Single crystal growth apparatus and single crystal growth method

Abstract

The temperature gradient of the target object can be maintained effectively. [Solution] A single crystal growth apparatus used in a single crystal growth method by induction heating, comprising: a high-frequency oscillator equipped with a vacuum tube; an induction heating coil that inductively heats a target object with a high-frequency current applied from the high-frequency oscillator; a measuring unit that measures a signal relating to the output of the high-frequency oscillator; a control unit that outputs a control signal relating to the adjustment of the inductance of a grid coil or anode coil in an inverter circuit of the high-frequency oscillator based on the signal relating to the output; and an adjustment unit that adjusts the inductance according to the control signal output from the control unit.

Description

[Technical Field]

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

[0002] Towards the construction of next-generation digital infrastructure, there is a need for energy conservation in power devices that perform power conversion, such as those used in home appliances, electric vehicles, industrial machinery, and renewable energy. While silicon-based power devices have traditionally been the mainstream, there is a demand for power semiconductor materials that have lower energy conversion losses compared to silicon. Research and development is being conducted on materials such as silicon carbide (SiC), gallium nitride (GaN), and gallium oxide. Among these, gallium oxide is attracting attention as a next-generation power semiconductor material because it has a high Barriga figure of merit, resulting in low resistance loss, and a large energy band gap, resulting in high breakdown voltage. Furthermore, gallium oxide, especially β-Ga2O3, melts at a lower temperature compared to silicon carbide and gallium nitride, making single crystal growth from the molten state possible, thus promising cost reduction. For these reasons, gallium oxide is also expected to be a fundamental technology from the perspective of single crystal growth technology for high-melting-point compounds.

[0003] For a long time, research and development have been conducted on the skull melt method, which involves growing single crystals by directly applying an electromagnetic field to a matrix material using an induction coil. For example, Patent Document 1 discloses a cold crucible for gallium oxide and a method for producing gallium oxide single crystals using the skull melt method. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-61396 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Maintaining an optimal temperature gradient in the liquid phase is crucial for producing high-quality crystals (e.g., crystals with few dislocations). However, our research has revealed that induction heating presents challenges in maintaining a stable heating state due to the influence of changes in the physical properties of the material being molten.

[0006] For example, since the induction heating coil that heats the object to be heated by induction heating (hereinafter sometimes referred to as the "object") is driven by an LCR resonant circuit, the impedance of the molten object is connected as an external load to the LCR circuit. In this case, a change in the impedance of the molten object results in a change in the impedance of the external load, and the drive current, drive voltage, and drive frequency flowing through the LCR circuit also fluctuate in conjunction. For this reason, it is difficult to maintain the temperature gradient in an optimal state. Note that the change in the impedance of the molten object is caused by changes in the physical properties of the object, such as the difference in resistivity between the solid and the molten state, the temperature dependence of resistivity, the change in the volume of the molten object and the Curie point (ferromagnetic to paramagnetic), etc.

[0007] If the fluctuations move away from the resonance point, the molten material (e.g., gallium oxide) will solidify and cannot maintain its molten state. On the other hand, if the fluctuations move closer to the resonance point, high-frequency noise may be generated, or overcurrent may flow through the drive circuit, potentially damaging the circuit. In the case of induction heating devices using vacuum tubes, the circuit configuration automatically adjusts, allowing it to track subtle fluctuations in physical properties. However, at the timing of large changes in physical properties, such as a change from solid to liquid, the output fluctuates significantly, making it difficult to track these changes. This problem is particularly pronounced in the skull melting method, which, unlike conventional methods that heat the crucible with induction heating, applies a magnetic field to the raw material itself for heating.

[0008] Therefore, the present invention has been made in view of the above points, and aims to provide a technology that can suitably maintain the temperature gradient of an object. [Means for solving the problem]

[0009] One aspect of the present invention is a single crystal growth apparatus used in a single crystal growth method by induction heating, comprising: a high-frequency oscillator equipped with a vacuum tube; an induction heating coil that inductively heats a target object with a high-frequency current applied from the high-frequency oscillator; a measuring unit that measures a signal relating to the output of the high-frequency oscillator; a control unit that outputs a control signal relating to the adjustment of the inductance of a grid coil or anode coil in an inverter circuit of the high-frequency oscillator based on the signal relating to the output; and an adjustment unit that adjusts the inductance according to the control signal output from the control unit.

[0010] Furthermore, in one embodiment of the present invention, the adjustment unit includes an adjustment mechanism that adjusts the inductance by expanding or contracting the grid coil or the anode coil.

[0011] Furthermore, in one embodiment of the present invention, the control unit receives a signal relating to the output, and outputs a control signal to the adjustment unit when the value of the signal relating to the output changes, and the adjustment unit expands or contracts the grid coil or the anode coil in accordance with the control signal while current is flowing through the grid coil and the anode coil.

[0012] Furthermore, in one embodiment of the present invention, the adjustment unit expands and contracts the grid coil.

[0013] Furthermore, in one embodiment of the present invention, the output value is the value of the grid current flowing from the grid of the vacuum tube.

[0014] Furthermore, in one embodiment of the present invention, the single crystal growth method is a skull melt method comprising a cooling basket arranged around the target object and an induction heating coil that directly heats and melts the target object.

[0015] Furthermore, in one embodiment of the present invention, the single crystal growth method involves growing a single crystal by relatively moving a molten material heated by the induction heating coil and the single crystal.

[0016] Furthermore, in one embodiment of the present invention, the single crystal growth apparatus further comprises a drive unit that changes the relative position between the target object and the induction heating coil, wherein the induction heating coil heats a part of the target object and gradually melts the target object.

[0017] Furthermore, one aspect of the present invention is a single crystal growth method by induction heating, comprising a single crystal growth apparatus comprising a high-frequency oscillator equipped with a vacuum tube, an induction heating coil that inductively heats a target object with a high-frequency current applied from the high-frequency oscillator, and an adjustment unit that adjusts the inductance of a grid coil or anode coil in an inverter circuit of the high-frequency oscillator, the method comprising a measurement step of measuring a signal relating to the output of the high-frequency oscillator, and an adjustment step of adjusting the inductance of the grid coil or anode coil in an inverter circuit of the high-frequency oscillator based on the signal relating to the output.

[0018] Furthermore, in the adjustment step according to one aspect of the present invention, an adjustment mechanism is driven to adjust the inductance by expanding or contracting the grid coil or the anode coil.

[0019] Furthermore, in the adjustment step according to one aspect of the present invention, when the value of the signal relating to the output fluctuates, the grid coil or the anode coil is expanded or contracted while current is flowing through the grid coil and the anode coil.

[0020] Furthermore, in the adjustment step according to one aspect of the present invention, the grid coil is expanded or contracted.

[0021] Furthermore, a single crystal growth method according to one aspect of the present invention further comprises a driving step of changing the relative position between the target object and the induction heating coil, wherein in the driving step, a part of the target object is heated by the induction heating coil, and the target object is gradually melted. [Effects of the Invention]

[0022] According to the present invention, the temperature gradient of the target object can be suitably maintained. [Brief explanation of the drawing]

[0023] [Figure 1] This is a cylinder representing an example of the configuration of a single crystal growth apparatus according to an embodiment. [Figure 2] This figure illustrates an example of the circuit configuration of a high-frequency oscillator and RLC circuit according to an embodiment. [Figure 3] This diagram shows an example of the current waveforms flowing through various parts of a high-frequency oscillator. [Figure 4] This is a diagram illustrating one example of a method for expanding and contracting a coil. [Figure 5] This diagram illustrates the relationship between the degree of coil expansion and contraction and the coil's parameters. [Figure 6] This is a flowchart illustrating an example of the inductance adjustment process for a single crystal growth apparatus according to the embodiment. [Figure 7] This is a diagram illustrating the first example of a single crystal growth method. [Figure 8] This is a block diagram showing an example of the configuration of a single crystal growth apparatus according to a second example of a single crystal growth method. [Figure 9] This is a diagram illustrating a second example of a single-cosmetic growth method. [Modes for carrying out the invention]

[0024] The single crystal growth apparatus and single crystal growth method according to this embodiment will be described in detail below with reference to the attached drawings, with reference to preferred embodiments. In the drawings, identical or similar parts are denoted by the same or similar reference numerals. Note that this embodiment is not limited to these embodiments and includes various modifications or improvements. In other words, the components described below include those that can be easily imagined by those skilled in the art, and those that are substantially the same, and the components described below can be combined as appropriate. Furthermore, this embodiment may include various omissions, substitutions, or modifications of components without departing from the spirit of the present invention. [Overview of Single Crystal Growth Equipment]

[0025] Figure 1 is a block diagram showing an example of the configuration of a single crystal growth apparatus 1 according to an embodiment. The outline of each functional part of the single crystal growth apparatus 1 will be described with reference to Figure 1. The single crystal growth apparatus 1 comprises a high-frequency oscillator 10, an RLC circuit 20, a measuring unit 30, a control unit 40, an adjustment unit 50, and a drive unit 60. The single crystal growth apparatus 1 is used in a single crystal growth method in which a target object O is melted by induction heating and a single crystal is grown from the melt.

[0026] The control unit 40, adjustment unit 50, and drive unit 60 are implemented, for example, using a computer and software equipped with a central processing unit (CPU) and memory. Alternatively, the control unit 40, adjustment unit 50, and drive unit 60 may be implemented using electronic circuits as needed. Furthermore, the control unit 40, adjustment unit 50, and drive unit 60 do not necessarily have to be included in a single device; the single crystal growth apparatus 1 may be composed of multiple devices.

[0027] Object O is, for example, a cylindrical shape formed from a raw material. The raw material for object O is a high-melting-point compound, for example, a high-melting-point oxide, such as gallium oxide (β-Ga2O3) or gadolinium aluminum gallium garnet (Gd3(Al,Ga)5O3). 12Examples include lithium tantalate (LiTaO3), lithium niobate (LiNbO3), and yttrium oxide (Y2O3). High melting point oxides may also include high melting point oxides containing various other elements besides those listed above.

[0028] Because oxides have high resistivity, heating oxide raw materials requires the application of high frequencies. The single crystal growth apparatus 1 can output frequencies on the order of several hundred kHz to 10 MHz, enabling heating of oxide raw materials. Furthermore, because it can output high frequencies, the diameter of the molten material inside the raw material can be increased, thereby increasing the diameter of the crystal. In addition, since the frequency of the high-frequency oscillator 10 can be adjusted, the temperature of the molten material near the seed crystal can be brought to a temperature close to its melting point, allowing crystal growth to proceed.

[0029] The high-frequency oscillator 10 is a vacuum tube type oscillator. The high-frequency oscillator 10 has an induction heating coil L coil It outputs a high-frequency current to the conductor. The vacuum tube-type high-frequency oscillator 10 is self-excited, with automatic adjustment to track frequency fluctuations, and is therefore capable of automatically responding to fine frequency variations. Furthermore, the high-frequency oscillator 10 addresses the problem of transistor-type oscillators, which are susceptible to damage from overcurrents generated by fluctuations approaching the resonant point.

[0030] The RLC circuit 20 is a circuit in which a coil, a capacitor, and a resistor are electrically connected. The RLC circuit 20 may be an RLC series circuit or an RLC parallel circuit. In the RLC circuit 20, the coil is an induction heating coil L. coil It is equipped with.

[0031] Induction heating coil L coil A magnetic field is generated around it by the high-frequency current applied from the high-frequency oscillator 10. Induction heating coil L coilSince the object O inside contains a conductive material, induction heating begins from this conductive material. Eddy currents flow through the object O in a direction that opposes the change in the magnetic field, which changes in response to the change in high-frequency current. Due to the electrical resistance of the object O, Joule heat is generated, and the object O is heated.

[0032] The properties of the object O differ when it is in a solid state compared to when it is molten (liquid). Therefore, the optimal frequency for induction heating the object O varies depending on the ratio of solid to liquid portions of the object O.

[0033] [Configuration of a high-frequency oscillator] Figure 2 is a diagram illustrating an example of the circuit configuration of the high-frequency oscillator 10 and RLC circuit 20 according to the embodiment. The high-frequency oscillator 10 includes a three-phase AC power supply 11, a rectifier circuit 12, a vacuum tube 13, an inverter circuit 14, and a smoothing capacitor C in And the cathode resistor R cathode And, cathode capacitor C cathode It is equipped with the following.

[0034] The three-phase AC power supply 11 is an AC power supply that outputs three-phase power. The three-phase AC power supply 11 outputs a voltage, for example, between 0[V] and 10[kV], with a magnitude that corresponds to the settings of the designer or user of the single crystal growth apparatus 1.

[0035] The rectifier circuit 12 is a circuit that rectifies the three-phase power output from the three-phase AC power supply 11. For example, the rectifier circuit 12 shown in Figure 2 employs a configuration in which, for each phase output from the three-phase AC power supply 11, diodes are provided on the low-potential and high-potential sides of the connection point between each phase of the three-phase AC power supply 11 and the rectifier circuit 12. Each diode in the rectifier circuit 12 is arranged so that the high-potential side becomes the cathode and the low-potential side becomes the anode.

[0036] The low-potential side of the rectifier circuit 12 is connected to the reference voltage. The reference voltage may be, for example, 0 [V], or a small voltage close to 0 [V], or any voltage set by the designer of the single crystal growth apparatus 1 or the like. Also, the low-potential side of the rectifier circuit 12 is connected to the first point P1. That is, the voltage value of the first point P1 is the same as the reference voltage. The high-potential side of the rectifier circuit 12 is connected to the second point P2.

[0037] Smoothing capacitor C in has one end connected to the high-potential side of the rectifier circuit 12 and the second point P2, and the other end connected to the low-potential side of the rectifier circuit 12 and the first point P1. That is, the smoothing capacitor C in is connected in parallel with the rectifier circuit 12. The smoothing capacitor C in smoothes the DC voltage rectified by the rectifier circuit 12 by charging and discharging, and makes the pulsating current smooth. In the following description, the voltage applied between the two points of the first point P1 and the second point P2 may be referred to as the input voltage V in .

[0038] The vacuum tube 13 is, for example, a directly heated cathode type triode. The plate of the vacuum tube 13 is connected to the plate coil L plete and the coupling capacitor C Coupling included in the inverter circuit 14. In the following description, the plate of the vacuum tube 13 may be referred to as the anode. The plate coil L plete has one end connected to the second point P2, and the other end connected to the plate of the vacuum tube 13 and the coupling capacitor C Coupling .

[0039] The grid of the vacuum tube 13 is connected to the grid coil L Grid and the first grid capacitor C Grid1 included in the inverter circuit 14.

[0040] One end of the cathode of the vacuum tube 13 is connected to the cathode resistor R cathode and the cathode capacitor C cathode , and the other end is connected to the reference voltage. The cathode resistor R cathode and cathode capacitor C cathode These are connected in parallel. Cathode resistor R cathode and cathode capacitor C cathode One end of the wire is connected to the cathode of vacuum tube 13, and the other end is connected to a reference voltage. In the following explanation, the current flowing from the cathode of vacuum tube 13 to the plate is called the plate current I. p It is sometimes referred to as such.

[0041] The inverter circuit 14 generates a high-frequency voltage. The high-frequency voltage generated by the inverter circuit 14 drives the RLC circuit 20. The RLC circuit 20, and consequently the induction heating coil L coil When a high-frequency current flows through it, the target object O is inductively heated.

[0042] The inverter circuit 14 includes a coupling capacitor C Coupling And, anode coil L Anode And, grid coil L Grid And the grid resistor R Grid And the first grid capacitor C Grid1 And the second grid capacitor C Grid2 It is equipped with the following.

[0043] Grid coil L Grid And the grid resistor R Grid And the first grid capacitor C Grid1 And the second grid capacitor C Grid2 This is electrically connected to the grid of vacuum tube 13. First grid capacitor C Grid1 One end of the wire is connected to the grid and grid coil L of the vacuum tube 13. Grid It is connected to one end, and the other end is connected to the reference voltage. Grid coil L Grid One end of the first grid capacitor C is connected to the grid of the vacuum tube 13. Grid1 It is connected to the second grid capacitor C, and the other end is connected to the second grid capacitor C. Grid2 and grid resistor R Grid It is connected to the second grid capacitor C. Grid2 One end is a grid coil L Grid and grid resistor R GridIt is connected to one end, and the other end is connected to a reference voltage. Grid resistor R Grid One end is a grid coil L Grid and the second grid capacitor C Grid2 It is connected to the first terminal, and the other end is connected to the reference voltage. That is, the second grid capacitor C Grid2 and grid resistor R Grid These are connected in parallel. Grid resistor R Grid The low-potential side is connected to the third point P3. That is, the voltage value at the third point P3 is the same as the reference voltage. The third point P3 is the point on the low-potential side of the point where the inverter circuit 14 and the RLC circuit 20 are electrically connected.

[0044] Coupling capacitor C Coupling And, anode coil L Anode It is electrically connected to the plate of vacuum tube 13. Coupling capacitor C Coupling One end is a plate coil L plete It is connected to the plate of vacuum tube 13, and the other end is the anode coil L. Anode It is connected to the anode coil L. Anode One end is a coupling capacitor C Coupling It is connected to the anode coil L, and the other end is connected to the fourth point P4. Anode This is the grid coil L Grid It is magnetically connected, but not electrically connected. Anode coil L Anode This is the grid coil L Grid It resonates (tunes) with the anode coil L. Anode This is the grid coil L Grid It has fewer turns than [another component]. Point 4 P4 is the point on the high-potential side of the points where the inverter circuit 14 and the RLC circuit 20 are electrically connected. In the following explanation, the current flowing through point 4 P4 will be referred to as the output current I out It is sometimes referred to as the plate voltage E. p It is sometimes referred to as such.

[0045] Anode coil L Anode and grid coil L GridBy causing resonance, the induction heating coil L reacts to the frequency fluctuations of the target object O. coil Even if the frequency fluctuates slightly, the induction heating coil L will follow that fluctuation. coil The output frequency can be adjusted.

[0046] [RLC circuit configuration] The RLC circuit 20 shown in Figure 2 consists of RLC parallel resistors R RLC And, RLC parallel capacitor C RLC And, induction heating coil L coil This is a parallel RLC circuit equipped with the following: RLC parallel resistor R RLC RLC parallel capacitor C RLC , and induction heating coil L coil One end is connected to the fourth point P4, and the other end is connected to the third point P3 (reference voltage).

[0047] [Current waveform] Figure 3 shows an example of the current waveform flowing through various parts of the high-frequency oscillator 10. In Figure 3, the vertical axis represents the current value, and the horizontal axis represents time.

[0048] Figure 3(A) shows the plate current I p The current waveform is shown. The vacuum tube 13 has a rectifier circuit 12 and a smoothing capacitor C in Because the DC power converted to DC is connected, the plate current I p It is direct current.

[0049] Figure 3(B) shows the grid current I g The current waveform is shown. First grid capacitor C Grid1 and the second grid capacitor C Grid2 As it charges and discharges, the grid current I g This will become an exchange.

[0050] Figure 3(C) shows the output current I out The current waveform is shown. Plate coil L plete The DC current flowing through is through the coupling capacitor C Coupling Because it is cut off, the output current I outNo direct current component flows. From Fig. 3(C), it can be seen that the anode coil L Anode resonates with the grid coil L Grid and outputs an alternating current of the same frequency. Since the number of turns of the anode coil L Anode is less than that of the grid coil L Grid , the current value of the output current I Anode output from the anode coil L out is higher than the current value of the grid current I g . That is, the output current I out is amplified.

[0051] [Functional part of single crystal growth apparatus] The measurement unit 30 measures a signal related to the output of the high-frequency oscillator 10 from the high-frequency oscillator 10, the RLC circuit 20, or the induction heating coil L coil . The signal related to the output is a signal related to the output of the target object O, and is a signal that changes according to the change in the impedance of the target object O.

[0052] In Fig. 2, the measurement unit 30 is a current sensor that measures the grid current I g flowing from the grid of the vacuum tube 13 as a signal related to the output. The measurement unit 30 may measure the current flowing through an element or wire electrically connected to the grid of the vacuum tube 13 in the inverter circuit 14, for example, the current flowing through the grid coil L Grid .

[0053] Note that the measurement unit 30 according to the embodiment may measure a signal related to the output that changes according to the fluctuation of the output of the high-frequency oscillator 10. For example, the plate current I p or the output current I out etc. may be measured. Also, the measurement unit 30 according to the embodiment is not necessarily limited to a current sensor. For example, it may be a frequency sensor that measures the frequency of the induction heating coil L coil [[ID=�2]]etc.

[0054] The control unit 40 acquires an output signal from the measurement unit 30. In the following description, acquiring an output signal may be referred to as receiving an output signal. The control unit 40 may perform processing on the output signal, such as amplification or removal of high-frequency components, as necessary. By removing high-frequency components, i.e., high-frequency noise, using a low-pass filter or the like, the control unit 40 can appropriately grasp the fluctuations in the output signal. Based on the degree of fluctuation in the output signal, the control unit 40 controls the anode coil L Anode or grid coil L Grid A control signal is output to the adjustment unit 50, which adjusts the inductance. The control signal includes information regarding the adjustment of the inductance.

[0055] Specifically, the control unit 40 may calculate the fluctuation range per unit time for the output signal. The fluctuation range per unit time may be calculated using various analytical methods, such as a moving average. Hereinafter, the fluctuation range per unit time may simply be referred to as the fluctuation range. The control unit 40 determines whether or not to output a control signal to adjust the inductance by comparing the calculated fluctuation range with a threshold value set for the fluctuation range. If the calculated fluctuation range exceeds the threshold value, the control unit 40 outputs a control signal to the adjustment unit 50 to adjust the inductance. On the other hand, if the calculated fluctuation range does not exceed the threshold value, the control unit 40 does not output a control signal to the adjustment unit 50. The threshold value may be set in advance by the designer of the single crystal growth apparatus 1, for example.

[0056] The adjustment unit 50 includes an adjustment mechanism 51. The adjustment unit 50 receives a control signal from the control unit 40. The adjustment unit 50 drives the adjustment mechanism 51 according to the received control signal, thereby controlling the anode coil L Anode and grid coil L Grid The adjustment unit 50 adjusts the inductance of at least one of the anode coil L. Anode and grid coil L GridThe inductance may be adjusted by switching the tap position of at least one of the coils, or by expanding or contracting the coil. The adjustment unit 50 may also adjust the inductance by temporarily stopping the current flowing through the coil. By adjusting the inductance by expanding or contracting the coil, the adjustment unit 50 can adjust the inductance while current is flowing through the coil. Since it is not necessary to stop the current, induction heating can be continued without stopping, and the temperature gradient can be maintained and stabilized.

[0057] The control unit 40 acquires an output signal from the measurement unit 30, but this is not limited to that. For example, an external monitor (not shown) may be provided, and the operator may input an instruction to adjust the inductance based on the output signal, which the control unit 40 receives as an output signal. In this case, the output signal measured by the measurement unit 30 is displayed to the operator on the monitor, and the operator adjusts the anode coil L based on this signal. Anode and grid coil L Grid The amount of adjustment for at least one of the inductances is determined. Based on the input instruction and adjustment amount, the control unit 40 outputs a control signal to drive the adjustment mechanism 51. In this way, the inductance can also be adjusted based on the output signal. This allows for precise temperature gradient adjustment by the operator, and is particularly user-friendly as it enables crystal growth while adjusting conditions when experimentally manufacturing crystals with new materials and sizes.

[0058] Figure 4 illustrates an example of a method for expanding and contracting a coil. Figure 4 shows a cylindrical solenoid coil wound in a spiral shape as an example. In describing the movement of the coil, the direction of the magnetic field created by the coil may be referred to as the axial direction (x-direction or -x-direction), and the direction of the current flowing through the coil, perpendicular to the axial direction, may be referred to as the circumferential direction.

[0059] Figure 4(A) shows a first example of the expansion / contraction method. In the first example, the adjustment mechanism 51 adjusts the inductance by applying an external expansion / contraction force in the direction of the long axis of the coil, thereby expanding or contracting the coil in the x direction.

[0060] Figure 4(B) shows a second example of the expansion / contraction method. In the second example, the adjustment mechanism 51 adjusts the inductance by expanding or contracting the coil by fixing one end of the coil and rotating the other end of the coil in the circumferential direction.

[0061] Figure 5 illustrates the relationship between the degree of coil expansion and contraction and the coil parameters. Figure 5(A) shows the coil contracting, and Figure 5(B) shows the coil expanding. Figure 5(C) shows a table illustrating the relationship between the degree of coil expansion and contraction and the coil parameters. The "gap" shown in Figure 5 refers to the gap between the coil windings.

[0062] Figure 5 shows that the shorter the coil height and the larger the gap, the smaller the inductance and impedance of the coil. Conversely, the longer the coil height and the smaller the gap, the larger the inductance and impedance of the coil. It can also be seen that the winding resistance of the coil remains constant regardless of the degree of expansion or contraction of the coil.

[0063] Figure 6 is a flowchart illustrating an example of the inductance adjustment process for the single crystal growth apparatus 1 according to this embodiment. The processing flow performed by the measurement unit 30, the control unit 40, and the adjustment unit 50 will be explained with reference to this figure.

[0064] The single crystal growth apparatus 1 has a grid current I as a value related to its output. gThe single crystal growth apparatus 1 measures the value (step S101). The single crystal growth apparatus 1 calculates the fluctuation range per unit time for the output value (step S102). The single crystal growth apparatus 1 compares the calculated fluctuation range with a threshold value to determine whether the fluctuation is within the range that can be automatically tracked by the vacuum tube high-frequency oscillator 10 (step S103). If the fluctuation range is less than the threshold value (step S103; less than the threshold value), the single crystal growth apparatus 1 determines that the fluctuation is within the range that can be automatically tracked and sets the grid current I g The changes in the grid coil L are continuously monitored. If the fluctuation range is greater than or equal to a threshold (step S103; greater than or equal to a threshold), the single crystal growth apparatus 1 determines that the fluctuation exceeds the range that can be automatically tracked, and the grid coil L Grid or anode coil L Anode The inductance is adjusted by extending or retracting the wire (step S104).

[0065] Furthermore, when the raw material is melted, it changes from solid to liquid, so the resistivity changes as it melts, and the grid current decreases. The inductance is adjusted by detecting the decrease in grid current and adjusting the grid length so that the grid current returns to its original value. Also, when seed crystals are attached and crystal growth is initiated after melting, the grid current will fluctuate up and down, and the inductance is similarly adjusted by the grid length. Control is not limited to the range of grid current fluctuations; it may also be possible to set a threshold value based on the absolute value and control the current accordingly.

[0066] Figure 7 is a diagram illustrating a first example of a single crystal growth method. Figure 7 shows the induction heating coil L in the skull melt method. coil An embodiment of a method for growing a single crystal by relatively moving a molten liquid, which has been molten by induction heating, with the single crystal is shown.

[0067] A cooling basket placed around the target object O has, for example, a cooling passage through which cooling water flows, and is cooled by the cooling water. The target object O is cooled by this cooling basket. The target object O is heated by an induction heating coil L coilBecause the object O is being inductively heated while being cooled by the cooling basket, the outside of the object does not melt, thus acting as a substitute for a crucible.

[0068] In conventional crystal growth methods using crucibles, induction heating primarily heats the crucible rather than the raw material itself. However, in the skull melt method, there is no crucible, and the raw material itself is directly induction heated. Therefore, it is highly susceptible to changes in physical properties when the raw material changes from solid to liquid. In particular, oxides require high frequency and high power for melting, making them highly susceptible to changes in physical properties. Accordingly, the present invention provides a remarkable effect in which, when growing oxides using the skull melt method, the temperature gradient is stabilized and high-quality crystals are obtained.

[0069] The drive unit 60 gradually pulls up, for example, a seed crystal immersed in the molten target object O, or a single crystal grown after seeding with a seed crystal. As the drive unit 60 pulls upward, surface tension acts between the seed crystal or single crystal and the melt, and the melt pulled upward by the surface tension becomes a single crystal. The drive unit 60 continues this pulling up process to grow the single crystal. The drive unit 60 only needs to move the seed crystal or single crystal and the melt relative to each other; for example, it may move the target object O downward. In the above description, some explanation of the single crystal growth process by the skull melt method has been omitted, but in the CZ (Czochralski) method, the single crystal is actually grown through processes such as seeding, necking, cone, straight body, and tail. Furthermore, the single crystal growth method described above can be used in single crystal growth methods such as the Kyropulos method and the VB (Vertical Bridgeman) method.

[0070] [Second example of a single crystal growth method] Next, a second example of the single crystal growth method will be explained with reference to Figures 8 and 9. In the first example of the single crystal growth method, the entire target object O is heated, and then the single crystal is grown by relatively moving the molten material and the single crystal. In contrast, in the second example of the single crystal growth method, a part of the target object O is heated, and the single crystal is grown by gradually changing the heated area.

[0071] Figure 8 is a block diagram showing an example of the configuration of a single crystal growth apparatus 1A according to a second example of a single crystal growth method. The single crystal growth apparatus 1A differs from the single crystal growth apparatus 1 in that it includes a drive unit 60A. The drive unit 60A controls the relative movement of the single crystal and the solution, while the drive unit 60A controls the induction heating coil L coil Move the object O relative to the object.

[0072] Figure 9 is a diagram illustrating a second example of the single-coating growth method. In Figure 9, the drive unit 60A is an induction heating coil L coil By heating a portion of the target object O and gradually changing the area being heated, the object is gradually melted and a single crystal is grown. The drive unit 60A controls the target object O and the induction heating coil L coil All that is needed is to change the relative position to the object; for example, the position of the target object O may be changed.

[0073] In addition, as described above, the high-frequency oscillator 10 includes an anode coil L Anode An example of a configuration is shown. However, this embodiment is not limited to this example, for example, an anode coil L Anode This does not need to be provided in the high-frequency oscillator 10. This prevents the impedance from becoming too large and allows the high-frequency oscillator 10 to output a high frequency.

[0074] [Summary of this embodiment] According to the embodiment described above, the single crystal growth apparatus 1 used in the single crystal growth method by induction heating comprises a high-frequency oscillator 10 equipped with a vacuum tube 13, and an induction heating coil L that induction heats the target object O with a high-frequency current applied from the high-frequency oscillator 10. coilThe measurement unit 30 measures the signal related to the output of the high-frequency oscillator 10, and based on the signal related to the output, the grid coil L in the inverter circuit 14 of the high-frequency oscillator 10 Grid or anode coil L Anode A control unit 40 outputs a control signal for adjusting the inductance of the grid coil L, and according to the control signal output from the control unit 40, Grid or anode coil L Anode The apparatus includes an adjustment unit 50 for adjusting the inductance of the coil. Maintaining a stable temperature gradient in an optimal state is important for producing high-quality crystals. According to the single crystal growth apparatus 1 of this embodiment, small frequency fluctuations are automatically tracked by the vacuum tube 13, and large fluctuations that cannot be handled by automatic tracking are addressed by adjusting the inductance of the coil with the adjustment unit 50 to adjust the frequency, thereby effectively reducing the output decrease due to changes in the physical properties of the target object O. Therefore, the single crystal growth apparatus 1 of this embodiment can suitably maintain the temperature gradient of the target object O.

[0075] Furthermore, according to the above-described embodiment, the adjustment unit 50 is the grid coil L Grid or anode coil L Anode The apparatus is equipped with an adjustment mechanism 51 that adjusts the inductance by expanding and contracting the coil. When adjusting the inductance of a coil, it is common to switch the tap position. However, when switching the tap position, it has been difficult to discretely switch the inductance of the coil. With the single crystal growth apparatus 1 that adjusts the inductance by expanding and contracting the coil, the inductance of the coil can be switched continuously, and frequency adjustment can be performed more precisely. Therefore, the single crystal growth apparatus 1 according to this embodiment can effectively reduce the output decrease due to changes in the physical properties of the target object O and can suitably maintain the temperature gradient of the target object O.

[0076] Furthermore, according to the above-described embodiment, the control unit 40 receives a signal related to the output from the measurement unit 30, and outputs a control signal to the adjustment unit 50 when the value of the signal related to the output changes, and the adjustment unit 50 adjusts the grid coil L according to the control signal. Grid and anode coil L Anode With current flowing through the grid coil L Grid or anode coil L Anode The coil is expanded or contracted. That is, the adjustment unit 50 expands or contracts the coil while the current is still flowing. Maintaining a precise temperature gradient is important for growing high-quality single crystals, but it becomes difficult to maintain the temperature gradient when the current is turned off. According to the single crystal growth apparatus 1 of this embodiment, the inductance can be adjusted while the current is still flowing, so the temperature gradient can be maintained effectively.

[0077] When the device is energized, adjusting the inductance by switching the tap position can cause sparks, potentially leading to mechanical failure. However, the single-crystal growth apparatus 1, which adjusts the inductance by expanding and contracting the coil, avoids sparks and thus prevents mechanical failure.

[0078] Furthermore, according to the above-described embodiment, the adjustment unit 50 is the grid coil L Grid Expand and contract. Anode coil L amplifies the current. Anode A very large current of over 100[A] flows through it. In contrast to this, the grid coil L Grid The current flowing through it is approximately 1[A]. Grid coil L Grid The single crystal growth apparatus 1, which expands and contracts the crystal, allows for safe adjustment of the inductance.

[0079] Furthermore, according to the embodiment described above, the value relating to the output is the grid current I flowing from the grid of the vacuum tube 13. g This is the value of the grid current I. g The induction heating coil L coil Because the behavior of output reduction due to the grid current I is reflected, gBy measuring the grid current I, it is possible to properly identify power degradation and easily take countermeasures. g is the plate current I p or induction heating coil L coil Because it can be easily measured by comparing it with the frequency, etc., grid current I g The measurement unit 30, which measures the grid current I, can easily reduce the output drop. g The output current I out Compared to that, the current value is small, so the current value can be easily measured.

[0080] Furthermore, according to the above-described embodiment, the single crystal growth method is a skull melt method, in which the induction heating coil L coil This method involves growing a single crystal by relatively moving a molten metal heated by induction heating with a single crystal. Relative movement refers to, for example, a pulling method in which the single crystal is pulled up from the molten metal. In the case of the pulling method, it becomes even more difficult to stabilize the temperature gradient due to the influence of the pulling speed, etc. In the pulling method, even a vacuum tube type high-frequency oscillator is greatly affected by fluctuations in output, but the single crystal growth apparatus 1 according to this embodiment can appropriately adjust the inductance.

[0081] Furthermore, according to the above-described embodiment, the target object O and the induction heating coil L coil The system further includes a drive unit 60A that changes the relative position with respect to the induction heating coil L coil This method involves heating a portion of the target object O and gradually melting it. When using the single crystal growth method described above, the target object O intermittently changes from solid to liquid. As a result, intermittent changes in the physical properties of the target object O occur, making it even more difficult to stabilize the temperature gradient in the single crystal growth method described above. However, the single crystal growth apparatus 1 according to the embodiment allows for appropriate adjustment of the inductance. Therefore, the single crystal growth apparatus 1 according to the embodiment allows for the favorable maintenance of the temperature gradient even in single crystal growth methods where maintaining the temperature gradient is difficult.

[0082] At least some of the functions of the control unit 40 can be implemented using a computer. As shown in the figure, the computer consists of a central processing unit, RAM, input / output ports, input / output devices, and a bus. The computer itself can be implemented using existing technology. The central processing unit executes instructions contained in programs read from RAM, etc. The central processing unit writes data to RAM, reads data from RAM, and performs arithmetic and logical operations according to each instruction. RAM stores data and programs. Each element in RAM has an address and can be accessed using that address. RAM is an abbreviation for "Random Access Memory". Input / output ports are ports for the central processing unit to exchange data with external input / output devices, etc. Input / output devices are input / output devices. Input / output devices exchange data with the central processing unit via input / output ports. The bus is a common communication path used inside the computer. For example, the central processing unit reads and writes data to RAM via the bus. Also, for example, the central processing unit accesses input / output ports via the bus. Furthermore, all or part of the functional units of the control unit 40 may be implemented using hardware such as an ASIC, PLD, or FPGA. Alternatively, all or part of the functional units may be implemented through a combination of software and hardware.

[0083] Furthermore, the functions of all or part of the components of the control unit 40 in the above-described embodiment may be realized by recording a program for realizing these functions on a computer-readable recording medium, having a computer system read the program recorded on this recording medium, and executing it. The term "computer system" here includes hardware such as an operating system and peripheral devices.

[0084] Furthermore, "computer-readable recording media" refers to portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, as well as recording units such as hard disks built into computer systems. In addition, "computer-readable recording media" may include those that dynamically hold programs for a short period of time, such as communication lines used when transmitting programs over networks such as the Internet or communication lines such as telephone lines, and those that hold programs for a certain period of time, such as volatile memory inside computer systems that act as servers or clients in such cases. Moreover, the above-mentioned program may be for the purpose of realizing some of the functions described above, and may also be able to realize the above-mentioned functions in combination with programs already recorded in the computer system.

[0085] Although one embodiment of this invention has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes can be made without departing from the spirit of this invention. Furthermore, the configurations described in each embodiment and example above may be combined. [Explanation of Symbols]

[0086] 1...Single crystal growth apparatus, 10...High-frequency oscillator, 11...Three-phase AC power supply, 12...Rectifier circuit, 13...Vacuum tube, 14...Inverter circuit, 20...RLC circuit, 30...Measurement unit, 40...Control unit, 50...Adjustment unit, 51...Adjustment mechanism, 60...Drive unit, C in ...smoothing capacitor, V in ...input voltage, L plete ...plate coil, I p ...plate current, I g ...Grid current, I out ...Output current, E p ...plate voltage, C cathode ...cathode capacitor, R cathode ...cathode resistor, C Coupling ...coupling capacitor, L Anode ...anode coil, C Grid1 ...First grid capacitor, C Grid2...Second grid capacitor, L Grid ...Grid coil, R Grid ...Grid resistor, R RLC …RLC parallel resistance, C RLC ...RLC parallel capacitor, L coil ...Induction heating coil, O...Target object

Claims

1. A single crystal growth apparatus used in a single crystal growth method by induction heating, A high-frequency oscillator equipped with a vacuum tube, An induction heating coil that inductively heats an object by a high-frequency current applied from the aforementioned high-frequency oscillator, A measuring unit for measuring the signal related to the output of the aforementioned high-frequency oscillator, A control unit that outputs a control signal for adjusting the inductance of the grid coil or anode coil in the inverter circuit of the high-frequency oscillator based on the signal relating to the output, An adjustment unit that adjusts the inductance according to the control signal output from the control unit, A single crystal growth apparatus equipped with the following features.

2. The adjustment unit includes an adjustment mechanism that adjusts the inductance by expanding or contracting the grid coil or the anode coil. The single crystal growth apparatus according to claim 1.

3. The control unit receives a signal relating to the output, and outputs the control signal to the adjustment unit when the value of the signal relating to the output changes. The adjustment unit expands or contracts the grid coil or the anode coil while current is flowing through the grid coil and the anode coil, in accordance with the control signal. The single crystal growth apparatus according to claim 2.

4. The adjustment unit expands and contracts the grid coil. The single crystal growth apparatus according to claim 2.

5. The output value mentioned above is the value of the grid current flowing from the grid of the vacuum tube. A single crystal growth apparatus according to any one of claims 1 to 4.

6. The aforementioned single crystal growth method is a skull melt method consisting of a cooling basket placed around the target object and an induction heating coil that directly heats and melts the target object. A single crystal growth apparatus according to any one of claims 1 to 4.

7. The single crystal is grown by causing relative movement between the molten metal, which has been induced and heated by the aforementioned induction heating coil, and the single crystal. The single crystal growth apparatus according to claim 6.

8. A drive unit that changes the relative position between the target object and the induction heating coil, Furthermore, The induction heating coil heats a portion of the target object and gradually melts the target object. A single crystal growth apparatus according to any one of claims 1 to 4.

9. A method for growing single crystals by induction heating, A single crystal growth apparatus comprising a high-frequency oscillator equipped with a vacuum tube, an induction heating coil that inductively heats a target object with a high-frequency current applied from the high-frequency oscillator, and an adjustment unit that adjusts the inductance of the grid coil or anode coil in the inverter circuit of the high-frequency oscillator, comprises a measurement step of measuring a signal related to the output of the high-frequency oscillator, An adjustment step of adjusting the inductance of the grid coil or the anode coil in the inverter circuit of the high-frequency oscillator based on the signal relating to the output, A single crystal growth method having the following characteristics.

10. In the adjustment step, an adjustment mechanism is driven to adjust the inductance by expanding or contracting the grid coil or the anode coil. The single crystal growth method according to claim 9.

11. In the adjustment step, when the value of the signal relating to the output fluctuates, the grid coil or the anode coil is expanded or contracted while current is flowing through the grid coil and the anode coil. The single crystal growth method according to claim 10.

12. In the adjustment step, the grid coil is expanded or contracted. The single crystal growth method according to claim 10.

13. The output value mentioned above is the value of the grid current flowing from the grid of the vacuum tube. A method for growing a single crystal according to any one of claims 9 to 12.

14. The aforementioned single crystal growth method is a skull melt method consisting of a cooling basket placed around the target object and an induction heating coil that directly heats and melts the target object. A method for growing a single crystal according to any one of claims 9 to 12.

15. The single crystal is grown by causing relative movement between the molten metal, which has been induced and heated by the aforementioned induction heating coil, and the single crystal. The single crystal growth method according to claim 14.

16. A driving step that changes the relative position between the target object and the induction heating coil, Furthermore, In the aforementioned driving step, the induction heating coil heats a portion of the target object, causing the target object to gradually melt. A method for growing a single crystal according to any one of claims 9 to 12.

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