Crystal growth method, crystal growth apparatus, and program

Abstract

To provide a crystal growth method that can industrially advantageously manufacture a crystal that is excellent in homogeneity of additive concentration.SOLUTION: A first feedstock layer (4) and a second feedstock layer (6) having different additive concentrations are prepared inside a cooling copper vessel (2). The additive concentration in the first feedstock layer (4) is set to be approximately the same as the in-crystal additive concentration multiplied by the reciprocal of an effective segregation coefficient, and the additive concentration in the second feedstock layer (6) is set to be approximately the same as the in-crystal additive concentration. While the cooling copper vessel (2) cools the surroundings, a high frequency induction coil (1) melts the first feedstock layer (4), whereby a growing crystal (7) is produced in a double crucible. In addition, the high frequency induction coil (1) is controlled to move downward so as to melt the second feedstock layer (6) and supply the resulting melt in accordance with the growth of the growing crystal (7). Furthermore, feedstock is additionally supplied to the first feedstock layer (4), which shrinks as the growing crystal (7) grows. In this way, the additive concentration is kept so as to be substantially constant, and long, high-quality crystals having excellent homogeneity are obtained at low cost.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a crystal growth method, a crystal growth apparatus, and a program for growing crystals from a melt without using a precious metal crucible, and in particular to a crystal growth method, a crystal growth apparatus, and a program for stably growing high-quality, long crystals. [Background technology]

[0002] Known methods for growing large, high-quality single crystals include the pulling method, edge-defined film-fed growth (EFG) method, zone melt method, chiroporous method, top-seeded melt growth (TSMG) method, Bridgman method, vertical temperature gradient growth (VGF) method, and heat exchange method (HEM). These methods are suitable for growing large crystals with congruent melt composition, and are known as melt growth methods in which a seed crystal is brought into contact with a melt filled in a crucible and a temperature gradient is used to produce a single crystal.

[0003] The melt growth method is currently the most widely used industrial method for growing oxide single crystals and semiconductor single crystals, but it has the drawback of being difficult to control the uniformity of the dopant concentration, resulting in the loss of uniformity.

[0004] Furthermore, in order to increase the proportion of crystals with a substantially uniform additive concentration, for example, the double crucible method has been devised in the pulling method (Patent Documents 1 and 2). However, the double crucible method has many problems, such as the complexity of the apparatus, the need for multiple expensive noble metal crucibles, and the need for a large noble metal crucible to ensure the diameter of the crystal, and further improvements have been sought. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2729243 [Patent Document 2] Patent No. 3551242 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a crystal growth method that can industrially advantageously produce crystals with excellent uniformity in additive concentration. [Means for solving the problem]

[0007] The means for solving the above problems and their effects will be described below.

[0008] The crystal growth method according to the present invention comprises applying a high frequency wave to a source material containing an additive to directly heat the source material while cooling the outer periphery of the source material below its melting point, thereby melting the source material and growing a crystal from the melt, and the source material is characterized in that the source material comprises multiple layers with different additive concentrations. With this configuration, a grown crystal reflecting the additive concentrations of the multiple layers can be obtained at low cost by utilizing the segregation phenomenon.

[0009] In the crystal growth method, the plurality of layers are composed of a first source layer and a second source layer adjacent to each other, the dopant concentration of the first source layer is approximately equal to the dopant concentration of the crystal multiplied by the reciprocal of an effective segregation coefficient, and the dopant concentration of the second source layer is approximately equal to the dopant concentration of the crystal. With this configuration, a crystal having a dopant concentration obtained by multiplying the dopant concentration of the first layer by the effective segregation coefficient can be obtained by the segregation phenomenon, and a grown crystal having a substantially uniform dopant concentration of the desired dopant concentration can be obtained.

[0010] In the crystal growth method, the raw material is directly heated by the high frequency wave, and the crystal is grown while a high frequency coil for applying the high frequency wave is moved relatively from the first raw material layer to the second raw material layer so as to melt the raw material in a weight approximately equal to the weight of the crystal grown from the melt of the raw material. With this configuration, the thermal environment at the solid-liquid interface can be kept approximately constant, and a long grown crystal with approximately uniform additive concentration and approximately uniform quality can be obtained.

[0011] The crystal growth method is characterized in that when the high-frequency coil is moved relatively in the direction of the second raw material layer, the weight of the second raw material layer melted per unit time is approximately the same as the weight of the crystal growing per unit time.

[0012] The crystal growth method is characterized in that the raw material is added to the melt at a concentration of additives substantially equal to that of the crystal. With this configuration, the balance of the additive concentrations between the grown crystal and the added raw material is maintained, making it possible to obtain a long crystal with a desired additive concentration and substantially uniformity.

[0013] The crystal growth method is characterized in that the weight of the raw material added per unit time is equal to the weight of the crystal grown per unit time. With this configuration, the weight balance between the growing crystal and the added raw material is maintained, so the liquid level is kept approximately the same, the thermal environment at the solid-liquid interface can be kept approximately constant, and long crystals with a desired additive concentration and approximately uniformity can be obtained.

[0014] In the crystal growth method, the added raw material is in the form of a liquid, powder, shot, wire, rod, or pellet. With this configuration, even if the raw material is in various forms, the liquid level is kept approximately the same and the thermal environment at the solid-liquid interface is also kept approximately the same, so that a long crystal with a desired additive concentration and approximately uniformity can be obtained.

[0015] The crystal growth method is characterized in that the additive is the luminescence center of the luminescent material. According to this configuration, by using the luminescence center of the luminescent material as the additive, it is possible to obtain a long, substantially homogeneous luminescent material crystal with a desired additive concentration.

[0016] In the crystal growth method, the crystal is a scintillator crystal. According to this configuration, the dopant uses the luminescence center of the scintillator material, so that a long, substantially homogeneous scintillator crystal with a desired dopant concentration can be obtained.

[0017] The crystal growth method is characterized in that the crystal is a laser crystal. With this configuration, since the dopant is the luminescence center of the laser material, it is possible to obtain a long laser crystal that is substantially homogeneous and has a desired dopant concentration.

[0018] The crystal growth method is characterized in that the additive is a donor or acceptor of the semiconductor material. With this configuration, since the additive is a donor or acceptor of the semiconductor material, it is possible to obtain a long semiconductor crystal with a desired additive concentration and substantially uniformity.

[0019] The present invention also provides a crystal growth apparatus comprising: a heating means for directly heating a raw material containing an additive by high-frequency heating; a cooling means for cooling the outer periphery of the raw material containing the additive to below the melting point of the raw material; a memory for storing information about the position of each layer of the raw material having different additive concentrations; a control means for controlling the heating means to move based on the information about the positions so as to melt the raw material in one of the raw material layers and at least partially melt the raw material in another layer; and a crystal holding means for holding a crystal formed from the melted raw material. This configuration allows for a crystal growth apparatus capable of growing a long crystal with a desired additive concentration and substantially uniformity, using the control means for controlling the concentration of the additive based on the effective segregation coefficient at the interface of the crystal.

[0020] In the crystal growth apparatus, the one layer is a layer of the raw material having an additive concentration determined based on an effective segregation coefficient at the interface between the melt and the crystal, and the control means moves the heating means so as to first melt all of the raw material in the one layer and then melt at least a portion of the other layer.

[0021] In the crystal growth apparatus, the control means further controls the crystal holding means to move in a direction away from the melt, and moves the heating means in parallel with the movement so as to melt at least a portion of the raw material of the other layer.

[0022] The crystal growth apparatus is provided with a load cell that measures the change in weight of the crystal held by the crystal holding means, and the control means controls the amount of movement of the heating means for melting the other layer based on the change in weight measured by the load cell.

[0023] The crystal growth apparatus includes a supply unit for additionally supplying the raw material having substantially the same additive concentration as that of the other layer.

[0024] The crystal growth apparatus is characterized in that it grows crystals by a pulling method. With this configuration, since the crystal growth apparatus has a pulling mechanism, it is possible to obtain a crystal growth apparatus that can grow long crystals by the pulling method with a substantially uniform quality and with a target additive concentration.

[0025] The crystal growth apparatus is characterized in that the crystal is grown by the Bridgman method. With this configuration, a mechanism for the Bridgman method can be adopted as part of the crystal growth apparatus, thereby obtaining a crystal growth apparatus that can grow long crystals with a desired additive concentration and substantially uniformity by the Bridgman method.

[0026] The crystal growth apparatus is characterized in that it grows crystals by the Vertical Gradient Freeze (VGF) method. With this configuration, a mechanism for the VGF method can be adopted as part of the crystal growth apparatus, and therefore a crystal growth apparatus can be obtained that can grow long crystals with a desired additive concentration and substantially uniformity by the VGF method.

[0027] The crystal growth apparatus is characterized in that it grows crystals by the chiroporous method. With this configuration, a mechanism for the chiroporous method can be adopted as part of the crystal growth apparatus, thereby obtaining a crystal growth apparatus that can grow substantially homogeneous, long crystals with a desired additive concentration by the chiroporous method.

[0028] The crystal growth apparatus is characterized in that it grows crystals by the heat exchange method (HEM). With this configuration, a mechanism for the heat exchange method (HEM) can be adopted as part of the crystal growth apparatus, and therefore a crystal growth apparatus can be obtained that can grow long crystals with a desired additive concentration and approximately uniformity by the heat exchange method (HEM).

[0029] The crystal growth apparatus is characterized in that it grows crystals by the Edge-defined Film-fed Growth (EFG) method. With this configuration, an EFG mechanism can be adopted as part of the crystal growth apparatus, thereby obtaining a crystal growth apparatus that can grow long, substantially homogeneous crystals with a desired additive concentration by the EFG method.

[0030] The crystal growth apparatus is characterized in that it grows crystals by the zone melt method. With this configuration, a zone melt mechanism can be adopted as part of the crystal growth apparatus, and therefore a crystal growth apparatus can be obtained that can grow long crystals with a desired additive concentration and substantially uniformity by the zone melt method.

[0031] The present invention also provides a program for causing a computer to execute a process for controlling the concentration of an additive in a crystal growth method in which a raw material containing the additive is directly heated by high-frequency heating and a crystal is produced from the melt of the raw material, based on an effective segregation coefficient at the interface between the melt and the crystal. According to this configuration, a crystal growth apparatus is provided with a program for growing a crystal while executing a process for controlling the concentration of the additive, so that it is possible to control the growth of a long crystal that is substantially homogeneous and has a desired additive concentration. [Effects of the Invention]

[0032] As described above, the present invention can provide a manufacturing method, an apparatus, and a program that can obtain long, substantially homogeneous crystals with a desired additive concentration at low cost. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 1 is a diagram showing the configuration of a crystal growth apparatus. [Figure 2] FIG. 2 is a flow chart illustrating the crystal growth method. [Figure 3] FIG. 3 is a diagram showing the configuration of a crystal growth apparatus. [Figure 4]FIG. 4 is a flow chart illustrating the crystal growth method. [Figure 5] FIG. 5 is a diagram showing the state of each raw material layer when subjected to a thermal history. [Figure 6] FIG. 6 is a graph showing the relationship between the additive concentration in the solid phase and the crystallization rate. [Figure 7A] FIG. 7A is a graph showing the relationship between additive concentration and crystallization rate in Examples 1, 2, and 3. [Figure 7B] FIG. 7B is a graph showing the relationship between the additive concentration and the crystallization rate in Comparative Examples 1, 2, and 3. DETAILED DESCRIPTION OF THE INVENTION

[0034] Preferred embodiments of the present invention will be described in more detail below with reference to the drawings, but the present invention is not limited to these specific examples.

[0035] A crystal growth method according to an embodiment of the present invention includes applying a high frequency wave to a source body containing an additive while cooling the outer periphery of the source body below its melting point, directly heating the source body to melt the source body, and growing a crystal from the melt of the source body, wherein the source body is composed of multiple layers with different concentrations of the additive.This crystal growth method can grow single crystals from sources such as zirconium oxide, titanium, titanium-aluminum alloy, iron oxide, magnesium oxide, germanium oxide, calcium oxide, strontium oxide, yttrium oxide, chromium oxide, lanthanum chromium oxide, strontium titanate, cadmium oxide, scandium oxide, lutetium oxide, lanthanum nickel oxide, gallium oxide, aluminum oxide, magnesium-aluminum oxide, yttrium-aluminum garnet, gadolinium-aluminum gallium garnet, lanthanum gadolinium silicon oxide, strontium iodide, cerium bromide, lithium calcium aluminum fluoride, lithium tantalate, and lithium niobate.

[0036] First, a crystal growth apparatus 10 according to an embodiment of the present invention will be described with reference to Fig. 1. The crystal growth apparatus 10 includes a water-cooled copper vessel 2, a high-frequency induction coil (high-frequency coil) 1 as a heating means, a holding rod (crystal holding means) (not shown), and a seed crystal 8 held by the holding rod (not shown). A first layer of sintered raw material 4 and a second layer of sintered raw material 6, which are raw material bodies, are stacked within the water-cooled copper vessel 2. The raw material bodies are a mixture of raw material and additives, and in this embodiment, the raw material bodies 4 for the first layer and the raw material bodies 6 for the second layer have different concentrations of additives relative to the raw material.

[0037] The first layer of sintered raw materials 4 and the second layer of sintered raw materials 6 are molded, for example, into a cylindrical shape according to the shape of the water-cooled copper container 2. The upper surface sides (upper side on the paper in FIG. 1) of the first layer of sintered raw materials (first raw material layer) 4 and the second layer of sintered raw materials (second raw material layer) 6 are referred to as one end side, and the lower surface sides (lower side on the paper in FIG. 1) of the first layer of sintered raw materials 4 and the second layer of sintered raw materials 6, which are closer to the ground, are referred to as the other end side. The first layer of sintered raw materials 4 and the second layer of sintered raw materials 6 do not have to be cylindrical, and may have any shape as long as they are stacked from one end side to the other end side.

[0038] The water-cooled copper container 2 is made of copper, which has excellent thermal conductivity and is inexpensive. The water-cooled copper container 2 is configured so that a part or all of the outer wall of the water-cooled copper container 2 can be cooled with a fluid containing water by a cooling mechanism (not shown).

[0039] The high-frequency induction coil 1 is disposed so as to surround the periphery of the water-cooled copper container 2. The high-frequency induction coil 1 is disposed along the outer wall of the water-cooled copper container 2 so as to be relatively movable. More specifically, it can move from the upper end to the lower end (from the upper side to the lower side on the paper surface of FIG. 1) of the water-cooled copper container 2 while maintaining a constant distance from the outer wall of the water-cooled copper container 2. The high-frequency induction coil 1 is configured to heat (directly heat) the first layer of sintered raw materials 4 and the second layer of sintered raw materials 6 shown in FIG. 1 by high-frequency induction.

[0040] A holding rod (not shown) holds the seed crystal 8. The holding rod is movable in the vertical direction and is configured to be axially rotatable at a predetermined speed during seeding.

[0041] Next, a crystal growth method according to an embodiment of the present invention will be described with reference to FIG. 2. First, in step S101, the periphery of the first layer sintering raw materials 4 and the second layer sintering raw materials 6 is cooled below the melting point using the cooling function (cooling means) of the water-cooled copper container 2, while the center of one end of the first layer sintering raw materials 4 is heated and melted using the high-frequency induction coil 1. It is also possible to use metals or semiconductors that easily absorb magnetic fields for the initial heating of the first layer sintering raw materials 4. Using such metals or semiconductors as the metallic elements contained in the raw materials reduces contamination of the grown crystal with unwanted impurities. When the first layer sintering raw materials 4 are molten due to heat generated by the starter through heating using the high-frequency induction coil 1, their resistivity drops significantly, improving their absorption of the magnetic field and forming a stable molten zone 41 (see FIG. 3). The metal that quickly transitions the first layer sintering raw materials 4 to the stable molten zone 41 (see FIG. 3) is called a starter. For example, when the raw material for the sintered body is gallium oxide, Ga metal is used. (Lu, Y)2SiO5(LYSO), Y3Al5O 12 When YAG (YAG) and Y2O3 are used as raw materials, for example, Y metal is used. When LYSO4 or La-GPS are used as raw materials, Si semiconductors are used. When LiTaO3 (LT) is used as raw material, Ta metal is used as the starter, and when LiNbO3 (LN), Nb metal is used. Next, the high-frequency induction coil 1 is gradually moved to the other end, and after the first layer is melted, one end of the sintered raw material 6 of the second layer is melted. The surroundings of the sintered raw material 4 of the first layer and the sintered raw material 6 of the second layer are cooled below the melting point by the cooling function of the water-cooled copper container 2, forming a sintered raw material maintenance layer 3 that maintains the solid state.

[0042] Next, in the second step S102, the seed crystal 8 is brought into contact with the melt at the center of one end of the first layer of sintering raw material 4. As described above, by heating with the high-frequency induction coil 1, the raw material at the center of one end of the first layer of sintering raw material 4 becomes a melt, and one end of this melt is brought into contact with the seed crystal 8 to create a so-called seeding state (not shown).

[0043] Next, in the third step S103, while maintaining cooling of the surroundings of the raw materials, the heating area of ​​the first layer of sintered raw materials 4 is moved from one end to the other end by the high-frequency induction coil 1, and the melting area of ​​the raw material in the center of the first layer of sintered raw materials 4 is moved from one end to the other end of the first layer of sintered raw materials 4. This movement allows a grown crystal 7 with an additive concentration reflecting the effective segregation coefficient to be obtained from the contact point between the seed crystal 8 and the melt of the first layer of sintered raw materials 4 in the direction from one end to the other end of the first layer of sintered raw materials 4. That is, the grown crystal 7 gradually grows longer as the high-frequency induction coil 1 descends. At this time, the grown crystal 7 can also be pulled away from the melt at a predetermined speed. Pulling is preferred when using the Cz method as the crystal growth method.

[0044] It is also possible to rotate a holding rod (not shown) supporting the seed crystal 8 about its axis. This allows the melt of the sintering raw material 4 of the first layer to be stirred, so that the temperature of the melt of the sintering raw material 4 of the first layer can be quickly stabilized.

[0045] Here, at least in the second step S102 and the third step S103, the central portion of the first layer of sintered raw material 4 is heated by the high-frequency induction coil 1 with the induction heating frequency set within a range offset from the resonant frequency of the melt. By setting the frequency offset within this range, the temperature gradient can be appropriately controlled while avoiding excessive heating. The depth of the magnetic field penetrating the heated material depends on the induction heating frequency. The unmelted outer periphery remains solid by cooling, and by appropriately setting and controlling the frequency, the temperature is relatively lower toward the center of the melt in a plane perpendicular to the direction from one end of the raw material to the other (the melt temperature gradient). In this way, by changing the induction heating frequency within a range offset from the resonant frequency of the melt and controlling the temperature gradient within the plane, crystallization can be promoted and the diameter of the raw material crystals can be controlled. However, such control is not necessarily required; any other means that can create a temperature gradient, such as changing the coil position or controlling the rod lifting speed, can be used.

[0046] When the seed crystal 8 is pulled up, the growing crystal 7 is separated from the melt and then heating is gradually stopped to solidify the growing crystal 7. Alternatively, the growing crystal 7 is grown from the point where the seed crystal 8 contacted to a predetermined point in the direction from one end to the other end of the first layer of sintering raw material 4, and then heating of the high-frequency induction coil 1 is stopped and the molten material inside the growing crystal 7 is slowly cooled and solidified. As a result, a single crystal of the raw material for the growing crystal 7 that has grown from the seed crystal 8 is formed inside the growing crystal 7. After slow cooling, the raw material around the growing crystal 7 (the first layer of sintering raw material 4) is removed and the growing crystal 7 is taken out.

[0047] According to the above-described embodiment, the first layer of sintering raw materials 4 and the second layer of sintering raw materials 6 are surrounded by a sintering raw material support layer 3, which is cooled below the melting point and maintained in a solid state by a water-cooled copper container 2. The sintering raw material support layer 3 can be considered a crucible containing the melt of the first layer of sintering raw materials 4 and the second layer of sintering raw materials 6. Typically, metal crucibles release impurities when heated. These impurities are known to degrade the quality of the grown crystal. However, according to this embodiment, the sintering raw material support layer 3 is free from contamination by impurities. Furthermore, since a precious metal crucible made of an expensive material is not required, production costs are reduced. Furthermore, by appropriately controlling the frequency of the induction heating while lowering the high-frequency induction coil 1 from one end of the melt of the first layer of sintering raw materials 4 to the other, the temperature of the center of the grown crystal 7 can be maintained lower in a plane perpendicular to the direction from one end to the other of the grown crystal 7. This allows for the production of higher-quality crystals.

[0048] One end of the seed crystal 7 is held by a holding rod (not shown), while the other end is placed so as to come into contact with the melt 41 of the first layer shown in FIG.

[0049] As shown in FIG. 1, the first layer of sintered raw materials 4 and the second layer of sintered raw materials 6, which are the raw materials that form the basis for producing the crystal, are placed in a water-cooled copper container 2. More specifically, the second layer of sintered raw materials 6 are placed on the bottom side of the water-cooled copper container 2. The first layer of sintered raw materials 4 are placed on the upper side of the water-cooled copper container 2, above the second layer of sintered raw materials 6. For example, when producing a Ce-doped Gd3(Al,Ga)5O12 (Ce:GAGG) crystal, powders such as Gd2O3, Al2O3, Ga2O3, and CeO2 can be used as the raw materials for the first layer of sintered raw materials 4 and the second layer of sintered raw materials 6.

[0050] The sintering raw material body 4 of the first layer and the sintering raw material body 6 of the second layer are formed, for example, as a green compact obtained by compressing powder, and are constructed by adding different concentrations of additives to the same raw material in each layer. The raw material itself may be different for each layer. In this embodiment, the additive concentration of the sintering raw material body 4 of the first layer is higher than the additive concentration of the sintering raw material body 6 of the second layer. The additive of the sintering raw material body 4 of the first layer and the sintering raw material body 6 of the second layer is, for example, Ce-added Gd3(Al,Ga)5O 12 When producing (Ce:GAGG) crystals, cadmium oxide (Gd2O3) is used, and cerium (Ce) is used as an additive.

[0051] The ratio of the raw materials and additives in the sintering raw material 4 of the first layer is, for example, Ce:(Ce+Gd)=2.98:100. This ratio of components is determined taking into consideration the effective segregation coefficient at the interface between the molten liquid formed by melting the sintering raw material 4 of the first layer by the high-frequency induction coil 1 and the grown crystal 7. In other words, the additive concentration in the sintering raw material 4 of the first layer is adjusted to be approximately the same as the additive concentration in the grown crystal 7 multiplied by the reciprocal of the effective segregation coefficient. Note that other additives are weighed out in stoichiometric ratios, mixed, and added as appropriate.

[0052] Similarly, the ratio of the raw materials and additives in the sintering raw material 6 of the second layer is, for example, Ce:(Ce+Gd)=1:100. The additive concentration in the sintering raw material 4 of the second layer is adjusted to be approximately the same as the additive concentration in the crystal. Note that other additives are weighed in stoichiometric ratios, mixed, and added as appropriate.

[0053] Note that "approximately the same" generally means adjusted to ±0.001%, but it can be outside that range. What is important is that the variation in the concentration of the additive in the crystal falls within a certain range that meets the required specifications. To achieve this, the proportion of the additive in the first layer must be appropriately determined based on the segregation phenomenon. This allows for the production of a crystal that is approximately homogeneous and meets the required specifications.

[0054] Here, the concentration of the additive in the sintered raw material for the second layer is set to be approximately the same as that of the additive in the crystal, but it is not limited to this and may be determined based on the effective segregation coefficient.

[0055] The first layer of sintering raw material 4 and the second layer of sintering raw material 6, whose raw material and additive concentrations have been adjusted in this way, become molten when heated by a high-frequency induction coil 1, as shown in Figure 3, and a layer of first molten liquid 41 and a layer of second molten liquid 51 are formed. For ease of explanation, the first layer of molten liquid 41 and the second layer of molten liquid 51 are clearly shown in the figure, but the second molten liquid 51 generated by melting one end of the second sintering raw material 6 mixes with the first molten liquid 41 simultaneously with melting, so they are not clearly separated as molten liquid layers. The second molten zone that temporarily occurs when the second sintering raw material 6 continues to melt in accordance with the crystal growth rate is shown as molten liquid 51 in Figure 3.

[0056] Next, a control method for growing a crystal using the crystallization method and apparatus according to this embodiment will be described.

[0057] In the third step S103 shown in Fig. 2, the high-frequency induction coil 1 is moved from one end side to the other end side of the melt 41 of the first layer shown in Fig. 3 as the grown crystal 7 grows. At this time, in the third step S103, control from the fourth step S201 to the fifth step S202 is executed as shown in Fig. 4. The fourth step S201 to the fifth step S202 are repeatedly executed while the grown crystal 7 is being grown, with an additive concentration that reflects the effective segregation coefficient at the interface between the melt and the crystal.

[0058] As shown in FIG. 4, in the fourth step S201, when the growth of the growing crystal 7 with the additive concentration reflecting the effective segregation coefficient is started, a load cell (not shown) measures the weight W of the growing crystal 7 precipitated on the seed crystal 8. C Measurement of the weight increase ΔW of the growing crystal 7 is started. C is stored as the weight change per unit time, and then the volume change ΔV of the growing crystal 7 per unit time is calculated using equation (1). CThe density ρ of the grown crystal 7 is converted into the density ρ of the grown crystal 7 and stored in a control unit (control means) not shown. C is a known value determined for each selected raw material and is stored in advance in the control unit. C is the volume ΔV of the melt obtained by mixing the first layer melt 41 and the second layer melt 51 shown in FIG. melt2 That is, the volumes of the first layer melt 41 and the second layer melt 51 decrease by the amount of the increase in volume due to the growth of the grown crystal 7 [equation (2)].

[0059]

number

[0060] Here, a control unit (not shown) controls the high frequency induction coil 1 to move to one end of the sintering raw material 6 of the second layer, which is located on the other end side of the melt 51 of the second layer. That is, the high frequency induction coil 1 is lowered relative to the water-cooled copper container 2, while heating one end of the sintering raw material 6 of the second layer to melt a part of it. In this way, the melted part of the sintering raw material 6 of the second layer is reduced in volume ΔV melt2 is supplied to the second layer melt 51 so as not to cause any change in the total volume of the first layer melt 41 and the second layer melt 51.

[0061] Such control is realized by a control unit (not shown) controlling the moving speed of the high frequency induction coil 1 so as to satisfy equation (3): where D is the inner diameter of the water-cooled copper vessel 2, V coil is the moving speed of the high frequency induction coil 1, W t1 and W t2 is the weight of the growing crystal 7 at a given time, and Δt is time. In other words, the moving speed of the high-frequency induction coil 1 is determined by the weight ((W t1 -W t2 ) / Δt) is the area of ​​the water-cooled copper container 2 (π / 4×D 2 ) to the movement amount per unit time of high frequency induction coil 1 (V coil ×Δt) and density ρ CIn practice, as described above, the weight is converted into volume, and therefore the calculation is performed as shown in equation (4). That is, the moving speed of the high-frequency induction coil 1 is controlled so as to be equal to the value obtained by multiplying the volume (ΔV melt2 ) is the area of ​​the water-cooled copper container 2 (π / 4×D 2 ) and the movement amount per unit time of high frequency induction coil 1 (V coil × Δt) is controlled so that it is equal to the volume calculated by multiplying

[0062]

number

[0063] The control unit (not shown) is equipped with a computer program that executes the above-described control procedures, and controls the output of the high-frequency induction coil 1, the lowering speed, and the amount of raw material supplied based on an input signal from a load cell (not shown). The control unit (not shown) is configured to display the volume of the sintered raw material 6 of the second layer that has melted and decreased on a display unit (not shown), and to instruct the supply of raw material having approximately the same additive concentration as the sintered raw material 6 of the second layer to the sintered raw material 6 of the second layer, or is provided with a supply unit (not shown) that supplies raw material directly to the sintered raw material 6 of the second layer.

[0064] Next, events occurring in the first layer melt 41 and the second layer melt 51 will be described.

[0065] As shown in FIG. 3, when heated by the high-frequency induction coil 1, the second layer of sintered raw material 6, the second layer of melt 51, and the first layer of melt 41 are stacked in this order from the bottom side inside the water-cooled copper container 2.

[0066] FIG. 5 shows a phase diagram of each raw material in FIG. 3. The solid phase region shown in FIG. 5 corresponds to the state of the crystal 7 in FIG. 3, where the solid state is maintained. The liquid phase region corresponds to the state in which the raw material is molten by heating, which corresponds to the state of the first layer melt 41 and the second layer melt 51. Between the solid phase region and the liquid phase region is a coexistence region in which the solid phase and the liquid phase coexist, such as the state between the grown crystal 7 and the first layer melt 41 shown in FIG. 3. In this embodiment, the additive concentrations of the first layer melt 41 and the second layer melt 51 are adjusted to be different. Since the solid solubility differs between the crystal 7 and the first layer melt 41 in the solid phase and the liquid phase, a segregation phenomenon occurs.

[0067] Here, as shown in Figure 5, at the same temperature (e.g., TX), the concentration of B in the liquid phase, B L1 is the concentration of B in the solid phase, B S1 It can be seen that it is higher than S1 Darker than B. S1 When the crystal (solid phase) is pulled up from the melt, the concentration B L1 is along the liquidus line L2 It changes (becomes darker) until B L2 The concentration in the solid phase obtained at this time is B S2 and (B S1 In this way, the B concentration in the solid phase continues to change along the solidus line, which creates the problem that the additive concentration is not constant.

[0068] To solve this problem, a double crucible consisting of an inner crucible and an outer crucible has been used in the past, as shown in Figure 6. In detail, the inner crucible contains an additive with a concentration of B L The inner crucible is filled with a melt of raw material with an additive concentration of BS, and the outer crucible is filled with a melt of raw material with an additive concentration of BS. The inner crucible is provided with a plurality of communication holes that communicate with the outer crucible. In this configuration, when growing a crystal, the following control is performed. That is, the amount of the additive concentration B S The weight of the grown crystal and the concentration B of the additive supplied from the outer crucible to the grown crystal through the communicating hole provided in the inner crucible STo maintain the weight balance with the weight of additive concentration B S By controlling the amount of raw material in the inner crucible, the additive concentration B L is kept constant, and the additive concentration B in the solid phase that crystallizes from it S However, this double crucible method has problems such as the need to use two types of crucibles, and when both the inner and outer crucibles are made of precious metals, the method becomes very expensive.

[0069] In this embodiment, the growth of the grown crystal 7 is controlled by regarding the first layer of melt 41 as the concentration in the inner crucible and the second layer of melt 51 as the concentration in the outer crucible. According to the configuration of this embodiment, a simple configuration consisting of the water-cooled copper container 2 and the sintering source material supporting layer 3 shown in FIG. 3 , and the stacking of the first layer of sintering source materials 4 and the second layer of sintering source materials 6, realizes a function equivalent to that of a double crucible. The sintering source material supporting layer 3 corresponds to the outer wall of the inner crucible in the double crucible, and the portion of one end of the second layer of sintering source materials that is appropriately melted and supplied as a molten liquid to the first melting zone corresponds to the function of the communicating hole of the inner crucible in the double crucible. As the grown crystal 7 grows, the high-frequency induction coil 1 is controlled to lower so as to melt the second layer of sintering source materials 6 in order to supply the second layer of melt 51. Furthermore, this structure differs from the conventional double crucible in that it is only necessary to melt a portion of the sintered body in the second layer as appropriate, which is also highly effective in terms of energy consumption.

[0070] Furthermore, as in the conventional double crucible method shown in FIG. 6, the additive concentration B SBy continuously supplying the raw material of , the additive concentration BL of the first layer melt 41 can be maintained constant, and it is therefore possible to produce a long grown crystal 7. The method of continuously supplying the raw material of additive concentration BS can be done by pouring it from above one end side (liquid surface) of the first layer melt 41, but this is not limitative. For example, it is also possible to provide a communication hole in part of the water-cooled copper vessel 2 that communicates with the outside, and supply the raw material from the communication hole. The communication hole may be provided on the side or bottom of the water-cooled copper vessel 2 as appropriate. In addition, when the additive concentration B S The raw material may be in the form of, for example, liquid, powder, shot, wire, rod, or pellet.

[0071] Such crystal growth methods may include, for example, the pulling method, the Bridgman method, the Vertical Gradient Freeze (VGF) method, the chiroporous method, the heat exchange method (HEM), the Edge-defined Film-fed Growth (EFG) method, and the zone melt method, but are not limited to these, and various methods may be applied.

[0072] In this embodiment, the sintering raw material 4 of the first layer is melted, followed by the sintering raw material 6 of the second layer. However, when the sintering raw material 4 of the first layer is first melted, the sintering raw material 4 of the first layer and a portion of the sintering raw material 6 of the second layer may be melted simultaneously. If the size of the high-frequency induction coil 1 is large enough to encompass the size of the sintering raw material 4 of the first layer in the thickness direction, simultaneous melting is possible. After that, the sintering raw material 6 of the second layer is additionally melted as appropriate, similar to this embodiment.

[0073] In addition, when a manufacturing method is used in which the grown crystal 7 is pulled up in a direction away from the melt at a predetermined speed, the sintering raw material body 6 of the second layer is controlled to melt in parallel with the pulling, so that the volume of the melt layer in which the melt 41 of the first layer and the melt 51 of the second layer are mixed can be kept constant.

[0074] In this embodiment, the sintered raw materials for the first layer are stacked in the order of the second sintered raw materials from one end to the other end. However, depending on the value of the segregation coefficient, the sintered raw materials for the second layer may be stacked in the order of the first sintered raw materials. In this case, the melting order remains the same. After the first molten liquid layer 41 is formed by controlling the position of the high-frequency induction coil 1, the second sintered material is gradually melted to sequentially form the second molten liquid layer 51. In this configuration, the second sintered material is located at the top, making it easier to supply additional raw materials from a supply unit (not shown), simplifying the structure of the device.

[0075] In this embodiment, melting was controlled so that the volume of the melt layer formed by mixing the first layer melt 41 and the second layer melt 51 was constant. However, other methods are also possible. By maintaining a constant concentration of the additive in at least the melt layer formed by mixing the first layer melt 41 and the second layer melt 51, the additive concentration in the growing crystal can be kept constant. Therefore, for example, if it is assumed that the volume of the mixed melt layer is allowed to gradually decrease, the additive concentration in the second sintered body may be made lower than the concentration in the crystal, and the volume of the additional melted second sintered body may be controlled to be less than the increase in the volume of the growing crystal. In this case, since the mixed melt gradually decreases, the manufacturing continuity is inferior to that of this embodiment. However, the amount of melted second sintered body during the crystal growth process can be reduced, thereby reducing the power consumption used for melting.

[0076] In addition, the amount of additives may not only be mixed in advance based on the segregation phenomenon, but may also be adjusted and controlled in real time within the manufacturing equipment. For example, storage sections for the raw materials and additives (not shown) are provided, and when the additive concentration required in the crystal is input from the display section, the amount of additive to be mixed into the first sintered raw material is determined according to that value and the effective segregation coefficient, and mixing is controlled.

[0077] Next, a more detailed explanation will be given using an example.

[0078] [Example 1] First, a Ce:GAGG crystal was grown in advance by the pulling method using a conventional noble metal crucible, and the Ce concentration distribution in the growth direction was evaluated by composition analysis. From the data, it was confirmed that the effective segregation coefficient of Ce is 0.336 when Ce is contained at a molar ratio of 1% at the Gd site during crystal growth by the pulling method.

[0079] Next, the production of Ce:GAGG crystals will be described as Example 1. First, taking into account the effective segregation coefficient of Ce (0.336) at the interface between the GAGG melt and the crystal, the additive (Ce) concentration of the raw material powder was divided into two raw material layers: the first raw material layer and the second raw material layer. That is, the additive concentration of the first raw material layer was Ce:(Ce + Gd) = 2.98:100 so that the Ce ratio was the reciprocal of the effective segregation coefficient (1 / 0.336 ≒ 2.98), and the other additives were weighed and mixed in stoichiometric ratios. The additive concentration of the second raw material layer was Ce:(Ce + Gd) = 1:100 so that the Ce ratio was approximately the same as the effective segregation coefficient, and the other additives were weighed and mixed in stoichiometric ratios. In this example, a green compact was used for the second raw material layer.

[0080] The prepared raw materials were loaded into a water-cooled copper basket, and a raw material melt was produced by high-frequency heating using the first raw material layer. A GAGG single crystal cut along the b-axis direction and measuring 3 mm x 3 mm x 50 mm in length was used as the seed crystal. The growth conditions were a crystal rotation speed of 5 rpm, a pulling rate of 0.5 to 1 mm / h, and an atmospheric air. As the crystal grew, the melt reached the second raw material layer, and crystal production proceeded while melting the raw materials in the second raw material layer. The crystal obtained in this manner is designated Example 1.

[0081] The distribution of Ce concentration in the growth direction of the obtained crystal is shown in Figure 7A. The vertical axis represents the additive concentration, and the horizontal axis represents the crystallization rate. The crystallization rate is the value obtained by dividing the weight of the grown crystal at a certain point in time, measured based on the input signal of a load cell (not shown), by the total weight of the sintering raw material 4 of the first layer and the sintering raw material 6 of the second layer. As shown in Figure 7A, the Ce concentration is low in the early stages when the crystallization rate is low, but gradually increases, then stabilizes and becomes a nearly uniform additive concentration.

[0082] Next, Ce:GAGG crystals were produced in the same manner as in Example 1, except that the raw material layers were not separated. The crystals thus obtained are designated as Comparative Example 1.

[0083] The distribution of the Ce concentration in the growth direction of the obtained crystal is shown in Figure 7B. As shown in Figure 7B, the Ce concentration was low in the early stages when the crystallization rate was low, and gradually increased, resulting in a state in which a substantially uniform additive concentration was not obtained.

[0084] As shown in Figures 7A and 7B, the results of Example 1 and Comparative Example 1 confirm that by providing the first raw material layer and the second raw material layer, it is possible to increase the proportion of crystals in which the additive concentration is approximately uniform.

[0085] [Example 2] Next, the production of Ce-doped (La, Gd)2SiO7 (Ce:La-GPS) crystals will be described as Example 2. First, as in Example 1, a Ce:La-GPS crystal was grown in advance by a pulling method using a normal noble metal crucible, and the Ce concentration distribution in the growth direction was evaluated by composition analysis. From the data, it was confirmed that the effective segregation coefficient of Ce was 1.02 when 1% Ce was included in the molar ratio at the Gd site during crystal growth by the pulling method.

[0086] Commercially available high-purity GdO, LaO, SiO, and CeO (each 99.999% pure) raw material powders were prepared. Taking into account the effective segregation coefficient (1.02) at the interface, the additive (Ce) concentration of the raw material powders was divided into two raw material layers: the first raw material layer and the second raw material layer. Specifically, the additive concentration of the first raw material layer was Ce:(Ce + La + Gd) = 0.980:100, so that the Ce ratio was the reciprocal of the effective segregation coefficient (1 / 1.02 ≒ 0.980). The other additives were weighed and mixed in stoichiometric ratios. The additive concentration of the second raw material layer was Ce:(Ce + La + Gd) = 1:100, so that the Ce ratio was approximately equal to the effective segregation coefficient. The other additives were weighed, mixed, and processed in stoichiometric ratios. In this example, a compact was used for the second raw material layer.

[0087] The prepared raw materials were loaded into a water-cooled copper basket, and a raw material melt was produced by high-frequency heating using the first raw material layer. The seed crystal was a 3 mm x 3 mm x 50 mm long La-GPS single crystal cut along the b-axis orientation. The growth conditions were a crystal rotation speed of 5 rpm, a pulling rate of 0.5-1 mm / h, and an atmospheric air. As the crystal grew, the melt reached the second raw material layer, and crystal production proceeded while melting the raw materials in the second raw material layer. The crystal obtained in this manner is designated Example 2.

[0088] The distribution of the Ce concentration in the growth direction of the obtained crystal is shown in Figure 7A. As shown in Figure 7A, the Ce concentration was high in the early stages when the crystallization rate was low, and gradually decreased, then stabilized and became a nearly uniform additive concentration.

[0089] Next, a Ce:La-GPS crystal was produced in the same manner as in Example 2, except that the raw material layers were not separated. The crystal thus obtained is designated as Comparative Example 2.

[0090] The distribution of the Ce concentration in the growth direction of the obtained crystal is shown in Figure 7B. As shown in Figure 7B, the Ce concentration was high in the early stage when the crystallization rate was low, and gradually decreased, resulting in an almost uniform additive concentration state.

[0091] As shown in Figures 7A and 7B, the results of Example 2 and Comparative Example 2 confirm that by providing the first raw material layer and the second raw material layer, it is possible to increase the crystallization rate at which the additive concentration in the crystal is approximately uniform. [Example 3]

[0092] Next, Nd-doped Y3Al5O 12The case of producing a (Nd:YAG) crystal will be described as Example 3. First, as in Example 1, Nd:YAG crystal was grown in advance by a pulling method using a normal noble metal crucible, and the Nd concentration distribution in the growth direction was evaluated by composition analysis. From the data, it was confirmed that the effective segregation coefficient of Ce was 0.18 when Nd was contained at a molar ratio of 1% at the Y site during crystal growth by the pulling method.

[0093] Commercially available high-purity Y2O3, Al2O3, and Nd2O3 (each 99.999% pure) raw material powders were prepared. Taking into account the effective segregation coefficient (0.18) at the interface, the additive (Nd) concentration of the raw material powders was divided into two raw material layers: the first raw material layer and the second raw material layer. Specifically, the additive concentration of the first raw material layer was Nd:(Nd + Y) = 5.56:100, so that the Nd ratio was the reciprocal of the effective segregation coefficient (1 / 0.18 ≒ 5.56), and the other additives were weighed and mixed in stoichiometric ratios. The additive concentration of the second raw material layer was Nd:(Nd + Y) = 1:100, so that the Ce ratio was approximately equal to the effective segregation coefficient, and the other additives were weighed and mixed in stoichiometric ratios, and then melted and placed. In this example, a compacted powder was used for the second raw material layer.

[0094] The prepared raw materials were loaded into a water-cooled copper basket, and a raw material melt was produced by high-frequency heating using the first raw material layer. A YAG single crystal cut along the b-axis direction and measuring 3 mm x 3 mm x 50 mm in length was used as the seed crystal. The growth conditions were a crystal rotation speed of 5 rpm, a pulling rate of 0.5 to 1 mm / h, and an atmospheric air atmosphere. As the crystal grew, the melt reached the second raw material layer, and crystal production proceeded while melting the raw materials in the second raw material layer. The crystal obtained in this manner is designated Example 3.

[0095] The distribution of the Nd concentration in the growth direction of the obtained crystal is shown in Figure 7A. As shown in Figure 7A, the Nd concentration was low in the early stage when the crystallization rate was low, and gradually increased, then stabilized and became a nearly uniform additive concentration.

[0096] Next, a Nd:YAG crystal was produced in the same manner as in Example 3, except that the raw material layers were not separated. The crystal thus obtained was designated Comparative Example 3.

[0097] The distribution of the Nd concentration in the growth direction of the obtained crystal is shown in Figure 7B. As shown in Figure 7B, the Nd concentration was low in the early stage when the crystallization rate was low, and gradually increased, resulting in a state in which a substantially uniform additive concentration was not obtained.

[0098] As shown in Figures 7A and 7B, the results of Example 3 and Comparative Example 3 confirmed that by providing the first raw material layer and the second raw material layer, it was possible to increase the crystallization rate at which the additive concentration in the crystal was approximately uniform.

[0099] An example of a crystal that can be controlled with such additives is Ce-doped Gd3(Ga,Al)5O 12 (Ce:GAGG, for example, manufactured by C&A, is preferred), Ce-doped Lu2SiO5 (Ce:LSO, for example, manufactured by Crystal Photonics, Inc. is preferred), Ce-doped (Lu,Y)SiO5 (Ce:LYSO, for example, manufactured by Crystal Photonics, Inc. is preferred), Ce-doped (Lu,Gd)2SiO5 (Ce:LGSO, for example, manufactured by Oxide Corporation is preferred), Tl:CsI, Tl:NaI, CeBr3, Ce:LaBr3, Tb3Ga5O 12 (Preferably manufactured by Oxide Corporation, for example), Ce:LiCAF (Preferably manufactured by C&A Corporation, for example), Eu-doped LiCalAlF6 (Eu:LiCAF, preferably manufactured by C&A Corporation, for example), Ce-doped LiSrAlF6 (Ce:LiSAF, preferably manufactured by C&A Corporation, for example), Eu-doped LiSrAlF6 (Eu:LiSAF, preferably manufactured by C&A Corporation, for example), Mg-doped LiTaO3 (Preferably manufactured by Yamaju Ceramics, for example), Mg-doped LiNbO3 (Preferably manufactured by Yamaju Ceramics, for example), sapphire, Nd-doped Y3Al5O 12 (Nd:YAG), Nd-doped Lu3Al5O 12 (Nd:LuAG), Yb-added Y3Al5O 12(Yb:YAG), Yb-added Lu3Al5O 12 Examples of suitable crystals include (Yb:LuAG), Ga2O3 (preferably manufactured by Novel Crystal Technology Co., Ltd.), REAlO3, REVO4, (RE = rare earth element), gallium oxide, silicon, alloys (preferably manufactured by C&A Co., Ltd., for example, Ruscaloy®), and iridium, but the crystals are not limited to these.

[0100] When the additive is the luminescence center of the luminescent material, it is possible to obtain a long, substantially homogeneous scintillator crystal or laser crystal with a desired additive concentration, or when the additive is a donor or acceptor of the semiconductor material, it is possible to obtain a long, substantially homogeneous semiconductor crystal with a desired additive concentration.

[0101] In this embodiment, melting and heating is performed by moving the high-frequency induction coil based on information about the position of the first sintering raw material or the second sintering raw material. For example, a setting means may be provided on a display unit (not shown) that can set the thickness of each of the first sintering raw material and the second sintering raw material stacked in the crystal growth direction, and the initial position information of at least one of the first sintering raw material or the second sintering raw material. Alternatively, the position information of each of the first sintering raw material and the second sintering raw material may be set and stored. These values ​​are stored in a memory (not shown), and the movement of the high-frequency induction coil 1 described in this embodiment is controlled based on these values. However, this is not limited to this. A sensor that detects the position of the first sintering raw material or the second sintering raw material may be provided to acquire the position information, or predetermined position information may be acquired by receiving it from an external computer or the like.

[0102] Alternatively, assuming that a sintering raw material of a predetermined size is used, the amount of movement of the high-frequency induction coil itself may be controlled to move a fixed amount each time based on that. In this case, the fixed amount of movement is a value that reflects the position of each layer, and this corresponds to information about the position. The location where the program containing this fixed amount is recorded corresponds to the memory. In either case, as long as the positions of the first and second layers can be determined, the amount of movement of the high-frequency induction coil can be appropriately controlled by the control unit, so any other means may be used to obtain information about the position.

[0103] In this embodiment, two layers are used, a first sintered body layer and a second sintered body layer, but this is not limiting and three or more layers may be used, such as providing a third sintered body layer. It is conceivable to gradually decrease the concentration of additives in each layer to utilize the raw material without waste to the end.

[0104] As described above, according to the embodiment of the present invention, the raw material is composed of multiple layers with different concentrations, so that a crystal growth method can be provided that can industrially advantageously produce crystals with excellent homogeneity in additive concentration. In conventional melt growth methods, batch production is performed, completing crystal production while the crystal ratio is still low, before variations in properties begin to appear. This method can also cause poor yields. However, with the present invention, it has been confirmed that variations in properties do not occur even when the crystallization rate is high, improving yields. Furthermore, since crystals can be grown continuously rather than in batch production, this method is advantageous for industrial mass production.

[0105] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0106] 1...high frequency induction coil, 2...water-cooled copper container, 3...sintering raw material holding layer, 4...first layer of sintering raw material, 6...second layer of sintering raw material, 7...growing crystal, 8...seed crystal, 10...crystal growth apparatus, 41...first layer of melt, 51...second layer of melt.

Claims

1. A crystal growth method in which a raw material containing an additive is melted by applying high frequency waves to the raw material and directly heating the raw material while cooling the outer periphery of the raw material below the melting point of the raw material, and a crystal is grown from the melt of the raw material, wherein the raw material consists of multiple layers with different concentrations of the additive.

2. 2. The crystal growth method according to claim 1, a crystal growth method in which the plurality of layers are composed of a first source layer and a second source layer adjacent to each other, the dopant concentration of the first source layer being approximately the same as the dopant concentration of the crystal multiplied by the reciprocal of an effective segregation coefficient, and the dopant concentration of the second source layer being approximately the same as the dopant concentration of the crystal.

3. 3. The crystal growth method according to claim 2, A crystal growth method in which the raw material is directly heated by the high frequency waves, and a crystal is grown while a high frequency coil for applying the high frequency waves is moved relatively from the first raw material layer toward the second raw material layer so as to melt the raw material in a weight that is approximately the same as the weight of the crystal grown from the melt of the raw material.

4. 4. The crystal growth method according to claim 3, A crystal growth method in which the weight of the second raw material layer melted per unit time when a high-frequency coil is moved relatively in the direction of the second raw material layer is approximately the same as the weight of the crystal grown per unit time.

5. The crystal growth method according to any one of claims 1 to 4, A crystal growth method in which the raw material is added to the melt at an additive concentration substantially the same as that of the additive concentration of the crystal.

6. 6. The crystal growth method according to claim 5, A crystal growth method in which the weight of the raw material added per unit time is equal to the weight of the crystal grown per unit time.

7. 7. The crystal growth method according to claim 6, The crystal growth method, wherein the added raw material is in the form of a liquid, powder, shot, wire, rod or pellet.

8. 8. The crystal growth method according to claim 7, A crystal growth method in which the additive added to the raw material is a luminescence center of a luminescent material.

9. 9. The crystal growth method according to claim 8, The crystal growing method, wherein the crystal is a scintillator crystal.

10. 9. The crystal growth method according to claim 8, A crystal growth method wherein the crystal is a laser crystal.

11. 8. The crystal growth method according to claim 7, A crystal growth method in which the additive is a donor or acceptor of the semiconductor material.

12. a heating means for directly heating the raw material containing the additive by a high-frequency heating method; a heating means for directly heating the raw material containing the additive by a high-frequency heating method; a cooling means for cooling the outer periphery of the raw material containing the additive to a temperature below the melting point of the raw material; a memory storing information about the position of each layer for a plurality of layers of raw materials having different concentrations of the additive; a control means for controlling the movement of the heating means based on the information about the position so as to melt the raw material in one layer among the plurality of raw material layers and melt at least a portion of the raw material in another layer; a crystal holding means for holding crystals generated from the melt of the raw material; A crystal growth apparatus comprising:

13. 13. The crystal growing apparatus of claim 12, the one layer is a layer of the raw material having an additive concentration determined based on an effective segregation coefficient at an interface between the melt and the crystal, The crystal growing apparatus, wherein the control means moves the heating means so as to first melt all of the raw material of the one layer, and then melt at least a portion of the other layer.

14. 13. The crystal growing apparatus of claim 12, The control means further controls the crystal holding means to move in a direction away from the melt, and moves the heating means in parallel with the movement so as to melt at least a portion of the raw material of the other layer.

15. 13. The crystal growing apparatus of claim 12, a load cell for measuring a change in weight of the crystal held by the crystal holding means; The control means controls the amount of movement of the heating means for melting the other layer based on the change in weight measured by the load cell.

16. 13. The crystal growing apparatus of claim 12, a crystal growth apparatus including a supply section for additionally supplying the raw material having an additive concentration substantially the same as that of the other layer;

17. The crystal growth apparatus according to any one of claims 12 to 16, A crystal growth apparatus for growing crystals by any of the following methods: pulling method, Bridgman method, Vertical Gradient Freeze (VGF) method, Chiroporous method, Heat Exchange Method (HEM), Edge-defined Film-fed Growth (EFG) method, and Zone Melt method.

18. A program for causing a computer to execute a process for controlling the concentration of an additive based on an effective segregation coefficient at the interface between the melt and the crystal, in a crystal growth method in which a raw material containing an additive is directly heated by a high-frequency heating method and a crystal is produced from the melt of the raw material.

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