JP2018203575A - Crystal growth apparatus and crystal growth method using the same - Google Patents

Abstract

To provide a crystal growth apparatus and a crystal growth method using the same such that a single-crystal growth apparatus employing a Czochralski method can efficiently and easily prevent raw material solidification at a crucible bottom part resulting from an increase in length of a grown crystal body.SOLUTION: A crystal growth apparatus has: a metallic crucible 10 capable of containing and holding a raw material melt 160; an induction coil 80 provided at a circumference of the crucible; a crucible base 20 capable of mounting and supporting the crucible on an upper surface 21; and a bottom-part auxiliary heating body 90 provided in the crucible base, the crucible base having a through hole 22 penetrating between the upper surface and bottom-part auxiliary heating body. A single-crystal growth method comprises the processes of: containing the raw material melt in the crucible; heating the raw material melt in a state in which a lower part of the through hole of a movable part moving in an annular cavity is not linked to an upper part of the through hole of a frame part, and lifting a single crystal 170; and lifting the single crystal while the movable part is moved so that the lower part of the through hole of the movable part is linked to the upper part of the through hole of the frame part.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a crystal growth apparatus and a crystal growth method using the same.

  As a method for producing an oxide single crystal, a crucible filled with a raw material to be an oxide single crystal is heated to a high temperature to melt the raw material, and a seed crystal is brought into contact with the liquid surface of the raw material melt in the crucible from above. After that, a crystal growth method by the Czochralski method for growing an oxide single crystal having the same orientation as that of the seed crystal by raising it while rotating is widely implemented.

  In single crystal growth by the Czochralski method, an induction coil is arranged around the crucible, and an eddy current is generated in the crucible when a high-frequency current is passed through the induction coil. As a result, the crucible generates heat and the raw material in the crucible is Melt.

  As the pulling progresses, the upper part of the single crystal is cooled by the low-temperature heat transmitted from the seed rod (pulling shaft), but when the heating element is only a crucible, the temperature distribution in the growing single crystal is In order to increase the size of the crucible, the upper part of the crucible is kept warm. For example, in order to suppress cracks due to thermal stress due to temperature differences in the crystal, a cylindrical after heater, which is a heating element other than the crucible, is disposed on the upper part of the crucible. Also, a donut-shaped reflector may be arranged to keep the upper part of the crucible warm.

  By the way, in recent years, the market for oxide single crystals, particularly lithium tantalate, is expanding as a surface acoustic wave device material, and the pulling length of the single crystal is gradually increased in order to secure the production amount. Accompanying this increase in length, it is easy to cause crystal crystallization, cracking due to thermal distortion during cooling, or solidification of the raw material at the bottom of the crucible. It is a cause to reduce the rate. In particular, solidification of the raw material at the bottom of the crucible is a big problem for lengthening. In single crystal growth by the Czochralski method, a seed crystal is brought into contact with the raw material melting surface of the crucible and rotated, and the crystal is grown while being gradually pulled up. In order to grow the crystal, the temperature gradient in the furnace must be properly controlled, and the temperature in the furnace must be lowered within an appropriate range as the crystal grows longer. However, even if the upper part where the crystal is pulled is at a temperature suitable for crystal growth, the temperature is lowered at the bottom of the crucible, and in some cases, solidification may start from the center of the bottom of the crucible. The center of the bottom of the crucible is away from the induction coil and is easy to solidify. In addition, if the crystal growth is continued in this state, the solidified crystal grows upward from the bottom of the crucible, and is fused with the crystal being grown, resulting in a situation where the growth must be stopped. There is.

  For this reason, Patent Document 1 discloses a method of installing an auxiliary heating element having a predetermined length in the height direction of the crucible that is smaller than the area of the bottom surface of the crucible in the space in the crucible base below the crucible. Has been. The auxiliary heating element has various shapes, and there is a description that any shape can be used.

  Further, Patent Document 2 discloses a configuration in which a disk-shaped member forming the bottom surface of a crucible made of a cylindrical member protrudes radially outward from the outer peripheral surface of the cylindrical member to form a flange-shaped outer peripheral portion. . Since the flange-like outer peripheral portion is located closest to the heating coil, the temperature can be increased quickly with high efficiency, and a temperature gradient can be added to the crucible such that the lower portion has a higher temperature than the upper portion.

JP 54-162686 A JP 2004-284854 A

  However, the configuration described in Patent Document 1 has a problem that heat transfer efficiency from the auxiliary heating element to the crucible is not good because the auxiliary heating element is provided in the crucible base. In addition, the effect of heating the bottom of the crucible by placing the auxiliary heating element under the crucible is within a certain range. However, the eddy current is generated in the auxiliary heating element by passing a high-frequency current through the induction coil and heated. The position and amount of heat generated vary depending on the shape of the auxiliary heating element. Of course, there is also an influence on the melt in the crucible, but Patent Document 1 does not consider the shape of the auxiliary heating element and the influence on the melt in the crucible, and the temperature control of the melt is sufficient. There was a problem that was not made.

  In the configuration described in Patent Document 2, the crucible can be directly heated by the flange-shaped outer peripheral portion. However, since the temperature is closest to the heating coil and becomes the highest, the deterioration is most severe. However, since it is formed integrally with the crucible, there is a problem that the entire crucible must be frequently replaced due to frequent deterioration of the outer peripheral portion of the flange.

  Therefore, in view of the above circumstances, the present invention provides a crystal growth apparatus that can efficiently and easily prevent the solidification of the crucible bottom accompanying the lengthening of the crystal to be grown in the single crystal growth apparatus by the Czochralski method, and An object of the present invention is to provide a crystal growth method using this.

In order to achieve the above object, a crystal growth apparatus according to one aspect of the present invention includes a metal crucible capable of storing and holding a raw material melt,
An induction coil provided around the crucible;
A crucible base capable of placing and supporting the crucible on the upper surface;
A bottom auxiliary heating element provided in the crucible base,
The crucible base has a through-hole penetrating between the upper surface and the bottom auxiliary heating element.

  According to the present invention, it is possible to provide a single crystal growth apparatus and a crystal growth method using the single crystal growth apparatus that can cope with an increase in the crystal growth length without generating defects such as cracks at low cost.

It is the schematic which showed an example of the crystal growth apparatus which concerns on the 1st Embodiment of this invention. It is sectional drawing which showed the bottom part auxiliary | assistant heat generating body and crucible base of an example of the crystal growth apparatus which concerns on embodiment of this invention. It is the figure which showed the crucible base of an example of the crystal growing apparatus which concerns on the 1st Embodiment of this invention. It is the perspective sectional view showing an example of the crucible stand of the crystal growth device concerning a 2nd embodiment of the present invention. It is the figure which showed the bottom part auxiliary heating element and crucible base of an example of the crystal growth apparatus concerning the 2nd Embodiment of the present invention. It is the figure which showed an example of the rotation mechanism of a movable part. It is the result of having simulated the temperature distribution near the crucible of the last stage of the growth of an example of the crystal growth apparatus which concerns on embodiment of this invention. It is the figure which showed the structure of the crystal growth apparatus used as the simulation model of Fig.7 (a). It is the graph which simulated temperature distribution of the melt in the crucible of the last stage of the growth of an example of the crystal growth device concerning a 2nd embodiment of the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

The crystal growth apparatus using the chocoskey method of the present invention includes lithium niobate LiNbO ₃ (hereinafter referred to as LN), lithium tantalate LiTaO ₃ (hereinafter referred to as LT), and yttrium aluminum garnet grown in the air or in an inert gas atmosphere. This is a crystal growth apparatus used for manufacturing an oxide single crystal such as Y ₃ Al ₅ O ₁₂ (hereinafter referred to as YAG). The Czochralski method is called a seed cut out according to a certain crystal orientation. Usually, the tip of a rectangular parallelepiped with a side of about several millimeters is infiltrated into the melt of the same composition, and gradually pulled up while rotating. Thus, the single crystal is manufactured by increasing the diameter while propagating the properties of the seed crystal.

[First Embodiment]
FIG. 1 is a schematic diagram showing an example of a crystal growth apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the crystal growing apparatus according to the first embodiment includes a crucible 10, a crucible base 20, a reflector 30, an after heater 40, heat insulating materials 50 and 51, and a refractory 60. The lifting shaft 70, the induction coil 80, the bottom auxiliary heating element 90, the power source 100, and the control unit 110 are provided. The heating means is the crucible 10, the after heater 40, the bottom auxiliary heating element 90, and the induction coil 80 for heating them. The power source 100 is provided to supply high frequency power to the induction coil 80.

  In the crystal growing apparatus according to the present embodiment, the crucible 10 is placed on the upper surface 21 of the crucible base 20. An after heater 40 is installed above the crucible 10 through a reflector 30. A heat insulating material 50 is installed so as to surround the crucible 10. Furthermore, a heat insulating material 51 is provided so as to surround the after heater 40. A refractory 60 is provided outside the heat insulating materials 50 and 51 to cover the entire periphery of the crucible 10. An induction coil 80 is disposed outside the side surface of the refractory 60.

  A bottom auxiliary heating element 90 is installed in a part of the crucible base 20. In addition, a part of the crucible base 20 is provided with a through hole 22 that connects the bottom auxiliary heating element 90 to the bottom of the crucible. That is, a through-hole 22 that passes between the upper surface 21 of the crucible base 20 and the bottom auxiliary heating element 90 is provided. Although details will be described later, the bottom surface of the crucible 10 can be directly heated by the heat generated in the bottom auxiliary heating element 90 by providing the through hole 22.

  The refractory 60 having the induction coil 80 provided outside is placed on a support base (not shown). In addition, a chamber (not shown) covers the periphery of the induction coil 80.

  The crucible 10 and the heat insulating material 50 provided around the crucible 10 constitute a hot zone part. Further, a lifting shaft 70 is provided above the crucible 10. The pulling shaft 70 has a seed crystal holding portion 71 at the lower end, and is configured to be lifted and lowered by a pulling shaft driving portion 72. Furthermore, a power source 100 and a control means 110 are provided outside the periphery of the chamber (not shown).

  In FIG. 1, a seed crystal 150, a crystal raw material 160, and a pulled single crystal (also referred to as a crystal) 170 are shown as related constituent elements.

  Next, individual components will be described.

  The crucible 10 is a container for storing and holding the crystal raw material 160 and growing the single crystal 170. The crystal raw material 160 is held in the state of a melt in which a metal to be crystallized is melted. The material of the crucible is made of platinum, iridium or the like having heat resistance although it depends on the crystal raw material 160.

  Since the single crystal 170 to be grown moves away from the crucible 10 as the pulling of the single crystal 170 progresses, the temperature distribution of the single crystal 170 becomes large and problems such as cracking of the single crystal 170 may occur. In order to improve this, an after heater 40 is installed above the crucible 10 to maintain an appropriate temperature distribution. The shape of the after heater 40 is a cylindrical shape whose inner diameter is larger than the diameter of the oxide single crystal 170 to be obtained and smaller than the diameter of the crucible 10. The total length is set, for example, longer than half of the total length of the oxide single crystal 170 to be obtained and shorter than twice. As a material of the crucible 10, for example, a metal such as iridium or platinum is used.

  The bottom auxiliary heating element 90 is installed in the crucible base 20 so as to form a part of the crucible base 20. Further, a through hole 22 is provided in a part of the upper crucible base 23 between the bottom heating element 90 of the crucible base 20 and the crucible bottom so as to connect the bottom auxiliary heating element 90 to the crucible bottom. Details of the bottom auxiliary heating element 90 and the crucible base 20 will be described later.

  The induction coil 80 is means for heating the crucible 10, the after heater 40 and the bottom auxiliary heating element 90, and is arranged so as to surround the crucible 10, the after heater 40 and the bottom auxiliary heating element 90. The induction coil 80 may be in any form as long as it can induction-heat the crucible 10, the after-heater 40, and the like. For example, the induction coil 80 is configured as a high-frequency induction heating device including a high-frequency heating coil. In this case, the power source 100 is configured as a high frequency power source that supplies high frequency power to the induction coil 80.

  The power supply 100 supplies power not only to the induction coil 80 but also to the entire crystal growth apparatus.

  A chamber (not shown) has a function of blocking high heat from the crucible 10 and the induction coil 80 and accommodating them.

  A support base (not shown) is a support base for supporting the entire refractory 60.

  The pulling shaft 70 is a means for holding the seed crystal 150, bringing the seed crystal 150 into contact with the surface of the crystal raw material (melt) 160 held in the crucible 10, and pulling up the single crystal 170 while rotating. The pulling shaft 70 has a seed crystal holding portion 71 for holding the seed crystal 150 at the lower end portion, and also has a pulling shaft drive mechanism 72 having a motor as a rotation mechanism. The motor is a rotational drive mechanism for performing an operation of pulling up the crystal while rotating the crystal.

  The controller 110 is a means for controlling the entire crystal growth apparatus, and controls the operation of the entire crystal growth apparatus including the crystal growth process. For example, the control unit 110 includes a CPU (Central Processing Unit), a central processing unit, and a memory such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and may be configured by a microcomputer that operates according to a program. However, it may be composed of an electronic circuit such as an ASIC (Application Specified Integra Circuit) developed for a specific application.

  The crystal growth apparatus according to this embodiment can be applied to various crystal raw materials 160, and the type of the crystal raw material 160 is not limited, but, for example, a lithium tantalate raw material may be used. In addition, a crystal raw material 160 for growing various oxide single crystals can be used.

  Next, the bottom auxiliary heating plate 90 and the crucible base 20 which are features of the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view showing the bottom auxiliary heating element 90 and the crucible base 20 as an example of the crystal growth apparatus according to the embodiment of the present invention.

  As shown in FIG. 2, the bottom auxiliary heating element 90 according to the embodiment of the present invention is installed in the crucible base 20 so as to constitute a part of the crucible base 20. A portion between the bottom auxiliary heating element 90 and the bottom of the crucible (the upper surface 21 of the crucible base 20) of the crucible base 20 is referred to as an upper crucible base 23. A part of the upper crucible base 23 between the bottom auxiliary heating element 90 and the bottom of the crucible (the upper surface 21 of the crucible base 20) is provided with a plurality of through holes 22 connecting the bottom auxiliary heating element 90 to the bottom of the crucible. .

  First, the bottom auxiliary heating element 90 will be described in more detail.

  In the single crystal growth by the Czochralski method, the seed crystal 150 is brought into contact with the melted crystal raw material 160 in the crucible 10 and pulled up to cool the crystal 170 to grow a crystal. As the crystal length increases, the crystal body 170 is cooled, and the temperature in the upper part of the furnace decreases. The raw material melt 160 in the crucible 10 also decreases and the amount of heat generation also decreases, and the solidification of the raw material starts from the center of the bottom of the crucible farthest from the induction coil 80. In order to prevent this, in the crystal growing apparatus according to the present embodiment, the bottom auxiliary heating element 90 is arranged in the crucible base 20 below the crucible bottom so as to form a part of the crucible base 20.

  As shown in FIG. 2, the bottom auxiliary heating element 90 is disposed at a predetermined height position of the crucible base 20 so as to form a part of the crucible base 20 below the crucible 10. The crucible base 20 is composed of a plurality of heat-resistant materials 26. The bottom auxiliary heating element 90 is installed between the stacked heat-resistant materials 26. That is, a plurality of heat-resistant materials 26 configured to form a cylindrical block are stacked to constitute the crucible base 20, and are inserted into predetermined positions between the plurality of heat-resistant materials 26. A bottom auxiliary heating element 90 is disposed. For this reason, it is preferable to adjust the thickness of the heat-resistant material 26 so that the bottom auxiliary heating element 90 has a predetermined height. The bottom auxiliary heating element 90 has a circular or disk-like flat plate shape. The outer diameter of bottom auxiliary heating element 90 may be larger than the bottom surface of the crucible or may be smaller. FIG. 2 shows an example in which the bottom auxiliary heating element 90 has an area smaller than the bottom surface of the crucible 10.

  The outer diameter of the bottom auxiliary heating element 90 is preferably smaller than the bottom surface of the crucible. For example, the bottom auxiliary heating element 90 having an outer diameter 40 mm to 100 mm smaller than the outer diameter of the crucible may be used. When the bottom auxiliary heating element 90 is installed below the crucible 10, the magnetic field of the induction coil 80 generally tends to concentrate on the outer end near the induction coil 80. However, if this position moves away from the induction coil 80, the amount of generated heat naturally becomes small. In the present embodiment, it is necessary to generate heat at the center of the bottom of the crucible farthest from the induction coil 80, and the optimum position that satisfies both of these is a position having an outer diameter that is 40 mm to 100 mm smaller than the outer diameter of the crucible. is there. Although it is possible to make the bottom auxiliary heating element 90 larger than the outer shape of the crucible, in this case, the outer end of the bottom auxiliary heating element 90 is larger than the outer diameter of the crucible, so this portion is the end of the bottom surface of the crucible 10. It is necessary to significantly change the conditions from the conventional process conditions when the temperature of the melt is higher than the temperature of the melt, the temperature of the entire melt in the crucible 10 is high, and the bottom auxiliary heating element 90 is not provided. Then, it takes a lot of time to establish new process conditions. For this reason, in the present invention, the outer shape of the bottom auxiliary heating element 90 is configured to be smaller than the outer shape of the bottom surface of the crucible 10. This makes it possible to grow crystals under substantially the same conditions as the conventional conditions. For example, if the crucible diameter is φ200 mm, the size of the bottom auxiliary heating element 90 is preferably φ100 mm to φ160 mm, and may be set to φ130 mm, for example.

  The thickness of the bottom auxiliary heating element 90 is preferably in the range of 0.5 mm to 3 mm. In the heating method of the crystal growing apparatus according to the present embodiment, the induction coil 80 is used, a high-frequency current is passed through the induction coil 80 to generate a magnetic field, and an eddy current is generated in the heating element in the magnetic field, thereby heating the heating element. This is a heating method. Although it largely depends on the area of the heating body due to the skin effect, the thickness dependence of the heating body is small. For this reason, although there is no restriction | limiting in the thickness of the bottom part auxiliary | assistant heat generating body 90 which is a heating body, From a viewpoint of the ease of handling etc., the thickness of 0.5 mm or more is required. The material of the bottom auxiliary heating element 90 is made of heat-resistant platinum, iridium or the like, although it depends on the crystal raw material 160. For this reason, considering the cost, it is possible to manufacture the bottom auxiliary heating element 90 at a lower thickness when the thickness is smaller. Therefore, the thickness of the bottom auxiliary heating element 90 is preferably 3 mm or less, and more preferably in the range of 1 mm to 2 mm.

  The bottom auxiliary heating element 90 is disposed below the bottom surface of the crucible 10 and above the height position where the strength of the magnetic field generated by the induction coil 80 is strongest. As described above, the crystal growing apparatus according to the present embodiment uses the induction coil 80 and heats the induction coil 80 by causing a high frequency current to flow and generating an eddy current in the bottom auxiliary heating element 90 that is a heating element. ing. Such an eddy current becomes the highest when the heating element is arranged in the region where the magnetic field generated by the induction coil 80 is the highest, and the heating temperature becomes the highest. However, the target final heating target is near the center of the bottom surface of the crucible 10, and if the bottom auxiliary heating element 90 moves away from this position, the target crucible 10 is maintained even if the bottom auxiliary heating element 90 becomes hot. There may be a case where the vicinity of the center of the bottom surface cannot be efficiently heated. Therefore, the bottom auxiliary heating element 90 is preferably set in consideration of the balance between the strength of the magnetic field of the induction coil 80 and the distance from the bottom surface of the crucible 10.

  In the present invention, below the bottom of the crucible, above the strongest position of the magnetic field due to high frequency, and below the bottom of the crucible 10, the position where the magnetic field strength is high and the distance from the bottom of the crucible 10 is close is high. It is preferable to arrange the bottom auxiliary heating element 90 on the bottom. For example, you may arrange | position in the position below 50 mm-80 mm from the bottom of a crucible.

  As shown in FIG. 2, the crucible base 20 has an upper crucible base 23 and a lower crucible base 24. That is, the upper crucible base 23 is installed between the bottom auxiliary heating element 90 and the crucible bottom. A part of the upper crucible base 23 is provided with a plurality of through holes 22 connecting the bottom auxiliary heating element 90 to the crucible bottom (the upper surface 21 of the crucible base 20). The through-hole 22 connects the bottom auxiliary heating element 90 and the crucible bottom with a space. In general, heat generated in the bottom auxiliary heating element 90 is transmitted to the bottom of the crucible by heat conduction and radiation. When there is no through hole 22, the heat generated by the bottom auxiliary heating element 90 is transmitted to the bottom of the crucible according to the thermal conductivity of the material of the crucible base 20. When the through-hole 22 is provided, the portion of the through-hole 22 is a space, and heat is moved by radiation in the space, so that the bottom of the crucible can be further heated. The heat generated by the bottom auxiliary heating element 90 is concentrated near the outer diameter of the bottom auxiliary heating element 90 due to the edge effect. Therefore, it is effective to provide the through hole 22 around the outer diameter portion along the outer diameter of the bottom auxiliary heating element 90. It is preferable from the viewpoint of thermal efficiency that the through hole 22 overlaps at least a part of the outer diameter portion of the bottom auxiliary heating element 90. Specifically, it is preferable to arrange so that the center of the through hole 22 is formed on the circumference in the range of the outer diameter of the bottom auxiliary heating element 90 to a diameter 20 mm smaller than the outer diameter.

  FIG. 3 is a view showing a crucible base 20 as an example of the crystal growth apparatus according to the first embodiment. Hereinafter, the crucible base 20 will be described in more detail with reference to FIG.

  FIG. 3A is a perspective view of the crucible base 20. As shown in FIG. 3A, a plurality of through holes 22 are formed on the upper surface 21 of the crucible base 20. The crucible base 20 has an upper crucible base 23 and a lower crucible base 24, and a bottom auxiliary heating element 90 is installed between the upper crucible base 23 and the lower crucible base 24. That is, the bottom auxiliary heating element 90 is provided on the lower crucible base 24, and the upper crucible base 23 is provided on the bottom auxiliary heating element 90. The upper crucible base 23 constitutes from above the bottom auxiliary heating element 90 to the upper surface 21 of the crucible base 20, and the lower crucible base 24 constitutes from the bottom auxiliary heating element 90 to the bottom to the bottom. A central through hole 25 is formed at the center of the crucible base 20.

  FIG. 3B is a perspective sectional view of the crucible base 20. As shown in FIG. 3 (b), the through hole 22 is provided so as to penetrate the upper crucible base 23 above the bottom auxiliary heating element 90. Thereby, the heat generated in the bottom auxiliary heating element 90 can be directly transmitted to the bottom surface of the crucible 10 through the through hole 22, and the heating efficiency of the bottom surface of the crucible 10 can be increased. That is, when there is no through hole 22, the heat generated by the bottom auxiliary heating element 90 is transmitted to the bottom of the crucible according to the thermal conductivity of the material of the crucible base 20. When the through-hole 22 is provided, the portion of the through-hole 22 is a space, and heat is moved by radiation in the space, so that the bottom of the crucible can be further heated. Therefore, by partially providing the through hole 22 in the crucible base 20, a heat transfer path with high transfer efficiency can be provided between the bottom auxiliary heating element 90 and the bottom surface of the crucible 10. The heating efficiency at the bottom of the crucible 10 can be increased.

  On the other hand, the lower crucible base 24 is not provided with the through hole 22. This is because the lower crucible base 20 stably supports the bottom auxiliary heating element 90 and the upper crucible base 23, and therefore it is preferable that the lower crucible base 20 has a structure that increases the strength without providing unnecessary through holes 22.

  The central through hole 25 penetrates the entire crucible base 20. When center positioning, fixing, or the like is necessary, the center through hole 25 may be provided as necessary.

  The upper crucible base 23 and the lower crucible base 24 may be configured as a single refractory as a whole, or may be configured by laminating a plurality of heat-resistant materials 26. 3A and 3B, the lower crucible base 24 is configured by stacking two heat-resistant materials 26, and the upper crucible base 23 is configured by stacking three refractories 26. Has been. In this manner, a plurality of heat-resistant materials 26 may be stacked to form the upper crucible base 23 and the lower crucible base 24, and the crucible base 20 as a whole may be formed.

  FIG. 3C is a top view of the crucible base 20. As shown in FIG. 3, by providing the through hole 22 in the upper crucible base 23, a portion where the bottom auxiliary heating element 90 is exposed from the upper surface 21 is formed, and the bottom surface of the crucible 10 can be directly heated. It becomes.

  There is no particular limitation on the shape, size, and the like of the through hole 22. However, it is desirable that the crucible bottom can be heated uniformly. For example, it is preferable to arrange the through holes 22 radially evenly around the crucible central axis. For example, as shown in FIGS. 3A to 3C, the shape is preferably a substantially trapezoid whose upper side and lower side are arcs. As will be described later in the second embodiment, when the opening of the through-hole 22 is adjusted by rotating a part of the crucible base 20, it is efficient to have a substantially trapezoidal shape as described above. In addition, the shape of the through hole 22 may be circular for ease of processing. The size is preferably 20 mm to 40 mm in consideration of radiation and the like. Although the number of the through holes 22 depends on the size, about eight is efficient. For example, if the crucible diameter is φ225 mm and the bottom auxiliary heating element has an outer diameter of φ130 mm, the outer diameter is φ150 mm, the inner diameter is φ80 mm, and the upper and lower sides surrounded by a 20 ° angle around the crucible central axis are arcuate. The substantially trapezoidal through-holes are uniformly and radially arranged at eight locations.

  Further, as shown in FIGS. 3A to 3C, the plurality of through-holes 22 are arranged so as to form a uniform circular shape radially about the crucible central axis. In this way, the plurality of through holes 22 may be arranged in a circle. Since the distance from the center of the crucible 10 is equal, the bottom surface of the crucible 10 can be uniformly heated as a whole.

  However, as described above, the shape of the plurality of through-holes 22 can be various shapes and arrangements depending on the application. For example, a triangle such as an isosceles triangle arranged so that the apex angle faces the center. However, it may be a trapezoid whose upper and lower sides are linear.

  3A to 3C show an example in which a plurality of through-holes 22 are provided, but when only one is sufficient, a configuration in which only one through-hole 22 is provided. It is good. In this case, for example, an annular through hole 22 may be provided.

  Thus, according to the crystal growing apparatus according to the first embodiment, the bottom auxiliary heating element 90 is provided in the crucible base 20, and the through hole 22 reaching the upper surface of the crucible base 20 is provided above the bottom auxiliary heating element 90. By this, the heating efficiency of the bottom face of the crucible 10 can be improved and the high quality single crystal 170 can be grown.

[Second Embodiment]
FIG. 4 is a perspective sectional view showing an example of the crucible base 200 of the crystal growing apparatus according to the second embodiment of the present invention. Note that in the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 4A is a view showing a state in which the through hole 220 of the crucible base 200 is formed. As shown in FIG. 4A, the crucible base 200 of the crystal growing apparatus according to the second embodiment includes the lower crucible base 24 and the upper crucible base 230 in that the crystal according to the first embodiment. Although it is common with the crucible base 20 of the growing apparatus, the upper crucible base 230 is different from the crucible base 20 in the first embodiment in that the upper crucible base 230 has a frame portion 231 and a movable portion 232. Thus, the crucible base 200 in the second embodiment has a configuration in which the upper crucible base 230 is divided into the frame portion 231 and the movable portion 232. Note that the upper surface 210 of the frame portion 231 constitutes the upper surface of the crucible base 200.

  The frame portion 231 is formed in a bowl shape (or a gate shape) by connecting a part of the center side and the outer periphery side of the crucible base 200, and has an annular space portion 231a between the center side and the outer periphery side. . That is, in the radial direction of the crucible base 200, the upper part of the center side and the outer peripheral side are connected to form a bowl-like shape such as a pier, and the bowl shape extends along the circumferential direction. A donut-shaped space 231a having a rectangular cross section is formed in a region between the outer peripheral side. A donut-shaped or ring-shaped movable portion 232 having a rectangular cross section is provided in the space portion 231a. A slight gap (clearance) is provided between the outer surface of the movable portion 232 and the inner surface of the space portion 231a so that the movable portion 232 can move in the space portion 231a.

  As shown in FIG. 4A, a plurality of through holes 221 and 222 are provided in the frame portion 231 and the movable portion 232, respectively, and a plurality of through holes 221 provided in the frame portion 231 and the movable portion 232 are provided. The plurality of through-holes 222 overlap and communicate with each other, whereby a through-hole 220 through which the upper surface 210 of the crucible base 200 and the bottom auxiliary heating element 90 communicate with each other is formed. That is, in the state shown in FIG. 4A, the heat generated in the bottom auxiliary heating element 90 is directly transferred to the bottom surface of the crucible 10 through the through-hole 220 as in the crystal growth apparatus according to the first embodiment. The heating efficiency can be increased.

  FIG. 4B is a view showing a state where the movable portion 232 moves and the through hole 220 penetrating the entire upper crucible base 230 is not formed. Since the frame portion 231 is fixed, the through hole 221 is fixed. However, when the movable portion 232 rotates and moves, the position of the through hole 222 of the movable portion 232 does not overlap with the through hole 221 of the frame portion 231. Thus, the movable portion 232 blocks the communication between the through hole 221 and the bottom auxiliary heating element 90. In other words, the movable portion 232 is rotated around the vertical axis of the crucible 10 (and the crucible base 200), and the through hole 221 of the frame portion 231 overlaps with the region other than the through hole 222 of the movable portion 232, thereby assisting the bottom portion. A plurality of through-holes 220 connected from the heating element 90 to the bottom of the crucible are closed. As described above, the upper crucible base 230 is divided into a plurality of parts in the vertical direction, and the through crucibles 221 and 222 are individually provided. The movable part 232 that is one of the divided parts is rotated. That is, it has a mechanism capable of adjusting the aperture ratio of the through hole 220). By adjusting the aperture ratios of the through holes 221 and 222 of the upper crucible base 230, it becomes possible to adjust the amount of heating at the bottom of the crucible. When the opening ratios of the through holes 221 and 222 are large, the heat generated by the bottom auxiliary heating element 90 can be efficiently transferred to the crucible bottom. By using such a mechanism, for example, the opening ratio of the through-holes of the auxiliary heating element is set to “0” at the initial stage of growth, and the heat generated by the bottom auxiliary heating element 90 is not transferred to the crucible bottom as much as possible, and there is no bottom auxiliary heating element 90. To be able to grow under conventional growth conditions. Thereafter, during straight body part growth, the movable part 232 is rotated to increase the aperture ratio of the through holes 221 and 222 communicating with the bottom auxiliary heating element 90. As a result, the vicinity of the center of the bottom of the crucible can be heated to prevent the melt from solidifying at the bottom of the crucible at the end of the growth.

  FIG. 5 is a view showing a bottom auxiliary heating element 90 and a crucible base 200 as an example of the crystal growth apparatus according to the second embodiment of the present invention. FIG. 5A is a diagram showing a state in which the through hole 221 and the through hole 222 are communicated to form the through hole 200, and FIG. 5B is a diagram in which the through hole 221 and the through hole 222 are communicated with each other. It is the figure which showed the state where the through-hole 200 was not formed.

  As shown in FIGS. 5A and 5B, the upper crucible base 230 between the bottom auxiliary heating element 90 and the crucible bottom is divided vertically. There may be a plurality of divisions, but two divisions are preferable because the structure and installation are simple. Moreover, it has the structure which rotates the movable part 232 equivalent to one divided | segmented. 5A and 5B, the movable portion 232 corresponding to the divided lower upper crucible base 230 rotates. The frame portion 231 corresponding to the divided upper side of the upper crucible base 230 is in contact with the lower crucible base 24 and the bottom auxiliary heating element 90 at the center. The movable portion 232 is disposed in a space portion 231 a surrounded by the frame portion 231 and the bottom auxiliary heating element 90 so as to be rotatable around the center portion of the crucible base 200. Further, a reinforcing frame portion may be provided in a portion where the through hole 222 is not formed and the rotation is not hindered. The size of the movable portion 232 is not particularly limited as long as it can be accommodated in the space portion 231a, can be rotated, and the through hole 222 can be formed. The through holes 221 and 222 are arranged so that the aperture ratio can be adjusted by rotating the lower movable portion 232. There is no restriction | limiting in particular in arrangement | positioning of the through-holes 221,222. For example, you may arrange | position at equal intervals by the space | interval more than twice the magnitude | size of the through-holes 221 and 222 on the same periphery. Since they are arranged on the same circumference, the opening ratios of the upper and lower frame parts 231 and the through holes 221 and 222 of the movable part 232 are adjusted by rotating the distance of the through holes 221 and 222 around the center of the circle. Can be adjusted.

  For example, if the crucible diameter is φ225 mm and the outer diameter of the bottom auxiliary heating element 90 is φ130 mm, the frame portion 231 corresponding to the upper side of the divided upper crucible base 230 has a frame portion with an outer diameter of φ245 mm and an outer peripheral width of 15 mm, The center is an outer diameter of φ50 mm. Further, for example, the frame portion 231 has a substantially trapezoidal through-hole 221 having an outer diameter of φ150 mm, an inner diameter of φ80 mm, and an upper side surrounded by an angle around the central axis of the crucible at 20 °, and a lower side having an arc shape. In this way, it is formed radially in 8 locations in the vertical direction. For example, the movable portion 232 corresponding to the lower side of the divided upper crucible base 230 has an outer diameter of φ213 mm and an inner diameter of 52 mm, an outer diameter of φ150 mm, an inner diameter of φ80 mm, and an angle centered on the crucible central axis is 20 °. A substantially trapezoidal through-hole having an arcuate upper and lower side surrounded by 8 is formed radially at 45 ° intervals in the vertical direction. In such a configuration, the aperture ratio of the through holes 221 and 222 can be adjusted by rotating the movable portion 232. When the frame portion 231 of the upper crucible base 230 and the through holes 221 and 222 of the movable portion 232 are overlapped with each other by 22.5 °, the through hole 221 can be closed.

  That is, when the movable part 232 is rotated from the state in which the through holes 221 and 222 in FIG. 5A overlap and the through hole 220 is formed, the through hole 221 as shown in FIG. The movable portion 232 can be closed. And the aperture ratio of the through-holes 221 and 222 can be adjusted by setting the through-holes 221 and 222 to a state where only a part thereof overlaps and adjusting the overlapping region.

  FIG. 6 is a diagram illustrating an example of a rotation mechanism of the movable portion 232. There is no particular limitation on the method of rotating the movable portion 232. For example, as shown in FIG. 6, a wire 120 made of a high-strength material such as zirconium is attached to a part of the outer diameter side of the movable part 232 around the rotation axis, and this wire 120 is placed outside the furnace in the rotation direction. The movable portion 232 may be moved by winding up with the motor 130 attached to the motor. Thus, the wire 120 functions as a movable means. In FIG. 6, the wires 120 are drawn out from two locations and connected to the two motors 130 so that the movable portion 232 can be moved to the left and right sides. For example, it may be configured such that it can be rotated and moved in both directions (oscillating movement) in this way, and the opening ratios of the through holes 221 and 222 can be adjusted even in rotation in only one direction, so only one direction can be adjusted. The structure which can be rotated may be sufficient.

  In addition, for example, the mechanism may be a combination of a screw and a rod. If the movable portion 232 is moved by a predetermined angle to create the states of FIGS. 5A and 5B, the movable means and the drive mechanism for moving the movable portion 232 may be various means and methods depending on the application. Can be adopted. Note that the rotation speed of the movable portion 232 can be appropriately set in consideration of the growth conditions and the like.

  4 and 5 show an example in which the through holes 221 and 222 are provided vertically, the through holes 221 and 222 are more efficiently heated in order to heat the central portion of the bottom surface of the crucible 10 more efficiently. You may provide the inclined through-holes 221 and 222 which extend toward the center from the outside. By defining the heat supply direction and intensively heating the central portion of the bottom surface of the crucible 10, efficient heating becomes possible. The configuration in which the inclined through holes 221 and 222 are inclined can also be applied to the crystal growth apparatus according to the first embodiment. In the crucible base 20 shown in FIGS. You may comprise so that the made through-hole 22 was provided. Moreover, the inclination direction of the through holes 22, 221, 222 is not limited to the inclination rising from the outside toward the center, and the configurations of the through holes 22, 221, 222 may be various configurations depending on the application. It can be.

  FIG. 7 shows the result of simulating the temperature distribution in the vicinity of the crucible at the end of the growth of an example of the crystal growth apparatus according to the embodiment of the present invention. FIG. 7A shows the result of simulating the temperature distribution in the furnace when the upper crucible base 230 is not provided with the through holes 221 and 222. FIG. 7B is a result of simulating the temperature distribution in the furnace when the upper crucible base 230 is provided with the through-holes 220 penetrating vertically in the vertical direction. FIG. 7C shows the result of simulating the temperature distribution in the furnace when the movable part 232 of the upper crucible base 230 is rotated to close the opening of the through hole 221.

  FIG. 8 is a diagram showing a configuration of a crystal growth apparatus serving as a simulation model of FIG. As shown in FIG. 8, the upper crucible base 235 includes a frame portion 233 that does not have the through hole 221 and a movable portion 234 that does not have the through hole 222.

  The simulation models of FIGS. 7B and 7C correspond to the crystal growth apparatuses having the configurations of FIGS. 5A and 5B, respectively.

  Further, the simulation in FIG. 7 was performed with a model in which a bottom auxiliary heating element 90 having a crucible diameter of φ225 mm and an outer diameter of φ130 mm, an inner diameter of φ25 mm, and a thickness of 0.5 mm was installed 60 mm below the bottom of the crucible 10. The crucible base was larger than the diameter of the crucible and was φ245 mm. 7B and 7C, the upper side of the upper crucible base 230 surrounded by an outer diameter of φ130 mm, an outer diameter of φ150 mm, an inner diameter of φ80 mm, and an angle about the crucible central axis of 20 °. Eight substantially trapezoidal through-holes having a circular arc on the lower side were arranged radially evenly in the vertical direction.

  In FIG. 7, the high temperature region is shown in five stages of regions A to E in descending order of temperature, and the low temperature region is shown in three stages of F, G, and H.

  As can be seen from FIG. 7, it can be seen that in FIG. 7B, the bottom of the crucible with the through holes 221, 222 generates heat compared to the case where the through holes 221, 222 of FIG. That is, when FIG. 7A is compared with FIG. 7B, the high temperature region C expands in the region where the through hole 220 is provided below the bottom surface of the crucible 10 in FIG. It can be seen that the bottom surface of 10 is hot. In addition, as shown in FIG. 7B, it can be seen that the center part of the bottom part of the crucible sandwiched between the through holes 220 generates heat as compared with the case where there is no through hole. That is, it is shown that the high temperature region A expands downward in the center of the bottom surface of the crucible 10 between the through holes 220.

  Further, as shown in FIG. 7C, when the movable portion 232 is rotated and the through hole 221 is closed, heat is generated as compared with heat generated when the through holes 221 and 222 of FIG. Is larger, but the amount of heat generation is smaller than when the through-hole 220 in FIG. That is, the downward expansion of the high temperature regions A and C in FIG. 7C is smaller than that in FIG. Thus, it was shown that the heat generation at the bottom of the crucible can be adjusted by dividing the upper crucible base 230 and rotating the lower movable portion 232 to adjust the opening ratio of the through hole 221.

  As described above, the simulation experiment shown in FIG. 7 shows that the amount of heat generated can be adjusted by providing the upper crucible base 230 with the through holes 221 and 222 whose aperture ratio can be adjusted.

  FIG. 9 shows the temperature distribution of the melt in the crucible at the end of the growth of an example of the crystal growth apparatus according to the second embodiment of the present invention. The temperature distribution at the bottom of the crucible is changed from the center of the crucible bottom to the outer diameter of the crucible bottom. It is a graph when simulating. 9, the simulation result of the model shown in FIG. 8 where the through holes 221 and 222 are not present is P, the simulation result of the model where the vertical through hole 220 shown in FIG. 5A is formed is Q, FIG. A simulation result of a model in which the through-hole 221 shown in FIG.

  The simulation conditions are the same as in FIG. The temperature at the bottom of the crucible is 1650 ° C. in the characteristic P without a through hole, and the characteristic Q when the through hole is arranged in the vertical direction is 1610 ° C., which is improved. The melt assumed in the present invention is lithium tantalate (TL), the melting point is 1650 ° C., and the solidification of the raw material can be sufficiently prevented by arranging the through holes. Further, in the characteristic R when the divided lower upper crucible base is rotated to close the through hole, the temperature at the bottom of the crucible is 1655 ° C., which is almost in the middle of having no through hole. It is also possible to adjust this temperature by adjusting the thickness of the movable body 232 to be rotated.

  During crystal growth, it is required that the temperature of the bottom surface of the crucible 10 is set lower in the initial stage of pulling up the single crystal 170 and the temperature of the bottom surface of the crucible 10 is increased in the second half. Therefore, in the initial stage of pulling up the single crystal, the through hole 221 is closed as shown in FIG. 5B, and thereafter the aperture ratio of the through hole 221 is gradually increased, and finally FIG. 5B. Control may be performed such that the through holes 221 and 222 shown in FIG. These controls are possible when the control unit 110 controls the operation of the motor 130 and moves the movable unit 232 by the wire 120.

  In addition, it is possible to perform control to switch from the state of FIG. 5B to the state of FIG. 5A at a certain predetermined stage, instead of gradually increasing the aperture ratio of the through hole 221. Thus, an intermediate state between the state in which the through hole 220 is formed with the aperture ratio of the through holes 221 and 222 being maximized and the state in which the through hole 221 shown in FIG. In addition, single crystals can be grown by a desired method.

  As described above, according to the crystal growing apparatus and the crystal growing method according to the second embodiment, the heating amount of the bottom surface of the crucible 10 can be controlled according to the stage and the state, and the heating efficiency is sufficiently increased, and the length of the single crystal is increased. Scale can be achieved.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

10 Crucible 20, 200 Crucible base 21, 210 Upper surface 22, 220, 221, 222 Through hole 23, 230 Upper crucible base 231 Frame part 232 Movable part 24 Lower crucible base 25 Central through hole 26 Heat-resistant material 30 Reflector 40 After heater 50 51 Insulating material 60 Refractory material 70 Lifting shaft 71 Seed crystal holding unit 72 Lifting shaft drive unit 80 Inductive coil 90 Bottom auxiliary heating element 100 Power source 110 Control unit 120 Wire 130 Motor 150 Seed crystal 160 Crystal raw material 170 Crystal

Claims (10)

A metal crucible capable of storing and holding the raw material melt;
An induction coil provided around the crucible;
A crucible base capable of placing and supporting the crucible on the upper surface;
A bottom auxiliary heating element provided in the crucible base,
The crucible base is a crystal growth apparatus having a through hole penetrating between the upper surface and the bottom auxiliary heating element.   The crystal growth apparatus according to claim 1, wherein the bottom auxiliary heating element has a flat plate shape and is installed horizontally.   The crystal growth apparatus according to claim 1, wherein a plurality of the through holes are provided.   The crystal growth apparatus according to claim 3, wherein the plurality of through-holes are radially and uniformly arranged around the crucible central axis. The crucible base has a lower crucible base fixed to the lowermost part,
The crystal growing apparatus according to claim 1, wherein the bottom auxiliary heating element is installed on the lower crucible base. The crucible base is installed on the bottom auxiliary heating element, includes the upper surface and the upper part of the through hole, connects a part of the center side and the outer peripheral side of the crucible base, and has an annular cavity therebetween A bowl-shaped frame portion having
The crystal growing apparatus according to claim 5, further comprising: a movable portion including a lower portion of the through hole provided so as to be movable in the cavity.   The crystal growing apparatus according to claim 6, wherein the movable part is provided with a movable means for moving the movable part.   The crystal growing apparatus according to claim 7, wherein the movable means includes a wire connected to the movable portion and drawn out of the crucible base.   The crystal growing apparatus according to claim 7 or 8, wherein the movable means is provided so that the movable portion can be rotated by a predetermined angle in both directions. A crystal growth method using the crystal growth apparatus according to any one of claims 6 to 9,
Storing the raw material melt in the crucible;
Heating the raw material melt in a state where the lower part of the through hole of the movable part does not communicate with the upper part of the through hole of the frame part, and pulling up the single crystal;
A step of pulling up the single crystal in a state where the movable part is moved so that a lower part of the through hole of the movable part communicates with an upper part of the through hole of the frame part. Method.