Crystal growth method and crystal growth apparatus

Abstract

The crystal growth method of the present disclosure, in the crystal growth process using the pulling method, controls the induction coil to move downward relative to the crucible, so that after the crystal enters the isodiameter stage, the induction coil is moved with an acceleration, and the moving speed of the induction coil tends to continuously increase during the whole process of the induction coil moving. The crystal growth method of the present disclosure can compensate for the change in temperature gradient at the crystal growth interface caused by the temperature distribution inside the crucible, provide a continuous and stable temperature field environment for the crystal growth, and reduce the defects occurring during the crystal growth.

Description

[Technical field]

[0001] This application claims priority to patent applications No. 202111487322.X and No. 202123056897.4 filed in China on December 8, 2021, the contents of which are incorporated herein by reference.

[0002] The present invention relates to the technical field of crystal growth methods, and in particular to a crystal growth method and a crystal growth apparatus. [Background technology]

[0003] The pulling method is a traditional method for growing crystals from a melt, and is often used to grow crystalline materials with high melting points and low volatility. The pulling method mainly includes the following steps: a raw material melting step, which uses the eddy current effect of induction heating of a medium-frequency current coil to heat a metal crucible and melt the raw material in the crucible into a melt; a crystal guiding step, which inserts an oriented seed crystal into the melt to guide the crystal orientation of the melt; a shouldering step, which accelerates the crystallization speed and gradually increases the crystal diameter by controlling the heating power or melt temperature; an equalizing step, which controls the crystal growth speed so that the crystal blank (unprocessed crystal) becomes a uniform cylinder; and a finishing step, which reduces the crystal growth speed after the growth of the equalizing part is completed, until the blank separates from the melt, and then removes the crystal blank after cooling.

[0004] The crystal growth process using the pulling method requires relatively stable temperature field conditions (i.e., stable interface temperature, etc.) at the crystal growth interface. If the temperature field conditions are not stable, macroscopic defects such as inclusions, clouds, and bubbles may occur in the crystal.

[0005] In a process where a crystal is growing uniformly, the melt level in the crucible drops at a constant rate and the temperature above the melt level changes, i.e., in a crystallization process, as the melt level drops, the temperature of the growth interface in the crystallization process differs from the temperature of the growth interface at the start of crystallization.

[0006] Prior art has disclosed a solution in which a heating coil is moved according to the drop in the melt level. For example, Patent Document 1 describes a method in which a heating coil is moved downward relative to a crucible so that the center position of the heating coil coincides with the center of the melt in the crucible. And Patent Document 2 describes a method in which a heating coil is lowered at a uniform speed relative to the crucible at a speed that is 15% to 25% of the descending speed of the melt in the crucible. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japan Patent Publication No. 54-9174 [Patent Document 2] Japanese Patent Publication No. 56-54299 Summary of the Invention

[0008] Disclosure of the Invention Technical Problems to be Solved by the Invention However, the above-mentioned conventional technology only considers the effect of a change in the relative position between the heating coil and the melt surface on the temperature field at the growth interface, and does not consider the effect of the temperature distribution in the crucible on the temperature field at the growth interface, so the effect of reducing crystal defects is still not satisfactory.

[0009] The present disclosure has been made in light of the above technical problems, and aims to provide a crystal growth method, an apparatus, and a crystal that can solve the problem of macroscopic defects such as inclusions, clouds, and bubbles occurring inside a crystal due to changes in temperature field conditions during crystal growth using the pulling method in the prior art.

[0010] Means to solve the problem A crystal growth method according to one aspect of the present disclosure includes controlling an induction coil to move downward relative to a crucible during a crystal growth process using a pulling method, so that after the crystal enters an isodiameter stage, the induction coil is moved with an acceleration, and the moving speed of the induction coil tends to continuously increase during the entire process in which the induction coil moves.

[0011] According to a crystal growth method according to one aspect of the present disclosure, the moving speed of the induction coil tends to increase continuously, thereby compensating for the change in temperature gradient at the crystal growth interface caused by the temperature distribution in the crucible, thereby stabilizing the temperature field in the crystal growth process at a constant level and reducing defects occurring during the crystal growth process.

[0012] The crystal growing method of the present disclosure may further comprise the step of moving the induction coil downward with a variable acceleration relative to the crucible during the entire process of the induction coil moving.

[0013] In the crystal growing method of the present disclosure, the induction coil may move downward with respect to the crucible at a constant acceleration throughout the entire process of the induction coil moving.

[0014] The crystal growth method of the present disclosure may include dividing the distance or time that the induction coil moves relative to the crucible into a plurality of target sections in advance, each of which corresponds to a different speed, and the corresponding speed of the target section arranged in the rear is greater than the corresponding speed of the target section arranged in the front, and when the distance or time that the induction coil moves relative to the crucible reaches the target section, the induction coil is controlled to move at a constant speed corresponding to each of the target sections. In this case, the moving speed of the induction coil is gradually increased to meet the gradually increasing requirement for compensation of the temperature gradient as the liquid level decreases, so that the temperature field during the crystal growth process is continuously stabilized and defects occurring during the crystal growth process are reduced.

[0015] The crystal growth method of the present disclosure may divide in advance the distance or time that the induction coil moves relative to the crucible into a plurality of target intervals each corresponding to a different acceleration, and when the distance or time that the induction coil moves relative to the crucible reaches one of the target intervals, the induction coil is controlled to move at a constant acceleration corresponding to each of the target intervals.

[0016] In the crystal growth method of the present disclosure, the corresponding acceleration of the target section arranged at the rear may be greater than the corresponding acceleration of the target section arranged at the front, which can better accommodate the change in temperature gradient at different locations of the crucible (especially the bottom of the crucible), so as to continuously stabilize the temperature field during the crystal growth process, and reduce defects occurring during the crystal growth process. In the crystal growth method of the present disclosure, the speed at which the induction coil moves relative to the crucible may be 0.001 mm / h or more and 0.1 mm / h or less.

[0017] In the crystal growth method of the present disclosure, the position of the raw material melt surface of the crystal relative to the bottom of the crucible when the induction coil starts moving may be set as the initial liquid surface position, and the acceleration of the induction coil may be set based on the initial liquid surface position, so that the higher the initial liquid surface position, the greater the acceleration. Depending on the requirements for crystallization (e.g., the type of crystal, the length of the crystal), the initial position of the crystal growth relative to the bottom of the crucible may differ, and by setting different accelerations of the coil according to the initial position, the temperature gradients at different initial liquid surface positions in the crucible can be made more consistent, and defects in the crystal growth process can be reduced.

[0018] In the crystal growth method of the present disclosure, the acceleration of the induction coil may be set based on the distance between the top end of the induction coil and the melt surface of the crystal raw material when the induction coil starts moving, so that the acceleration decreases as the distance increases. Depending on the requirements for crystallization, the initial position of the coil (the distance between the coil and the melt surface of the crystal raw material) may be different, and by setting different accelerations of the coil according to the initial position of the coil, the temperature gradients at the initial positions of the coil can be more consistent and defects in the crystal growth process can be reduced. A crystal growth apparatus according to another aspect of the present disclosure includes a growth furnace having an internal growth furnace chamber, a crucible provided in the growth furnace chamber and capable of containing a crystal raw material, an induction coil provided in the growth furnace chamber and surrounding the outside of the crucible, and an induction coil driving mechanism connected to the induction coil and controlling the induction coil to move downward relative to the crucible during the crystal growth process, thereby moving the induction coil with an acceleration after the crystal enters the isodiameter stage, and causing the moving speed of the induction coil to tend to continuously increase during the entire process in which the induction coil moves. In the crystal growth apparatus of the present disclosure, the induction coil driving mechanism includes a holder, a micromotion table, and a motion mechanism, wherein the holder is provided below the induction coil and has one end connected to the induction coil and the other end connected to the micromotion table through a bottom of the growth furnace having an opening for passing the holder therethrough, the micromotion table is provided below the growth furnace and has one side connected to the holder and the other side connected to the motion mechanism, and the motion mechanism is provided below the micromotion table and can drive and move the micromotion table, and when the micromotion table moves, it can drive and move the holder and the induction coil connected to the holder.

[0019] In the crystal growth apparatus of the present disclosure, the motion mechanism and the micromotion table may be connected by a transmission mechanism.

[0020] The crystal growing apparatus of the present disclosure may further include a heat-retaining barrel disposed within the growth furnace chamber, with the crucible disposed therein and the induction coil surrounding the exterior thereof. A radiation detector according to another aspect of the present disclosure comprises a substrate, a scintillator provided on the substrate, and a photodetector that detects scintillator light emitted from the scintillator when irradiated with radiation, the scintillator being obtained by cutting and polishing a crystal produced by any of the crystal growth methods described above.

[0021] A method for manufacturing a scintillator for a radiation detector according to another aspect of the present disclosure includes a crystal blank obtaining step of obtaining a crystal blank by any of the crystal growth methods described above, a cutting step of selecting a portion of the crystal blank having a uniform diameter and cutting it to form one or more crystals of a desired shape, and a polishing step of polishing the one or more crystals obtained in the cutting step to obtain the scintillator for a radiation detector.

[0022] Effect of the Invention According to the present disclosure, it is possible to provide a crystal growth method, an apparatus, and a crystal that can solve a problem present in the prior art in which macroscopic defects such as inclusions, clouds, and bubbles occur inside a crystal due to changes in temperature field conditions during the crystal growth process using the pulling method. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram showing the structure of a crystal growth apparatus according to the present disclosure. [Diagram 2] FIG. 2 is a schematic diagram showing the movement of the induction coil of the crystal growing apparatus of the present disclosure. [Diagram 3] FIG. 3 is a schematic diagram showing the temperature distribution in the vertical direction inside the crucible. [Figure 4] FIG. 4 is a schematic diagram showing the crystal growth method of the present disclosure. [Diagram 5] FIG. 5 is a diagram for explaining the relationship between the moving speed of the induction coil and the temperature gradient at the crystal growth interface. [Figure 6]FIG. 6 is a diagram showing a change in speed of the induction coil according to the first embodiment. [Figure 7] FIG. 7 is a diagram showing the speed change of the induction coil according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing the speed change of the induction coil according to the third embodiment. [Figure 9] FIG. 9 is a graph showing a speed change graph of the induction coil according to the fourth embodiment. [Figure 10] FIG. 10 is a laser scanned photograph of the crystal blank. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] [Specific embodiment] The technical solutions in the present disclosure are described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, but not all of them. All other embodiments that a person skilled in the art can obtain from the embodiments of the present disclosure are included in the protection scope of the present disclosure.

[0025] The terms "first", "second", and the like in the specification and claims of this application are intended to distinguish between similar objects, and are not intended to describe a particular order or sequence. It should be understood that the terms so used are interchangeable under appropriate circumstances, so that the embodiments of this application may be performed in an order other than that shown or described herein, and the objects distinguished by "first" and "second" are generally of the same kind and are not limited in number, e.g., the first object may be one or more. Also, "and / or" in the specification and claims indicates at least one of the objects it refers to, and the sign " / " indicates an "or" relationship between the related objects before and after it.

[0026] [Crystal growth equipment] Before describing the crystal growth method according to the embodiment of the present disclosure, a crystal growth apparatus according to the present disclosure will first be described.

[0027] 1, the crystal growth apparatus of the present disclosure includes a growth furnace 41 having a growth furnace chamber 411 therein, a crucible 43 that is provided in the growth furnace chamber 411 and can accommodate a crystal raw material, an induction coil 44 that is provided in the growth furnace chamber 411 and surrounds the outside of the crucible 43, and an induction coil driving mechanism 45 that is connected to the induction coil 44 and drives the induction coil 44 to move relative to the crucible 43 during the crystal growth process. When a current is applied to the induction coil 44, a magnetic field indicated by a dotted line in FIG. 1 is generated, and the crucible 43 is heated by this magnetic field.

[0028] Moreover, the induction coil driving mechanism 45 may include a holder 451, a micro-motion table 452, and a motion mechanism 553. The holder 451 is provided below the induction coil 44, with one end connected to the induction coil 44 and the other end connected to the micro-motion table 452 through a bottom portion of the growth furnace 41, which has an opening for allowing the holder 451 to pass through.

[0029] The micro-motion table 452 is provided below the growth furnace 41, and one side is connected to the holder 451 and the other side is connected to the motion mechanism 453. The motion mechanism 453 can be provided below the micro-motion table 452 and can drive and move the micro-motion table 452. When the micro-motion table 452 moves, the holder 451 and the induction coil 44 connected to the holder 451 can be driven and moved.

[0030] 2 shows a state in which the driving mechanism 45 drives and moves the induction coil 44. At this time, as shown in FIG. 2, when the motion mechanism 453 moves, it drives the fine adjustment table 452 to move at the same time, and the induction coil 44 also moves accordingly, so that the induction coil 44 can be driven using the motion mechanism 453. As a result, the induction coil 44 can be moved at a very small moving speed or moving acceleration by the fine adjustment table 452 and the motion mechanism 453.

[0031] The moving speed of the fine adjustment table 452 may be set to 0.001 mm / h or more and 0.1 mm / h or less, thereby allowing the induction coil 44 to be controlled and moved within a speed range of 0.001 mm / h to 0.1 mm / h. Furthermore, the fine adjustment table 452 can withstand a certain weight in order to support the holder 451 and the induction coil 44. The method of moving the induction coil 44 will be described in detail later.

[0032] In addition, the motion mechanism 453 and the micro-motion table 452 may be connected by a transmission mechanism. In this case, the motion mechanism 453 may drive and move the micro-motion table 452 and the induction coil 44 via the transmission mechanism 454.

[0033] The crystal growing apparatus may further include a heat-insulating body 42 disposed in the growth furnace chamber 411, with a crucible 43 disposed therein and an induction coil 44 surrounding the outside of the body. At this time, the heat-insulating body 42 is fixed in the growth furnace chamber 411 and can play a role in insulation and heat retention. The crucible 43 is disposed in the heat-insulating body 42 and is a heating element of the crystal growing furnace 41 and also a container for receiving the crystal raw material. The induction coil 44 is located outside the heat-insulating body, is fixed and connected to a holder, and can move downward toward the crucible 43.

[0034] A fixing mechanism can be installed at a predetermined position of the heat-insulating body 42, and the crucible 43 is fixed in the heat-insulating body 42 by the fixing mechanism. At this time, the crucible 43 is placed at a fixed position in the heat-insulating body 42, and is stably held during the crystal growth process, and shaking that may affect the quality of the crystal growth is avoided. The crucible 43 is, for example, a metal crucible. At this time, the metal crucible can generate an eddy current effect in the magnetic field of the induction coil 44 to generate heat and realize the crystal growth.

[0035] [Temperature distribution inside the crucible] The inventors have investigated and studied the temperature distribution inside the crucible during crystal growth.

[0036] The inventors have found through extensive research that when the induction coil is stationary, the temperature distribution in the crucible during crystal growth exhibits a tendency as shown in FIG.

[0037] In FIG. 3, the vertical axis indicates different positions in the vertical direction inside the crucible, with 0 mm on the scale indicating the top of the crucible, and the negative direction of the vertical axis (opposite to the direction indicated by the arrow on the vertical axis) indicating the direction toward the bottom of the crucible. The horizontal axis indicates the temperature inside the crucible, and the arrow on the horizontal axis indicates the direction of temperature increase. As shown in FIG. 3, the temperature gradually increases from the top to the bottom of the crucible, and changes in an overall parabolic shape. That is, the temperature gradient dT (= △T / △h) in a certain height range (height difference range) △h (e.g., 10 mm) gradually becomes smaller. Specifically, the temperature gradient dT1 in the height change range Δh of the top of the crucible is larger than the temperature gradient dT2 in the height change range Δh of the middle of the crucible, and the temperature gradient dT2 in the height change range Δh of the middle of the crucible is larger than the temperature gradient dT3 in the height change range Δh of the bottom of the crucible, i.e., dT1>dT2>dT3. That is, not only does the temperature differ depending on the vertical position inside the crucible (the temperature at the bottom of the crucible is higher than that at the top and middle), but the temperature gradient also changes significantly, i.e., the temperature gradient gradually decreases from the top to the bottom of the crucible.

[0038] The inventors speculate that the main reasons why the temperature distribution inside the crucible in the crystal growth process becomes as shown in Fig. 3 are (i) the non-uniform distribution of the magnetic field lines of the induction coil as a heater, and (ii) the accumulation of heat inside the crucible. Regarding the above reason (i), the magnetic field lines of the induction coil are sparse at both ends and dense in the center, and the denser the magnetic field lines are, the stronger the eddy current induction generated in the metal in that part becomes, and the higher the temperature becomes. In a crystal growth process using a general pulling method, the entire crucible is located in the upper half of the induction coil as a heater, and the magnetic field lines of the induction coil are relatively dense in the central region and sparse along the upward direction, so that the temperature of the metal crucible changes at different positions relative to the induction coil. That is, a non-uniform temperature field distribution is formed in the metal crucible, and generally, the temperature of the middle and bottom of the crucible located in the part where the magnetic field lines are dense is high, and the temperature of the top of the crucible located in the part where the magnetic field lines are sparse is slightly lower. Regarding the above cause (ii), the heat in the crucible is stored in the vertical bottom of the crucible, so the temperature of the bottom of the crucible is higher than that of the top of the crucible, and the temperature difference of the bottom of the crucible is small. According to the temperature distribution curve in the crucible, as the melt level in the crucible gradually decreases, the temperature above the melt level gradually increases, and the temperature field conditions at the growth interface become different from the initial temperature field conditions. Furthermore, the effects of the above factors (i) and (ii) on the temperature field at the bottom of the crucible are particularly significant. As can be seen from FIG. 3, the temperature change becomes very small toward the bottom of the crucible, and the temperature gradient approaches zero.

[0039] 3, when the melt level just starts to drop after crystallization starts, the temperature gradient at the growth interface is smaller than the initial temperature gradient at the start of crystallization, but a large temperature gradient can be maintained, and as the melt level gradually drops, the difference between the temperature gradient at the growth interface and the initial temperature gradient gradually increases, and when the melt level drops to the middle or bottom of the crucible, the difference between the temperature gradient at the growth interface and the initial temperature gradient becomes significant. Therefore, as the melt level drops, the compensation amount for maintaining the initial temperature gradient gradually increases.

[0040] [Crystal growth method] The crystal growth method of the present disclosure will be described below with reference to Fig. 4. The crystal materials of the present disclosure include YAG, YVO4, LSO, LYSO, RGBS, BGO, GAGG, LiNbO3, LiTaO3, and the like.

[0041] The crystal growth process according to the present disclosure mainly includes the following steps.

[0042] Raw material blending process: According to the stoichiometric ratio, the weight of each raw material required to prepare a certain weight of crystal is calculated, and each raw material is weighed out at the calculated weight, mixed uniformly, and pressed into an ingot.

[0043] Furnace loading process: After the heating coil is adjusted to a predetermined position relative to the crucible (as shown in Figure 4(a)), the ingot is placed into the crucible, and the hearth of the crystal growth furnace is treated to create a vacuum. Once a vacuum is created, the hearth of the growth furnace is filled with protective gas to prevent the metal crucible from oxidizing at high temperature.

[0044] Raw material melting process: An intermediate frequency induction current is passed through the induction coil to inductively heat the crucible, which heats and melts the raw materials to form a molten material.

[0045] Crystallization process: A seed crystal is brought into contact with the melt, and a crystal is grown on the seed crystal by adjusting the current and position of the induction coil.

[0046] Removal step: The temperature in the crucible is gradually lowered to room temperature, and the crystal blank is removed from the growth furnace.

[0047] Among them, the crystallization process (i.e., the crystal growth process by the pulling method) may include the following steps:

[0048] Crystal guiding stage: The seed crystal is brought into contact with the melt, the temperature of the melt is adjusted to an appropriate temperature, and the seed crystal is pulled up to grow the crystal. At this time, the melt level in the crucible begins to drop, as shown in Figure 4(b). The downward arrow in Figure 4 indicates the drop in the melt level.

[0049] Shouldering stage: The temperature of the melt is further adjusted to increase the crystallization speed and gradually increase the crystal diameter. As shown in Figure 4(c), the melt level in the crucible further drops.

[0050] Isodiametric stage: After the crystal diameter reaches the set value, the shouldering stage ends and the crystal growth enters the isodiametric stage. The crystal growth speed is controlled to make the crystal blank into a uniform cylinder. In the isodiametric stage, the melt level drops significantly and the temperature gradient at the growth interface changes. In order to make the temperature gradient at the crystal growth interface consistent with the initial state, in this stage, the induction coil can be controlled to move downward relative to the crucible at a continuously increasing speed. The induction coil movement method and the definition of "continuously increasing speed" will be described later.

[0051] End Phase: When the length of the crystal in the isodiametric phase reaches a predetermined value, the isodiametric phase ends and the descent of the coil is stopped (as shown in Figure 4(d)). The temperature of the melt is adjusted again, and the rate of crystallization is reduced to gradually reduce the crystal diameter until the crystal leaves the melt.

[0052] The coil movement method in the above crystal growth method will now be described.

[0053] <Relationship between coil movement and temperature gradient> Next, the effect of the coil movement method on the temperature gradient at the melt surface will be described with reference to FIG. 5. FIG. 5(a) shows an example showing the relative positions of the induction coil, crucible, and melt surface target in the crystal growth process. FIG. 5(b) shows the temperature and temperature gradient near the melt surface in FIG. 5(a) in accordance with the temperature distribution curve in FIG. 3. As shown in FIG. 5(a), the induction coil 44 is the heat source for the crucible 43, and the magnetic field line distribution of the induction coil 44 is sparser above the liquid surface A than below the liquid surface A. The temperature 5 mm above the liquid surface A is defined as T 液上 The temperature of 5 mm below the liquid surface A is T 液下 Then, since the magnetic field distribution of the induction coil 44 is sparse and dense, the temperature at 5 mm above the liquid surface is lower than the temperature at 5 mm below the liquid surface, i.e., T 液上 <T 液下 If the temperature gradient at the liquid surface A is dT0, then dT0 = (T液下 -T 液上 ) / Δh (where Δh=10 mm).

[0054] When the induction coil 44 moves downward at a speed v, the magnetic field lines of the coil change accordingly, and the magnetic field lines above and below the liquid surface A become sparse, and T 液上 and T 液下 The temperature change at 5 mm above the liquid surface is called ΔT 液上 The temperature change at 5 mm below the liquid surface is ΔT 液下 Since the magnetic field lines of the induction coil 44 become weaker as they move away from the center, the temperature drops faster above the liquid surface A, which is farther from the center of the coil. 液上 -ΔT 液下 >0. Also, the greater the velocity v, the greater the ΔT 液上 -ΔT 液下 >The value becomes larger.

[0055] The temperature gradient at the liquid surface A when the coil descends at a speed v is dT. V Let dT V =[(T 液下 -ΔT 液下 )-(T 液上 -ΔT 液上 )] / Δh = dT0+(ΔT 液上 -ΔT 液下 ) / Δh, where ΔT 液上 -ΔT 液下 > 0, when the coil descends at a speed v, the temperature gradient dT at the liquid surface A is (ΔT 液上 -ΔT 液下 ) / Δh. The faster the speed v, the larger this compensation value.

[0056] Based on the above principle, the inventors of the present disclosure have found, based on the temperature curve in the crucible shown in FIG. 3, that if the induction coil descends uniformly at a predetermined speed as in the prior art, in the initial stage of the liquid level descending, i.e., in the top region of the crucible, the temperature above the liquid level drops rapidly, destroying the original temperature gradient (i.e., the temperature gradient compensation caused by the movement of the induction coil becomes excessive), or, when the liquid level descends to the middle or bottom of the crucible, the temperature of the molten material above the liquid level drops too slowly, and the temperature gradient required for crystal growth cannot be obtained (i.e., the temperature gradient compensation caused by the movement of the induction coil is too small).

[0057] Based on the above research, the present disclosure proposes a method to control the movement of the induction coil downward relative to the crucible, and maintains the temperature gradient required for crystal growth at the beginning of the descent of the melt level in the crucible and as it descends to the middle and bottom of the crucible, and compensates for the change in the temperature gradient by moving the induction coil to prevent defects from occurring in the crystal growth process.

[0058] <Coil movement method> First Embodiment In the first embodiment, as shown in the speed curves (a), (b), and (c) of Fig. 6, when the crystal enters the isodiametric stage, the induction coil moves with acceleration, and in the whole process of the induction coil moving, the moving speed of the induction coil tends to continuously increase. Here, "when the crystal enters the isodiametric stage, the induction coil moves with acceleration" may include two cases: (1) when the crystal enters the isodiametric stage, the induction coil starts to move with acceleration (acceleration>0), and (2) before the crystal enters the isodiametric stage, the induction coil has already started to move, and when the crystal enters the isodiametric stage, the induction coil continues to move with acceleration (acceleration>0).

[0059] Optionally, the speed at which the induction coil moves relative to the crucible is greater than or equal to 0.001 mm / h and less than or equal to 0.1 mm / h during the entire process of the coil movement, although it should be understood that the initial speed at the start of the induction coil movement may be 0 mm / h.

[0060] After the crystal growth by the pulling method is completed, the crystal grown in the isodiametric stage is mainly used, so it is more important to continuously maintain the temperature field in the isodiametric stage than in other stages of the crystal growth by the pulling method. Meanwhile, after the crystal enters the isodiametric stage, the melt level begins to change obviously, that is, the temperature gradient begins to change obviously. Therefore, in the first embodiment, the induction coil can start to move with acceleration after entering the isodiametric stage, so that the temperature above the melt level in the crucible can be adjusted by adjusting the relative position of the metal crucible and the induction coil. It should be understood that in other stages of the crystal growth by the pulling method, such as the shouldering stage, the temperature above the melt level in the crucible may increase due to the lowering of the melt level in the crucible, so at this time, the induction coil also starts to move downward relative to the crucible, so that when the crystal enters the isodiametric stage, the induction coil already has an initial speed, and then the moving speed of the induction coil can be controlled to increase continuously.

[0061] Here, "the moving speed of the induction coil tends to increase continuously" includes the case where the speed of the induction coil increases continuously, i.e., the case where the acceleration is constantly greater than 0 (see curves (a) and (b) in FIG. 6), and also the case where the speed of the induction coil increases stepwise, i.e., includes a stage where the acceleration is 0 (see curve (c) in FIG. 6).

[0062] As shown by curve (a) in Figure 6, during the whole process of the induction coil movement, the induction coil moves downward with a variable acceleration relative to the crucible, and the acceleration increases. As shown by curve (b) in Figure 6, during the whole process of the induction coil movement, the coil speed increases uniformly.

[0063] According to the coil movement manner of the first embodiment, when the coil starts to move (i.e., when the liquid level is located at the top region of the crucible), the coil speed is relatively small, and the compensation of the temperature gradient caused by the movement of the induction coil is also relatively small, and then, as the liquid level descends, the speed of the induction coil tends to continuously increase, and the compensation of the temperature gradient caused by the movement of the induction coil also becomes larger, thereby satisfying the compensation requirement due to the temperature gradient (i.e., the required temperature gradient compensation amount increases as the liquid level descends). According to the coil movement manner of the first embodiment, the temperature gradient required for crystal growth can be maintained at the beginning of the descent of the melt level in the crucible and when it descends to the middle or bottom of the crucible, and the temperature field in the crystal growth process can be stably maintained so as to prevent defects from occurring in the crystal growth process. Among them, when the induction coil moves as shown by curves (a) and (b) in FIG. 6, especially when the liquid level is in the middle and bottom of the crucible, it can better compensate for the change in temperature gradient at different positions in the crucible, and can maintain the temperature gradient required for crystal growth when the melt level in the crucible is in the initial stage of descent and when it descends to the middle or bottom of the crucible.

[0064] Second Embodiment In the second embodiment, as shown in FIG. 7, the distance S or time t that the induction coil moves relative to the crucible is divided into N target sections (N is an integer greater than 2) in advance. The distance or time that the induction coil moves relative to the crucible is the target section (t / S). n When the target section (t / S) is reached, the induction coil is turned on. n corresponds to a constant velocity v n Each target section corresponds to a different speed, and the target section (t / S) arranged behind the target section (t / S) n+1 corresponds to the velocity v n+1 The target section (t / S) to be arranged forward n corresponds to the velocity v n Among them, before entering the first target section or when in the first target section, the induction coil can be accelerated to v1 at a constant acceleration.

[0065] In the method of moving the coil according to the second embodiment, the target section (t / S) arranged backward is n+1 corresponds to the velocity v n+1 The target section (t / S) to be arranged forward n corresponds to the velocity v n Since it is larger than the above, the compensation of the temperature gradient caused by the movement of the induction coil is large, so that the compensation requirement due to the temperature gradient (i.e., the required temperature gradient compensation amount increases with the decrease in the liquid level) can be satisfied, and the temperature field in the crystal growth process can be kept stable so as to prevent defects from occurring in the crystal growth process.

[0066] In addition, as a modification of the second embodiment, the moving distance or moving time of the induction coil relative to the crucible is monitored, and when the moving distance or moving time of the induction coil reaches a preset condition, the speed of the induction coil can be controlled to increase, or when the moving distance or moving time of the induction coil relative to the crucible increases by a preset threshold, the speed of the induction coil can be controlled to increase by a preset increment. Among them, the set condition, the set threshold, and the set increment are not particularly limited, and can be set to reasonable values ​​as required. Thus, by controlling the speed of the induction coil to gradually increase according to the change in the temperature difference at different positions of the crucible, the temperature field in the crystal growth process can be maintained stable to prevent defects from occurring in the crystal growth process.

[0067] Third embodiment In the third embodiment, as shown in Fig. 8, the total distance S or the total time t that the induction coil moves relative to the crucible is divided into N (N is an integer greater than 2) target sections based on the total distance S or the total time t that the induction coil moves relative to the crucible. n When the target section (t / S) is reached, the induction coil is turned on. n The corresponding speed a nControl it to perform uniformly accelerated motion. Note that each of the target intervals corresponds to a different acceleration, that is, (t / S) n+1 corresponds to the acceleration a n+1 is the target interval (t / S) n corresponds to the acceleration a n is not equal to

[0068] Here, (t / S) n+1 corresponds to the acceleration a n+1 is the target interval (t / S) n corresponds to the acceleration a n not being equal to means that in the entire process of the induction coil moving, the induction coil moves downward relative to the crucible with a variable acceleration. In the third embodiment, as shown in FIG. 8(b), when the acceleration gradually increases (i.e., a n+1 > a n ), and as shown in FIG. 8(a), when there is a target interval where the acceleration decreases (i.e., a n+1 < a n ) is also included. However, in the above two cases, as shown in FIG. 8, the acceleration of each target interval is all greater than 0, that is, the speed of the induction coil is continuously increasing. Therefore, the compensation of the temperature gradient caused by the movement of the induction coil continuously increases, and the compensation requirement due to the temperature gradient (that is, the required amount of temperature gradient compensation increases as it descends to the liquid surface) can be satisfied, and the temperature field in the crystal growth process can be stably maintained so as to prevent defects from occurring in the crystal growth process.

[0069] As an example of the movement method of the induction coil in FIG. 8, the time for the induction coil to move can be divided into a plurality of target intervals at intervals of 25 h. In the first 25-h target interval, that is, when the coil starts to move, the acceleration is a1 (0 < a1 < 0.001 mm / h 2 ), and after the first 25 h, the moving distance of the coil is 0 < s1 < 1 mm. Then, in the second 25-h target interval, the acceleration at which the coil moves is a2 (0 < a2 < 0.005 mm / h 2) is adjusted to, and after the second 25 h, the moving distance of the coil becomes 1 mm < s2 < 3 mm. In the target interval of the third 25 h, the acceleration at which the coil moves is a3 (0.0001 mm / h 2 < a3 < 0.01 mm / h 2 ) is adjusted to, and after the third 25 h, the moving distance of the coil becomes 3 mm < s3 < 5 mm. In the fourth 25 h, the acceleration at which the coil moves is a4 (0.0005 mm / h 2 < a4 < 0.01 mm / h 2 ) is adjusted to, and after the fourth 25 h, the moving distance of the coil becomes 5 mm < s4 < 9 mm. Thereafter, a4 is maintained until crystal growth ends. By controlling the induction coil in this way, it is possible to stably maintain the temperature field in the crystal growth process so as to prevent and reduce the occurrence of defects in the crystal growth process.

[0070] The continuous increase method of the acceleration in (b) in FIG. 8 has a better effect than the acceleration change method in (a) in FIG. 8. This is because as the liquid level drops, in order to maintain the temperature gradient required for crystallization, especially at the bottom of the crucible where the temperature gradient is close to zero, the requirement for compensation of the required temperature gradient also gradually increases. When the induction coil is moved so that the acceleration continuously increases, when the liquid level approaches the bottom of the crucible, a larger moving speed can be obtained to compensate for a larger temperature gradient difference required at the bottom of the crucible, and the temperature field can be stably maintained even in the final stage of crystal growth, further reducing the defects generated during crystal growth.

[0071] (Fourth Embodiment) In the fourth embodiment, when the induction coil starts to move, the initial position of the molten liquid surface relative to the bottom of the crucible may vary depending on the type of crystal, the required amount of crystallization, etc. In this case, in order to always maintain a temperature gradient close to the initial state during the liquid level drop process and improve the crystallization quality of the crystal, the velocity curve of the coil moving downward with respect to the crucible may be set according to the actual temperature distribution near the growth interface.

[0072] In the fourth embodiment, the position of the molten liquid surface of the crystal raw material relative to the bottom of the crucible when the induction coil starts to move may be defined as the initial liquid surface position, and the acceleration of the induction coil may be set based on the initial liquid surface position so that it increases as the initial position increases.

[0073] For example, as shown in Figure 9(a)-(c), in case (A), after crystal A enters the isodiametric stage, the initial position of the melt surface is at position (A) in Figure 9(a) and (b), and at this time, the induction coil descends with a uniform acceleration relative to the crucible, the acceleration is a1, and the speed curve is shown in curve (A) in Figure 9(c). In case (B), after crystal B enters the isodiametric stage, the initial position of the melt surface is at position (B) in Figure 9(a) and (b), and at this time, the induction coil descends with a uniform acceleration relative to the crucible, the acceleration is a2, and the speed curve is shown in curve (B) in Figure 9(c). In addition, in the two cases, the initial position relationship of the melt surface is that position (A) is higher than position (B), and the acceleration relationship is a1>a2. As shown in Figure 9(a), since the initial position (A) is higher than the initial position (B), the temperature gradient at the initial position (A) is larger, and a larger gradient compensation value is required. Therefore, by making the acceleration a1 larger than the acceleration a2, the velocity value of the velocity curve (A) as shown in FIG. 9(c) can always be larger than the velocity value (B) of the velocity curve, and the temperature gradients at different initial positions in the crucible can be matched, thereby further reducing defects occurring in the crystal growth process. In FIG. 9, the constant acceleration descent of the induction coil is taken as an example for explanation, but if the induction coil is descending at a variable acceleration, the acceleration a1 may always be larger than the acceleration a2 throughout the entire descent process. It should also be understood that as long as the velocity value of the velocity curve of the induction coil when the initial position of the liquid level is high is always larger than the velocity value of the velocity curve of the induction coil when the initial position of the liquid level is low, the accelerations a1 and a2 of both can be appropriately set.

[0074] Similarly, the acceleration of the induction coil may be set to be smaller as the distance between the top end of the induction coil and the surface of the molten crystal material increases based on the distance between the top end of the induction coil and the surface of the molten crystal material when the induction coil starts moving. When the distance between the top end of the induction coil and the surface of the molten crystal material is large, the surface of the molten crystal material is at a low position, and the acceleration at this time is set to be small, so that the temperature gradients at different initial positions in the crucible can be matched, and defects occurring in the crystal growth process can be further reduced. Similarly, as long as the speed value of the speed curve of the induction coil when the distance is large is always larger than the speed value of the speed curve of the induction coil when the distance is small, the accelerations of both can be set appropriately.

[0075] <Confirmation of crystal defects> In the actual manufacturing process, the crystal blank is scanned with a laser to evaluate the crystallization quality of the crystal. As shown in Figure 10(b), if there are defects such as cores or scattering particles inside the blank, the laser will be refracted and bright spots will appear around the defects. As shown in Figure 10(a), if there are no defects inside the blank, the laser will not be refracted because it moves within the same medium, and the overall brightness of the blank will be the same.

[0076] <Method of manufacturing a radiation detector and a scintillator for a radiation detector> The crystals produced by the above crystal growth methods of the present disclosure can further be used in the manufacture of scintillators for radiation detectors.

[0077] The radiation detector of the present disclosure includes a substrate, a scintillator provided on the substrate, and a photodetector for detecting scintillator light emitted from the scintillator when irradiated with radiation, and the scintillator may be obtained by cutting and polishing a crystal produced by any one of the crystal growth methods described above. The radiation detector of the present disclosure can improve the accuracy of radiation detection.

[0078] In addition, the manufacturing method for a scintillator for a radiation detector of the present disclosure may include a crystal blank obtaining step of obtaining a crystal blank by any of the crystal growth methods described above, a cutting step of selecting a portion of the crystal blank having a uniform diameter and cutting it to form one or more crystals of a desired shape, and a polishing step of polishing the one or more crystals obtained in the cutting step to obtain the scintillator for a radiation detector.

[0079] In addition, after the polishing step, a plurality of crystals can be arranged on the reflective layer to form a crystal array, thereby obtaining a scintillator array for a radiation detector. The reflective layer can contain, for example, TiO2 or Ba2SO4.

[0080] <Example> Hereinafter, a specific embodiment of the induction coil control method of the present disclosure will be described in detail, and the quality of the crystal blank of the specific embodiment will be evaluated according to the above-mentioned crystal quality evaluation method.

[0081] Example 1 In the embodiment, the process of growing LYSO crystals was completed according to the raw material mixing step, furnace loading step, raw material melting step, crystallization step, and removal step in the above-mentioned crystal growth method. The steps related to the movement of the coil are described below.

[0082] During the loading process, the upper edge of the heating coil was adjusted to coincide with the upper edge of the crucible (see the dotted line mark in Figure 4(a)). During the isodiameter stage, the induction coil was rotated at a speed of v = 0.001t mm / h (i.e., acceleration = 0.001 mm / h). 2 ) was controlled to start linear motion at a constant acceleration in the direction opposite to the direction of pulling the crystal. When the length of the crystal in the constant diameter stage reached a predetermined value in the final stage, the constant diameter stage ended and the descent of the coil was stopped.

[0083] The crystal blank was scanned with a laser to evaluate the quality of the crystal growth, and it was found that the crystal blank was perfect and transparent, and there were no obvious defects such as inclusions, clouds, bubbles, etc. inside. Therefore, in the process of controlling the induction coil to move downward relative to the crucible, Example 1 was performed at a speed of a=0.001 mm / h. 2 It is believed that by performing uniform acceleration motion with an acceleration of 0.15, the temperature gradient at the crystal growth interface during the initial descent of the melt surface in the crucible and as it descends to the middle and bottom of the crucible is maintained to be consistent with the initial state, providing stable temperature field conditions for crystal growth and reducing defects that occur in the crystal growth process.

[0084] Example 2 Example 2 differs from Example 1 in that the induction coil is moved at a gradually increasing acceleration in the equal diameter stages. Since the other stages of crystal growth in Example 2 are the same as those in the examples, we will not go into detail about them and will only explain the differences.

[0085] After the crystal entered the isodiameter stage, the time for the induction coil to move was divided into multiple target intervals with an interval of 25 h. In the first target interval of 25 h, that is, when the coil starts to move, the acceleration is a1 (a1 = 0.001 mm / h 2 ) for the first 25 hours, and then in the second 25-hour target period, the acceleration at which the coil moves is a2 (a2 = 0.003 mm / h 2 ) for the second 25 hours, and in the third 25-hour target period, the acceleration at which the coil moves becomes a3 (a3 = 0.005 mm / h 2 ) for the third 25 hours, and for the fourth 25 hours, the acceleration of the coil movement becomes a4 (a4 = 0.008 mm / h 2 The temperature was then adjusted to a4 for the fourth 25 h. The temperature was then held at a4 until the crystal growth was complete.

[0086] The crystal blank was scanned with a laser to evaluate the quality of the crystal growth, and it was found that the crystal blank was perfect and transparent, and there were no obvious defects such as inclusions, clouds, or bubbles inside. Therefore, it is believed that Example 2 can better accommodate the change in temperature gradient at different positions in the crucible (i.e., the required temperature gradient compensation requirement increases with the descent of the melt level) by controlling the induction coil to move with a gradually increasing acceleration. Therefore, according to Example 2, the temperature field can be continuously and stably maintained during the crystal growth process, and the temperature gradient at the crystal growth interface can be kept consistent with the initial state when the melt level in the crucible is initially descending and when it descends to the middle and bottom of the crucible, thereby reducing defects caused by the change in the crystal temperature gradient.

[0087] It should be noted that the crystal growth apparatus of the present disclosure can realize each process of the crystal growth method embodiments, and can achieve the same technical effects. In order to avoid repetitive description, the above apparatus embodiments will not be described in detail.

[0088] The present disclosure also provides crystals grown by the crystal growth methods as described in the examples above.

[0089] It should be noted that the crystals provided by the present disclosure are crystals grown by the methods provided by the embodiments of the crystal growth method, and can achieve the same technical effects as the embodiments of the crystal growth method. In order to avoid repetitive explanations, the above embodiments of the crystals will not be described in detail.

[0090] It should be explained that in this specification, the terms "comprise", "include", or any other similar terms are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a set of elements includes not only those elements, but also other elements not expressly listed. Unless further limited, an element defined by the phrase "comprises" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element. It should also be explained that the scope of the method and apparatus in the embodiments of this application is not limited to performing functions in the order shown or described, but may include performing functions substantially simultaneously or in reverse order depending on the relevant functions, for example, performing the method described in an order different from that described, or adding, omitting, or combining various steps. Also, features described with reference to some examples may be combined in other examples.

[0091] Although the embodiments and examples of the present application have been described above with reference to the drawings, the present application is not limited to the above specific embodiments and examples, and the above specific embodiments and examples are merely illustrative and not intended to be limiting. Those skilled in the art can make various configurations according to the suggestions of the present application without departing from the spirit of the present application and the scope of protection of the claims. For example, when one embodiment or example is applied to another embodiment or example, all modifications are protected by the present disclosure. For example, if the crucible is not located at the upper half of the induction coil, the trend of the vertical temperature distribution in the crucible changes. In this case, in order to maintain a temperature gradient close to the initial state throughout the process of the liquid level descent to prevent defects from occurring in the crystal growth process, the speed or acceleration of the induction coil moving downward relative to the crucible may be controlled according to the trend of the actual temperature distribution in the crucible. Also, for example, the position of the top of the induction coil may be located above the melt surface when the induction coil stops moving. This makes it possible to more suitably utilize the change in magnetic field strength of the induction coil to compensate for the temperature gradient of the melt surface.

Claims

1. In a crystal growth process using the pulling method, the induction coil is controlled to move downward relative to the crucible, After the crystal has reached the isodiameter stage, the induction coil is moved with an acceleration; and A method for growing crystals, characterized in that the moving speed of the induction coil tends to continuously increase during the entire process of the induction coil moving.

2. 2. The method of claim 1, wherein the induction coil moves downward with a variable acceleration relative to the crucible during the entire process of the induction coil moving.

3. 2. The method of claim 1, wherein the induction coil moves downward with a constant acceleration relative to the crucible during the entire process of the induction coil moving.

4. 2. The crystal growth method according to claim 1, characterized in that the distance or time that the induction coil moves relative to the crucible is divided into a plurality of target sections in advance, each of the target sections corresponds to a different speed, the corresponding speed of the target section arranged in the rear is higher than the corresponding speed of the target section arranged in the front, and when the distance or time that the induction coil moves relative to the crucible reaches the target section, the induction coil is controlled to move at a constant speed corresponding to each of the target sections.

5. 3. The crystal growth method according to claim 2, further comprising the steps of: dividing a distance or time that the induction coil moves relative to the crucible into a plurality of target intervals each corresponding to a different acceleration; and controlling the induction coil to move at a constant acceleration corresponding to each of the target intervals when the distance or time that the induction coil moves relative to the crucible reaches the target interval.

6. 6. The method of claim 5, wherein the corresponding acceleration of the rearwardly arranged target zone is greater than the corresponding acceleration of the forwardly arranged target zone.

7. 7. The method of claim 1, wherein the speed at which the induction coil moves relative to the crucible is 0.001 mm / h or more and 0.1 mm / h or less.

8. a position of the melt surface of the raw material of the crystal relative to the bottom of the crucible when the movement of the induction coil starts is defined as an initial liquid surface position; Acceleration of the induction coil based on the initial liquid level position; 2. The crystal growth method according to claim 1, wherein the initial position is set to be larger as the initial position is higher.

9. The acceleration of the induction coil is determined based on the distance between the top end of the induction coil and the surface of the melt of the crystal raw material when the induction coil starts to move.

2. The method of claim 1, wherein the distance is set to be smaller as the distance increases.

10. a growth furnace having a growth furnace chamber therein; a crucible provided in the growth furnace chamber and capable of containing a crystal raw material; an induction coil provided in the growth furnace chamber and surrounding the outside of the crucible; an induction coil driving mechanism connected to the induction coil, for controlling the induction coil to move downward relative to the crucible during the crystal growing process, so that the induction coil moves with an acceleration after the crystal enters the isodiameter stage, and the moving speed of the induction coil tends to be continuously increased during the whole process of the induction coil moving; A crystal growth apparatus comprising:

11. The induction coil driving mechanism includes a holder, a fine adjustment table, and a motion mechanism; the holder is provided below the induction coil, one end of the holder is connected to the induction coil, and the other end of the holder is connected to the micromotion table through a bottom of the growth furnace having an opening for passing the holder therethrough; the micromotion table is provided below the growth furnace, one side of the micromotion table is connected to the holder, and the other side of the micromotion table is connected to the motion mechanism; The crystal growth apparatus of claim 10, wherein the motion mechanism is provided below the micro-motion table and is capable of driving and moving the micro-motion table, and when the micro-motion table moves, the motion mechanism is capable of driving and moving the holder and an induction coil connected to the holder.

12. 12. The crystal growing apparatus according to claim 11, wherein the motion mechanism and the fine movement table are connected by a transmission mechanism.

13. The crystal growing apparatus according to any one of claims 10 to 12, further comprising a heat-retaining cylinder disposed within the growth furnace chamber, the crucible disposed therein, and the induction coil surrounding the outside of the heat-retaining cylinder.

14. A substrate; a scintillator provided on the substrate; a photodetector that detects scintillator light emitted from the scintillator in response to irradiation with radiation; 10. A radiation detector, wherein the scintillator is obtained by cutting and polishing a crystal produced by the crystal growth method according to claim 1.

15. A method for producing a scintillator for a radiation detector, comprising the steps of: A crystal blank obtaining step of obtaining a crystal blank by the crystal growth method according to any one of claims 1 to 9; a cutting step of selecting a uniform diameter portion of the crystal blank and cutting it to form one or more crystals of a desired shape; and a polishing step of polishing one or more crystals obtained in the cutting step to obtain the scintillator for a radiation detector.

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