δ##5.03×(ρ / (μ×F))1 / 2…(4) Formula

[0025] In equation (1), D represents the width of the molten band (cm), ρ represents the resistivity of the raw material solution (μΩcm), μ represents the relative permeability of the raw material solution, and F represents the frequency of the high-frequency induction heating coil (Hz).

[0026] [4] The manufacturing apparatus according to [3] above, wherein the manufacturing apparatus further comprises a cooling container used in the cold crucible method, the width of the molten zone being the inner dimension of the cooling container, and the crystal growth is performed by a melt growth method, wherein the melt growth method uses a melt that is directly heated by the high frequency.

[0027] [5] According to the manufacturing apparatus described in [1] above, the raw material solution contains Ga.

[0028] [6] A method for manufacturing a crystal, wherein the method uses high-frequency induction heating based on a high-frequency induction heating coil to form a molten band of a raw material solution, and manufactures a crystal by crystal growth along the long side direction in the molten band, characterized in that,

[0029] The upper end of the high-frequency induction heating coil is positioned at a depth of 5 mm or less from the surface of the raw material molten liquid, and the crystal growth is carried out while maintaining the positional relationship between the depth position and the upper end.

[0030] [7] According to the manufacturing method described in [6] above, wherein,

[0031] The crystal growth is carried out while the high-frequency induction heating coil or the molten zone is moved.

[0032] [8] According to the manufacturing method described in [6] above, wherein,

[0033] The manufacturing method performs the crystal growth in a manner that satisfies the following formula (1):

[0034] δ=5.03×(ρ / (μ×F))1 / 2…(4) Formula

[0035] In equation (1), D represents the width of the molten band (cm), ρ represents the resistivity of the raw material solution (μΩcm), μ represents the relative permeability of the raw material solution, and F represents the frequency of the high-frequency induction heating coil (Hz).

[0036] [9] According to the manufacturing method described in [6] above, the crystal is grown by a melt growth method, wherein the melt growth method uses a melt that is directly heated by high frequency.

[0037]

[10] In the crystal manufacturing method described in [6] above, the raw material solution contains Ga.

[0038] Invention Effects

[0039] According to the manufacturing apparatus and method of the present invention, crystals can be advantageously manufactured industrially. Attached Figure Description

[0040] Figure 1 This is a flowchart illustrating the crystal growth method of Embodiment 1 of the present invention.

[0041] Figure 2A This is a structural diagram showing the structure of the crystal growth apparatus according to Embodiment 1 of the present invention.

[0042] Figure 2B This is a structural diagram showing the structure of the crystal growth apparatus according to Embodiment 1 of the present invention.

[0043] Figure 2C This is a structural diagram showing the structure of the crystal growth apparatus according to Embodiment 1 of the present invention.

[0044] Figure 2D This is a structural diagram showing the structure of the crystal growth apparatus according to Embodiment 1 of the present invention.

[0045] Figure 2E This is a structural diagram showing the structure of the crystal growth apparatus according to Embodiment 1 of the present invention.

[0046] Figure 3 This is a flowchart illustrating the crystal growth method of Embodiment 2 of the present invention.

[0047] Figure 4 This is a flowchart illustrating the method for controlling the diameter of the raw material crystal in the crystal growth method according to an embodiment of the present invention.

[0048] Figure 5 This is a structural diagram showing the structure of the crystal diameter control mechanism in the crystal growth apparatus according to an embodiment of the present invention.

[0049] Figure 6This is a structural diagram of a high-frequency heating device according to one embodiment of the present invention.

[0050] Figure 7 (A) is a schematic circuit diagram of the inverter section. Figure 7 (B) is a schematic diagram of high frequencies generated using transistors.

[0051] Figure 8 This is a schematic diagram showing a portion of the circuitry of the inverter section in the same embodiment, including an LCR circuit containing a heating coil.

[0052] Figure 9 (A) is a conceptual diagram used to illustrate the phase difference between the output current waveform and the reference waveform. Figure 9 (B) is a waveform diagram representing an example of the output current waveform and the output voltage waveform.

[0053] Figure 10 This is a graph showing the time changes of driving frequency, phase difference, current, and voltage during the crystal growth process in a crystal manufacturing method according to one embodiment of the present invention, when frequency control based on phase difference is performed.

[0054] Figure 11 This is a graph showing the phase difference, driving frequency, current, and voltage during the melting process in a crystal manufacturing method according to one embodiment of the present invention, when frequency control based on phase difference is performed.

[0055] Figure 12 This is a graph showing the phase difference, driving frequency, current, and voltage during the crystal growth process in a crystal manufacturing method according to one embodiment of the present invention, when frequency control based on phase difference is performed.

[0056] Figure 13 This is a graph showing the results of temperature distribution calculations performed on the preferred embodiment of the present invention.

[0057] Figure 14 The graph shows the relationship between the position of the coil and the crystal defect density, and the graph shows the improved crystallinity of the present invention. Detailed Implementation

[0058] The manufacturing apparatus of the present invention is characterized by having at least a high-frequency induction heating coil for forming a molten band of a raw material solution using high-frequency induction heating, and manufacturing a crystal by crystal growth in the molten band along its long side. The apparatus is characterized by having an upper end of the high-frequency induction heating coil disposed at a depth of 5 mm or less from the surface of the raw material molten liquid, and the manufacturing apparatus having a positional relationship maintaining unit that maintains the positional relationship between the depth position and the upper end while performing crystal growth.

[0059] In this invention, it is more preferable that the position relationship maintaining unit includes a movable unit of the high-frequency induction heating coil. According to this preferred range, crystal growth can be performed more easily. It should be noted that the position relationship maintaining unit and the movable unit are not particularly limited as long as they do not hinder the purpose of this invention, and known units can be used respectively.

[0060] Furthermore, in this invention, the width of the molten band is configured to satisfy the following formula (1), which is preferred because it allows for better crystal growth.

[0061]

[0062] In the formula, D represents the width of the molten zone (cm), ρ represents the resistivity of the raw material solution (μΩcm), μ represents the relative permeability of the raw material solution, and F represents the frequency of the high-frequency induction heating coil (Hz).

[0063] In addition, the present invention also includes a cooling container used in the cold crucible method, wherein the width of the molten zone is the inner dimension of the cooling container, and the crystal growth is performed by the melt growth method. Since better crystal growth can be performed without a crucible, it is preferred that the melt growth method uses a melt that is directly heated by the high frequency.

[0064] Furthermore, in this invention, since it is easier to obtain Ga-containing crystals such as gallium oxide through crystal growth, it is preferable that the raw material solution contains Ga.

[0065] Furthermore, the manufacturing method of the present invention uses high-frequency induction heating based on a high-frequency induction heating coil to form a molten band of raw material solution, and manufactures crystals by crystal growth in the long side direction of the molten band. The method is characterized in that the upper end of the high-frequency induction heating coil is arranged at a depth of 5 mm or less from the liquid surface of the raw material molten liquid, and the crystal growth is carried out while maintaining the positional relationship between the depth position and the upper end.

[0066] In this invention, it is more preferable to perform the crystal growth while moving the high-frequency induction heating coil. Based on this preferred range, crystal growth can be performed more easily.

[0067] The preferred method described in this invention is used to calculate the temperature distribution, and the calculation results are shown below. Figure 13 . Figure 13 The temperature distribution diagram illustrates the temperature distribution during gallium oxide crystal growth using the method of the present invention. Figure 13It is evident that the temperature gradient in the solution zone becomes a downward-convex temperature gradient that facilitates crystal growth, and the preferred method of the present invention is more suitable for crystal growth. This insight is a novel insight obtained by the inventors for the first time.

[0068] The preferred embodiments of the invention are described in more detail below with reference to the accompanying drawings, but the invention is not limited to these specific examples.

[0069] refer to Figure 1 This will be explained below. According to the preferred crystal growth method, single crystals of raw materials such as zirconium oxide, titanium, titanium-aluminum alloy, iron oxide, magnesium oxide, calcium oxide, strontium oxide, yttrium oxide, chromium oxide, lanthanum chromium oxide, strontium titanate, gadolinium oxide, scandium oxide, lutetium oxide, lanthanum nickel oxide, gallium oxide, aluminum oxide, magnesium aluminum oxide, yttrium aluminum garnet, gadolinium aluminum gallium garnet, lanthanum gadolinium silicon oxide, strontium iodide, cerium bromide, and lithium calcium aluminum fluoride can be obtained by crystal growth.

[0070] First, in the first step S101, while cooling the area around the solid raw material body, the central portion of the raw material body at one end is heated and melted by induction heating. At this time, a metal that readily absorbs magnetic fields can be used as the starting material for the initial heating. Using a metal element contained in the raw material body reduces the impact of contamination. If the raw material body becomes liquid due to the heating of the starting material, the resistivity decreases significantly, magnetic field absorption becomes better, and a stable molten zone is formed. For example, in the case of gallium oxide, Ir and Ga metals can be used as the starting material.

[0071] The raw material body can be, for example, cylindrical. The raw material body can be, for example, a cylinder with a bottom diameter of 100 mm and a height of 100 mm. The other end (lower surface) of the raw material body is designated as the ground side, and the raw material body is positioned such that the axis of the cylinder is perpendicular to the ground.

[0072] Next, in the second step S102, the seed crystal is brought into contact with the molten material at the center of one end (upper surface) of the raw material body. By heating as described above, the center of one end of the raw material body becomes the molten material after the raw material has melted, and the seed crystal is brought into contact with it. In this step, the frequency of induction heating is continuously set to a range deviating from the resonant frequency of the molten material, and the temperature gradient of the molten material as described above is maintained. This temperature gradient is also maintained in subsequent steps described later.

[0073] Then, in the third step S103, while cooling the area around the raw material body, the portion heated by induction heating is moved from one end of the raw material body to the other, and the portion of the raw material in the center of the raw material body that has melted is moved from one end of the raw material body to the other. Here, the above-described movement is performed from one end of the raw material body to the other end of the raw material body located on the ground side. Through this movement, starting from the part in contact with the seed crystal, the raw material crystal grows from one end of the raw material body to the other. At this time, the seed crystal can also be pulled at a constant speed. It should be noted that when using the Cz method as the crystal growth unit, pulling is preferred.

[0074] Here, at least in the second step S102 and the third step S103 described above, the heating of the central portion of the raw material body based on induction heating is implemented by setting the frequency of induction heating to a range deviating from the resonant frequency of the melt. This results in a temperature gradient in the melt that decreases closer to the center of the raw material body in a plane perpendicular to the direction from one end of the raw material body to the other (temperature gradient of the melt). Thus, by changing the frequency of induction heating within a range deviating from the resonant frequency of the melt and controlling the temperature gradient of the melt in a plane, the diameter of the raw material crystals can be controlled. However, this is not necessarily required in the present invention; such a control unit can be appropriately used, or other control units (e.g., units that change the output of the magnetic field or units that change the position of the coil, etc.) can be appropriately used.

[0075] It should be noted that when the raw material is an oxide, the second step S102 and the third step S103 can be carried out in an atmosphere with an oxygen concentration of 10% or more by volume. It is even more preferable to carry out the process with an oxygen concentration of 50% or more, and more preferably with an oxygen concentration of 80% or more.

[0076] Here, by changing the concentration of the dopant impurities added to the raw material from one end to the other, the impurity concentration can be made uniform throughout the entire region in the direction of crystal growth. Furthermore, in the third step S103, at least one of the seed crystal and the raw material can be rotated about an axis pointing in the direction of movement.

[0077] For example, in the case of gallium oxide, the added dopants can be silicon, germanium, tin, iron, lithium, magnesium, or chromium. Additionally, in the case of oxides or ionic crystals, cerium, europium, ytterbium, neodymium, terbium, erbium, holmium, thulium, and praseodymium can be added as dopants.

[0078] In the case of seeding, after the grown crystal is cut from the melt, heating is slowly stopped to allow the raw material to solidify.

[0079] Alternatively, starting from the point of contact with the seed crystal, the raw material crystal is grown from one end of the raw material body to a predetermined location along the direction from the other end. Heating is then stopped, and the molten material inside the raw material body is slowly cooled and solidified. As a result, a single crystal of the raw material, grown from the seed crystal, is formed inside the raw material body. Afterward, the raw material surrounding the raw material body is removed, thereby extracting the single crystal of the raw material.

[0080] According to the embodiment described, the periphery of the raw material body, which is cooled and maintained in a solid state, becomes a crucible for containing the melt. Therefore, there is no problem of contamination from impurities originating from the crucible. Furthermore, since it is not necessary to use a crucible made of costly materials, manufacturing costs can be reduced. Additionally, by maintaining a state where the temperature is lower closer to the center of the raw material body in a plane perpendicular to the direction from one end to the other, the area of ​​the melt used for crystal growth can be further expanded.

[0081] Next, refer to Figures 2A to 2E This describes a crystal growth apparatus for implementing the crystal growth method described above. This crystal growth apparatus is for growing oxide crystals, ionic crystals, etc., and includes a holding stage 101, a cooling mechanism 102, and a high-frequency induction heating coil 103. It also includes a growth chamber 104 that houses the holding stage 101, the cooling mechanism 102, and the high-frequency induction heating coil 103.

[0082] The holding stage 101 is used to hold a raw material body 151 made of solid raw material. The raw material body 151 is, for example, a cylinder. The raw material body 151 is placed on the holding stage 101 with the other end side (lower surface) of the raw material body 151 as the ground side and the axis of the cylinder perpendicular to the ground. A seed crystal 161 is disposed on one end side (upper surface) of the raw material body 151. In addition, in Embodiment 1, a holding rod 162 for holding the seed crystal 161 is provided. It should be noted that the seed crystal 161 is made of a crystal made of the same material as the raw material body, or an oxide crystal, an ionic crystal, or a covalent crystal.

[0083] The cooling mechanism 102 is configured to cover the circumferential surface of the raw material body 151 held by the holding stage 101, and is used to cool the raw material body 151. The cooling mechanism 102 is, for example, composed of copper piping for the flow of cooling medium, which is configured in a coiled, wavy, or bundled U-shaped configuration. Furthermore, the cooling mechanism 102 has the capability to completely cover the raw material body 151 from the top to the bottom relative to the crystal growth direction, or to move simultaneously with the high-frequency induction heating coil 103.

[0084] A high-frequency induction heating coil 103 is arranged around the cooling mechanism 102. The high-frequency induction heating coil 103 constitutes a heating mechanism for heating the raw material 151 in the area covered by the cooling mechanism 102 using high-frequency induction heating. In addition, the heating mechanism includes a mechanism (not shown) that applies the frequency of induction heating to the high-frequency induction heating coil 103 by deviating the resonant frequency of the molten raw material.

[0085] When the region of the raw material 151 cooled by the cooling mechanism 102 is heated to, for example, 1000°C using a heating mechanism based on a high-frequency induction heating coil 103, the central portion of the raw material 151 becomes a melt. On the other hand, the peripheral portion of the raw material 151 surrounding this region remains solid due to being cooled by the cooling mechanism 102. In this state, the peripheral portion of the raw material 151, which remains solid due to being cooled by the cooling mechanism 102, becomes a crucible for containing the melt 152.

[0086] The growth chamber 104 includes an exhaust pipe 105 and a gas inlet pipe 106. An exhaust mechanism (not shown) for venting the interior of the growth chamber 104 is connected to the exhaust pipe 105. The gas inlet pipe 106 includes a gas inlet mechanism (not shown) for introducing oxygen-containing gas into the interior of the growth chamber 104. After venting the interior of the growth chamber 104 by the exhaust mechanism, a mixture of oxygen (with an oxygen concentration of 10% or more by volume) and an inert gas such as argon or nitrogen is introduced by the gas inlet mechanism, thereby setting the interior of the growth chamber 104 to have an oxygen concentration of 10% or more by volume.

[0087] Furthermore, this crystal growth apparatus includes a moving mechanism (not shown) that moves the cooling mechanism 102 and the high-frequency induction heating coil 103 relative to the raw material body 151 from one end of the raw material body 151 to the other end. First, the cooling mechanism 102 and the high-frequency induction heating coil 103 are positioned at one end (upper surface) of the raw material body 151. By activating the cooling mechanism 102 and the heating mechanism, the second process S102 can be performed. Then, in this state, the moving mechanism is activated to move (lower) the cooling mechanism 102 and the high-frequency induction heating coil 103 to the other end (downward), thereby enabling the third process S103.

[0088] Additionally, it may include a moving mechanism (not shown) that moves the holding rod 162 in a direction that moves the seed crystal 161 away from the raw material body 151. Furthermore, it may also include a rotating mechanism (not shown) that rotates the seed crystal 161 and the raw material body 151 in different directions about an axis that is aligned with the direction of movement based on the moving mechanism.

[0089] Using this crystal growth apparatus, firstly, as Figure 2A As shown, the raw material body 151 is fixed on the holding stage 101. Raw material powder, for example, a mixture of Y₂O₃, Al₂O₃, and CeO₂ powders in a molar ratio of 3:5:0.015 and sintered, is filled into a water-cooled furnace bed with an inner diameter of 150 mm inside the cooling mechanism 102, thereby forming a raw material body 151 with a diameter of 150 mm. Furthermore, metallic aluminum is disposed in the raw material body 151. The water-cooled furnace bed is fixed on the holding stage 101.

[0090] Furthermore, a seed crystal 161, composed of a single crystal of yttrium aluminum garnet (YAG), is held by a holding rod 162 while it is separated from one end of the raw material body 151. Additionally, a moving mechanism (not shown) is used to position a cooling mechanism 102 and a high-frequency induction heating coil 103 at one end (upper part) of the raw material body 151.

[0091] In the above state, the growth chamber 104 is set to a sealed state, and the cooling mechanism 102 and the high-frequency induction heating coil 103 are activated, such as... Figure 2B As shown, aluminum metal in one end of raw material body 151 is heated and melted using induction heating at a high frequency of 1MHz. Using the molten aluminum metal melted by this induction heating as a heat source, the raw material powder constituting raw material body 151 is melted, thereby obtaining a molten body (molten material) 152 with a diameter of 140mm. In this example, the resonant frequency of the molten body 152 is 1MHz.

[0092] Next, as Figure 2C As shown, while controlling the frequency of the high frequency applied to the high frequency induction heating coil 103 in the range of 0.8MHz to 1.2MHz, the holding rod 162 is lowered, so that the lower end of the seed crystal 161 comes into contact with the upper surface of the melt 152 formed in the center of one end side (upper surface) of the raw material body 151.

[0093] When alternating current flows in the molten body 152, which acts as a conductor, as the alternating frequency increases, the current concentrates on the surface of the molten body 152 (current density increases), and as it moves towards the center of the molten body 152, the current becomes difficult to flow (current density decreases) (skin effect). By adjusting the frequency applied to the high-frequency induction heating coil 103 relative to the resonant frequency of the molten body 152, the heating efficiency of the area penetrated by the skin effect is controlled, and the in-plane temperature gradient of the molten body 152 is optimized.

[0094] In the control of the applied frequency, since the resonant frequency changes with the temperature and melting area of ​​the melt 152, the resonant frequency of the melt 152 is measured in real time, and the applied frequency is controlled so that the phase difference between the applied frequency and the measured resonant frequency becomes constant.

[0095] As described, by controlling a moving mechanism (not shown) to optimize the in-plane temperature gradient of the melt 152, the cooling mechanism 102 and the high-frequency induction heating coil 103 are moved (lowered) to the other end, thereby moving the part heated by induction heating from one end of the raw material body 151 to the other end, and moving the melt 152, which is the molten material in the center of the raw material body 151, from one end of the raw material body 151 to the other end. Thus, as... Figure 2D As shown, one end of the raw material body 151 in contact with the seed crystal 161 is in an unheated state, and the temperature decreases.

[0096] As the temperature decreases, the raw material crystal 153 grows from the point of contact with the seed crystal 161, proceeding from one end of the raw material body 151 towards the other. As a result, a yellow, transparent Y3Al5O3 with Ce additive and a diameter of 100 mm is obtained. 12 Crystal 153.

[0097] In addition, such as Figure 2E As shown, as the fourth step, while cooling the area around the raw material body 151 using the cooling mechanism 102, the seed crystal 161 is pulled up along the direction of pulling away from the melt 152, while rotating. Alternatively, along with the cooling mechanism 102 and the high-frequency induction heating coil 103, the melt 152 is pulled down towards the ground along the direction of pulling away from the seed crystal 161, while rotating. Through this movement, the crystal 153 of the raw material can grow from one end of the raw material body 151 to the other end, starting from the part in contact with the seed crystal 161.

[0098] As explained above, from the point where the seed crystal 161 contacts and begins to be pulled, until the crystal 153 has grown to the set length of the straight portion, the crystal 153 is cut off and slowly cooled, and then heating is stopped. After sufficient cooling, the crystal 153 is removed.

[0099] [Implementation Method 2]

[0100] Next, refer to Figure 3The crystal growth method according to Embodiment 2 of the present invention will be described below. First, in the first step S201, the seed crystal is positioned so that one end of a raw material body made of solid raw material is in contact with the raw material body. The raw material body may be, for example, cylindrical. One end (lower surface) of the raw material body is designated as the ground side, and the raw material body is arranged such that the axis of the cylinder is perpendicular to the ground. The seed crystal is pre-embedded inside the raw material body attached to the other end (upper surface).

[0101] Next, in the second process S202, while cooling the area around the raw material, high-frequency induction heating is used to heat and melt the central portion of the raw material near the region where the seed crystal is embedded. Thus, the central portion of the raw material becomes a molten material, while the surrounding area and the other end of the raw material remain solid. Then, the molten portion is expanded to bring the molten material into contact with the seed crystal. In this state, the peripheral portion of the raw material, which remains solid after cooling, becomes a crucible for containing the molten material. Therefore, there is no problem of impurity contamination from the crucible. Furthermore, since a crucible made of costly materials is not required, manufacturing costs can be reduced.

[0102] Next, in the third step S203, while cooling the area around the raw material body, the portion heated by induction heating is moved from one end of the raw material body to the other, and the portion of the raw material melting in the center of the raw material body is moved from one end to the other. Here, the movement is performed from one end (lower surface side) located on the earth side of the raw material body to the other end (upper surface side). Through this movement, the crystals of the raw material grow from the point of contact with the seed crystal, moving from one end of the raw material body to the other. When the raw material is an oxide, the second step S202 and the third step S203 can be performed in an atmosphere with an oxygen concentration of 10% or more by volume.

[0103] Here, at least in the second step S202 and the third step S203 described above, in the heating of the central portion of the raw material body based on induction heating, the induction heating frequency is set to a range deviating from the resonant frequency of the melt. This results in a temperature gradient in the melt that decreases closer to the center of the raw material body (the temperature gradient of the melt) within a plane perpendicular to the direction from one end of the raw material body to the other. Thus, by changing the induction heating frequency within a range deviating from the resonant frequency of the melt to control the temperature gradient of the melt within a plane, the diameter of the raw material crystals can be controlled.

[0104] It should be noted that by changing the concentration of dopant impurities added to the raw material from one end to the other, as described above, the concentration of dopant impurities in the crystal during crystal growth can be made uniform throughout the entire region along the crystal growth direction.

[0105] As described above, starting from the point of contact with the seed crystal, the raw material crystal is grown from one end of the raw material body to a predetermined location on the other end. Heating is then stopped, and the molten material inside the raw material body is slowly cooled to solidify. As a result, a single crystal of the raw material grown from the seed crystal is formed inside the raw material body. Afterward, the raw material surrounding the raw material body is removed, thereby extracting the single crystal of the raw material.

[0106] According to the above embodiment, the periphery of the raw material body, which is cooled and maintained in a solid state, becomes the crucible for containing the melt. Therefore, there is no problem of impurity contamination from the crucible. In addition, since it is not necessary to use a crucible made of costly materials, manufacturing costs can be reduced. Furthermore, since the temperature is maintained at a lower level closer to the center of the raw material body in a plane perpendicular to the direction from one end of the raw material body to the other, the area of ​​the melt used for crystal growth can be further expanded.

[0107] Next, the control of crystal diameter in the crystal growth method and apparatus according to embodiments of the present invention will be described. In the third step, by changing the frequency of high-frequency induction heating within a range deviating from the resonant frequency of the melt, the temperature gradient of the melt can be controlled in-plane, thereby controlling the diameter of the raw material crystal.

[0108] For a more detailed explanation, such as Figure 4 As shown, the third process includes a weight measurement process S301, a diameter calculation process S302, and a magnetic field output control process S303.

[0109] The weight measurement step S301 measures the weight of the raw material crystal at a set period. The diameter calculation step S302 calculates the diameter of the raw material crystal grown during the period based on the weight assumed in the weight measurement step S301. The magnetic field output control step S303 controls the output and frequency of the magnetic field applied to the coil in a manner that eliminates the difference between the diameter calculated in the diameter calculation step S302 and the set reference value.

[0110] Furthermore, the crystal growth apparatus according to embodiments of the present invention can be equipped with a crystal diameter control mechanism for implementing the above-described crystal diameter control method. For example... Figure 5 As shown, the crystal diameter control mechanism includes a weight measuring unit 301, a diameter calculation unit 302, and a magnetic field output control unit 303.

[0111] The weight measuring unit 301 measures the weight of the crystal, the raw material used for crystal growth using seed crystals, at a set cycle. The weight measuring unit 301 may be configured as, for example, a load sensor. The load sensor may be provided, for example, on the holding rod that holds the seed crystal.

[0112] The diameter calculation unit 302 calculates the diameter of the raw material crystal grown during the cycle based on the weight assumed by the weight measurement unit 301. The magnetic field output control unit 303 controls the frequency output from the high-frequency power supply 304 to the high-frequency induction heating coil for high-frequency induction heating in a manner that eliminates the difference between the diameter calculated by the diameter calculation unit 302 and a set reference value. Thus, by using the result of measuring the weight of the crystal being grown and controlling the frequency applied to the high-frequency induction heating coil, an automatic diameter control system for controlling the diameter of the crystal being grown can be constructed.

[0113] It should be noted that the diameter calculation unit 302 and magnetic field output control unit 303 of the crystal diameter control mechanism in the above embodiment can also be configured as computer devices equipped with a CPU (Central Processing Unit), main memory, external memory, and network connection device. The CPU executes actions (executes the program) through a program deployed in the main memory, thereby realizing the above-mentioned functions (the crystal diameter control method). The program described above is a program used to make the computer execute the crystal diameter control method shown in the above embodiment. The network connection device is connected to a network. Alternatively, the functions can be distributed across multiple computer devices.

[0114] In the method of the present invention, when the growing material is gallium oxide, sapphire, gadolinium aluminum gallium garnet, lithium tantalate, lithium niobate, yttrium oxide, or yttrium aluminum garnet, and the frequency of the magnetic field is controlled between 400 kHz and 5 MHz, and the width of the molten zone is controlled between 50 mm and 150 mm, it can be seen that it has good crystallinity.

[0115] It should be noted that the high-frequency heating device suitable for use in this invention will be described below using the accompanying drawings.

[0116] <High-frequency heating device 1>

[0117] refer to Figure 6 This invention will be used to illustrate the high-frequency heating device 1 according to an embodiment of the present invention. It should be noted that, in this invention, not only... Figure 6 The semiconductor heating device shown can also be used with a vacuum tube heating device. Figure 6 This is a structural diagram of the high-frequency heating device according to this embodiment. The high-frequency heating device 1 of this embodiment includes at least a phase difference detection unit 2, a frequency control unit 3, an inverter unit 4, and an LCR circuit 5.

[0118] (Phase difference detection unit 2)

[0119] The phase difference detection unit 2 is used to detect the phase difference between the high-frequency voltage generated in the frequency control unit 3 and the high-frequency current flowing through the LCR circuit 5. Here, phase difference refers to, for example, Figure 6 As shown, this is the phase difference between the voltage of the reference waveform applied to the gate of transistor 19 and the phase difference between the operating current. Furthermore, this phase difference also coincides with the phase difference between the operating voltage and the operating current of the output of transistor 19, which switches according to the reference waveform input to the gate of transistor 19. Therefore, the phase difference detection unit 2 detects either the phase difference between the voltage of the reference waveform applied to the gate of transistor 19 and the phase difference between the operating current, or the phase difference between the operating voltage and the operating current of transistor 19. Figure 6 As shown, the phase difference detection unit 2 includes at least a phase comparator 12, a low-pass filter 13, an A / D converter 14, and a portion of a computer 15.

[0120] [Phase Comparator 12]

[0121] Phase comparator 12 is used to detect the phase difference between two input signals. Specifically, phase comparator 12 converts the phase difference between the output current waveform of LCR circuit 5 and the reference waveform generated in arbitrary waveform generator 16 into a voltage, which is output as an error signal.

[0122] [Low-pass filter 13]

[0123] Low-pass filter 13 smooths the error signal (pulse) corresponding to the phase difference output by phase comparator 12, and outputs it as a DC voltage. For example, a DC voltage of 0V to 5V can be output through low-pass filter 13. It should be noted that this low-pass filter 13 is sometimes referred to as a loop filter.

[0124] [A / D Converter 14]

[0125] A / D converter 14 converts the DC voltage output by low-pass filter 13 into a digital signal.

[0126] [Computer Science 15]

[0127] Computer 15 detects the phase difference between the voltage phase of the reference waveform applied to the gate of transistor 19 (described later) and the phase difference between the voltage phase of the reference waveform and the operating current phase of transistor 19 (phase difference), and compares it with a set threshold. When the phase difference crosses the threshold (from a value exceeding the threshold to a value less than the threshold, or from a value less than the threshold to a value exceeding the threshold), the computer increases or decreases the driving frequency by a preset change range and updates the driving frequency. A control signal for generating the updated driving frequency is input to arbitrary waveform generator 16. Additionally, computer 15 compares the detected phase difference with the set threshold. When the phase difference crosses the threshold, the computer updates the driving frequency by a constant frequency variation and inputs a signal for generating the updated driving frequency to arbitrary waveform generator 16. The constant frequency variation range can be an amplitude predetermined based on actual manufacturing conditions. The phase difference threshold mentioned here is the threshold at which the driving frequency approaches the resonant frequency by a constant frequency variation range; this threshold has an upper threshold and a lower threshold. In feedback control, when the phase difference is greater than a set phase difference value, that set phase difference value is used as the upper threshold of the phase difference. Conversely, when the phase difference is less than the set phase difference value, the driving frequency is moved away from the resonant frequency by a constant frequency variation. The set phase difference value at this point is used as the lower threshold of the phase difference. The upper and lower thresholds are collectively referred to as the phase difference threshold. The frequency variation refers to the amount by which the driving frequency changes when deviating from the set phase difference threshold.

[0128] (Frequency Control Unit 3)

[0129] like Figure 6 As shown, the frequency control unit 3 includes at least an arbitrary waveform generator 16 and a portion of the computer 15. The frequency control unit 3 generates arbitrarily set waveforms (frequency pulses) using the computer 15 and the arbitrary waveform generator 16.

[0130] [Arbitrary Waveform Generator 16]

[0131] Arbitrary waveform generator 16 generates a reference waveform. Additionally, arbitrary waveform generator 16 generates a waveform with a drive frequency updated by a control signal input from computer 15 and outputs it to the gate of transistor 19. Simultaneously, it is also output as a reference signal to phase comparator 12. Arbitrary waveform generator 16 generates frequency pulses based on the phase difference detected by phase difference detection unit 2. Computer 15 uses the updated frequency pulses to control transistor 19, generating a high-frequency voltage with an updated drive frequency applied to LCR circuit 5.

[0132] (Inverter Section 4)

[0133] Inverter section 4 generates a high-frequency voltage. This high-frequency voltage drives the LCR circuit 5. Consequently, a high-frequency current flows from the LCR circuit 5 through the heating coil 51, heating the raw material. Figure 6 As shown, the inverter section 4 includes at least a thyristor regulator 17, a step-up transformer 18, and multiple transistors 19.

[0134] [Thyristor Regulator 17]

[0135] The thyristor regulator 17 controls the AC current output from the power supply.

[0136] [Step-up Transformer 18]

[0137] The step-up transformer 18 increases the voltage output from the power supply.

[0138] [Transistor 19]

[0139] Transistor 19 acts as a switching element. Transistor 19 applies a high-frequency voltage at the drive frequency to LCR circuit 5. Transistor 19 is preferably made of SiC. The transistor preferably has the structure of a metal-oxide-semiconductor field-effect transistor (MOSFET), a metal-semiconductor field-effect transistor (MESFET), or an insulated-gate bipolar transistor (IGBT).

[0140] Figure 7 (A) shows a schematic circuit diagram of the inverter section. Figure 7 (B) shows a schematic diagram of the high frequencies generated by transistors. (As shown) Figure 7 As shown in (A), multiple transistors 19 are connected in parallel in the inverter section 4. The inverter section 4 uses bridge diodes to rectify the three-phase current output from the thyristor regulator 17, stores the charge in a capacitor, and allows the current to flow as direct current from the capacitor to the multiple transistors 19 (AC / DC conversion). Thus, by applying a voltage (gate voltage) corresponding to the charge stored in each transistor 19, the transistor 19 functions as a switching element. Frequency control is performed by receiving a frequency control signal output from the computer 15, applying a high-frequency waveform generated by the arbitrary waveform generator 16 to the gate of the transistor 19, and controlling the gate voltage. By making the gate voltage exceed the threshold voltage Vth of the transistor 19, the transistor 19 is turned on (conducted). Figure 7In the inverter circuit shown in (A), transistors 19A and 19D are combined, and transistors 19B and 19C are combined to form a rectangular wave that turns on and off. Figure 7 As shown in (B), the output voltage V is controlled by adjusting the gate voltage of each transistor 19. out The frequency is controlled. Through the above frequency control, transistor 19 outputs a rectangular wave frequency (drive frequency) in the range of several hundred kHz to 10 MHz. The drive frequency output by transistor 19 is preferably, for example, 20 MHz or less. This allows materials with higher melting points to be melted. The drive frequency output by transistor 19 is more preferably 10 MHz or less, and even more preferably 6 MHz or less. In addition, the drive frequency output by transistor 19 is preferably 100 kHz or more, and more preferably 300 kHz or more. Although the duty cycle of the rectangular wave is adjusted, a rectangular wave with a duty cycle of 40% is generated here.

[0141] Transistor 19 preferably uses SiC. Using SiC allows for higher voltage withstand capability and reduced switching losses and series resistance losses, enabling higher output and more precise frequency control. Even with high-melting-point materials, temperature distribution can be precisely controlled. Furthermore, as mentioned above, due to the achievable wide frequency range, the frequency can be adjusted based on the size of the molten liquid, the temperature dependence of resistivity, and the resistivity difference between the solid and liquid.

[0142] (LCR circuit 5)

[0143] LCR circuit 5 is a circuit in which a coil, a capacitor, and a resistor are connected in series (LCR series circuit). LCR circuit 5 contains heating coil 51. Heating coil 51 corresponds to the coil in the LCR circuit. The LCR circuit 5 removes the higher harmonic components of the rectangular wave, forming a fundamental sinusoidal current.

[0144] The induced current generated in the LCR circuit 5 by the high-frequency current produced by the high-frequency heating device 1 flows in the heating coil 51, generating a magnetic field around the heating coil 51. Inside the heating coil 51, the raw material disposed inside a basket (not shown) contains a conductive material, and induction heating begins from this conductive material. In the raw material, eddy currents flow in directions that oppose changes in the magnetic field that vary according to the high-frequency current, generating Joule heating through the resistance of the raw material to heat it and achieve temperature control.

[0145] The combined impedance of the LCR series circuit is expressed by the following equation (2).

[0146]

[0147] (2) In the formula,

[0148] Combined impedance (Ω)

[0149] R: Impedance of the resistor (Ω)

[0150] jωL: Impedance of the coil (Ω)

[0151] 1 / ωC: Impedance of the capacitor (Ω)

[0152] (2) In the formula, ωL is also called the inductive reactance X L 1 / ωC is also called capacitive reactance X C Here, since the frequency f = ω / 2π, the inductive reactance X can be changed by varying the frequency f. L Harmony Anti-X C This changes. Consequently, the phase difference (phase angle) θ between the AC voltage and AC current changes. For example, when the inductive reactance X... L Greater than or less than capacitive reactance X C When the phase angle θ is given by equation (3), the phase angle θ is expressed by equation (3) below. Additionally, when the inductive reactance X... L Harmony Anti-X C When they are equal, the phase angle θ is 0.

[0153]

[0154] As described above, when the frequency of the transistor's output voltage is updated, the phase difference θ between the high-frequency voltage and the high-frequency current changes, and the high-frequency voltage and current applied to the heating coil 51 change. Therefore, the heating efficiency of the raw material changes, and the temperature distribution of the raw material changes.

[0155] When using the cold crucible method to directly heat the raw material through induction heating to grow crystals, the convection state of the molten material, or in other words, the temperature distribution of the molten material, is extremely important.

[0156] Here, when a magnetic field is applied to a conductive molten liquid, the magnetic field that cancels the applied magnetic field is generated in the molten liquid due to the eddy current generated in the molten liquid. Therefore, the penetration depth δ of the applied magnetic field follows equation (4) which uses the resistivity ρ of the molten liquid, the relative permeability μ of the molten liquid and the frequency f.

[0157] δ=5.03×(ρ / (μ×F)) 1 / 2 …(4)

[0158] As shown in equation (4), since the penetration depth δ of the magnetic field depends on the frequency f, it is important to consider the size of the basket and heating coil used to design the overall system, as well as the resonant frequency and driving band of the system, in order to change the penetration depth δ of the magnetic field to optimally control the temperature distribution of the molten liquid.

[0159] For example, when the frequency is low and the magnetic field penetrates deeply into the molten liquid, the temperature of the raw material molten liquid near the center of the molten liquid containing the seed crystal is above the melting point, preventing crystal growth. On the other hand, by increasing the frequency to reduce the penetration depth of the magnetic field, the temperature of the raw material molten liquid near the seed crystal is lower than the melting point, enabling crystal growth.

[0160] [Current Sensor 7]

[0161] The high-frequency heating device 1 in this embodiment may also include a current sensor 7. The current sensor 7 is used to measure the amplitude and frequency of the alternating current output by the transistor 19. In this embodiment, the current sensor 7 is preferably a Rogowski-type current sensor. Compared with the output current waveform measured by a wound-type current sensor, the output current waveform measured by the Rogowski-type current sensor has less noise. Therefore, by using the Rogowski-type current sensor 7, the phase difference can be measured and controlled with high accuracy.

[0162] The output current waveform of current sensor 7 is the waveform of the current flowing through LCR circuit 5; this is the current waveform after feedback. The output voltage V is a rectangular wave output from transistor 19. out And the sinusoidal output current flowing through the heating coil.

[0163] The output current waveform after feedback is input to phase comparator 12, which compares the output current waveform with the reference waveform and outputs their phase difference from phase comparator 12.

[0164] The high-frequency heating device 1 of this embodiment can control the driving frequency of the LCR circuit 5, thus reducing output fluctuations. Suppression of output fluctuations by the high-frequency heating device 1 is extremely effective for the crystal growth of high-melting-point compounds requiring precise temperature distribution control.

[0165] (basket)

[0166] The high-frequency heating device 1 of this embodiment includes a basket (not shown). The basket is a coolable container (cooling container) with a cylindrical space inside, and raw materials can be placed inside it. For example, a cooling path (not shown) for cooling water to flow through is provided inside the basket, and the basket is cooled by the cooling water flowing through this cooling path. The basket is made of a material with high thermal conductivity. Examples of materials for the basket include copper, silver, aluminum, and iron. Because the basket is made of a material with high thermal conductivity, the raw materials placed inside it are cooled using the basket.

[0167] The raw material is heated by heating coil 51, melting it. However, near the water-cooled basket, the molten material solidifies and sinters due to the lower temperature. This sintered body (crucible) holds the molten material. The temperature of the molten material is adjusted by controlling the frequency of the high-frequency voltage applied to the heating coil 51 located on the outside of the basket.

[0168] (pole)

[0169] The high-frequency heating apparatus 1 of this embodiment preferably includes a rod (not shown). Crystal growth occurs as the rod moves in the opposite direction to the molten liquid. One end of the rod is designed to be inserted into the inside of a basket from above. A seed crystal is provided at this end of the rod, positioned at the center of the heating coil 51 on the horizontal plane. The rod is movable relative to the basket from one end to the other.

[0170] Using the high-frequency heating device 1, the temperature of the molten liquid at the center of the basket is controlled near its melting point. Therefore, by pulling the seed crystal upwards with a rod, the molten liquid is cooled, and crystal growth occurs to produce a crystal. The pulling speed (moving speed) of the rod is, for example, 0.1 to 100 (mm / hour). Preferably, it is 1 to 50 (mm / hour). More preferably, it is 3 to 20 (mm / hour).

[0171] (raw material)

[0172] The raw materials are high-melting-point compounds, such as high-melting-point oxides, such as gallium oxide (β-Ga₂O₃) and gadolinium aluminum gallium garnet (Gd₃(Al,Ga)₅O₂). 12 Examples of high-melting-point oxides include lithium tantalate (LiTaO3), lithium niobate (LiNbO3), and yttrium oxide (Y2O3). In addition to the above, high-melting-point oxides can also include those containing various other elements.

[0173] As described above, since oxides have a high resistivity ρ, heating with oxides as the raw material requires the application of a high frequency f. However, the high-frequency heating device 1 can output a frequency f in the range of hundreds of kHz to 10 MHz, thus enabling the heating of oxide raw materials. Furthermore, since it can output a high frequency f, the diameter of the molten liquid inside the raw material can be increased, thereby increasing the diameter of the crystal.

[0174] Furthermore, since the high-frequency heating device 1 can adjust the frequency, it can set the temperature of the molten liquid near the seed crystal to a temperature near its melting point, thereby enabling crystal growth.

[0175] (Control device)

[0176] The high-frequency heating device 1 may also include a control device (not shown). The control device is used to control various actions of the high-frequency heating device 1. Examples of control devices include the lifting speed of the control lever and the cooling capacity of the basket.

[0177] (Rotating mechanism)

[0178] Furthermore, the high-frequency heating device 1 preferably also includes a rotating mechanism (not shown), which rotates at least one of the rod or the raw material about its central axis in the extension direction of the rod. According to the rotating mechanism, by rotating the rod relative to the raw material, the unevenness of the temperature distribution within the device and in the molten liquid can be mitigated.

[0179] (action)

[0180] Here, for reference Figure 6 , 8 9. The operation of frequency control of high-frequency heating device 1 is explained. Figure 8 This is a schematic diagram showing a portion of the circuit including the inverter section 4, the LCR circuit 5, and the heating coil 51. Figure 9 (A) is a conceptual diagram used to illustrate the phase difference between the output current waveform and the reference waveform. Figure 9 (B) is a waveform diagram showing an example of the output current waveform and the output voltage waveform.

[0181] like Figure 8 As shown, a high-frequency voltage V, the drive frequency output from transistor 19 of inverter section 4, is applied to LCR circuit 5. out1 (High-frequency rectangular wave). When a high-frequency rectangular wave is applied to the LCR circuit 5, the induced voltage V generated by the LCR circuit 5... out2 The high-frequency current I of a sine wave out2 The current flows through heating coil 51. This is because the higher harmonics of the high-frequency voltage rectangular wave are filtered by the LCR circuit 5, leaving only a sine wave with the frequency of the fundamental rectangular wave. out2 The current is input to the current sensor 7, and the output current waveform is output from the current sensor 7.

[0182] like Figure 9 As shown in (A), when the output current waveform I is... out1 When the high-frequency voltage waveform (reference waveform) generated by the arbitrary waveform generator 16 is input to the phase comparator 12, the phase comparator 12 outputs a voltage (output voltage waveform) corresponding to the phase difference θ between the output current waveform and the reference waveform. When this voltage corresponding to the phase difference is applied to the low-pass filter 13, converted into a digital signal by the A / D converter 14, and input to the computer 15, the computer 15 detects the phase difference between the high-frequency current (output current waveform) and the output voltage waveform. The output current waveform and output voltage waveform are, for example... Figure 9 As shown in (B).

[0183] Furthermore, the computer 15 compares the detected phase difference with a set threshold. When the phase difference crosses the threshold, the drive frequency is updated with a constant frequency variation. The signal used to generate the updated drive frequency is input to the arbitrary waveform generator 16. The arbitrary waveform generator 16 generates a rectangular wave of the updated frequency, controlling the gate voltage of the transistor 19 in the inverter section 4. The transistor 19 outputs a high-frequency voltage of the updated drive frequency and applies it to the LCR circuit 5.

[0184] As described above, feedback control is implemented. That is, in at least one of the melting process and the crystal growth process, the driving frequency of the high-frequency voltage applied to the LCR circuit 5 is controlled based on the phase difference between the high-frequency voltage and the high-frequency current, or the phase difference between the gate voltage of the transistor that determines the frequency of the high-frequency heating device and the high-frequency current. In this way, the temperature distribution of the raw material molten liquid is controlled.

[0185] In this way, the phase difference between the output current waveform and the output voltage waveform is controlled by feedback to control the frequency of the high-frequency magnetic field within a predetermined range, thereby enabling stable heating control.

[0186] Furthermore, by constructing a high-frequency heating device consisting of a phase difference detection unit, a frequency control unit, an inverter unit, and an LCR circuit, it is possible to detect the phase difference between high-frequency voltage and high-frequency current and control the frequency. The phase difference detection unit detects the phase difference between high-frequency voltage and high-frequency current, the frequency control unit compares the detected phase difference with a threshold and feeds it back to the heating frequency, the inverter unit generates the frequency-controlled high-frequency voltage, and the LCR circuit performs induction heating.

[0187] Furthermore, in the aforementioned high-frequency heating device, high frequency is generated by using a frequency control unit including a computer and controlling the gate voltage of the transistor in the inverter unit using software, thereby enabling stable feedback control at low cost.

[0188] As an example of a preferred embodiment of the present invention, in the crystal growth process of a crystal manufacturing method using gallium oxide as raw material, the driving frequency is controlled based on the phase difference between the high-frequency voltage applied to the LCR circuit and the high-frequency current flowing through the LCR circuit.

[0189] Figure 10 This represents the time variations of temperature, driving frequency, phase difference between high-frequency voltage and high-frequency current, high-frequency voltage applied to the LCR circuit, and high-frequency current flowing through the LCR circuit in the crystal growth process based on the aforementioned phase difference control driving frequency.

[0190] By controlling the driving frequency, the voltage applied to the LCR circuit and the current flowing through it can be controlled, thereby enabling a stable crystal growth process.

[0191] Next, the process of controlling the driving frequency based on the phase difference between the high-frequency voltage applied to the LCR circuit and the high-frequency current flowing through the LCR circuit in the raw material melting process of the crystal manufacturing method using gallium oxide as raw material will be explained.

[0192] Figure 11 This example demonstrates controlling the drive frequency when the lower limit threshold of the phase difference is set to 9.17 degrees. In this process, the lower limit threshold is set to appropriately suppress damage caused by current flowing through the transistor. At this time, the phase difference varies within the range of 9.15 to 9.33 degrees. When the phase difference is lower than the lower limit threshold of 9.17, the drive frequency is shifted to the higher frequency side by a frequency change of 30 Hz.

[0193] Although the high-frequency current flowing through the LCR circuit contains noise, it decreases from 15.3A to 14.1A, and the high-frequency voltage applied to the LCR circuit, although containing noise, increases from 349V to 350.5V. Since these changes in current and voltage are smaller than the changes in phase difference, the method of controlling the frequency by monitoring the phase difference can control the temperature distribution in more detail compared to current and voltage control.

[0194] Next, the process of controlling the driving frequency based on the phase difference between the high-frequency voltage applied to the LCR circuit and the high-frequency current flowing through the LCR circuit in the crystal growth process of the crystal manufacturing method using gallium oxide as raw material will be explained.

[0195] Figure 12 The lower threshold is set to 11.5 degrees, and the upper threshold is set to 11.75 degrees. When the phase difference is lower than the lower threshold, the driving frequency is increased; when the phase difference is higher than the upper threshold, the driving frequency is decreased, thus controlling the temperature to achieve the optimal level. The frequency variation at this point is 10 Hz.

[0196] Current and voltage contain a lot of noise, while phase difference undergoes relatively stable changes.

[0197] Figure 14 This is a graph showing the relationship between the coil's position and defect density. The coil's position represents the height difference from the top of the molten metal to the top of the coil; the higher the value, the lower the coil's position. The defect density is calculated from measurements of dislocation density based on the Htch Pit method.

[0198] exist Figure 14 In the case where the coil position is less than 5mm, it becomes 1×10. 4 cm -2 The above high values, when greater than 5mm, become 1×10. 4 cm -2 The lower the position, the lower the defect density tends to be.

[0199] It should be noted that the present invention is not limited to the embodiments described above. It is clear that within the technical concept of the present invention, various modifications and combinations can be implemented by those skilled in the art.

[0200] Industrial availability

[0201] The manufacturing apparatus and method of the present invention are useful for crystal growth and can be used to manufacture various crystals.

[0202] Description of Reference Numerals

[0203] 1. High-frequency heating device

[0204] 2. Phase difference detection unit

[0205] 3. Frequency Control Unit

[0206] 4. Inverter Section

[0207] 5 LCR circuit

[0208] 7 Current Sensor

[0209] 12 Phase comparators

[0210] 13 Low-pass filter

[0211] 14 A / D Converters

[0212] 15 Computers

[0213] 16 Arbitrary Waveform Generator

[0214] 17 Thyristor Regulator

[0215] 18 Step-up transformer

[0216] 19 transistors

[0217] 51 Heating coil

[0218] 101 Maintain the stage

[0219] 102 Cooling mechanism (cooling container: basket)

[0220] 103 High-frequency induction heating coil

[0221] 104 Growth Chamber

[0222] 105 Exhaust Pipe

[0223] 106 Gas inlet piping

[0224] 151 Raw Material

[0225] 152 Melt

[0226] 161 Seed Crystals

[0227] 162 retaining bar

Claims

1. A crystal manufacturing apparatus, the apparatus comprising at least a high-frequency induction heating coil for forming a molten band of a raw material solution using high-frequency induction heating, and manufacturing a crystal by crystal growth along the long side direction of the molten band, characterized in that, The upper end of the high-frequency induction heating coil is disposed at a depth of 5 mm or less from the surface of the raw material molten liquid, and the manufacturing apparatus has a position relationship maintaining unit that maintains the position relationship between the depth position and the upper end while performing the crystal growth.

2. The manufacturing apparatus according to claim 1, wherein, The positional relationship maintaining unit includes a movable unit of the high-frequency induction heating coil or a movable unit of the molten strip.

3. The manufacturing apparatus according to claim 1, wherein, The manufacturing apparatus is configured such that the width of the molten zone satisfies the following equation (1): δ=5.03×(ρ / (μ×F))1 / 2…(4) In the formula, D represents the width of the molten zone (cm), ρ represents the resistivity of the raw material solution (μΩcm), μ represents the relative permeability of the raw material solution, and F represents the frequency of the high-frequency induction heating coil (Hz).

4. The manufacturing apparatus according to claim 3, wherein, The manufacturing apparatus also includes a cooling container used in the cold crucible method, the width of the molten zone being the inner dimension of the cooling container, and the crystal growth is performed by a melt growth method, which uses a melt that is directly heated by the high frequency.

5. The manufacturing apparatus according to claim 1, wherein, The raw material solution contains Ga.

6. A method for manufacturing a crystal, wherein the method uses high-frequency induction heating based on a high-frequency induction heating coil to form a molten zone of a raw material solution, and manufactures a crystal by crystal growth in the molten zone along its long side, characterized in that, The upper end of the high-frequency induction heating coil is positioned at a depth of 5 mm or less from the surface of the raw material molten liquid, and the crystal growth is carried out while maintaining the positional relationship between the depth position and the upper end.

7. The manufacturing method according to claim 6, wherein, The crystal growth is carried out while the high-frequency induction heating coil or the molten zone is moved.

8. The manufacturing method according to claim 6, wherein, The manufacturing method performs the crystal growth in a manner that satisfies the following formula (1): δ=5.03×(ρ / (μ×F))1 / 2…(4) In equation (1), D represents the width of the molten band (cm), ρ represents the resistivity of the raw material solution (μΩcm), μ represents the relative permeability of the raw material solution, and F represents the frequency of the high-frequency induction heating coil (Hz).

9. The manufacturing method according to claim 6, wherein, The crystal is grown using a melt growth method that utilizes a melt that is directly heated at high frequency.

10. The manufacturing method according to claim 6, wherein, The raw material solution contains Ga.

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