JP2013095610A - Apparatus and method for producing sapphire single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a hardly soluble material from getting mixed into a sapphire melt in a molybdenum crucible.SOLUTION: This apparatus includes: a molybdenum crucible 14 for holding a sapphire melt 21; a pulling-up mechanism 19 for pulling up a seed crystal dipped into the sapphire melt 21; a resistance heating heater 15 comprising an upper heater 15a and a lower heater 15b divided in the axial direction, and enclosing the molybdenum crucible 14; and a controller 23 for controlling each output from the upper heater 15a and the lower heater 15b, respectively. Since a heat load to be applied onto the molybdenum crucible 14 can be finely adjusted, generation of a hardly soluble material can be suppressed.

Description

  The present invention relates to a sapphire single crystal manufacturing apparatus and manufacturing method, and more particularly to a sapphire single crystal manufacturing apparatus and manufacturing method using the Czochralski method (CZ method).

  In recent years, the demand for a sapphire single crystal substrate as a substrate for manufacturing a light emitting diode (LED) has been increasing. Since a sapphire single crystal substrate is produced by slicing a sapphire single crystal into a wafer, it is necessary to use a large sapphire single crystal in order to produce a large sapphire substrate.

  As a method for producing a sapphire single crystal, the Kilopros method, the vertical Bridgman method, and the like are widely used. However, these methods have a problem that it is difficult to increase the size of a sapphire single crystal having a desired plane orientation. For this reason, the Czochralski method has attracted attention as a method for obtaining a larger sapphire single crystal (see Patent Document 1). The Czochralski method is widely used for pulling silicon single crystals and is a mature technology. By applying this to pulling sapphire single crystals, large sapphire single crystals can be produced at low cost. It is expected to be possible.

JP 2010-189242 A

  However, even with the same Czochralski method, the physical properties of silicon and sapphire differ greatly, so the knowledge obtained by pulling up a silicon single crystal cannot be directly applied to pulling up the sapphire single crystal. Rather, the pulling of the silicon single crystal and the pulling of the sapphire single crystal need to be regarded as completely different technologies, and various problems that have not occurred in the pulling of the silicon single crystal must be solved.

  For example, sapphire has a melting point of about 2323 K, which is much higher than that of silicon, so that usable crucible materials are limited to some refractory metals such as molybdenum and iridium. For this reason, a new problem peculiar to the pulling up of the sapphire single crystal which does not occur in the pulling up of the silicon single crystal using the quartz crucible may occur, and it is necessary to solve this.

  As a problem peculiar to pulling up a sapphire single crystal, there is generation of a hardly soluble material generated when a molybdenum crucible is used. The hardly soluble matter is an impurity that floats on the surface of the sapphire melt, and if it is present in a large amount, the seed crystal cannot be deposited. For this reason, when using a molybdenum crucible, it is important to suppress the generation of hardly soluble substances as much as possible. However, since such a problem does not occur when pulling up a silicon single crystal, It is difficult to solve using the knowledge obtained by the pulling.

  Therefore, an object of this invention is to provide the manufacturing apparatus and manufacturing method of a sapphire single crystal which can suppress generation | occurrence | production of a hardly soluble substance, even when it is a case where a molybdenum crucible is used.

  As a result of intensive studies on the cause of the poorly soluble material mixed in the sapphire melt when the molybdenum crucible is used, the present inventors have revealed that the component of the hardly soluble material is molybdenum and is derived from the crucible. It was. That is, it has been clarified that molybdenum, which is a material for the crucible, is mixed in the sapphire melt and precipitates as a hardly soluble material.

  Furthermore, the present inventor also studied the cause of molybdenum mixing into the sapphire melt, and after introducing the sapphire raw material into the molybdenum crucible, the heat load when melting the sapphire raw material by heating, particularly the heat of the inner wall of the crucible. It was found that the load was greatly affected.

  The present invention has been made based on such technical knowledge, and a sapphire single crystal manufacturing apparatus according to the present invention comprises a molybdenum crucible for holding a sapphire melt and a seed crystal immersed in the sapphire melt. A pulling mechanism for pulling up, a plurality of resistance heaters surrounding the molybdenum crucible and divided in the axial direction, and a controller for controlling the outputs of the plurality of resistance heaters, respectively.

  According to the present invention, since the resistance heating heater surrounding the molybdenum crucible is divided into a plurality of parts, the output of each heater can be controlled independently. Thereby, since the heat load concerning a molybdenum crucible can be finely adjusted, it becomes possible to suppress generation | occurrence | production of a hardly soluble material. In the pulling of a silicon single crystal using a quartz crucible, there is an example in which the resistance heater is divided into a plurality of parts. However, pulling up the silicon single crystal does not have the problem of generation of hardly soluble material, and therefore the idea of controlling the hardly soluble material mixed in the sapphire melt by dividing the heater is the silicon single crystal using a quartz crucible. It can not be obtained from the technology of raising. As described above, the present invention solves the problem peculiar to the pulling of the sapphire single crystal by the Czochralski method using the molybdenum crucible, and simply applies the pulling technique of the silicon single crystal using the quartz crucible as it is. It is not possible.

  In the present invention, the plurality of resistance heaters include an upper heater and a lower heater, and the controller controls the output of the upper heater when melting the sapphire material to 50% or less of the total output of the upper heater and the lower heater. It is preferable to set to. According to this, since the heat load applied to the inner wall of the molybdenum crucible when the sapphire raw material is melted is reduced, it is possible to suppress the generation of hardly soluble substances when the sapphire raw material is melted. In pulling up a silicon single crystal using a quartz crucible, there are examples in which the output of the upper heater and the output of the lower heater are different from each other. However, such output adjustment is intended to solve a problem peculiar to pulling a sapphire single crystal by the Czochralski method using a molybdenum crucible. Adjustments are not directly helpful.

  Also, the method for producing a sapphire single crystal according to the present invention includes a melting step of obtaining a sapphire melt by melting a sapphire raw material put into a molybdenum crucible, and a sapphire by pulling up a seed crystal immersed in the sapphire melt. A pulling step for obtaining a single crystal, and in the melting step, a resistance heating heater is used that surrounds the molybdenum crucible and is divided in the axial direction from an upper heater and a lower heater, and the output of the upper heater is set to the upper portion. Heating is performed by setting the output to 50% or less of the total output of the heater and the lower heater.

  According to the present invention, when the sapphire raw material is melted, the thermal load applied to the inner wall of the molybdenum crucible is reduced, so that it is possible to suppress the generation of hardly soluble materials when the sapphire raw material is melted.

  Thus, according to the present invention, the heat load applied to the molybdenum crucible can be finely adjusted, so that it is possible to suppress the generation of hardly soluble substances.

It is a schematic diagram which shows the structure of the manufacturing apparatus 10 of the sapphire single crystal by preferable embodiment of this invention. 4 is a flowchart for explaining a method of manufacturing the sapphire single crystal 20.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing a configuration of a sapphire single crystal manufacturing apparatus according to a preferred embodiment of the present invention.

  A sapphire single crystal manufacturing apparatus 10 shown in FIG. 1 includes a chamber 11, a support rotary shaft 12 that passes through the center of the bottom of the chamber 11 and is provided in the vertical direction, and a support fixed to the upper end of the support rotary shaft 12. A base 13, a molybdenum crucible 14 supported by the support base 13, a resistance heater 15 surrounding the molybdenum crucible 14, a support shaft rotating mechanism 16 for rotating the support rotating shaft 12, and a seed crystal attached to the tip A seed rod 18, a pulling mechanism 19 for pulling up the seed rod 18, and a controller 23 for controlling each part.

  A heat insulating material 22 is provided in the chamber 11, and the outer periphery of the resistance heater 15 is surrounded by a thick heat insulating material 22. Although the melting point of sapphire is very high at about 2323K, since the heat insulating material 22 is provided not only on the side of the resistance heater 15 but also on the upper and lower sides, sufficient heat retention can be secured, and the molybdenum crucible The sapphire raw material in 14 can be heated efficiently. Furthermore, a viewing window 17 is provided in the chamber 11, and the state of pulling up the sapphire single crystal can be confirmed. Thus, the structure in which the heat insulating material 22 is provided not only on the side of the resistance heater 15 but also above and below is a structure unique to the sapphire single crystal manufacturing apparatus 10 and is different from the silicon single crystal manufacturing apparatus. Structure. This is because sapphire has a melting point that is significantly higher than that of silicon, and thus requires higher heat insulation than a silicon single crystal manufacturing apparatus.

  A gas inlet 24 for introducing Ar gas into the chamber 11 is provided in the upper part of the chamber 11. Ar gas is introduced into the chamber 11 from the gas introduction port 24 through the gas pipe 25, and the introduction amount is controlled by the conductance valve 26.

  A gas discharge port 27 for exhausting Ar gas in the chamber 11 is provided at the bottom of the chamber 11. Ar gas in the sealed chamber 11 is discharged to the outside from the gas discharge port 27 via the exhaust gas pipe 28. A conductance valve 29 and a vacuum pump 30 are provided in the middle of the exhaust gas pipe 28, and the pressure inside the chamber 11 is reduced by controlling the flow rate with the conductance valve 29 while sucking the Ar gas in the chamber 11 with the vacuum pump 30. The state is maintained.

  As shown in FIG. 1, in the sapphire single crystal manufacturing apparatus 10 according to the present embodiment, the resistance heater 15 is divided into two in the axial direction. That is, it is constituted by the upper heater 15a and the lower heater 15b. The outputs of the upper heater 15a and the lower heater 15b can be controlled independently by the controller 23.

  The upper end of the upper heater 15 a is located slightly below the upper end of the molybdenum crucible 14, and the lower end of the upper heater 15 a is located slightly above the bottom of the molybdenum crucible 14. Further, the upper end portion of the lower heater 15 b is located slightly above the bottom portion of the molybdenum crucible 14, and the lower end portion of the lower heater 15 b is located below the bottom portion of the molybdenum crucible 14. As an example, when a molybdenum crucible 14 having a height of 225 mm is used, it is preferable that the heights of the upper heater 15a and the lower heater 15b are both designed to be about 175 mm.

  In pulling up the sapphire single crystal 20, the controller 23 controls the pulling speed of the sapphire single crystal 20 and the temperature gradient between the sapphire single crystal 20 and the sapphire melt 21 with high accuracy. The pulling speed of the sapphire single crystal 20 is controlled mainly by the pulling speed of the seed rod 18 by the pulling mechanism 19, and the temperature gradient is adjusted mainly by the output of the resistance heater 15.

  FIG. 2 is a flowchart for explaining a method of manufacturing the sapphire single crystal 20.

  First, a sapphire raw material is put into the molybdenum crucible 14 (step S1) and melted using the resistance heater 15 (step S2). When melting the sapphire raw material, a large heat load is applied to the inner wall of the molybdenum crucible 14, so that molybdenum is likely to be mixed into the sapphire melt 21 in this step. When molybdenum is mixed into the sapphire melt 21, it is deposited on the surface of the sapphire melt 21 as a hardly soluble material, making it difficult to deposit the seed crystal. In order to prevent this, it is preferable to suppress the output of the upper heater 15a. This is because, as shown in FIG. 1, the upper heater 15 a is disposed in the vicinity of the straight body portion of the molybdenum crucible 14, so that the radiant heat applied to the inner wall of the molybdenum crucible 14 is large. More specifically, it is preferable to perform melting by setting the output of the upper heater 15a to 50% or less with respect to the total output of the upper heater 15a and the lower heater 15b.

  The reason why the output of the upper heater 15a is set to 50% or less is to reduce the thermal load applied to the inner wall of the molybdenum crucible 14 when melting the sapphire raw material, and continuously from the lower part of the sapphire melt 21 toward the upper part. This is to create an ideal temperature gradient that lowers the temperature. On the other hand, in an apparatus for manufacturing a silicon single crystal, even when a heater divided into upper and lower parts is used, the output of the upper heater is usually set to more than 50%. The first reason is that, since a quartz crucible is used in a silicon single crystal manufacturing apparatus, it is necessary to suppress oxygen from being mixed into the silicon melt from the quartz crucible. Secondly, in the silicon single crystal manufacturing apparatus, the heat insulating material does not cover the upper part of the crucible, and the heat radiation to the upper side of the crucible is large. Therefore, it is necessary to supplement the amount of heat radiated by a high-power upper heater. It is. For this reason, in the silicon single crystal manufacturing apparatus, it is usual to set the output of the upper heater to more than 50%.

  However, when sapphire is pulled up under the same conditions as those of silicon, the upper portion of the molybdenum crucible 14 is excessively heated, and a large amount of hardly soluble material is supplied to the melt, thereby inhibiting crystal growth. Moreover, since the sapphire melt 21 has a high viscosity coefficient, it is impossible to produce an ideal temperature gradient in which the temperature continuously decreases from the bottom to the top of the melt. Such a problem can be solved by setting the output of the upper heater 15a to 50% or less. Such an output setting cannot be obtained from knowledge of a silicon single crystal manufacturing apparatus.

  When the sapphire raw material is completely melted, seed crystal is deposited (step S3). At the point where the seed crystal is deposited, the sapphire melt 21 needs to be correctly exposed, and when a hardly soluble substance is floating, it must be avoided to land. However, in this embodiment, since the mixing of molybdenum is suppressed by controlling the heater power in the sapphire raw material melting step (step S2), the number of hardly soluble substances floating on the surface of the sapphire melt 21 is very small. Become. For this reason, it becomes possible to perform liquid landing easily. After the liquid is deposited, the sapphire single crystal 20 is slowly pulled up by the pulling mechanism 19 while maintaining a predetermined temperature gradient by controlling the heater power (step S4). As described above, the sapphire single crystal 20 is produced.

  As described above, in the sapphire single crystal manufacturing apparatus 10 according to the present embodiment, the resistance heater 15 surrounding the molybdenum crucible 14 is divided into the upper heater 15a and the lower heater 15b, and these outputs are independent of each other. Therefore, it is possible to finely adjust the heat load of the molybdenum crucible 14 when the sapphire raw material is melted. Thereby, since the thermal load of the molybdenum crucible 14 at the time of melting | dissolving a sapphire raw material is suppressed, mixing of the molybdenum into the sapphire melt 21 can be suppressed. As a result, since the generation of hardly soluble substances is suppressed, seed crystal can be easily deposited.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in the above embodiment, the resistance heater 15 is divided into two in the axial direction, but the number of divisions of the resistance heater 15 is not limited to this, and may be divided into three or more. Further, the heights of the upper heater 15a and the lower heater 15b do not have to be the same, and the heights may be different from each other.

  Hereinafter, although the Example of this invention is described, this invention is not limited to this Example at all.

  A sapphire raw material was charged into a molybdenum crucible, and the sapphire raw material was melted using the sapphire single crystal manufacturing apparatus 10 shown in FIG. The height of the used molybdenum crucible 14 was 225 mm, and the heights of the upper heater 15a and the lower heater 15b were both 175 mm. The boundary between the upper heater 15a and the lower heater 15b was positioned slightly above the bottom of the molybdenum crucible 14, that is, at the curved portion.

  And the output of the upper heater 15a and the lower heater 15b was set to 1: 1, and the sapphire raw material was melted. Thereafter, the surface state of the sapphire melt 21 in the molybdenum crucible 14 was visually confirmed from a viewing window provided in the chamber. As a result, hardly dissolved matter was observed on the surface of the sapphire melt 21.

  On the other hand, when the outputs of the upper heater 15a and the lower heater 15b were set to 2: 1 and the sapphire raw material was melted, hardly dissolved substances were observed on the surface of the sapphire melt 21.

  Moreover, when the outputs of the upper heater 15a and the lower heater 15b were set to 1: 0 and the sapphire raw material was melted, a large amount of hardly dissolved matter was observed on the surface of the sapphire melt 21.

  From the above results, it was confirmed that the generation of hardly soluble substances becomes more remarkable as the output ratio of the upper heater 15a is larger than the total output. And it is confirmed that if the output of the upper heater 15a and the lower heater 15b is 1: 1, that is, the output of the upper heater 15a is reduced to 50% with respect to the total output, the generation of hardly soluble substances is prevented. It was.

  As a comparative example, the sapphire raw material was melted using a sapphire single crystal manufacturing apparatus of a type in which the resistance heater 15 is not divided. As a result, hardly soluble substances were observed on the surface of the sapphire melt 21. The amount was almost the same as when the output of the upper heater 15a and the lower heater 15b was set to 2: 1.

DESCRIPTION OF SYMBOLS 10 Sapphire single crystal manufacturing apparatus 11 Chamber 12 Support rotating shaft 13 Support base 14 Molybdenum crucible 15 Resistance heater 15a Upper heater 15b Lower heater 16 Support shaft rotating mechanism 17 Viewing window 18 Seed bar 19 Lifting mechanism 20 Sapphire single crystal 21 Sapphire melt Liquid 22 Heat insulating material 23 Controller 24 Gas inlet 25 Gas pipe 26 Conductance valve 27 Gas outlet 28 Exhaust pipe 29 Conductance valve 30 Vacuum pump

Claims (3)

Molybdenum crucible holding sapphire melt,
A pulling mechanism for pulling up the seed crystal immersed in the sapphire melt;
A plurality of resistance heaters surrounding the molybdenum crucible and divided in the axial direction;
And a controller for controlling the outputs of the plurality of resistance heaters, respectively. The plurality of resistance heaters include an upper heater and a lower heater,
2. The sapphire single crystal according to claim 1, wherein the controller sets an output of the upper heater when melting the sapphire material to 50% or less of a total output of the upper heater and the lower heater. manufacturing device. A melting step of obtaining a sapphire melt by melting the sapphire raw material put into the molybdenum crucible;
A pulling step of obtaining a sapphire single crystal by pulling up a seed crystal immersed in the sapphire melt,
In the melting step, a resistance heater composed of an upper heater and a lower heater that surround the molybdenum crucible and is divided in the axial direction is used, and the output of the upper heater is 50% of the total output of the upper heater and the lower heater. A method for producing a sapphire single crystal, characterized in that the heating is performed with the temperature set to not more than%.

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