JP2013155069A - Sapphire single crystal growing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sapphire single crystal growing apparatus with few commingling of impurities into the sapphire single crystal to be grown although the apparatus is configured relatively inexpensively.SOLUTION: An afterheater member 20 is arranged above a crucible 10, generates heat together with the crucible 10 by passing an electric current through an induction coil 32 to heat a sapphire single crystal body 15 pulled from the crucible 10. The afterheater member 20 is equipped with an exothermic part 22 comprising at least one kind of tantalum (Ta), tungsten (W) and molybdenum (Mo) as a main component, and a coating layer 24 free of oxygen and coating the exothermic part 22. With such configuration, the exothermic part 22 is prevented from oxidation while the exothermic part 22 is composed of relatively inexpensive high melting point metals.

Description

  The present invention relates to a sapphire single crystal growing apparatus.

  The crucible filled with sapphire raw material is heated to a high temperature to melt the sapphire raw material. Conventionally, a single crystal growth method called a so-called Czochralski method for growing a single crystal body of a scale has been practiced.

  In sapphire single crystal growth by the Czochralski method, an induction coil in which a high-frequency current flows is arranged around the crucible, and the crucible generates heat by induction heating generated by flowing a high-frequency current through the induction coil. The sapphire raw material is melted. In the Czochralski method, as the sapphire seed crystal rises, a sapphire single crystal grows so as to be pulled up from the sapphire raw material melt.

  The uppermost part of the sapphire single crystal body moves away from the crucible as the pulling proceeds. Heat from the crucible is difficult to be transmitted to a portion away from the crucible. For example, when the heating element is only the crucible, the temperature distribution in the growing single crystal increases.

  For example, in Patent Document 1, an after heater member, which is a heating element other than the crucible, is disposed on the upper part of the crucible in order to suppress damage to the sapphire single crystal due to thermal stress accompanying the temperature distribution. The after-heater member described in Patent Document 1 is a cylindrical member made of, for example, tungsten (W) or molybdenum (Mo), and is arranged at the upper part of the crucible so as to surround the periphery of the grown single crystal.

Japanese Patent Laid-Open No. 2005-1934

  The after heater member of Patent Document 1 is made of tungsten (W) or molybdenum (Mo), which is a relatively inexpensive metal having a high melting point. Tungsten (W), molybdenum (Mo), and tantalum (Ta) are less expensive than iridium (Ir), which is a metal having a high melting point like these metals, but oxidized compared to iridium (Ir). Easy to do. In the growing apparatus of Patent Document 1, an after heater made of tungsten (W) or molybdenum (Mo) reacts with oxygen in the atmosphere to be oxidized, and in some cases, a fragment of the oxide film may adhere to the single crystal. There was a problem that there was. On the other hand, when iridium (Ir), which is a metal that is difficult to oxidize, is used as an after-heater member, iridium (Ir) has a material price of several tens compared with tungsten (W), molybdenum (Mo), and tantalum (Ta). Since it is twice as expensive, there is a problem that the whole apparatus becomes expensive. The present invention has been made to solve such problems.

The present invention provides a crucible filled with a sapphire raw material, the crucible for melting the sapphire raw material by causing the crucible to generate heat by flowing an electric current, and obtaining a sapphire raw material melt stored in the crucible. Holding the sapphire seed crystal around the induction coil and the sapphire seed crystal, the sapphire seed crystal is brought into contact with the sapphire raw material melt in the crucible and then raised, thereby being continuous with the sapphire seed crystal. A pulling mechanism for pulling up the sapphire single crystal, and heat generated together with the crucible when a current flows through the induction coil disposed on the crucible, and heating the sapphire single crystal pulled from the crucible A sapphire single crystal growth apparatus comprising an after heater member for performing tantalum (Ta) A sapphire single crystal growth comprising: a heat generating portion mainly composed of at least one of tungsten (W) and molybdenum (Mo); and a coating layer that covers the heat generating portion and does not contain oxygen. Providing equipment.

  According to the sapphire single crystal growing apparatus of the present invention, the heat generating portion of the after heater member is configured using a relatively inexpensive high melting point metal material such as tantalum (Ta), tungsten (W), and molybdenum (Mo). The exothermic part is covered with a coating layer not containing oxygen to prevent oxidation of the exothermic part, and the contamination of the sapphire single crystal to be grown is small while the apparatus structure is relatively inexpensive.

It is a schematic block diagram which shows the structure of one Embodiment of the sapphire single crystal growth apparatus of this invention. It is a schematic perspective view of the after heater member with which the sapphire single crystal growth apparatus shown in FIG. 1 is provided. It is a schematic block diagram shown about the other example of a sapphire single crystal growth apparatus.

  Hereinafter, an embodiment of the sapphire single crystal growing apparatus of the present invention will be described. FIG. 1 is a schematic configuration diagram of a sapphire single crystal growing apparatus 1 (hereinafter also referred to as a growing apparatus 1) of the present invention. FIG. 2 is a schematic perspective view of the after heater member 20 provided in the growing apparatus 1.

  The growing apparatus 1 includes a crucible 10, a growing chamber 16, a heat insulating material 17, a coil 32 disposed so as to surround the side wall 10 a of the crucible 10 via a side wall 16 a of the growing chamber 16, and an alternating current for flowing the coil 32. The high frequency power supply 30, the crystal pulling mechanism 40, the gas supply unit 60, the exhaust unit 70, and the control unit 50 are configured. A control unit 50 is connected to the crystal pulling mechanism 40, the high frequency power supply 30, the gas supply unit 60, and the exhaust unit 70. The control part 50 consists of a well-known computer provided with CPU and memory, for example, and the control part 50 controls operation | movement of the cultivation apparatus 1 whole.

  The crucible 10 is a container body made of, for example, iridium (Ir) and having a circular cross section of the side wall 12a. The crucible 10 is filled with aluminum oxide powder, which is a raw material of sapphire single crystal, and further, a sapphire raw material melt obtained by melting the aluminum oxide by the heat generated by the crucible 10 itself is stored. In the growth apparatus 1, the pulling shaft 42 of the crystal pulling mechanism 40 is inserted into the crucible 10 from the opening 11 of the crucible 10.

The crucible 10 is disposed in the growth chamber 16. A heat insulating material 17 is filled around the crucible 10. The heat insulating material 17 is made of, for example, a so-called zirconia bubble, and suppresses release of heat from the crucible 10. The growth chamber 16 is a container body having an annular cross section of the side wall 16a, similar to the crucible 10, and is made of, for example, ceramics mainly composed of zirconia (ZrO ₂ ).

The growth chamber 16 is provided with a heat insulating plate 18 protruding from the inner surface of the growth chamber 16. The heat insulating plate 18 is also made of a ceramic mainly composed of zirconia (ZrO ₂ ), for example. The end of the crucible 10 on the opening 11 side is disposed close to the lower main surface of the heat insulating plate 18. The heat insulating plate 18 also suppresses the release of heat from the crucible 10.

A through hole 19a is provided in the top plate portion 19 of the growth chamber 16, and a pulling shaft 42 of the crystal pulling mechanism 40 is inserted into the through hole 19a. The pulling shaft 42 is also made of ceramics mainly composed of zirconia (ZrO ₂ ), for example. When growing the sapphire single crystal, the lower end of the pulling shaft 42 holds a sapphire seed crystal 13 (hereinafter referred to as a seed crystal 13), which serves as a base point for sapphire single crystal growth. The seed crystal 13 is a high-purity sapphire single crystal.

  The crystal pulling portion 40 includes a pulling shaft 42 and a pulling mechanism portion 44 that moves the pulling shaft 42 in the vertical direction in the drawing. The lifting mechanism 44 has a power source such as a motor (not shown) and a mechanism (not shown) that is driven by the power source to move the lifting shaft 42 in the vertical direction. When growing the sapphire single crystal, the seed crystal 13 is held at the tip of the pull-up shaft 42 (the lower end in FIG. 1), and the pull-up shaft 42 with the seed crystal 13 attached to the tip is provided from the opening 11 of the crucible 10. The seed crystal 13 comes into contact with the liquid surface of the sapphire raw material melt inserted in the crucible 10. The pulling shaft 42 is disposed at a position corresponding to the central axis C passing through the center of the opening 11 of the crucible 10, and a part of the seed crystal 13 is immersed in a position corresponding to the central axis C. Contact with the sapphire material melt.

  The gas supply unit 60 includes a gas cylinder, a gas flow meter, a gas pipe, and the like (not shown). The gas supply unit 60 is connected to the inside of the growth chamber 16 through a gas supply pipe 62. In the present embodiment, the gas supply unit 60 includes an argon (Ar) gas cylinder, and argon (Ar) gas is sent into the growth chamber 16 via the gas supply pipe 62. The exhaust unit 70 includes, for example, an exhaust pump (not shown). The exhaust unit 70 is connected to the growth chamber 16 via the exhaust pipe 72, and exhausts the gas in the growth chamber 16 via the exhaust pipe 72.

  An after heater member 20 is disposed on the upper side of the heat insulating plate 18 in the growth chamber 16. The after-heater member 20 includes a cylindrical heat generating portion 22 made of, for example, tungsten (W), and a coating layer 24 that does not contain oxygen and covers the heat generating portion 22. The covering layer 24 of the present embodiment is made of, for example, silicon carbide (SiC). The after-heater member 20 is not limited to tungsten (W), and may be a metal containing at least one of tantalum (Ta), tungsten (W), and molybdenum (Mo) as a main component. The material of the heat generating part 22 may be only one kind each of tantalum (Ta), tungsten (W) and molybdenum (Mo), and at least one kind of tantalum (Ta), tungsten (W) and molybdenum (Mo) is used. An alloy having a main component may be used.

The coil 32 is made of copper, for example, and is connected to the high frequency power supply 30. The coil 32 is disposed around the crucible 10 and the after-heater member 20, and a high-frequency voltage is applied from the high-frequency power source 30 to flow a high-frequency current. Due to the electromagnetic field caused by the high frequency current of the coil 32, an eddy current flows on the surface of the heat generating portion 22 of the crucible 10 and the after heater member 20, and the crucible 10 and the after heater member 20 generate heat. Tungsten (W) constituting the heating element 22 of the after heater member 20 is a metal, and has a high conductivity, for example, 5.29 × 10 ⁻⁸ Ω · m. On the other hand, silicon carbide (SiC) is semiconductive and has a significantly higher electrical resistance than the heating element 22. Due to the electromagnetic field energy caused by the alternating current of the coil 32, an eddy current is concentrated on the surface of the heating element 22, and the heating element 22 generates heat. SiC has high thermal conductivity, and the heat generated from the heating element 22 is transmitted well to the surface of the coating layer 24, and the surface of the coating layer 24 becomes high temperature.

In the present embodiment, the after heater member 20 includes the heat generating portion 22 made of a metal that easily generates heat, and the after heater member 20 can be heated to a relatively high temperature. Tantalum (Ta), tungsten (W), and molybdenum (Mo) have the characteristics that they have a high melting point, are relatively low in price, and tend to generate heat while being relatively easily oxidized. In the growth chamber 16, oxygen (O ₂ ) such as oxygen (O ₂ ) contained in the remaining air or oxygen (O ₂ ) gas desorbed from ceramics such as zirconia (ZrO ₂ ) that is a material of the growth chamber 16 is used. ₂ ) Gas is present. When a metal containing at least one of tantalum (Ta), tungsten (W), and molybdenum (Mo) as a main component and an oxygen (O ₂ ) gas are contacted at a high temperature, such a metal is easily oxidized. .

  The after-heater member 20 of this embodiment includes a coating layer 24 made of silicon carbide (SiC) that does not contain oxygen and covers the heat generating portion 22, and the coating layer 24 prevents oxidation of the heat generating portion 22. Yes. Here, not containing oxygen means that the oxygen content ratio is less than 1% by mass.

  The coating layer 24 made of silicon carbide (SiC) can be formed by, for example, a known plasma CVD method. Silicon carbide (SiC) formed by the plasma CVD method is dense and strong, and has high mechanical durability. For example, the surface of the heat generating portion 22 made of tungsten (W) is covered with the coating layer 24 made of silicon carbide (SiC) that does not contain oxygen, so that oxidation of the surface of the heat generating portion 22 can be suppressed. Silicon carbide (SiC) has a high melting point of 2000 ° C. or higher, is chemically stable, and silicon carbide (SiC) itself is hardly oxidized. By providing the coating layer 24 made of silicon carbide on the heat generating portion 22 made of tungsten (W) that is relatively easy to generate heat and relatively easy to oxidize, the after-heater member 20 that is easy to generate heat and whose surface is hardly oxidized is formed. Can be configured.

  For example, at least one of tantalum (Ta), tungsten (W), and molybdenum (Mo) that is easily oxidized but relatively inexpensive by having the coating layer 24 made of silicon carbide (SiC) that does not contain oxygen is used. A metal as a main component can be used for the after-heater member 20, and the price of the sapphire single crystal growing apparatus 1 can be suppressed from increasing. Moreover, since the surface of the after-heater member 20 of this embodiment is difficult to oxidize, it can be used repeatedly for single crystal growth multiple times, and the running cost when repeating sapphire single crystal growth multiple times is reduced. Can be made.

  The covering layer 24 of the after heater member 20 of the present embodiment is made of silicon carbide (SiC), but the covering layer 24 is not limited to silicon carbide (SiC), and may be any covering layer 24 that does not contain oxygen. Other examples of the coating layer 24 having relatively high heat resistance and not containing oxygen include silicon nitride (SiN). The coating layer 24 made of silicon nitride (SiN) can also be formed by, for example, a known plasma CVD method.

  In the growth of the sapphire single crystal in the single crystal growth apparatus 1, first, the crucible 10 is filled with aluminum oxide powder that is a raw material of the sapphire single crystal. Next, after exhausting the gas in the growth chamber 16 via the gas exhaust pipe 72 by the exhaust pump 70, the gas supply unit 60 fills the growth chamber 16 with the argon gas via the gas supply pipe 62. Thereafter, the argon gas is continuously evacuated while continuously supplying the argon gas into the growth chamber 16, and the growth chamber 16 is set to an atmospheric pressure argon gas atmosphere. In this state, a high frequency current is passed through the coil 32 by the high frequency power supply 30 to cause the side wall 12 of the crucible 10 and the after heater member 20 to generate heat. When the crucible 10 generates heat and becomes high temperature, the sapphire single crystal raw material in the crucible 10 is melted, and the molten sapphire single crystal raw material (sapphire raw material melt) is stored in the crucible 10.

Thus, the seed crystal 13 is brought into contact with the liquid surface of the sapphire raw material melt in the crucible 10 in a state where the sapphire raw material melt is stored in the crucible 10. The seed crystal 13 is held at the tip of the pulling shaft 42, and the pulling shaft 42 with the seed crystal 13 attached to the tip is inserted into the crucible 10 from the opening 11 of the crucible 10, so The seed crystal 13 contacts the surface. The pulling shaft 42 is disposed at a position corresponding to the central axis C passing through the center of the opening 11 of the crucible 10, and a part of the seed crystal 13 is immersed in a position corresponding to the central axis C.

  After bringing the seed crystal 13 into contact with the sapphire raw material melt, the pulling shaft 42 raises the seed crystal 13 upward while rotating about the central axis C. Thereby, starting from the seed crystal 13, the single crystal (sapphire single crystal 15) of the melting raw material is grown so as to be pulled upward.

  The temperature of the sapphire raw material melt in the crucible 10 is relatively easily increased by the induction-heated side wall 10a in the vicinity of the side wall 10a, and the temperature in the crucible 10 center portion (near the central axis C) away from the side wall 10a. It is relatively difficult to rise. Furthermore, the sapphire single crystal 15 is located in the vicinity of the central axis C, and the heat of the sapphire raw material melt in the crucible 10 is easily radiated out of the crucible 10 through the sapphire single crystal 15. For this reason, in the crucible 10, the temperature of the sapphire raw material melt tends to be relatively low in the vicinity of the central axis C as compared with the vicinity in the vicinity of the side wall 10a. In particular, in a crystal having a relatively high transmittance with respect to infrared rays or visible light, such as sapphire, the radiant heat is easily transferred inside the crystal, and the sapphire raw material melt in the crucible 10 is transmitted through the sapphire single crystal 15. The amount of heat that escapes is relatively large. When the sapphire single crystal is grown by the pulling method, the temperature in the vicinity of the central axis C tends to be relatively low.

  In this embodiment, the temperature of the sapphire single crystal 15 itself being pulled is kept relatively high by the after heater member 20, and the temperature difference between the sapphire raw material melt and the sapphire single crystal 15 is suppressed to be small. Inflow of heat from the sapphire raw material melt to the sapphire single crystal 15 is suppressed. For this reason, it is suppressed that the temperature of a sapphire raw material melt falls too much, and a malfunction occurs in the growth state of sapphire single crystal body 15. Further, since the long heater sapphire single crystal 15 is uniformly heated over a wide region along the pulling direction by the after heater member 20, the temperature distribution of the sapphire single crystal 15 itself is suppressed to be small. Generation of mechanical defects or the like due to thermal stress due to temperature distribution is also suppressed.

This is particularly noticeable when oxidizable metals such as tantalum (Ta), tungsten (W), and molybdenum (Mo) are used as the after heater member, but usually when using an after heater member made of only metal. Each time the single sapphire crystal is grown, the surface of the after heater member is remarkably oxidized, and the oxidized metal pieces are easily peeled off. This also the development chamber are purged with argon (Ar) or the like, or oxygen contained in the residual air (O _2), from various ceramic materials of the breeding room desorbed oxygen (O ₂₎ is a high temperature This is because it reacts with an after heater member made of heated metal. For this reason, in the conventional growing apparatus, for example, it is necessary to use a new after-heater member that is not used every time a single sapphire single crystal is grown, and the running cost when growing the crystal a plurality of times is high. In order to avoid oxidation of the after-heater member, there is a means for further reducing the oxygen concentration in the growth chamber, but for this purpose, it is necessary to improve the airtightness of the growth chamber, improve the performance of the exhaust pump, etc. Even in this case, a great cost is generated.

  In the present invention, a silicon carbide (SiC) coating is formed on the surface of a relatively inexpensive metal member whose after-heater member is mainly composed of at least one of tantalum (Ta), tungsten (W), and molybdenum (Mo). Although the formed structure is relatively inexpensive, it is difficult to oxidize and can be used repeatedly for a long period of time, and the cost of the growth apparatus and the running cost of repeated single crystal growth can be reduced. The sapphire single crystal grown using the growth apparatus of the present invention is less contaminated with metal oxides.

In the present embodiment, the shape of the after heater member 20 is cylindrical, but the shape of the after heater member 20 is not limited to being cylindrical. FIG. 3 is a schematic configuration diagram showing a growth apparatus 2 which is another example of the sapphire single crystal growth apparatus. In FIG. 3A, the same reference numerals as those in FIG. 3A is a schematic configuration diagram of a part of the growing apparatus 2, and FIG. 3B is a schematic perspective view of an after heater member 80 provided in the growing apparatus 2 shown in FIG. 3A.

  Similar to the after-heater member 20, the after-heater member 80 includes a heat generating portion 82 made of, for example, tungsten (W), and a coating layer 84 that covers the heat generating portion 82 and does not contain oxygen. The after-heater member 80 is a cylindrical body, and the inner peripheral surface 80A of the after-heater member 80 is being pulled up by the pulling mechanism 42 as it moves away from the crucible 10 in the pulling direction (upward in FIG. 3). The sapphire single crystal body 15 is inclined so as to approach. During the pulling up of the sapphire single crystal 15, the crucible 10 is heated to a high temperature of 2000 ° C. or higher, and so-called radiant heat is released from the crucible 10 and the sapphire raw material melt stored in the crucible 10. That is, thermal energy is radiated in the form of electromagnetic waves such as infrared rays from the crucible 10 and the sapphire raw material melt stored in the crucible 10. The after heater member 80 is inclined so that the inner peripheral surface 80A is closer to the sapphire single crystal 15 as the inner surface 80A is separated from the crucible 10, and infrared rays emitted from a high temperature portion such as the crucible 10 It is efficiently reflected toward the sapphire single crystal body 15 by the peripheral surface 80A. In the growth apparatus 2, the temperature distribution of the sapphire single crystal body 15 is efficiently reduced by using the after-heater member 80 in which the inner peripheral surface 80A is inclined as described above.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the above-mentioned various embodiment, In the range which does not deviate from the summary of this invention, it is possible to perform various improvements and changes. Of course.

1 Sapphire single crystal growth equipment (growth equipment)
DESCRIPTION OF SYMBOLS 10 Crucible 11 Opening 12 Side wall 13 Sapphire seed crystal 15 Sapphire single crystal body 16 Growth chamber 17 Heat insulating material 19 Top plate part 20 After heater member 22 Heating body 24 Covering layer 18 Side wall 32 Coil 30 High frequency power supply 40 Crystal pulling mechanism 42 Pulling shaft 44 Pull-up mechanism 50 Control unit 60 Gas supply unit 62 Gas supply pipe

Claims (5)

A crucible filled with sapphire raw materials;
An induction coil disposed around the crucible for obtaining a sapphire raw material melt stored in the crucible by causing the crucible to generate heat by flowing current to melt the sapphire raw material;
Holding the sapphire seed crystal and moving up and down, and raising the sapphire single crystal continuous to the sapphire seed crystal by raising the sapphire seed crystal in contact with the sapphire raw material melt in the crucible A lifting mechanism;
A sapphire single crystal growth comprising an after heater member disposed on the crucible and generating heat with the crucible when an electric current flows through the induction coil and heating the sapphire single crystal body pulled up from the crucible. A device,
The after-heater member includes a heat generating part mainly composed of at least one of tantalum (Ta), tungsten (W), and molybdenum (Mo);
An apparatus for growing a sapphire single crystal, comprising: a coating layer that covers the heat generating portion and does not contain oxygen.   The sapphire single crystal growing apparatus according to claim 1, wherein the multilayer is made of silicon carbide (SiC). The after-heater member is cylindrical and is disposed so as to surround the sapphire single crystal being pulled by the pulling mechanism,
3. The sapphire single crystal growing apparatus according to claim 1, wherein the induction coil is also disposed around the after heater member.   The inner peripheral surface of the after-heater member is inclined so as to approach the sapphire single crystal being pulled up by the pulling mechanism as it moves away from the crucible in the pulling direction. Item 3. A sapphire single crystal growth apparatus according to item 3.   The sapphire single crystal growing apparatus according to claim 1, wherein the crucible contains iridium (Ir) as a main component.

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