JP5772719B2 - Oxide single crystal growth equipment - Google Patents

Description

  The present invention relates to a structure for installing a constituent member such as a reflector in a crystal growth apparatus for an oxide single crystal, particularly a sapphire single crystal.

  A sapphire single crystal is a crystal having a corundum structure of aluminum oxide, and has already been used in many fields because it has excellent mechanical and thermal properties, chemical stability, and light transmittance. In particular, sapphire single crystals are used as substrates for growing light emitting layers of light emitting diodes in the optical field or as substrates for silicon on sapphire (SOS) devices in the semiconductor field. As importance increases, the demand is growing dramatically.

  Czochralski method (Cz method) in which a sapphire single crystal is produced by melting a sapphire raw material in a crucible and bringing the seed crystal into contact with the surface of the raw material melt and gradually pulling it up. The Kyropulous method is also known. The grown sapphire single crystal is processed into a substrate shape, and the surface is polished to form a sapphire substrate.

  In order to manufacture a sapphire single crystal from a sapphire raw material melt by the Czochralski method, a sapphire single crystal growing apparatus as shown in FIG. 4 is used (for example, refer to Japanese Patent Application Laid-Open No. 2011-195423). This sapphire single crystal growing apparatus heats a crucible 1 filled with a sapphire raw material in a chamber formed by a furnace body 7, a cylindrical heater portion 3 for heating the outer peripheral surface of the crucible 1, and a bottom surface of the crucible 1. And a carbon heat insulating material 6 that constitutes a heat insulating space 15 in which the carbon heaters 30a and 30b having the disk-shaped heater portion 4 are arranged. In addition, the cylindrical heater portion 3 and the disc-shaped heater extend from the outside of the heat insulating space 15 to the inside through an insulating cylinder 8 made of aluminum oxide inserted into an opening provided in the bottom surface portion 60 of the heat insulating material 6. The crucible 1 is supported by penetrating through two cylindrical heater electrodes 5a and 5b for supplying power, passing through the bottom surface portion 60 of the heat insulating material 6 and the opening of the disk-shaped heater portion 4 and connected to each of the portions 4. A support shaft 2 is provided. Further, a pulling shaft 9 having a seed crystal 11 attached to the tip is inserted through an opening provided in the upper surface portion 61 of the heat insulating material 6, and sapphire is obtained from the raw material melt 10 in the crucible 1 by the Czochralski method at the time of growth. The single crystal 12 can be grown.

  In the growth, the crucible 1 filled with the sapphire raw material is disposed from above with the upper surface portion 61 removed, and then the upper surface portion 61 is installed to form the heat insulating space 15, and the pulling shaft 9 serves as a seed. The crystal 11 is brought into contact with the sapphire raw material melt 10 to start growing. After the growth, it is necessary to remove the upper surface portion 61 again and take out the grown sapphire single crystal from above.

  By the way, when the oxide single crystal which has a high melting point exceeding 2000 degreeC including the sapphire whose melting point is 2040 degreeC is grown by the Czochralski method, the inside of a furnace similarly becomes a high temperature environment exceeding 2000 degreeC. For this reason, the constituent member of the oxide single crystal growing apparatus needs to be formed of a material having resistance to such a high temperature environment. For example, the crucible 1 is made of a material such as molybdenum, tungsten, or an alloy thereof. Further, when a zirconia heat insulating material is employed as the heat insulating material 6, zirconia decomposes at a high temperature to generate oxygen, and this oxygen oxidizes molybdenum and tungsten constituting the crucible 1 to cause contamination of the crystal and the raw material melt 10. Since it connects, the carbon heat insulating material 6 which is stable also in a high temperature environment is employ | adopted. As for the heater, since the tungsten constituting the tungsten heater is fragile and expensive, a carbon heater is employed in the same manner as the heat insulating material 6.

  In addition, in the growth of high melting point oxide single crystals exceeding 2000 ° C., the temperature gradient in the melt can be optimized due to heat release from the grown single crystals and the high viscosity of the raw material melt. It has become difficult. In particular, since the sapphire single crystal has a characteristic that crystal growth proceeds in the melt, the quality of the obtained sapphire single crystal is easily affected by the temperature gradient of the melt. For this reason, in order to obtain a sapphire single crystal with good yield, it is necessary to control crystal growth by forming an appropriate temperature gradient, thereby suppressing the occurrence of distortion inside the single crystal due to thermal stress, Generation of lattice defects can be prevented.

  Furthermore, in the growth of sapphire single crystals, the temperature gradient of the raw material melt at the initial stage is not properly controlled, and if the melt temperature becomes too low under a low temperature gradient, the growth is started in a short time from the start of the growth. Crystal shoulders are formed, and the solid-liquid interface becomes a concave interface that is recessed toward the crystal side, which may cause a problem of crystal defects (voids, polycrystallization). Therefore, in order to improve the yield of sapphire, it is necessary to control the temperature gradient and the melt temperature with high accuracy.

  As described above, in growing a high melting point oxide single crystal such as a sapphire single crystal, it is important to control the temperature distribution in the entire furnace including the raw material melt to form an appropriate temperature gradient. As one of means for realizing such an environment, it has been proposed to provide a heat reflecting plate 13 for returning the radiant heat emitted from the melt to the melt (Japanese Patent Laid-Open No. 2007-223830). reference).

  The material of the structural member for controlling the temperature distribution of the whole furnace including such a heat reflection plate 13 used in a high temperature environment for growth is also limited to molybdenum and tungsten having high temperature resistance. In use, these components are normally supported by a carbon heat insulating material 6.

JP 2011-195423 A JP 2007-223830 A

  As described above, in the growth of oxide single crystals such as sapphire single crystals having a melting point exceeding 2000 ° C., the raw materials of the constituent members such as the heat reflecting plate are limited to materials such as molybdenum and tungsten, but these constituent members are supported. The carbon heat insulating material, which is a supporting member, reacts in a high temperature environment exceeding 2000 ° C., and these constituent members are carbonized and fused. If the carbonization reaction further proceeds, the constituent members may become brittle and fall. Further, if fusion occurs, it is necessary to destroy the heat reflecting plate and the heat insulating material made of carbon when the single crystal ingot is taken out from the chamber after completion of the growth. This destruction work is difficult, and the productivity is deteriorated. In addition, the destroyed components cannot be reused, which increases the cost of training. Further, if the constituent member becomes brittle and falls, it not only causes a decrease in yield such as generating cracks in the grown crystal, but also the raw material remaining in the crucible is contaminated by the fallen material. In this case, at the time of the next growth, the contaminated raw material must be replaced with the crucible, and there is a problem that the growth cost increases more and more.

  In view of such a problem, the present invention, in the crystal growth of a sapphire single crystal by the Czochralski method, by the carbonization reaction between the constituent members, without reducing the effects of the constituent members, the installation of the necessary constituent members The object is to provide a structure that enables this.

  The oxide single crystal growth apparatus of the present invention has a basic structure similar to that of a conventional growth apparatus, and is attached to a carbon component member and the carbon component member, and molybdenum, tungsten, or molybdenum or tungsten. And a metal component made of an alloy containing at least one of the above as a main component.

  Examples of the carbon structural member include a heat insulating material disposed around the crucible or a supporting member supported by the heat insulating material, and this includes a carbon heater. On the other hand, examples of the metallic component member include a heat reflecting plate that is disposed above the crucible and returns radiant heat released from the melt to the melt.

  In one aspect of the present invention, the carbon component and the metal component are connected to each other so that the components do not contact each other, and tantalum carbide or a carbide containing tantalum carbide as a main component is used. It is characterized by disposing a configured connecting member.

  Further, in another aspect, instead of providing a connection member, at least a connection portion with the carbon component member of the surface of the metal component member is mainly composed of tantalum carbide or tantalum carbide. It is characterized by being coated with carbide. In addition, you may coat | cover the whole surface of this metal structural member.

  The oxide single crystal growing apparatus of the present invention is suitably used for growing an oxide single crystal having a melting point exceeding 2000 ° C., particularly for growing a sapphire single crystal.

  According to the present invention, even in a high temperature environment for growing a sapphire single crystal, the molybdenum or tungsten-based heat reflecting plate does not react with the support member made of carbon. Therefore, since the support members and the like are not embrittled by the carbonization reaction, these support members do not fall into the melt during the growth. Further, when taking out the grown crystal after the growth is completed, the work of disassembling the heat reflecting plate and the support member can be facilitated, and the production efficiency can be improved.

FIG. 1 shows an apparatus for growing an oxide single crystal according to the present invention, in which a molybdenum heat reflecting plate is connected to a carbon support member attached to a carbon heat insulating material via a connection member made of tantalum carbide. It is sectional drawing which shows the attached structure typically. FIG. 2 is a cross-sectional view schematically showing a structure in which a heat reflecting plate made of molybdenum is attached to a heat insulating material made of carbon via a connecting member made of tantalum carbide in the oxide single crystal growing apparatus of the present invention. is there. FIG. 3 is a cross-sectional view schematically showing a structure in which a molybdenum heat reflecting plate covered with tantalum carbide is attached to a carbon heat insulating material in the oxide single crystal growing apparatus of the present invention. FIG. 4 is a cross-sectional view schematically showing a conventional sapphire single crystal growth apparatus.

  When the sapphire single crystal is grown by the Czochralski method, the temperature of the heat insulating space 15 also exceeds 2000 ° C. because the melting point of the sapphire single crystal is 2000 ° C. or higher. Under such a high temperature environment, the heat reflecting plate made of molybdenum (Mo) or tungsten (W) or the like, and the carbon (C) heat insulating material 6a or the supporting member 21 supporting the heat reflecting plate partially react. This makes it difficult to disassemble the heat reflecting plate and the support member after completion of the growth, which hinders the production efficiency of sapphire single crystal growth.

  In order to solve such problems, the present inventors have a high melting point, and do not react with carbon even in a high temperature environment, and stably make a metal component such as a heat reflecting plate, We have earnestly researched about rigid members that can be supported by carbon insulation and support members. As a member that satisfies such conditions and can be used industrially, tantalum carbide (TaC) has been studied earnestly, tantalum carbide has high temperature resistance under the growth of sapphire single crystals, And the knowledge that it does not react with carbon and is optimal as such a connection member was acquired.

  The present invention has been made on the basis of such knowledge, and a carbon component member and a metal member used in a high temperature environment in a growth apparatus for a high melting point oxide single crystal such as a sapphire single crystal are provided. A connecting member is provided at a connecting portion of these constituent members so that they do not come into contact with each other, and the connecting member is made of tantalum carbide.

  The connecting member can be made of not only tantalum carbide but also a carbide mainly composed of tantalum carbide. That is, the hardness of tantalum carbide itself is very high (Mohs hardness 9 to 10), and when it is composed only of tantalum carbide, it may be difficult to process the connecting member into a desired shape. Further, by incorporating a metal such as molybdenum or a carbide thereof, it is possible to improve workability such as hardness while removing high temperature resistance such as strength under high temperature environment and possibility of reaction with carbon. In this case, the content of the metal or carbide other than tantalum carbide in the material constituting the connection member is 50% by mass or less, preferably 10% by mass or less.

  A connecting member made of tantalum carbide and a carbide mainly composed of tantalum carbide can be obtained by forming the raw material powder into a predetermined shape and sintering the obtained molded product.

  FIG. 1 schematically shows a heat reflecting plate mounting structure in an oxide single crystal growing apparatus of one embodiment of the present invention using such a connecting member. The heat reflecting plate 13a has a disk shape with an opening at the center. In the example of FIG. 1, the two heat reflecting plates 13 a are arranged apart in the vertical direction (the axial direction of the lifting shaft 9) and are supported by the columns 14. These heat reflecting plates 13a and their support columns 14 are made of molybdenum (Mo), tungsten (W), or an alloy containing Mo or W as a main component.

  On the other hand, a support member 21 for supporting the support column 14 that supports the heat reflecting plate 13a is fixed to a plurality of locations in the radial direction of the heat insulating material 6a so as to protrude from the inner wall in the radial direction. These support members 21 are made of a carbon (C) material, similarly to the heat insulating material 6a.

  According to the knowledge of the present inventors, molybdenum or tungsten and carbon easily react under a high temperature environment exceeding 2000 ° C. which is a growth temperature of sapphire, and these contact portions are changed to molybdenum carbide or tungsten carbide. Then, the members are fused at the contact portion. In this case, when the grown crystal is taken out from the furnace after the growth is completed, it is necessary to remove the support column 14 from the support member 21 and remove it from the heat insulating space 15 together with the heat reflecting plate 13a. It will be a thing.

  Therefore, in this aspect, the nut 22, the washer 23, and the collar 24 that constitute the connecting portion between the support column 14 and the support member 21 are all made of tantalum carbide (TaC). With such a configuration, the reaction between the support column 14 and the support member 21 is prevented during the growth in a high-temperature environment, and it becomes possible to smoothly disassemble these components after the growth.

  In the example of FIG. 1, the collar 24a for separating the heat reflecting plate 13a is also made of tantalum carbide. However, the collar 24a is not necessarily made of tantalum carbide.

  FIG. 2 schematically shows the mounting structure of the heat reflecting plate in the oxide single crystal growing apparatus according to another embodiment of the present invention using the connecting member. In this embodiment, only one disk-like heat reflecting plate 13b is provided directly on the inner wall of the heat insulating material 6a. In this example, protruding portions protruding outward are provided at a plurality of locations in the circumferential direction of the outer peripheral portion of the heat reflecting plate 13b. On the other hand, a connecting member 25 having a U-shaped cross section, which is adapted to the shape, size, and number of the protruding portions, is provided at a plurality of radial positions on the inner wall of the heat insulating material 6a by the support member 21a embedded in the heat insulating material 6a. The support is fixed. And the heat reflection board 13b is directly supported by the heat insulating material 6a by carrying out the internal fitting fixation of the protrusion part of the heat reflection board 13b to this connection member 25. FIG. In this example, the connection member 25 is made of tantalum carbide.

  In the present invention, instead of providing the connection member 25, the heat insulating material 6a and the support member that are at least carbon components among the surfaces of the heat reflecting plate 13c that is a molybdenum or tungsten component. The connection part with 21a can also be coat | covered with the carbide | carbonized_material which has tantalum carbide or a tantalum carbide as a main component. FIG. 3 is a cross-sectional view schematically showing an example in which a coating layer 26 is provided by coating tantalum carbide at the connection portion between the heat reflecting plate 13c and the support member 21a. In this case, the coated tantalum carbide or carbide containing tantalum carbide as a main component is applied to the entire surface of the heat reflecting plate or at least to the connection portion with the support member, and is fired at a predetermined temperature and time. Layer 26 can be formed.

  The oxide single crystal growth apparatus of the present invention is characterized by a structure for attaching a structural member such as a heat reflecting plate to a structure that supports it, such as a heat insulating material. The other basic structure is shown in FIG. This is the same as the conventional structure shown. Since such a basic structure is well known, a description thereof is omitted here. In addition, the present invention is particularly suitably applied to an apparatus for growing a sapphire single crystal. In addition, the melting point of yttrium aluminum garnet (YAG), gadolinium silicate (GSO), lutetium silicate (LSO), etc. is 2000. It can also be applied to the growth of oxide single crystals having a high melting point in the vicinity of ℃ or over 2,000 ℃.

Example 1
A sapphire single crystal was grown using a growth apparatus using the heat reflecting plate shown in FIG. 1 and its mounting structure (the basic structure is the same as that shown in FIG. 4). At this time, a molybdenum alloy was used as a material for the heat reflecting plate and the column. Carbides mainly composed of tantalum carbide as collars, washers, nuts, and collars for maintaining the distance between the two heat reflecting plates at the connecting portion between the support column and the carbon support member. The member which consists of was used. This tantalum carbide-based member was prepared by thoroughly mixing tantalum carbide powder: 90%, niobium pentoxide powder: 9%, and carbon black powder: 1%, and then molding into a desired shape at 2000 ° C. It is manufactured by baking for 1 hour.

First, aluminum oxide (Al ₂ O ₃ ) powder as a raw material was inserted into a crucible, and this crucible was placed on a support shaft of a crystal growth apparatus. Then, the support | pillar by which the two heat | fever reflecting plates were supported by the up-down direction was installed in the support member made from carbon extended from the inner wall of a heat insulating material using said tantalum carbide-type member.

Thereafter, an upper surface portion of the heat insulating material is placed to form a heat insulating space, and then an aluminum oxide (Al ₂ O ₃ ) powder is heated to 2200 ° C. by a carbon heater in an Ar gas atmosphere. (Al ₂ O ₃ ) powder was dissolved. After confirming that the aluminum oxide (Al ₂ O ₃ ) powder is completely dissolved, the sapphire seed crystal attached to the tip of the pulling shaft is brought into contact with the aluminum oxide (Al ₂ O ₃ ) melt and pulled up for 5 days. went. The temperature of the heat insulating space during crystal growth was 1500 to 2100 ° C.

  After the completion of the pulling, in order to take out the grown crystal from the furnace, the upper surface portion of the heat insulating material was removed, and the support column on which the heat reflecting plate was supported was removed from the support member. During this removal operation, no fusion or the like was confirmed between the support member and the tantalum carbide-based member. In addition, in the obtained sapphire single crystal, none of the distortion, lattice defect, or crystal defect (void, polycrystallization) inside the sapphire single crystal was confirmed.

(Comparative Example 1)
As the collar, washer, and nut used for the connecting portion between the heat reflecting plate and the support member, in the same manner as in Example 1, except that a molybdenum alloy member was used instead of the tantalum carbide member, A sapphire single crystal was grown. After the growth is completed, in order to remove the grown crystal from the furnace, it is confirmed that the support and the support member are partly fused when the support supporting the heat reflecting plate is removed from the support member. It could not be removed from the member.

  In the obtained sapphire single crystal, none of distortion, lattice defects, or crystal defects (voids, polycrystallization) inside the sapphire single crystal was confirmed.

(Comparative Example 2)
A sapphire single crystal was grown in the same manner as in Example 1 except that no heat reflecting plate was installed. When the grown sapphire single crystal was confirmed, it was confirmed that there were voids and polycrystalline portions inside the single crystal.

DESCRIPTION OF SYMBOLS 1 Crucible 2 Support shaft 3 Cylindrical heater part 4 Disc shaped heater part 5a, 5b Heater electrode 6 Heat insulating material 7 Furnace body 8 Insulating cylinder 9 Pulling shaft 10 Raw material melt 11 Seed crystal 12 Sapphire single crystal 13, 13b, 13c Heat reflection Board 14 Prop
DESCRIPTION OF SYMBOLS 15 Heat insulation space 21, 21a Support member 22 Nut 23 Washer 24, 24a Collar 25 Connection member 26 Coating layer 30a, 30b Carbon heater 60 Bottom part 61 Top part

Claims (4)

  Oxide single crystal growth comprising a carbon structural member and a metallic structural member attached to the carbon structural member and made of molybdenum, tungsten, or an alloy containing at least one of molybdenum or tungsten as a main component It is an apparatus, arranged at the connecting portion between the carbon component member and the metal component member so that these component members do not contact each other, and is composed of tantalum carbide or a carbide containing tantalum carbide as a main component. An oxide single crystal growth apparatus in which a connecting member is disposed.   Oxide single crystal growth comprising a carbon structural member and a metallic structural member attached to the carbon structural member and made of molybdenum, tungsten, or an alloy containing at least one of molybdenum or tungsten as a main component An apparatus for growing an oxide single crystal, wherein at least a connecting portion of the surface of the metal component member with the carbon component member is coated with tantalum carbide or a carbide containing tantalum carbide as a main component. apparatus.   The metal component is a heat reflecting plate, and the carbon component is a heat insulating material disposed around a crucible or a support member supported by the heat insulating material. The oxide single crystal growing apparatus described.   The oxide single crystal growth apparatus according to any one of claims 1 to 3, wherein the oxide single crystal is a sapphire single crystal.

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