Crystal production method, high-frequency heating device, and crystal production device

Abstract

The high-frequency heating device is provided with at least a phase difference detection unit, a frequency control unit, an inverter unit, and an LCR circuit, the phase difference detection unit detects the phase difference between a high-frequency voltage generated by the frequency control unit and a high-frequency current flowing through the LCR circuit, and the inverter unit controls the current of the LCR circuit by updating the drive frequency of the high-frequency voltage on the basis of the phase difference.

Description

Technical Field

[0001] The present invention relates to a crystal manufacturing method, a high-frequency heating device, and a crystal manufacturing device. This application claims priority based on Japanese Patent Application No. 2022-169953 filed in Japan on October 24, 2022, and the contents thereof are incorporated herein by reference. Background Art

[0002] In order to build the next generation of digital infrastructure, it is required to save energy in power devices that perform power conversion, such as home appliances, electric vehicles, industrial machinery, and renewable energy. In the past, power devices using silicon became the mainstream, but power semiconductor materials with less energy conversion loss than silicon are sought. As such materials, research and development of silicon carbide (SiC), gallium nitride (GaN), gallium oxide, etc. have been carried out. Among them, gallium oxide has a high Baliga figure of merit, so it has less resistance loss, and a large energy band gap, so it has high voltage resistance, so it has attracted attention as the next generation of power semiconductor materials. In addition, gallium oxide, especially β-Ga 2 O 3 Since it melts at a lower temperature than silicon carbide and gallium nitride, single crystal growth can be performed from the melt, so cost reduction is expected. Therefore, from the perspective of single crystal growth technology of high melting point compounds, gallium oxide is also expected to be a basic technology.

[0003] Currently, as a single crystal growth technique for gallium oxide, the Edge-Defined Film-fed Growth (EFG) method is known, and is disclosed in Patent Document 1 and Non-Patent Document 1. By using the EFG method, stable crystals can be obtained.

[0004] In order to solve the above problems, the research and development of the Skullmelting method has been conducted since ancient times. The Skullmelting method grows single crystals by directly applying an electromagnetic field to a base material on which a crystal is grown using an induction coil. Patent documents 2 and 3 disclose a cold crucible suitable for the Skullmelting method and an example of manufacturing a single crystal using the Skullmelting method. Patent document 4 discloses a gallium oxide cold crucible and a method for manufacturing a gallium oxide single crystal using the Skullmelting method using the Skullmelting method. Patent document 5 discloses the structure of an apparatus for manufacturing a single crystal using the Skullmelting method.

[0005] Prior art literature

[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 Laid-Open 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 literature 1: Hideo Aida et al., Growth of β-Ga 2 O 3 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] Technical problem to be solved by the invention

[0015] However, the techniques described in Patent Document 1 and Non-Patent Document 1 still have the following problems: in order to increase the size of the crystal, the crucible needs to be enlarged, and the crucible material that can be used at the melting point of gallium oxide is expensive material such as iridium, so it is difficult to reduce costs.

[0016] In addition, Patent Documents 2 to 5 do not disclose specific production conditions for a single crystal.

[0017] In addition, although research and development of crystal growth based on the cold crucible method is being carried out, industrial mass production and commercialization have not yet been achieved.

[0018] Therefore, the inventors of the present invention have conducted a review of a method and apparatus for producing a gallium oxide crystal by a cold crucible method using a cold crucible, and have extracted production issues.

[0019] The melting point of gallium oxide is about 1800°C. In order to determine the conditions required for induction coil heating, various experiments were repeated and theoretical studies were conducted. As a result, it was confirmed that in order to directly heat the raw material by induction heating, the frequency of the magnetic field f (Hz), the resistivity ρ (Ω·m) of the raw material as the heated body, and the volume D (m 3 ) satisfies the relationship expressed by the following formula (1).

[0020] f≥3×106 (ρ / D 2 )…(1)

[0021] Furthermore, since the resistivity ρ of oxides is large, a high-frequency magnetic field f needs to be applied during the heating of the oxide raw materials. 2 O 3 For the molten liquid, when its resistivity ρ is as large as 1.0×10 -3 About, and set D to 0.1m 3 In this case, a frequency f of several hundred kHz or higher is required.

[0022] Therefore, the inventors of the present invention succeeded in melting gallium oxide by applying a high-frequency magnetic field of about 400 kHz. However, they faced the problem that the high-frequency voltage and high-frequency current after the gallium oxide melted greatly fluctuated, making it difficult to maintain a stable heating state.

[0023] The change of high frequency voltage and high frequency current is caused by the change of impedance of raw materials due to heating and melting of raw materials. The change of impedance of raw materials is considered to be affected by the resistivity difference between solid and molten gallium oxide, the temperature dependence of resistivity, the molten liquid and the volume change of the molten liquid.

[0024] The induction heating coil is driven by an LCR resonant circuit, and the impedance of the molten liquid is connected as an external load of the LCR circuit. Therefore, a sharp change in the impedance of the molten liquid becomes a sharp change in the impedance of the external load, and the drive current, drive voltage, and drive frequency flowing through the LCR circuit also change in conjunction. At this time, if the change is far from the resonance point, the molten gallium oxide solidifies and cannot maintain the molten state. On the other hand, if the change is close to the resonance point, there is a possibility of high-frequency noise, overcurrent flowing through the drive circuit, transistor damage, and the situation that stable heating control cannot be achieved.

[0025] As another phenomenon, electromagnetic noise increases. Regarding electromagnetic noise, various causes are considered, but since a high frequency of 400kHz is used, it is believed that it is caused by the noise generated when the transistor is switched. Therefore, it can be inferred that this phenomenon is common in the melting process of high-melting-point oxides using high frequencies.

[0026] As described above, in the heating control of the melting step for melting the raw materials for crystal growth and the heating control of the crystal growth step, there is a problem that stable heating control cannot be performed due to large fluctuations in current and voltage if only conventional current control and voltage control are used.

[0027] An object of the present invention is to stabilize the unstable heating control during melting and crystal growth of a high melting point raw material using induction heating, which is the above-mentioned problem.

[0028] Therefore, in order to achieve not only output control (current control or voltage control) but also more precise control, the inventors of the present invention have repeatedly studied and found that by detecting the phase difference between voltage and current (the phase delay of current relative to the phase delay of voltage) and using the threshold to feed back to the frequency of the high-frequency magnetic field for control, a stable heating process can be achieved.

[0029] In addition, it was found that by forming a high-frequency heating device consisting of a phase difference detection unit, a frequency control unit, an inverter unit and an LCR circuit, the phase difference between the high-frequency voltage and the high-frequency current can be detected and the frequency can be controlled. The phase difference detection unit detects the phase difference between the high-frequency voltage and the high-frequency current, the frequency control unit compares the detected phase difference with a threshold and feeds back to the heating frequency, the inverter unit generates the frequency-controlled high-frequency voltage, and the LCR circuit performs induction heating.

[0030] Furthermore, it was found that in the high-frequency heating device, by using a frequency control unit including a computer and controlling the gate voltage of the transistor of the inverter unit by software to generate a high frequency, stable feedback control can be achieved at low cost.

[0031] Solutions to Solve Problems

[0032] The gist of the present invention is as follows.

[0033] [1] A crystal manufacturing method according to one embodiment of the present invention is a crystal manufacturing method using a high-frequency heating device, wherein the high-frequency heating device has an LCR circuit, wherein the LCR circuit contains a heating coil for heating a raw material, and the crystal manufacturing method is characterized in that it includes a melting step of the raw material for crystal growth and a crystal growth step, and in at least one of the melting step and the crystal growth step, the driving frequency of the induction heating is controlled to perform heating.

[0034] [2] In the crystal manufacturing method described in [1] above, the melting step may be a step in which a raw material arranged inside the heating coil is heated and dissolved by applying a high-frequency voltage and a high-frequency current generated by the high-frequency heating device to the heating coil included in the LCR circuit to generate a high-frequency magnetic field, and the crystal growth step is a step in which a seed crystal is brought into contact with a raw material melt obtained by dissolving the raw material to perform crystal growth, and at least one of the melting step and the crystal growth step controls the driving frequency of the high-frequency voltage applied to the LCR circuit based on a phase difference between the high-frequency voltage and the high-frequency current, or a phase difference between a gate voltage of a transistor for determining the frequency of the high-frequency heating device and the high-frequency current, thereby controlling the temperature distribution of the raw material melt.

[0035] [3] In the crystal production method described in [1] or [2] above, in the melting step, the raw material may be heated by the high-frequency magnetic field to dissolve the raw material.

[0036] [4] In the crystal manufacturing method described in any one of [1] to [3] above, the driving frequency may be a frequency shifted toward a higher frequency side or a lower frequency side than the resonant frequency of the LCR circuit.

[0037] [5] In the crystal manufacturing method described in any one of [1] to [3] above, the driving frequency used in the crystal growth step may be further away from the resonant frequency of the LCR circuit than the driving frequency used in the melting step.

[0038] [6] Another embodiment of the high-frequency heating device of the present invention is characterized in that it comprises at least a phase difference detection unit, a frequency control unit, an inverter unit and an LCR circuit, wherein the phase difference detection unit detects the phase difference between the high-frequency voltage generated by the frequency control unit and the high-frequency current flowing in the LCR circuit, and the phase difference between the high-frequency voltage applied to the LCR circuit and the high-frequency current flowing in the LCR circuit, and the inverter unit updates the driving frequency of the high-frequency voltage based on the phase difference to control the current of the LCR circuit.

[0039] [7] In the high-frequency heating device described in [6] above, the phase difference detection unit may include a phase frequency detector, an analog phase detector, or a digital phase detector for detecting the phase difference.

[0040] [8] In the high-frequency heating device described in [6] or [7] above, the inverter unit may also include a plurality of transistors in parallel that work as switching elements, and the frequency control unit may generate a reference waveform updated by the frequency control unit based on the phase difference detected by the phase difference detection unit, and control the transistor according to the voltage of the updated reference waveform to generate a high-frequency voltage and a high-frequency current with an updated driving frequency applied to the LCR circuit.

[0041] [9] The high-frequency voltage generated by the high-frequency heating device according to any one of [6] to [8] may have a driving frequency of 20 MHz or less.

[0042]

[10] The high-frequency heating device according to any one of [6] to [9] may include a Rogowski-type or winding-type current sensor, and the current sensor may detect the alternating current.

[0043]

[11] Another embodiment of the present invention is a crystal manufacturing device that uses a molten liquid of a raw material to perform crystal growth. The crystal manufacturing device is characterized in that the crystal manufacturing device has a high-frequency heating device and a coolable basket, the high-frequency heating device has an LCR circuit, and the LCR circuit contains a heating coil for heating the raw material. The coolable basket is used to hold the raw material. The crystal manufacturing device controls the frequency of the high-frequency voltage applied to the heating coil arranged on the outside of the basket, thereby adjusting the temperature of the molten liquid.

[0044]

[12] Alternatively, the crystal manufacturing device described in

[11] may include a rod having one end that can be inserted into the inner side of the basket from above, a seed crystal is held at the one end, and the rod is configured to be able to move relative to the basket from the one end side of the rod to the other end side.

[0045]

[13] The crystal manufacturing apparatus described in

[12] may include a rotating mechanism, wherein the rotating mechanism rotates at least one of the rod or the raw material using the central axis of the extending direction of the rod as the rotating axis.

[0046] Effects of the Invention

[0047] According to the present invention, the heating process can be stabilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a structural diagram of a high-frequency heating device according to one embodiment of the present invention.

[0049] Figure 2 (A) is a schematic circuit diagram of the inverter section. Figure 2 (B) is a schematic diagram of the high frequency generated by the transistor.

[0050] Figure 3 This is a diagram schematically showing a circuit in the above-mentioned embodiment, and the circuit includes a part of a circuit of an inverter unit and an LCR circuit including a heating coil.

[0051] Figure 4 (A) is a conceptual diagram for explaining the phase difference between the output current waveform and the reference waveform. Figure 4 (B) is a waveform diagram showing an example of an output current waveform and an output voltage waveform.

[0052] Figure 5 This is a graph showing time changes in driving frequency, phase difference, current, and voltage when frequency control based on phase difference in a crystal growth step is performed in a crystal production method according to one embodiment of the present invention.

[0053] Figure 6This is a graph of phase difference, driving frequency, current, and voltage when frequency control based on the phase difference in the melting step is performed in the crystal production method according to one embodiment of the present invention.

[0054] Figure 7 This is a graph of phase difference, driving frequency, current, and voltage when frequency control based on the phase difference in the crystal growth step is performed in the crystal production method according to one embodiment of the present invention. DETAILED DESCRIPTION

[0055] Hereinafter, a crystal production method, a high-frequency heating device, and a crystal production device according to embodiments of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments.

[0056] <High frequency heating device 1>

[0057] Reference Figure 1 , a high-frequency heating device 1 according to an embodiment of the present invention will be described. Figure 1 1 is a block diagram of a high-frequency heating device according to the present embodiment. A high-frequency heating device 1 according to the present embodiment includes at least a phase difference detection unit 2 , a frequency control unit 3 , an inverter unit 4 , and an LCR circuit 5 .

[0058] (Phase difference detection unit 2)

[0059] The phase difference detection unit 2 detects the phase difference between the high frequency voltage generated by the frequency control unit 3 and the high frequency current flowing through the LCR circuit 5. The phase difference here refers to the phase difference between the high frequency voltage generated by the frequency control unit 3 and the high frequency current flowing through the LCR circuit 5. Figure 1 As shown in FIG. 1 , the phase difference between the phase of the voltage of the reference waveform applied to the gate of the transistor 109 and the phase of the operating current is equal to the phase difference between the phase of the operating voltage of the transistor 109 outputted by the transistor 109 switched according to the reference waveform input to the gate of the transistor 109 and the phase of the operating current. Therefore, the phase difference detection unit 2 detects the phase difference between the phase of the voltage of the reference waveform applied to the gate of the transistor 109 and the phase of the operating current, or the phase difference between the phase of the operating voltage of the transistor 109 and the phase of the operating current. Figure 1 As shown, the phase difference detection unit 2 includes at least a phase comparator 102 , a low-pass filter 103 , and an A / D converter 104 , and also includes a part of a computer 105 .

[0060] [Phase comparator 102]

[0061] The phase comparator 102 detects the phase difference between the two input signals. Specifically, the phase comparator 102 converts the phase difference between the output current waveform of the LCR circuit 5 and the reference waveform generated by the arbitrary waveform generator 106 into a voltage and outputs it as an error signal. The phase comparator 102 can use a phase frequency detector, an analog phase detector, or a digital phase detector.

[0062] [Low pass filter 103]

[0063] The low pass filter 103 smoothes the error signal (pulse) corresponding to the phase difference outputted from the phase comparator 102 and outputs it as a DC voltage. For example, a DC voltage of 0 V to 5 V is outputted through the low pass filter 103. The low pass filter 103 is sometimes referred to as a loop filter.

[0064] [A / D converter 104]

[0065] The A / D converter 104 converts the DC voltage output from the low-pass filter 103 into a digital signal.

[0066] [Computer 105]

[0067] The computer 105 detects the difference between the phase of the voltage of the reference waveform applied to the gate of the transistor 109 described later and the phase of the working current, or the difference (phase difference) between the phase of the working voltage of the transistor 109 and the phase of the working current. When the voltage crosses the threshold (changes from a value exceeding the threshold to a value less than the threshold, or changes from a value less than the threshold to a value above the threshold) compared with the set threshold, the drive frequency is increased or decreased by a preset change amplitude, the drive frequency is updated, and a control signal for generating the updated drive frequency is input to the arbitrary waveform generator 106. In addition, the computer 105 compares the detected phase difference with the set threshold, and when the phase difference crosses the threshold, the drive frequency is updated by a certain constant frequency variation, and a signal for generating the updated drive frequency is input to the arbitrary waveform generator 106. The constant frequency variation can be an amplitude calculated in advance according to actual manufacturing conditions. The threshold of the phase difference mentioned here is a threshold when the drive frequency is close to the resonant frequency according to a certain constant frequency variation, and the threshold has two thresholds: an upper threshold and a lower threshold. In feedback control, when the phase difference is greater than the set phase difference value, the set phase difference value is used as the upper limit threshold of the phase difference. In addition, when the phase difference is smaller than the set phase difference value, the drive frequency is moved away from the resonant frequency by a certain constant frequency variation. The set phase difference value at this time is used as the lower limit threshold of the phase difference. The upper limit threshold and the lower limit threshold are collectively referred to as the threshold of the phase difference. In addition, the frequency variation refers to the amount by which the drive frequency changes when it deviates from the set phase difference threshold.

[0068] In the above description, a phase frequency detector is cited as the phase difference detection unit 2 , but the phase difference detection unit 2 may be an analog phase detector or a digital phase detector.

[0069] (Frequency Control Unit 3)

[0070] like Figure 1As shown, the frequency control unit 3 includes at least an arbitrary waveform generator 106 and a part of the computer 105. The frequency control unit 3 generates an arbitrarily set waveform (frequency pulse) using the computer 105 and the arbitrary waveform generator 106.

[0071] [Arbitrary Waveform Generator 106]

[0072] The arbitrary waveform generator 106 generates a reference waveform. In addition, the arbitrary waveform generator 106 generates a waveform of a driving frequency updated according to a control signal input from the computer 105, and outputs the waveform to the gate of the transistor 109. In addition, it is simultaneously output to the phase comparator 102 as a reference signal. The arbitrary waveform generator 106 generates a frequency pulse based on the phase difference detected by the phase difference detection unit 2. The computer 105 controls the transistor 109 with the updated frequency pulse, and generates a high-frequency voltage with an updated driving frequency applied to the LCR circuit 5.

[0073] (Inverter unit 4)

[0074] The inverter unit 4 generates a high frequency voltage. The high frequency voltage generated by the inverter unit 4 drives the LCR circuit 5. As a result, a high frequency current flows from the LCR circuit 5 to the heating coil 51 to heat the raw material. Figure 1 As shown, the inverter unit 4 includes at least a thyristor regulator 107 , a step-up transformer 108 , and a plurality of transistors 109 .

[0075] [Thyristor regulator 107]

[0076] The thyristor regulator 107 controls the AC current output from the power supply.

[0077] [Step-up transformer 108]

[0078] The step-up transformer 108 steps up the voltage output from the power source.

[0079] [Transistor 109]

[0080] The transistor 109 operates as a switching element. The transistor 109 applies a high-frequency voltage of a driving frequency to the LCR circuit 5. The transistor 109 is preferably made of SiC. The transistor preferably has a structure of a metal-oxide-semiconductor field-effect transistor (MOSFET), a metal-semiconductor field-effect transistor (MESFET), or an insulated gate bipolar transistor (IGBT).

[0081] Figure 2 (A) shows a schematic circuit diagram of an inverter section, Figure 2 (B) is a schematic diagram showing the high frequency generated by the transistor. Figure 2 As shown in (A), the inverter unit 4 is provided with a plurality of transistors 109 in parallel. The inverter unit 4 rectifies the three-phase current output from the thyristor regulator 107 using a bridge diode, accumulates the charge in the capacitor, and causes the current to flow from the capacitor to the plurality of transistors 109 as a direct current (AC / DC conversion). Thus, by applying a voltage (gate voltage) corresponding to the charge accumulated in each transistor 109, the transistor 109 functions as a switching element. Frequency control is performed by receiving a frequency control signal output from the computer 105 and applying a high-frequency waveform generated by the arbitrary waveform generator 106 to the gate of the transistor 109 to control the gate voltage. By making the gate voltage exceed the threshold voltage V of the transistor 109 th , so that the transistor 109 is turned on (conducting). Figure 2 In the inverter circuit shown in (A), transistor 109A and transistor 109D are combined, and transistor 109B and transistor 109C are combined to form a rectangular wave of on and off. Figure 2 As shown in (B), by controlling the gate voltage of each transistor 109, the output voltage V out frequency. Through the above-mentioned frequency control, transistor 109 outputs the frequency (driving frequency) of the rectangular wave in the range of several hundred kHz to 10MHz. The driving frequency output by transistor 109 is preferably below 20MHz. Thus, raw materials with higher melting points can be melted. The driving frequency output by transistor 109 is more preferably below 10MHz, and further preferably below 6MHz. In addition, the driving frequency output by transistor 109 is preferably above 100kHz, and more preferably above 300kHz. Although the duty cycle (Duty) of the rectangular wave can be adjusted, a rectangular wave with a duty cycle of 40% is generated here.

[0082] The transistor 109 is preferably a transistor using SiC. If SiC is used, it can be made high-voltage, can reduce switching loss and series resistance loss, so it can output higher and precisely control the frequency, and can precisely control the temperature distribution even for raw materials with high melting points. In addition, as described above, since a wide range of frequencies can be achieved, the frequency can also be adjusted according to the size of the melt, the temperature dependence of the resistivity, and the resistivity difference between solid and liquid.

[0083] (LCR circuit 5)

[0084] The LCR circuit 5 is a circuit (LCR series circuit) in which a coil, a capacitor, and a resistor are connected in series. The LCR circuit 5 includes a heating coil 51. The heating coil 51 corresponds to the coil in the LCR circuit. The LCR circuit 5 removes the higher harmonic components of the rectangular wave and forms a fundamental sinusoidal current.

[0085] The induced current generated in the LCR circuit 5 by the high-frequency current generated by the high-frequency heating device 1 flows in the heating coil 51, generating a magnetic field around the heating coil 51. The raw material placed inside the basket (not shown) inside the heating coil 51 contains a conductive material, and induction heating starts from the conductive material. In the raw material, eddy current flows in a direction that hinders the change of the magnetic field that changes according to the change of the high-frequency current, and Joule heat is generated by the resistance of the raw material to heat the raw material and perform temperature control.

[0086] The combined impedance of the LCR series circuit is expressed by the following equation (2).

[0087]

Number 1

[0088]

[0089] (2) In the formula,

[0090] Composite impedance(Ω)

[0091] R: Impedance of resistor (Ω)

[0092] jωL: Coil impedance (Ω)

[0093] 1 / ωC: Impedance of the capacitor (Ω).

[0094] (2) In the formula, ωL is also called inductive reactance X L , 1 / ωC ​​is also called capacitive reactance X C Here, since the frequency f = ω / 2π, by changing the frequency f, the inductive reactance X L and capacitive reactance X C As a result, the phase difference (phase angle) θ between the AC voltage and the AC current changes. For example, when the inductive reactance X L Greater or less than capacitive reactance X C When the phase angle θ is expressed by the following equation (3). L and capacitive reactance X C When they are equal to each other, the phase angle θ is 0.

[0095]

Number 2

[0096]

[0097] As described above, when the frequency of the transistor 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 high-frequency current applied to the heating coil 51 change. Therefore, the heating efficiency of the material changes, and the temperature distribution of the material changes.

[0098] When the raw material is directly heated by induction heating to grow crystals by the cold crucible method, the convection state of the raw material melt, in other words, the temperature distribution of the melt, is extremely important.

[0099] Here, when a magnetic field is applied to a conductive molten liquid, eddy currents are generated in the molten liquid, causing a magnetic field that cancels the applied magnetic field. Therefore, the penetration depth δ of the applied magnetic field follows equation (4) which uses the resistivity ρ of the molten liquid, the magnetic permeability μ of the molten liquid and the frequency f.

[0100] δ=5.03×(ρ / (μ×F)) 1 / 2 …(4)

[0101] As shown in formula (4), since the penetration depth δ of the magnetic field depends on the frequency f, in order to change the penetration depth δ of the magnetic field to optimally control the temperature distribution of the molten liquid, it is important to design the overall system taking into account the size of the basket and heating coil used, as well as design the resonant frequency and drive frequency band of the system.

[0102] For example, when the frequency is low and the magnetic field penetrates deeply into the melt, the temperature of the raw material melt near the center of the melt with the seed crystal is above the melting point, and crystal growth does not occur. On the other hand, by increasing the frequency to reduce the penetration depth of the magnetic field, the temperature of the raw material melt near the seed crystal is lower than the melting point, and crystal growth can occur.

[0103] [Current sensor 7]

[0104] The high-frequency heating device 1 of this embodiment may also include a current sensor 7. The current sensor 7 measures the amplitude and frequency of the alternating current output by the transistor 109. In this embodiment, the current sensor 7 is preferably a Rogowski-type current sensor. Compared with the output current waveform measured by the winding-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 with high accuracy and controlled.

[0105] The output current waveform of the current sensor 7 is the waveform of the current flowing through the LCR circuit 5, which is the current waveform after feedback. The output voltage V of the rectangular wave output from the transistor 109 is output out And a sinusoidal output current flows through the heating coil.

[0106] The output current waveform after feedback is input to the phase comparator 102 , the output current waveform is compared with the reference waveform, and the phase difference between them is output from the phase comparator 102 .

[0107] The high frequency heating device 1 of this embodiment can control the driving frequency of the LCR circuit 5, and thus can reduce output fluctuations. Suppression of output fluctuations by the high frequency heating device 1 is extremely effective for crystal growth of high melting point compounds requiring precise temperature distribution control.

[0108] (basket)

[0109] The high-frequency heating device 1 of this embodiment is equipped with a basket (not shown). The basket is a coolable container having a cylindrical space inside, and raw materials can be arranged inside. For example, a cooling path (not shown) for cooling water to flow is arranged inside the basket, and the cooling water flowing in the cooling path is used to cool the basket. The basket is made of a material with high thermal conductivity. Examples of the material of the basket include copper, silver, aluminum, and iron. Since the basket is made of a material with high thermal conductivity, the raw materials arranged inside the basket are cooled by the basket.

[0110] The raw material is heated by the heating coil 51, and the raw material is melted. However, near the water-cooled basket, the molten liquid formed by the molten raw material is solidified and sintered due to the low temperature. The sintered body (crucible) holds the molten liquid. The frequency of the high-frequency voltage applied to the heating coil 51 provided outside the basket is controlled to adjust the temperature of the molten liquid of the raw material.

[0111] (Rod)

[0112] The high-frequency heating device 1 of this embodiment preferably has a rod (not shown). The rod moves in the opposite direction relative to the molten liquid to grow crystals. The rod is arranged so that one end can be inserted into the inner side of the basket from above. A seed crystal is arranged at the end of the rod, and the seed crystal is arranged at the center of the heating coil 51 on the horizontal plane. The rod can move relative to the basket from one end side of the rod to the other end side.

[0113] The temperature of the molten liquid is controlled to be near the melting point at the center of the basket by the high-frequency heating device 1, so the molten liquid is cooled by lifting the seed crystal upward with a rod, and the crystal growth is performed to produce the crystal. The lifting 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).

[0114] (raw material)

[0115] The raw material is a high melting point compound, such as a high melting point oxide, gallium oxide (β-Ga 2 O 3 ), Gadolinium aluminum / gallium garnet (Gd 3 (Al, Ga)5 O 12 ), lithium tantalate (LiTaO 3 ), lithium niobate (LiNbO 3 ), yttrium oxide (Y 2 O 3 ) etc. The high melting point oxide may include high melting point oxides containing various elements in addition to the above.

[0116] As described above, since the resistivity ρ of the oxide is large, the heating of the raw material in the case of the oxide requires the application of a high frequency f, but the high-frequency heating device 1 can output a frequency f of several hundred kHz to 10 MHz, so the oxide raw material can be heated. In addition, since the high frequency f can be output, the diameter of the melt inside the raw material body can be increased, and the diameter of the crystal can be enlarged.

[0117] Furthermore, since the high-frequency heating device 1 can adjust the frequency, the temperature of the melt near the seed crystal can be set to a temperature near its melting point, thereby enabling crystal growth.

[0118] (Control device)

[0119] The high-frequency heating device 1 may also include a control device (not shown). The control device controls various operations of the high-frequency heating device 1. The control device controls, for example, the lifting speed of the rod, the cooling capacity of the basket, and the like.

[0120] (Rotation mechanism)

[0121] In addition, the high-frequency heating device 1 preferably also has a rotating mechanism (not shown), which rotates at least one of the rod or the raw material with the central axis of the extension direction of the rod as the rotation axis. According to the rotating mechanism, by rotating the rod relative to the raw material, the effect of alleviating the unevenness of the temperature distribution in the device and the temperature distribution in the molten liquid can be obtained.

[0122] (action)

[0123] Here, refer to Figure 1 , 3 4. The operation of frequency control of the high-frequency heating device 1 will be described. Figure 3 The schematic diagram shows a circuit including a part of the inverter unit 4 , the LCR circuit 5 , and the heating coil 51 . Figure 4 (A) is a conceptual diagram for explaining the phase difference between the output current waveform and the reference waveform. Figure 4 (B) is a waveform diagram showing an example of an output current waveform and an output voltage waveform.

[0124] like Figure 3As shown, a high-frequency voltage V of a driving frequency outputted from the transistor 109 of the inverter unit 4 is applied to the LCR circuit 5. out1 (High-frequency rectangular wave). When a high-frequency rectangular wave is applied to the LCR circuit 5, an induced voltage V generated by the LCR circuit 5 out2 , the high-frequency current I of the sinusoidal wave out2 Flows through the heating coil 51. This is because the high-order harmonics of the rectangular wave of the high-frequency voltage are filtered by the LCR circuit 5, leaving only the sine wave of the frequency of the rectangular wave as the fundamental wave. The sinusoidal high-frequency current I out2 The current is input to the current sensor 7, and the output current waveform is output from the current sensor 7.

[0125] like Figure 4 As shown in (A), when the output current waveform I out1 When the high-frequency voltage waveform (reference waveform) generated by the arbitrary waveform generator 106 is input to the phase comparator 102, a voltage (output voltage waveform) corresponding to the phase difference θ between the output current waveform and the reference waveform is output from the phase comparator 102. When the voltage corresponding to the phase difference is applied to the low-pass filter 103, converted into a digital signal by the A / D converter 104, and input to the computer 105, the phase difference between the high-frequency current (output current waveform) and the output voltage waveform is detected by the computer 105. The output current waveform and the output voltage waveform are, for example, Figure 4 As shown in (B).

[0126] Furthermore, the computer 105 compares the detected phase difference with a set threshold value, and when the phase difference crosses the threshold value, updates the drive frequency with a certain constant frequency variation, and inputs a signal for generating the updated drive frequency to the arbitrary waveform generator 106. The arbitrary waveform generator 106 generates a rectangular wave of the updated frequency, and controls the gate voltage of the transistor 109 of the inverter unit 4. The transistor 109 outputs a high-frequency voltage of the updated drive frequency and applies it to the LCR circuit 5.

[0127] As described above, feedback control is performed. That is, in at least one of the melting step and the crystal growth step, 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 melt is controlled.

[0128] In this way, by feedback-controlling the frequency of the high-frequency magnetic field so that the phase difference between the output current waveform and the output voltage waveform falls within a predetermined range, stable heating control can be performed.

[0129] In addition, by forming 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 the high-frequency voltage and the high-frequency current and control the frequency. The phase difference detection unit detects the phase difference between the high-frequency voltage and the high-frequency current, the frequency control unit compares the detected phase difference with a threshold and feeds back the detected phase difference to the heating frequency, the inverter unit generates the frequency-controlled high-frequency voltage, and the LCR circuit performs induction heating.

[0130] In the high-frequency heating device, a frequency control unit including a computer is used to control the gate voltage of the transistor of the inverter unit by software to generate a high frequency, thereby realizing stable feedback control at low cost.

[0131] <Crystal production equipment>

[0132] A crystal manufacturing device according to one embodiment of the present invention is a crystal manufacturing device for growing crystals using a molten liquid of a raw material, and comprises: a high-frequency heating device having an LCR circuit; and a coolable basket for holding the raw material, wherein the frequency of a high-frequency voltage applied to the LCR circuit of a heating coil provided outside the basket is controlled to adjust the temperature of the molten liquid. In the high-frequency heating device having an LCR circuit, for example, the high-frequency heating device 1 described above can be used.

[0133] <Crystal Production Method>

[0134] A crystal manufacturing method according to one embodiment of the present invention is a crystal manufacturing method using a high-frequency heating device, the high-frequency heating device having an LCR circuit, the LCR circuit having a heating coil for heating a raw material, and the crystal manufacturing method is characterized in that it includes a melting step and a crystal growth step of the raw material for crystal growth, and in at least one of the melting step and the crystal growth step, the driving frequency of the induction heating is controlled to perform heating. The melting step and the crystal growth step can be implemented, for example, by the operation of the high-frequency heating device 1 as described above. Therefore, the melting step is a step of dissolving the raw material arranged inside the above-mentioned heating coil by applying a high-frequency current generated by a high-frequency voltage generated by the high-frequency heating device to the above-mentioned LCR circuit, and the crystal growth step is a step of contacting a seed crystal with a raw material melt formed by dissolving the above-mentioned raw material to perform crystal growth. Furthermore, it is preferred that at least one of the melting step and the crystal growth step controls the driving frequency of the high-frequency voltage applied to the LCR circuit based on the phase difference between the high-frequency voltage and the high-frequency current to control the temperature distribution of the raw material melt.

[0135] In the crystal manufacturing method of this embodiment, the driving frequency is preferably a frequency shifted toward the high frequency side or the low frequency side relative to the resonant frequency of the LCR circuit. More preferably, the driving frequency is shifted toward the high frequency side. Thus, more stable heating control is achieved.

[0136] Furthermore, it is preferred that the driving frequency used in the crystal growth process is farther from the resonant frequency of the LCR circuit than the driving frequency used in the melting process. This is because in the melting process, a larger heat capacity is required to melt the raw material from a solid, but in the crystal growth process, it is necessary to control the heating more accurately. This is because when it is close to the resonant frequency, the thermal efficiency is high and a large heat capacity can be handled, and when it is far away from the resonance point, it is easy to perform more subtle control. Thus, further stable heating can be performed, and the temperature distribution of the solution can be made into a desired temperature distribution. As a result, more stable crystal growth is achieved.

[0137] Furthermore, it is preferred that the phase difference used in the crystal growth process is greater than the phase difference used in the melting process. Thus, in the melting process, sufficient output can be obtained to melt the raw material, and a stable temperature distribution can be achieved in the crystal growth process, thereby achieving more stable crystal growth.

[0138] Furthermore, in the feedback control, the frequency variation amount that changes when the phase difference threshold is deviated is preferably smaller in the crystal growth step than in the melting step, thereby achieving more stable crystal growth in the crystal growth step.

[0139] The present invention has been described above according to the embodiments of the present invention, but the present invention is not limited thereto. The above is merely illustrative, and any solution having substantially the same structure and having the same effect as the technical idea described in the claims of the present invention is included in the technical scope of the present invention.

[0140] Example

[0141] Next, the embodiments of the present invention are shown, but the conditions in the embodiments are examples of conditions used to confirm the feasibility and effect of the present invention, and the present invention is not limited to the conditions used in the following embodiments. As long as they do not deviate from the gist of the present invention and as long as the purpose of the present invention is achieved, the present invention can adopt various conditions.

[0142] <Example 1>

[0143] As Example 1, an example is described in which a driving frequency is controlled based on a phase difference between a high-frequency voltage applied to an LCR circuit and a high-frequency current flowing through the LCR circuit in a crystal growth step of a method for producing a crystal using gallium oxide as a raw material.

[0144] Figure 5 The temperature, driving frequency, phase difference between high frequency voltage and high frequency current, high frequency voltage applied to the LCR circuit, and time variation of high frequency current flowing in the LCR circuit in the crystal growth process based on the phase difference control driving frequency are shown.

[0145] By controlling the driving frequency to control the voltage applied to the LCR circuit and the current flowing, a stable crystal growth process can be achieved.

[0146] <Example 2>

[0147] As Example 2, a 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 step of a method for producing a crystal using gallium oxide as the raw material is described.

[0148] Figure 6 This is an example of 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 properly control the transistor in order to avoid damage caused by overcurrent flowing through the transistor. At this time, the phase difference varies within the range of 9.15 degrees to 9.33 degrees. When the phase difference is lower than the lower limit threshold of 9.17, the drive frequency is changed to the high frequency side by a frequency change amount of 30Hz.

[0149] The high-frequency current flowing through the LCR circuit contains noise, but it was reduced from 15.3A to 14.1A, and the high-frequency voltage applied to the LCR circuit, although it contains noise, was increased from 349V to 350.5V. Since the fluctuations of these currents and voltages are smaller than the changes in the phase difference, the method of monitoring the phase difference and controlling the frequency can control the temperature distribution in more detail than the current and voltage control.

[0150] <Example 3>

[0151] As Example 3, a 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 step of the method for producing a crystal using gallium oxide as a raw material is described.

[0152] Figure 7 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 drive frequency is increased, and when the phase difference is higher than the upper threshold, the drive frequency is decreased to control the temperature to the optimum. The frequency variation at this time is 10 Hz.

[0153] Current and voltage contain a lot of noise, but in contrast, the phase difference changes relatively steadily.

[0154] When comparing Example 2 and Example 3, the phase difference of the crystal growth process is larger than the phase difference of the raw material melting process. In addition, the frequency variation of the crystal growth process is smaller than the frequency variation of the melting process. This is because the latent heat and the volume of the molten liquid increase a lot in the raw material dissolving process, so it is necessary to increase the output, reduce the phase difference, and make the driving frequency close to the resonant frequency. In addition, for the process of melting the raw material, due to the large resistivity difference between the solid and the liquid and the large change in the volume of the molten liquid, the change in inductance is large, and the change in the resonant frequency is large, so the frequency variation is increased. In the crystal growth process, stable and high-precision temperature control is required. Therefore, by increasing the phase difference to make the driving frequency away from the resonant frequency, a stable output can be obtained. In addition, since the frequency variation is small, more detailed control can be performed.

[0155] Description of Reference Numerals

[0156] 1 High frequency heating device

[0157] 2 Phase difference detection unit

[0158] 3 Frequency control unit

[0159] 4 Inverter unit

[0160] 5 LCR circuit

[0161] 7 Current sensor

[0162] 51 Heating coil

[0163] 102 Phase Comparator

[0164] 103 Low-pass filter

[0165] 104A / D Converter

[0166] 105 Computer

[0167] 106 Arbitrary Waveform Generator

[0168] 107 Thyristor Regulator

[0169] 108 Step-up transformer

[0170] 109 Transistor

Claims

1. A method for producing a crystal, which is a method for producing a crystal using a high-frequency heating device, wherein the high-frequency heating device has an LCR circuit, and the LCR circuit includes a heating coil for heating a raw material, wherein the method for producing a crystal is characterized in that: It includes a step of melting the raw materials for crystal growth and a step of crystal growth. In at least one of the melting step and the crystal growth step, heating is performed by controlling a driving frequency of induction heating.

2. The method for producing a crystal according to claim 1, in, The melting step is a step of heating and melting the raw material disposed inside the heating coil by applying a high-frequency voltage and a high-frequency current generated by the high-frequency heating device to the heating coil included in the LCR circuit to generate a high-frequency magnetic field. The crystal growth step is a step of bringing a seed crystal into contact with a raw material melt obtained by dissolving the raw material to grow a crystal. In at least any one of the melting process and the crystal growth process, the driving frequency of the high-frequency voltage applied to the LCR circuit 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 used to determine the frequency of the high-frequency heating device and the high-frequency current, thereby controlling the temperature distribution of the raw material melt.

3. The method for producing a crystal according to claim 2, in, In the melting step, the raw material is heated by the high-frequency magnetic field to melt the raw material.

4. The method for producing a crystal according to any one of claims 1 to 3, in, The driving frequency is a frequency shifted toward a higher frequency side or a lower frequency side than the resonance frequency of the LCR circuit.

5. The method for producing a crystal according to any one of claims 1 to 3, in, The driving frequency used in the crystal growth step is farther from the resonance frequency of the LCR circuit than the driving frequency used in the melting step.

6. A high frequency heating device, It is characterized in that The device comprises at least a phase difference detection unit, a frequency control unit, an inverter unit and an LCR circuit. The phase difference detection unit detects a phase difference between the high-frequency voltage generated by the frequency control unit and the high-frequency current flowing in the LCR circuit, or a phase difference between the high-frequency voltage applied to the LCR circuit and the high-frequency current flowing in the LCR circuit. The inverter unit updates a driving frequency of a high-frequency voltage based on the phase difference to control a current of the LCR circuit.

7. The high frequency heating device according to claim 6, in, The phase difference detection unit includes a phase frequency detector, an analog phase detector, or a digital phase detector that detects the phase difference.

8. The high frequency heating device according to claim 6 or 7, in, The inverter unit includes a plurality of transistors connected in parallel and functioning as switching elements. The frequency control unit generates a reference waveform updated by the frequency control unit based on the phase difference detected by the phase difference detection unit, controls the transistor according to the voltage of the updated reference waveform, and generates a high-frequency voltage and a high-frequency current with an updated driving frequency applied to the LCR circuit.

9. The high frequency heating device according to claim 6 or 7, in, The driving frequency of the high-frequency voltage is 20 MHz or less.

10. The high frequency heating device according to claim 6 or 7, in, The high-frequency heating device includes a Rogowski-type or a winding-type current sensor, and the high-frequency current flowing through the LCR circuit is detected by the current sensor.

11. A crystal production device, using a molten liquid of a raw material to grow a crystal, in, The crystal manufacturing device includes a high-frequency heating device and a coolable basket, wherein the high-frequency heating device has an LCR circuit, wherein the LCR circuit includes a heating coil for heating the raw material, and the coolable basket is used to hold the raw material. The crystal production apparatus controls the frequency of a high-frequency voltage applied to the heating coil provided outside the basket to adjust the temperature of the melt.

12. The crystal production apparatus according to claim 11, in, The crystal production device includes a rod having one end that can be inserted into the inner side of the basket from above. A seed crystal is maintained at the one end, The rod is configured to be movable relative to the basket from the one end side to the other end side of the rod.

13. The crystal production apparatus according to claim 12, in, The crystal production apparatus includes a rotation mechanism that rotates at least one of the rod or the raw material with a central axis in the extending direction of the rod as a rotation axis.

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