JP6790927B2 - Crystal growth device - Google Patents

Description

The present invention relates to a crystal growing device.

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

In the single crystal growth by the Czochralski method, an induction coil is arranged around the crucible, and an eddy current is generated in the crucible by passing a high-frequency current through the induction coil, which causes the crucible to generate heat and the raw material in the crucible. Melt.

In addition, as the pulling progresses, the upper part of the single crystal is cooled along the seed rod (pulling shaft), but if the heating element is only a crucible, the temperature distribution in the growing single crystal becomes large. , The upper part of the crucible is kept warm. For example, in order to suppress cracks due to thermal stress due to a temperature difference in the crystal, a cylindrical after-heater, which is a heating element other than the crucible, is arranged above the crucible. In addition, a donut-shaped reflector may be placed to keep the upper part of the crucible warm.

By the way, in recent years, the market for oxide single crystals, particularly lithium tantalate, has been expanding as a surface acoustic wave device material, and the pulling length of the single crystal is gradually increasing in order to secure the production amount. Along with this lengthening, crystalliteization that occurs in the bending of the crystal and the straight body, cracks due to thermal strain during cooling, solidification of the raw material at the bottom of the rut, etc. are likely to occur, and it is a good crystal. It is a cause of lowering the rate. In particular, solidification of the raw material at the bottom of the crucible poses a big problem for lengthening. In the single crystal growth by the Czochralski method, the seed crystal is brought into contact with the melting surface of the raw material of the crucible and rotated, and the crystal is grown while gradually pulling it up. In order to grow crystals, the temperature gradient in the furnace must be properly controlled, and as the crystals grow longer, the temperature in the furnace must be lowered within an appropriate range. However, even if the temperature of the upper part where the crystal is pulled up is suitable for crystal growth, the temperature drops 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 separated from the induction coil and easily solidifies. In addition, if the crystal growth is continued in this state, the solidified crystal grows upward from the bottom of the crucible and fuses with the growing crystal, resulting in a situation in which the growth must be stopped. There is.

Therefore, Patent Document 1 discloses a method of installing an auxiliary heating element that is smaller than the area of the bottom surface of the crucible and has a predetermined length in the height direction of the crucible in the space inside the crucible stand below the crucible. Has been done. The shape of this auxiliary heating element shows various shapes, and it is described that the effect can be obtained by using any shape.

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 outward in the radial direction from the outer peripheral surface of the cylindrical member to form a flange-shaped outer peripheral portion. .. Since the flange-shaped outer peripheral portion is located closest to the heating coil, it is possible to add a temperature gradient to the crucible so that the temperature of the lower portion is higher than that of the upper portion.

JP-A-54-162686 Japanese Unexamined Patent Publication No. 2004-284854

However, in the configuration described in Patent Document 1, since the auxiliary heating element is provided in the crucible stand, there is a problem that the heat transfer efficiency from the auxiliary heating element to the crucible is not good. In addition, the effect of heating the bottom of the rutsubo by placing the auxiliary heating element under the rutsubo is within a certain range, but by passing a high-frequency current through the induction coil, an eddy current is generated in the auxiliary heating element and heated. The position and amount of heat generated vary depending on the shape of this auxiliary heating element. Naturally, there is an influence on the melt in the crucible, but Patent Document 1 does not consider the shape of such an 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 it was not done.

Further, in the configuration described in Patent Document 2, the crucible can be directly heated by the flange-shaped outer peripheral portion, but the crucible is closest to the heating coil and has the highest temperature, so that the deterioration is the most severe. However, since it is integrally formed with the crucible, there is a problem that the entire crucible must be replaced frequently 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 growing device capable of efficiently and easily preventing the solidification of the raw material at the bottom of the crucible due to the lengthening of the crystal to be grown in the single crystal growing device by the Czochralski method. The purpose is to provide.

In order to achieve the above object, the crystal growth device according to one aspect of the present invention is a crystal growth device that grows a single crystal by the Czochralski method.
A metal crucible that can store and hold the raw material melt,
A crucible stand that supports the crucible from below,
An induction coil provided around the crucible to induce and heat the crucible,
A bottom auxiliary heating element that is below the bottom surface of the crucible and is provided above the height position where the magnetic field generated by the induction coil is strongest below the crucible and is induced and heated by the induction coil.
It is a separate body from the bottom auxiliary heating element, and has a side cylindrical auxiliary heating element that covers the side surface of the crucible base in a cylindrical shape and has an inner diameter equal to or larger than the outer diameter of the bottom auxiliary heating element .

According to the present invention, it is possible to provide a single crystal growth apparatus capable of increasing the length of crystal growth without causing defects such as cracks at low cost.

It is a schematic diagram which showed an example of the crystal growth apparatus which concerns on 1st Embodiment of this invention. It is a figure which showed the bottom auxiliary heating element and the side cylindrical auxiliary heating element of an example of the crystal growth apparatus which concerns on embodiment of this invention. This is the result of simulating the distribution of the magnetic field near the crucible when the auxiliary heating element is not used. This is a result of simulating the temperature distribution in the vicinity of the crucible at the end of growing of an example of the crystal growing device according to the first embodiment of the present invention. FIG. 4A is a result of simulating the temperature distribution in the furnace when none of the auxiliary heating elements was arranged. FIG. 4B is a result of simulating the temperature distribution in the furnace when only the bottom auxiliary heating element is arranged. FIG. 4C is a result of simulating the temperature distribution in the furnace when the bottom auxiliary heating element and the side cylindrical auxiliary heating element are arranged. It is a figure which showed the temperature distribution of the raw material melt in the crucible of the crystal growth apparatus which concerns on 1st Embodiment. It is a figure which showed an example of the crystal growth apparatus which concerns on 2nd Embodiment of this invention. This is the result of simulating the temperature distribution near the crucible of an example of the crystal growing apparatus according to the second embodiment of the present invention. FIG. 7A is a result of simulating the temperature distribution in the furnace when only the bottom auxiliary heating element is arranged. FIG. 7B is a result of simulating the temperature distribution in the furnace when the bottom auxiliary heating element and the side cylindrical auxiliary heating element are arranged. FIG. 7C is a result of simulating the temperature distribution in the furnace when the bottom auxiliary heating element and the side ring auxiliary heating element are arranged. It is a figure which showed the temperature distribution of the raw material melt in the crucible of the crystal growth apparatus which concerns on 2nd Embodiment.

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

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

[First Embodiment]
FIG. 1 is a schematic view showing an example of a crystal growing apparatus according to the first embodiment of the present invention. As shown in FIG. 1, the crystal growing device according to the first embodiment includes a crucible 10, a crucible stand 20, a reflector 30, an after-heater 40, heat insulating materials 50 and 51, and a refractory 60. A pulling shaft 70, an induction coil 80, a bottom auxiliary heating element 90, a side cylindrical auxiliary heating element 91, a power supply 100, and a control unit 110 are provided. The heating means is an induction coil 80 that heats the crucible 10, the after heater 40, the bottom auxiliary heating element 90, and the side cylindrical auxiliary heating element 91. Further, the power supply 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 crucible stand 20. An after-heater 40 is installed above the crucible 10 via a reflector 30. A heat insulating material 50 is installed so as to surround the crucible 10. Further, a heat insulating material 51 is provided so as to surround the after heater 40. Further, a refractory material 60 is provided on the outside of the heat insulating materials 50 and 51 to cover the entire circumference of the crucible 10. An induction coil 80 is arranged on the outside of the side surface of the refractory material 60.

A bottom auxiliary heating element 90 is installed in a part of the crucible stand 20. Further, a side surface having a cylindrical shape and covering the side surface of the crucible base 20 in a strip shape on the side surface of the crucible base 20 at a height position above the bottom auxiliary heating element 90 and below the bottom surface of the crucible 10. A cylindrical auxiliary heating element 91 is provided.

The refractory material 60 provided with the induction coil 80 on the outside is placed on a support base (not shown). Further, 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 form a hot zone portion. A pull-up shaft 70 is provided above the crucible 10. The pull-up shaft 70 has a seed crystal holding portion 71 at the lower end thereof, and is configured to be able to be raised and lowered by the pull-up shaft drive portion 72. Further, a power supply 100 and a control means 110 are provided outside the periphery of the chamber (not shown) described above.

Further, in FIG. 1, as related components, a seed crystal 150, a crystal raw material 160, and a pulled-up single crystal (also referred to as a crystal) 170 are shown.

Next, the 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 a molten state in which a metal or the like to be crystallized is melted. The material of the crucible is made of heat-resistant platinum, iridium, or the like, although it depends on the crystal raw material 160.

Since the grown single crystal 170 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 in which the 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 to be longer than half of the total length of the oxide single crystal 170 to be obtained and shorter than twice, for example. As the material of the crucible 10, for example, a metal such as platinum or iridium is used.

The bottom auxiliary heating element 90 is installed in a part of the crucible stand 20. Further, the side cylindrical auxiliary heating element 91 is above the bottom auxiliary heating element 90, and at a predetermined position in a height range below the bottom surface of the crucible 10, the inner diameter is equal to the outer diameter of the bottom auxiliary heating element 90 or the bottom. It is installed so as to be larger than the outer diameter of the auxiliary heating element 90. The details of the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 will be described later.

The induction coil 80 is a means for heating the crucible 10, the after heater 40, the bottom auxiliary heating element 90 and the side cylinder auxiliary heating element 91, and the crucible 10, the after heater 40, the bottom auxiliary heating element 90 and the side cylinder. It is arranged so as to surround the auxiliary heating element 91. The form of the induction coil 80 is not limited as long as it can induce and heat the crucible 10, the after-heater 40, and the like, but is configured as, for example, a high-frequency induction heating device including a high-frequency heating coil. In this case, the power supply 100 is configured as a high frequency power supply that supplies high frequency power to the induction coil 80.

Further, the power supply 100 supplies power not only to the induction coil 80 but also to the entire crystal growing device.

A chamber (not shown) has a function of blocking high heat of 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 material 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 the single crystal 170 while rotating. The pull-up shaft 70 has a seed crystal holding portion 71 for holding the seed crystal 150 at the lower end portion, and also has a pull-up shaft drive mechanism 72 provided with a motor which is a rotation mechanism. The motor is a rotation drive mechanism for pulling up the crystal while rotating the crystal.

The control unit 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. The control unit 110 may be composed of, for example, 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), which are operated by 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 growing apparatus according to the present 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 element 90 and the side cylindrical auxiliary heating element 91, which are the features of the present invention, will be described with reference to FIG. FIG. 2 is a diagram showing a bottom auxiliary heating element 90 and a side cylindrical auxiliary heating element 91 as an example of the crystal growing device according to the embodiment of the present invention.

As shown in FIG. 2, there are two types of auxiliary heating elements of the crystal growing device according to the first embodiment of the present invention: a bottom auxiliary heating element 90 and a side cylindrical auxiliary heating element 91. The bottom auxiliary heating element 90 is installed in a part of the crucible stand 20. Further, the side cylindrical auxiliary heating element 91 is arranged at a predetermined height position in a range above the bottom auxiliary heating element 90 and below the bottom surface of the crucible 10. Further, the inner diameter of the side cylindrical auxiliary heating element 91 is set to be equal to or larger than the outer diameter of the bottom auxiliary heating element 90. The bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 are heated by the electromagnetic induction action from the induction coil 80.

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 upward to cool the crystal body 170 and grow the crystal. As the crystal length increases, the crystal body 170 is cooled and the temperature of the upper part of the furnace decreases. The raw material melt 160 in the crucible 10 also decreases, the calorific value also decreases, and solidification of the raw material starts from the central portion of the bottom of the crucible farthest from the induction coil 80. In order to prevent this, in the crystal growing device according to the present embodiment, the bottom auxiliary heating element 90 is arranged on a part of the crucible stand 20 under the bottom of the crucible.

As shown in FIG. 2, the bottom auxiliary heating element 90 is arranged at a predetermined height position of the crucible base 20 so as to form a part of the crucible base 20 under the crucible 10. The crucible stand 20 is composed of a plurality of heat-resistant materials 21. The bottom auxiliary heating element 90 is installed between the plurality of loaded heat-resistant materials 21. That is, a plurality of heat-resistant materials 21 configured to form a cylindrical block are loaded to form the crucible stand 20, but the crucible base 20 is formed so as to be inserted at a predetermined position between the plurality of heat-resistant materials 21. The bottom auxiliary heating element 90 is arranged. Therefore, it is preferable to adjust the thickness of the heat-resistant material 21 so that the bottom auxiliary heating element 90 has a predetermined height. Further, a part of the crucible base 20 is set larger than the outer diameter of the side cylindrical auxiliary heating element 91 to form a disc-shaped protrusion 22, and the side cylindrical auxiliary heating element 91 is placed on the disc-shaped protrusion 22. Install so that it has a predetermined height.

The bottom auxiliary heating element 90 has a circular or disk-shaped flat plate shape. The outer diameter of the bottom auxiliary heating element 90 is smaller than the bottom surface of the crucible. For example, an auxiliary heating element having an outer diameter 40 mm to 100 mm smaller than the outer diameter of the crucible is used. When the bottom auxiliary heating element 90 is installed below the crucible 10, the magnetic field of the induction coil 80 is generally likely to be concentrated on the outer end portion close to the induction coil 80. However, if this position is separated from the induction coil 80, the calorific value naturally decreases. In the present embodiment, it is necessary to heat the central portion of the bottom of the crucible farthest from the induction coil 80, and the optimum position for satisfying both of these is a position having an outer diameter 40 mm to 100 mm smaller than the outer diameter of the crucible. is there. It is possible to make the bottom auxiliary heating element 90 larger than the outer diameter of the crucible, but in this case, since the outer end of the bottom auxiliary heating element 90 is larger than the outer diameter of the crucible, this portion is the end of the bottom surface of the crucible 10. It is necessary to drastically change the conditions from the conventional process conditions when the temperature becomes higher than that of the crucible, the temperature of the entire melt in the crucible 10 becomes high, and the bottom auxiliary heating element 90 is not provided. Then, it takes a lot of time to establish new process conditions. Therefore, in the present invention, the outer shape of the bottom auxiliary heating element 90 is made smaller than the outer shape of the bottom surface of the crucible 10. As a result, crystal growth becomes possible under almost the same conditions as the conventional conditions. For example, when 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, for example, φ130 mm.

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 device according to the present embodiment, an 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 body in the magnetic field to generate a heating body. It is a heating method. The skin effect greatly depends on the area of the heating body, but the thickness of the heating body is small. Therefore, the thickness of the bottom auxiliary heating element 90 is not limited, but from the viewpoint of ease of handling and the like, a thickness of at least 0.5 mm or more is required. The material of the bottom auxiliary heating element 90 depends on the crystal raw material 160, but is made of heat-resistant platinum, iridium, or the like. Therefore, considering the cost, it is possible to manufacture the bottom auxiliary heating element 90 at a lower cost when the thickness is thinner. Therefore, the thickness of the bottom auxiliary heating element 90 is preferably 3 mm or less, and more preferably within the range of 1 mm to 2 mm.

The bottom auxiliary heating element 90 is arranged 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 the strongest. As described above, the crystal growing device according to the present embodiment uses the induction coil 80, and an eddy current is passed through the induction coil 80 to the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91, which are heating elements. Is heated by generating. The eddy current becomes the highest when the heating element is placed in the region where the magnetic field generated by the induction coil 80 is the highest, and the heating temperature also becomes the highest. However, the target final heating target is near the center of the bottom surface of the crucible 10, and when the bottom auxiliary heating element 90 and the side auxiliary heating element 91 are separated from this position, the auxiliary heating elements 90 and 91 become hot. However, it may not be possible to efficiently heat the vicinity of the center of the bottom surface of the target crucible 10. Therefore, the bottom auxiliary heating element 90 and the side auxiliary heating element 91 are 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.

FIG. 3 is a result of simulating the distribution of the magnetic field near the crucible 10 when the auxiliary heating element is not used. In FIG. 3, below the crucible, the strongest height position of the magnetic field generated by the induction coil 80 is indicated by a broken line as the maximum magnetic field height position Max. As can be seen from FIG. 3, the magnetic field is densely arranged in a place facing the induction coil 80 and close to the induction coil, and heat generation is large. The magnetic field on the bottom of the crucible is weakened because it is shielded by the bottom of the crucible. The magnetic field increases by placing a certain distance below the bottom of the crucible. However, as the distance from the bottom surface of the crucible increases, the amount of heat generated by the bottom auxiliary heating element 10 increases, but the heat transfer rate decreases at the crucible stand 20 and the like, so the bottom auxiliary heating element 90 is placed at the optimum position for both. Is preferable. For example, if the bottom auxiliary heating element 90 is placed above the maximum magnetic field height position Max, which has the strongest magnetic field, and below the bottom surface of the crucible 10, the strength of the magnetic field is high and the distance from the bottom surface of the crucible 10 is also high. Since it is close, the heating efficiency is high. Therefore, it is preferable that the bottom auxiliary heating element 90 is provided at a predetermined height position below the bottom surface of the crucible 10, which is higher than the maximum magnetic field height position Max where the magnetic field generated by the induction coil 80 is strongest. For example, when the crucible diameter is φ200 mm, the maximum magnetic field height position Max of the strongest magnetic field is 80 to 100 mm from the bottom surface of the crucible, and the position of the bottom auxiliary heating element 90 is 20 mm to 30 mm above the maximum magnetic field height position Max. Deploy. Therefore, the bottom auxiliary heating element 90 is located 50 mm to 80 mm below the bottom surface of the crucible. Further, it is more preferable that the position is 60 mm to 70 mm below the bottom surface of the crucible 10.

In addition, in FIG. 2, an example in which both the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 are provided as the auxiliary heating element is described, but as shown in FIG. 3, the bottom auxiliary heating element is described. If the installation position of the heating element 90 is appropriately determined in relation to the induced magnetic field generated by the induction coil 80, a considerable heating effect can be obtained even when only the bottom auxiliary heating element 90 is provided. Therefore, the configuration may be such that only the bottom auxiliary heating element 90 is provided.

As shown in FIG. 2, in the crystal growing device according to the first embodiment of the present invention, the side auxiliary heating plate 91 is arranged in the range below the bottom auxiliary heating element 90 and the bottom surface of the crucible. This is done by installing a side cylindrical auxiliary heating element 91 having an inner diameter equal to or larger than the outer diameter of the bottom auxiliary heating element 90 between the bottom auxiliary heating element 90 installed below the bottom of the crucible and the bottom surface of the crucible 10. This is to prevent heat from escaping laterally between the bottom auxiliary heating element 90 and the bottom surface of the crucible 10. When only the bottom auxiliary heating element 90 is provided, heat may be transferred from the side surface of the crucible stand 20 installed between the bottom auxiliary heating element 90 and the bottom of the crucible to the surroundings, and the bottom of the crucible may not be heated efficiently. As described above, it is difficult to dramatically increase the amount of heat generated by the bottom auxiliary heating element 90 in order to warm the bottom of the crucible due to restrictions such as the distribution of the magnetic field. Therefore, by adding a side cylindrical auxiliary heating element 91 around the bottom auxiliary heating element 90 to create a heat wall, heat is transferred to the bottom of the crucible without letting the heat of the bottom auxiliary heating element 90 at the bottom of the crucible escape to the surroundings. Can be made to.

Since the shape of the side cylindrical auxiliary heating element 91 is cylindrical, the heat from the bottom auxiliary heating element 90 can be efficiently surrounded and kept warm. However, as described above, by adding the side auxiliary heating plate 91 around the bottom auxiliary heating element 90 to create a heat wall, the heat of the bottom auxiliary heating element 90 at the bottom of the crucible is not released to the surroundings and is attached to the bottom of the crucible. As long as heat can be transferred, it may have various shapes. Regarding this point, in the second embodiment, another aspect of the auxiliary heating element will be described later.

Hereinafter, the side cylindrical auxiliary heating element 91 will be further described. The inner diameter of the side cylindrical auxiliary heating element 91 is equal to the outer diameter of the bottom auxiliary heating element 90 or larger than the outer diameter of the bottom auxiliary heating element 90. Preferably, the inner diameter of the side cylindrical auxiliary heating element 91 is equal to or greater than the outer diameter of the bottom auxiliary heating element 90, and is within the range of the outer diameter +40 mm. If the inner diameter of the side cylindrical auxiliary heating element 91 is larger than this, heat escapes from the gap with the crucible base 20, and the heat transfer efficiency deteriorates. If the inner diameter of the side cylindrical auxiliary heating element 91 is smaller than this, it is not possible to secure the heat of the outer diameter end portion where the bottom auxiliary heating element 90 generates the largest amount of heat. Further, the inner diameter of the side cylindrical auxiliary heating element 91 is more preferably in the range of the outer diameter +10 to the outer diameter +20 mm of the bottom auxiliary heating element. The height of the cylindrical shape of the side cylindrical auxiliary heating element 91 is not limited, but the height difference between the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 is preferably 20 mm or less. Further, the height difference between the bottom of the crucible and the side cylindrical auxiliary heating element 91 is also preferably within 20 mm. When the difference between these heights, that is, the gap between the two is large, the heat escapes from this gap portion becomes large, and the heat transfer efficiency deteriorates. Further, the same effect can be obtained by integrally processing the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91, but in this case, the heat generation is concentrated on the corner portion which is the connecting portion between the two, and the auxiliary heating element 90 , 91 becomes severely damaged, the life of the auxiliary heating elements 90 and 91 is shortened, and the parts are integrally processed, which makes the processing difficult. Therefore, it is preferable that the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 are arranged separately, and the distance between them is set to 10 mm to 20 mm so as to be separated from each other.

The thickness and material of the side cylindrical auxiliary heating element 91 may be set in various ways depending on the application, and may be, for example, the same as the bottom auxiliary heating element 90. The thickness is preferably set in the range of 0.5 mm to 3 mm. Further, it is more preferable to set the thickness in the range of 1 mm to 2 mm. The material depends on the type of the crystal raw material 160, but is preferably made of heat-resistant platinum, iridium, or the like.

FIG. 4 is a result of simulating the temperature distribution near the crucible at the end of growing of an example of the crystal growing device according to the first embodiment of the present invention. The crucible diameter was φ200 mm, and the bottom auxiliary heating element 90 had an outer diameter of φ130 mm, an inner diameter of φ20 mm, and a thickness of 0.5 mm 60 mm below the bottom of the crucible 10. The side cylindrical auxiliary heating plate 91 has a cylindrical shape with an outer diameter of φ140 mm, a height of 40 mm, and a plate thickness of 0.5 mm at a position where the upper end is 10 mm from the bottom of the crucible 10. FIG. 4A is a result of simulating the temperature distribution in the furnace when none of the auxiliary heating elements was arranged. FIG. 4B is a result of simulating the temperature distribution in the furnace when only the bottom auxiliary heating element 90 is arranged. FIG. 4C is a result of simulating the temperature distribution in the furnace when the bottom auxiliary heating element 90 and the cylindrical side cylindrical auxiliary heating element 91 are arranged. In FIGS. 4A to 4C, regions A, B, C, D, E, F, G, H, I, and J are defined and displayed in order from the region having the highest temperature.

The temperature distribution in the furnace when only the bottom auxiliary heating element 90 shown in FIG. 4 (b) is arranged is such that the entire part of the bottom auxiliary heating element becomes hotter than when there is no auxiliary heating element shown in FIG. 4 (a). It can be seen that the entire bottom surface is evenly warmed. More specifically, in the region below the bottom surface of the crucible 10 in FIG. 4B, the regions B to E are increased as compared with FIG. 4A. On the other hand, in FIG. 4C, the side cylindrical auxiliary heating element 91 has an inner diameter equivalent to the outer diameter of the bottom auxiliary heating element 90, and is between the bottom surface of the crucible and the bottom auxiliary heating element in the height direction. This is the result when it is arranged in a cylindrical shape. As shown in FIG. 4C, it is shown that the entire cylindrical portion of the side cylindrical auxiliary heating element 91 is generating heat, and the portions B to D extend downward along the side surface of the crucible stand 20. ing. Further, it can be seen that the change in temperature of the space surrounded between the side cylindrical auxiliary heating element 91 and the bottom auxiliary heating element 90 is smaller than that in FIG. 4B, and the temperature is kept warm.

As described above, from the comparison between FIGS. 4 (a) and 4 (b), the lower part of the bottom surface of the crucible 10 is heated by providing the bottom auxiliary heating element 90, and the heated region is increased. You can see that. Further, from the comparison between FIGS. 4 (b) and 4 (c), the heat of the bottom auxiliary heating element 90 is generated by the crucible stand 20 by further providing the side cylindrical auxiliary heating element 91 in addition to the bottom auxiliary heating element 90. It can be seen that the heat cannot be kept in the vicinity of the crucible stand 20 without escaping to the outside from the side surface of the crucible, and the lower part of the bottom surface of the crucible 10 can be further heated.

FIG. 5 is a diagram showing the temperature distribution of the raw material melt in the crucible, and is a graph of the temperature distribution when the temperature distribution in the central part of the crucible is simulated upward from the bottom surface of the crucible. In FIG. 5, the curve K shows the simulation result when no auxiliary heating element is provided, and the curve L shows the simulation result when only the bottom auxiliary heating element 90 is provided. Further, the curve M shows the simulation result when the bottom auxiliary heating element 90 and the cylindrical side cylindrical auxiliary heating element 91 are provided.

The temperature at the bottom of the crucible at the point where the vertical axis is zero is 1642 ° C. as shown in the curve K without the auxiliary heating element, and 1650 ° C. as shown in the curve L only with the bottom auxiliary heating element 90. Therefore, even when only the bottom auxiliary heating element 90 is provided, the temperature at the bottom of the crucible 10 is high and improved. Further, when both the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 are provided, the temperature is improved by 10 ° to 1660 ° C. as shown by the curve M. The raw material melt 160 assumed in the crystal growing apparatus according to the first embodiment of the present invention is lithium tantalate (TL) and has a melting point of 1650 ° C. Therefore, as shown in the curve L, it can be seen that solidification of the raw material does not occur even when only the bottom auxiliary heating element 90 is provided. Further, as shown by the curve M, by further providing the side cylindrical auxiliary heating element 91 in addition to the bottom auxiliary heating element 90, the temperature of the bottom surface of the crucible greatly exceeds 1650 ° C., which is the melting point of lithium tantalate (TL). It can be set to 1660 ° C. and can have a margin. Further, as can be seen from the graph of FIG. 5, the temperature distributions of the two are almost the same at a position higher than 15 mm from the bottom surface of the crucible, although the temperature of the bottom surface of the crucible is different. This means that even if the side cylindrical auxiliary heating element 91 is provided, it does not need to be changed from the conventional crystal growth conditions. The side cylindrical auxiliary heating element 91 is not intended to heat the bottom of the crucible, and prevents the heated heat of the bottom auxiliary heating element 90 from escaping from the side surface of the crucible stand 20 to the outside while being conducted to the crucible 10. The purpose is to heat the bottom of the crucible efficiently. In this way, the cooperation between the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 efficiently generates heat from the bottom auxiliary heating element 90 without significantly changing the temperature distribution of the raw material melt 160 in the crucible 10. It can be transmitted to the bottom of 10.

As described above, according to the crystal growing apparatus according to the first embodiment, by providing the bottom auxiliary heating element 90 below the crucible 10, the temperature drop of the bottom surface of the crucible 10 is suppressed and kept at a high temperature. Can be done. Further, by providing the bottom auxiliary heating element 90 on a part of the crucible stand 20, the bottom surface of the crucible 10 can be efficiently heated in a space-saving manner. Further, by providing the side cylindrical auxiliary heating element 91 on the side surface of the crucible stand 20, the heat transferred from the bottom auxiliary heating element 90 to the bottom surface of the crucible 10 is prevented from being released from the side surface of the crucible stand 20 and escaping. be able to.

[Second Embodiment]
FIG. 6 is a diagram showing an example of a crystal growing apparatus according to a second embodiment of the present invention. The crystal growing device according to the second embodiment has a first embodiment in that an annular side annular auxiliary heating element 92 is provided on the crucible base 20a instead of the side cylindrical auxiliary heating element 91. It is different from the crystal growing device according to. Since the other components are the same as those of the crystal growing apparatus according to the first embodiment, the description thereof will be omitted. Further, the components corresponding to the first embodiment are designated by the same reference numerals, and the description thereof will be omitted.

The annular side annular auxiliary heating element 92, like the side cylindrical auxiliary heating element 91, has an inner diameter equal to or larger than the outer diameter of the bottom auxiliary heating element 90. More specifically, it is preferable that the inner diameter of the side annular auxiliary heating element 92 is equal to or larger than the outer diameter of the bottom auxiliary heating element 90 and is within the range of the outer diameter +40 mm. When the inner diameter of the side annular auxiliary heating element 92 is larger than the outer diameter of the bottom auxiliary heating element 90 + 40 mm, heat escapes from the gap with the side surface of the crucible base 20a, and the heat transfer efficiency deteriorates. When the inner diameter of the side annular auxiliary heating element 92 is smaller than the outer diameter of the bottom auxiliary heating element 90, the heat of the outer diameter end portion where the bottom auxiliary heating element 90 generates a large amount of heat cannot be secured. Further, the inner diameter of the side annular auxiliary heating element 92 is more preferably in the range of the outer diameter +10 to the outer diameter +20 mm of the bottom auxiliary heating element 90. The outer shape of the side annular auxiliary heating element 92 is preferably equal to or smaller than the crucible diameter. Since the outer diameter end of the annular auxiliary heating element 92 is close to the induction coil 80, the temperature tends to be locally high, and if it is larger than the crucible diameter, it may be higher than the heat generated by the crucible 10. Is high. Therefore, the outer shape of the side ring auxiliary heating element 92 is preferably 20 mm to 30 mm smaller than the crucible diameter. The height at which the side annular auxiliary heating element 92 is arranged is not limited, but it is preferable to arrange the side ring auxiliary heating element 92 at an intermediate point between the bottom surface of the crucible and the bottom auxiliary heating element 90, or within 20 mm of the bottom auxiliary heating element 90 side of the intermediate point. .. As will be described later, since the heating element of the side annular auxiliary heating element 92 generates heat at a high temperature, the heat of the bottom auxiliary heating element 90 is released by arranging the side annular auxiliary heating element 92 closer to the bottom auxiliary heating element 90 side than the intermediate point. It is possible to keep warm without having to. The plate thickness and material of the side annular auxiliary heating element 92 are the same as those of the cylindrical side cylindrical auxiliary heating element 91.

As shown in FIG. 6, the side annular auxiliary heating element 92 may be provided by being placed on an annular flat plate of the disc-shaped protruding portion 22a of the crucible base 20a. Since it may be placed on the disc-shaped protrusion 22a, it is extremely easy to install and replace. The disk-shaped protrusion 22a of the crucible base 20a shown in FIG. 6 has a shape thicker than that of the disk-shaped protrusion 22 shown in FIG. 2, which is a side ring auxiliary heating element. This is because the 92 is arranged at a substantially intermediate point between the bottom surface of the crucible 10 and the bottom auxiliary heating element 90. That is, since the side cylindrical auxiliary heating element 91 shown in FIG. 2 extends in the vertical direction, the side cylindrical auxiliary heating element 91 is arranged at a substantially intermediate point between the bottom surface of the crucible 10 and the bottom auxiliary heating element 90. It is necessary to reduce the thickness of the disc-shaped protruding portion 22 in consideration of the height of the side cylindrical auxiliary heating element 91. On the other hand, since the side annular auxiliary heating element 92 has a flat plate shape, the disc-shaped protruding portion 22a needs to be thickened in order to arrange the side annular auxiliary heating element 92 above. is there.

Next, the simulation result in which the side auxiliary heating element has a disk shape will be described.

FIG. 7 is a result of simulating the temperature distribution near the crucible of an example of the crystal growing apparatus according to the second embodiment of the present invention. FIG. 7A is a result of simulating the temperature distribution in the furnace when only the bottom auxiliary heating element 90 is arranged. FIG. 7B is a result of simulating the temperature distribution in the furnace when the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 are arranged. FIG. 7C is a result of simulating the temperature distribution in the furnace when the bottom auxiliary heating element 90 and the side ring auxiliary heating element 92 are arranged. In addition, in FIGS. 7A to 7C, the temperature distribution is shown using the regions A to J in descending order of temperature.

The side ring auxiliary heating element 92 has an inner diameter of 130 mm, an outer diameter of 185 mm, and a thickness of 0.5 mm. The outer diameter of the side ring auxiliary heating element 92 was set to be 15 mm inside the outer diameter of the crucible 10. Further, the side ring auxiliary heating element 92 was set at a position intermediate between the bottom surface of the crucible and the bottom auxiliary heating element.

FIG. 7B shows that the inner diameter of the side cylindrical auxiliary heating element 91 is equal to or larger than the outer diameter of the bottom auxiliary heating element 90, and the side cylindrical auxiliary heating element 91 is attached to the bottom surface and the bottom of the crucible in the height direction. This is the result when placed between the auxiliary heating element 90. In FIG. 7B, the entire cylindrical portion of the side cylindrical auxiliary heating element 91 is generating heat, and the change in temperature of the space surrounded between the side cylindrical auxiliary heating element 91 and the bottom auxiliary heating element 90 is shown in FIG. It can be seen that it is smaller than 7 (a) and is kept warm. That is, the regions B and C, which are high temperature regions, extend below the bottom surface of the crucible 10 along the side cylindrical auxiliary heating element 91.

On the other hand, FIG. 7C is a simulation result in which the side ring auxiliary heating element 92 is installed. As can be seen from FIG. 7C, the high temperature regions A and B expand downward from the bottom surface of the crucible 10, and the portion where the side ring auxiliary heating element 92 is located is the hottest region A. There is. As described above, from FIG. 7C, it can be seen that the side annular auxiliary heating element 92 has a large amount of heat generation and a high temperature because the annular outer diameter end portion is close to the induction coil 80. Therefore, compared to the side cylindrical auxiliary heating element 91, although the bottom auxiliary heating element 90 is not surrounded, the amount of heat generated is large, so that the temperature gradient near the center of the bottom surface of the crucible has the same effect as the side cylindrical auxiliary heating element 91. is there.

Further, FIG. 8 is a diagram showing the temperature distribution of the raw material melt 160 in the crucible, and is a graph of the temperature distribution when the temperature distribution in the central part of the crucible is simulated upward from the bottom surface of the crucible. In FIG. 8, the horizontal axis represents the melt temperature (° C.) and the vertical axis represents the distance (mm) from the bottom of the crucible. Further, the temperature characteristic when no auxiliary heating element is provided including the bottom auxiliary heating element 90 is a curve K, and the temperature characteristic when only the bottom auxiliary heating element 90 is provided is a curve L, the bottom auxiliary heating element 90 and the side surface. The temperature characteristic when the cylindrical auxiliary heating element 91 is provided is shown by a curve M. Further, the temperature characteristics when the bottom auxiliary heating element 90 and the side ring auxiliary heating element 92 are provided are shown by a curve N.

In FIG. 8, the temperature at the bottom of the crucible when the vertical axis is zero is 1650 ° C. as shown in the curve L only for the bottom auxiliary heating element 90, but the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 90 When 91 is provided, it is 1660 ° C. as shown by the curve M, which is an improvement of 10 ° C. Further, when the bottom auxiliary heating element 90 and the side ring auxiliary heating element 92 are provided, the temperature is 1663 ° C, which is 13 ° C. higher than when only the bottom auxiliary heating element 90 is provided. Even when the annular side annular auxiliary heating element 92 is provided, the effect of raising the temperature at the center of the bottom surface of the crucible is the same as when the side cylindrical auxiliary heating element 91 is provided. However, as can be seen from FIG. 7C, the annular side annular auxiliary heating element 92 has a large amount of heat generation and a high temperature because the annular outer diameter end is close to the induction coil 80. Become. Therefore, it can be seen that the bottom surface (outer portion) of the crucible corresponding to the portion where the side ring auxiliary heating element 92 is installed is locally hot. Therefore, the temperature distribution in the crucible 10 needs to be changed with respect to the conventional conditions. Further, since the outer diameter end portion of the annular shape becomes locally hot, the side annular auxiliary heating element 92 may be significantly damaged.

Therefore, comprehensively judging from the simulation results of FIGS. 7 and 8, the combination of the bottom auxiliary heating element 90 and the side cylindrical auxiliary heating element 91 is considered to be the most preferable combination, but the side annular auxiliary heating element 92 This has the advantage that the temperature can be raised to a higher temperature, the installation only needs to be placed on the disc-shaped protrusion 22a provided on the crucible stand 20a, and the installation and replacement are extremely easy. Depending on the situation, an appropriate combination can be used.

Further, as described above, the effect of heating can be obtained even when only the bottom auxiliary heating element 90 is provided. Therefore, when it is sufficient to provide the bottom auxiliary heating element 90, only the bottom auxiliary heating element 90 is provided. May be good.

As described above, according to the crystal growing device according to the second embodiment of the present invention, the bottom surface of the crucible 10 can be efficiently heated, and the side ring auxiliary heating element 92 can be installed extremely easily. It can be carried out.

As described above, according to the crystal growing apparatus according to the embodiment of the present invention, the heat retention effect of the bottom surface of the crucible 10 can be enhanced by providing the bottom auxiliary heating element 90 below the bottom surface of the crucible 10. Further, by providing the side cylindrical auxiliary heating element 91 or the side annular auxiliary heating element 92 as necessary, it is possible to prevent the heat from the bottom auxiliary heating element 90 from escaping from the side surface of the crucible stand 20, and further to have a heat retaining effect. Can be enhanced. Further, since each of the auxiliary heating elements 90 to 92 is a replaceable single component, it can be easily replaced, and even if deterioration of the component occurs, it can be easily dealt with.

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

10 Crucible 20, 20a Crucible stand 30 Reflector 40 After heater 50, 51 Insulation material 60 Refractory 70 Pull-up shaft 71 Seed crystal holding part 72 Pull-up shaft drive part 80 Induction coil 90 Bottom auxiliary heat generator 91 Side cylindrical auxiliary heat generator 92 side Crucible auxiliary heating element 100 Power supply 110 Control unit 150 Seed crystal 160 Crystal raw material 170 Single crystal

Claims (12)

A crystal growth device that grows single crystals by the Czochralski method.
A metal crucible that can store and hold the raw material melt,
A crucible stand that supports the crucible from below,
An induction coil provided around the crucible to induce and heat the crucible,
A bottom auxiliary heating element that is below the bottom surface of the crucible and is provided above the height position where the magnetic field generated by the induction coil is strongest below the crucible and is induced and heated by the induction coil.
A crystal growing device having a side cylindrical auxiliary heating element which is separate from the bottom auxiliary heating element, covers the side surface of the crucible base in a cylindrical shape, and has an inner diameter equal to or larger than the outer diameter of the bottom auxiliary heating element . The crystal growing device according to claim 1, wherein the outer shape of the bottom auxiliary heating element is smaller than the outer shape of the bottom surface of the crucible. The crystal growing device according to claim 1 or 2, wherein the crucible and the bottom auxiliary heating element are made of the same material. The crystal growing apparatus according to claim 3, wherein the same material is platinum or iridium. Before Kisoko unit auxiliary heating element, the crystal growing apparatus according to any one of claims 1 to 4 arranged in a predetermined height position of the crucible base. The crystal growing device according to claim 5, wherein the bottom auxiliary heating element has a plate shape and is loaded and arranged between two cylindrical blocks forming at least a part of the crucible base. The crystal growing device according to any one of claims 1 to 6, wherein the side cylindrical auxiliary heating element is provided at a height position between the bottom surface of the crucible and the bottom auxiliary heating element. The crystal growing device according to any one of claims 1 to 7, wherein the side cylindrical auxiliary heating element is made of the same material as the bottom auxiliary heating element. The crystal growing apparatus according to claim 5 or 6, further comprising a side annular auxiliary heating element that surrounds the side surface of the crucible stand with an annular horizontal plane. The crystal growing device according to claim 9 , wherein the side annular auxiliary heating element is provided at a height position between the bottom surface of the crucible and the bottom auxiliary heating element. The crucible stand has a disc-shaped protrusion whose outer diameter is equal to or larger than the outer diameter of the side annular auxiliary heating element, and the side annular auxiliary heating element is placed on the surface of the protruding portion. The crystal growing apparatus according to claim 9 or 10 , wherein the crystal growing apparatus is provided. The crystal growing device according to any one of claims 9 to 11 , wherein the side annular auxiliary heating element is made of the same material as the bottom auxiliary heating element.