JP5838727B2 - Method and apparatus for producing sapphire single crystal - Google Patents

Description

  The present invention relates to a method and apparatus for manufacturing a sapphire single crystal, and more particularly to a method and apparatus for manufacturing a sapphire single crystal 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 method and manufacturing apparatus 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 has also studied the cause of molybdenum being mixed into the sapphire melt, and found that the oxide film on the inner wall surface of the molybdenum crucible is greatly affected.

  The present invention has been made based on such technical knowledge, and the method for producing a sapphire single crystal according to the present invention includes a degassing step of degassing by heat-treating a sapphire raw material in a reduced-pressure inert atmosphere. And a melting step of obtaining a sapphire melt by melting the sapphire raw material in a molybdenum crucible, and a pulling step of obtaining a sapphire single crystal by pulling up a seed crystal immersed in the sapphire melt. To do.

  According to the present invention, the degassing treatment is performed before the sapphire raw material is melted, so that the reaction between the impurities caused by the sapphire raw material and molybdenum can be suppressed. Therefore, the amount of hardly soluble matter floating on the surface of the melt can be greatly reduced, and high quality sapphire single crystals can be stably grown.

  In the present invention, in the degassing step, the surface of the sapphire raw material is heated to be 500 ° C. or higher and 1000 ° C. or lower, and the oxygen concentration in the exhaust gas discharged from the chamber is 0.1 ppm or lower. It is preferable to continue the degassing process.

  In the present invention, it is preferable that the process from degassing to melting of the sapphire raw material is carried out continuously in the molybdenum crucible. According to this, a high quality sapphire single crystal can be manufactured efficiently.

  The apparatus for producing a sapphire single crystal according to the present invention measures a chamber, a molybdenum crucible for supporting a sapphire raw material in the chamber, a heater for heating the molybdenum crucible, and an oxygen concentration in exhaust gas discharged from the chamber. An oxygen concentration meter for controlling the heater and a controller for controlling the heater, and the controller maintains the temperature in the chamber within a first temperature range after the sapphire material is charged into the molybdenum crucible. The sapphire raw material is degassed by controlling the heater, and the oxygen concentration in the exhaust gas during the degassing process is monitored by the oxygen concentration meter, so that the oxygen concentration is below a predetermined level. After that, the temperature in the chamber becomes the second temperature range higher than the first temperature range. By increasing the power of the coater, characterized in that to start the melting of the sapphire material. In this case, the first temperature range is preferably 500 ° C. or higher and 1000 ° C. or lower, and the second temperature range is preferably higher than or equal to the melting point of the sapphire raw material.

  According to the present invention, since the degassing process is performed before the sapphire raw material is melted, it is possible to suppress the generation of hardly soluble substances when the sapphire raw material is melted.

  Thus, according to this invention, it becomes possible to suppress generation | occurrence | production of the hardly soluble material in the sapphire melt resulting from a molybdenum crucible.

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

  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 lifting mechanism 19 for lifting 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.

A gas inlet 24 for introducing an inert gas such as argon gas (Ar) or hydrogen gas (H ₂ ) into the chamber 11 is provided in the upper portion 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.

  During the pulling of the sapphire single crystal, Ar gas is supplied from the gas inlet 24 and the inside of the chamber 11 is set to an Ar gas atmosphere. Also, in the crucible emptying process described later, Ar gas containing a trace amount of hydrogen gas is supplied from the gas inlet 24, and the inside of the chamber is set to a trace amount hydrogen atmosphere.

  A gas exhaust port 27 for exhausting the gas in the chamber 11 is provided at a position at the bottom of the chamber 11 and facing the gas inlet 24. The 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 installed in the middle of the exhaust gas pipe 28, and the pressure in the chamber 11 is controlled by controlling the flow rate with the conductance valve 29 while sucking the gas in the chamber 11 with the vacuum pump 30. Be controlled.

  Further, an oxygen concentration meter 31 is provided in the middle of the exhaust gas pipe 28. The oxygen concentration meter 31 is used to measure the oxygen concentration in the exhaust gas during the degassing process described later. The end timing of the degassing process is determined by whether or not the oxygen concentration in the exhaust gas has become a predetermined level or less.

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

  As shown in FIG. 2, in the manufacture of the sapphire single crystal according to the present embodiment, first, the molybdenum crucible 14 is heat-treated (emptied) in a reducing atmosphere (step S1). Specifically, after placing the molybdenum crucible 14 into which the sapphire raw material is not charged in the chamber 11, an argon gas containing a trace amount of hydrogen is introduced into the chamber 11 to form a trace hydrogen atmosphere, and then the heater is heated. The inside of the chamber is set to 1000 ° C to 1500 ° C.

The reason why the baking temperature is 1000 to 1500 ° C. is that molybdenum oxide (MoO ₂ ) on the surface of the crucible does not decompose at a temperature lower than 1000 ° C. (the reaction of MoO ₂ → Mo + MoO ₃ does not proceed). This is because when the temperature exceeds ℃, molybdenum (Mo) itself may evaporate under vacuum. In other words, within this temperature range, MoO ₃ can be sublimated to leave only Mo.

  In the present embodiment, the hydrogen concentration in the trace hydrogen atmosphere is preferably 10 ppm or more and 5 vol% or less. This is because if it is less than 10 ppm, a sufficient reduction effect cannot be obtained, and if it is more than 5 vol%, there is a possibility that if the gas leaks from the chamber, it may burn violently, which is not preferable for operation. Baking is carried out for several hours, whereby the oxide film on the surface of the crucible is removed. In addition, the crucible after baking is improved in the glossiness of the surface, and it can be easily grasped that the oxide is reduced.

  Next, a sapphire raw material is put into the molybdenum crucible 14 (step S2). As the sapphire raw material, high-purity alumina powder can be used. The sapphire raw material may be charged into the molybdenum crucible 14 after the crucible is once taken out from the chamber 11 or may be charged without providing the raw material hopper in the chamber 11 and taking out the crucible from the chamber 11.

Next, the sapphire raw material is degassed (step S3). When the sapphire raw material to be used is in the form of a powder having an average particle size of 100 μm or less, the total surface area of the raw material is increased, and as a result, impurity components adsorbed on the raw material are increased. Some of the impurity components are removed in the firing process before the sapphire raw material is shipped as a product, but the impurity components adsorbed on the powder are not completely removed. In addition, since the sapphire raw material is exposed to the atmosphere, moisture and impurity gases (N ₂ gas and O ₂ gas) in the air are re-adsorbed. In order to remove such impurities, a degassing process is performed in this embodiment.

  The degassing process is performed over a long period of time in a relatively low-temperature reduced-pressure atmosphere. Specifically, the power of the heater is measured while measuring the surface temperature with an IR thermometer so that the inside of the chamber has a reduced Ar atmosphere and the surface temperature of the sapphire raw material is 500 ° C. to 1000 ° C., more preferably around 780 ° C. To control. This is because the impurity gas is not completely desorbed at 500 ° C. or lower, and molybdenum oxide gas is generated when the temperature exceeds 1000 ° C., and a hardly soluble substance is formed.

  During the degassing, the oxygen concentration in the exhaust gas is always monitored, and the degassing process is continued until the oxygen concentration becomes 0.1 ppm or less (step S4N). This is because when the oxygen concentration in the exhaust gas is 0.1 ppm or less, the oxidation of molybdenum does not proceed, and as a result, hardly soluble substances are not generated. Although depending on the amount of sapphire material input, the time required for such treatment is, for example, about 12 hours. When the degassing process is performed, a phenomenon that the observation window 17 of the chamber is clouded in white is observed, and from this, it can be confirmed that any gas is clearly generated in the chamber 11.

  Next, the sapphire raw material is melted (steps S4Y and S5). The melting step is performed in a relatively high temperature reduced pressure atmosphere. Specifically, the power of the heater 15 is controlled so that the surface temperature of the sapphire raw material becomes 2250 ° C. or higher while the inside of the chamber 11 is maintained in a reduced-pressure Ar atmosphere. The power at the time of degassing is about 8 kW, whereas the power at the time of melting is about 40 kW.

  When the sapphire raw material is completely melted, the seed crystal is deposited while the inside of the chamber 11 is maintained in a reduced-pressure Ar atmosphere (step S6). 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, the molybdenum crucible is baked (step S1) and the degassing of the sapphire raw material (step S3) prevents the molybdenum from entering, so that it floats on the surface of the sapphire melt 21. The number of difficult-to-dissolves is very small. For this reason, it becomes possible to perform liquid landing easily.

  After the liquid deposition, 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 S7). As described above, the sapphire single crystal 20 is produced.

  After the single crystal growth is completed, the molybdenum crucible is sufficiently cooled to 100 ° C. or less and then taken out (step S8). Thereby, it is possible to suppress the oxidation of the surface at the time of taking out the crucible, and when using it for the next pulling of the sapphire single crystal, the time required for the empty baking step (step S2) can be shortened, and the crystal cost is reduced. Can be realized.

  As described above, the method for producing a sapphire single crystal according to the present invention melts after degassing the sapphire raw material, so that the reaction between impurities and molybdenum resulting from the sapphire raw material can be suppressed. The amount of difficult-to-dissolve floating on the surface can be greatly reduced. Therefore, it is possible to stably grow a high quality sapphire single crystal.

  In addition, since the method for manufacturing a sapphire single crystal according to the present embodiment performs the baking of the molybdenum crucible to remove the oxide film on the surface of the crucible, the oxygen partial pressure in the chamber during the raw material melting step can be reduced. it can. As a result, the reaction between molybdenum and oxygen can be suppressed, and the amount of hardly soluble matter floating on the surface of the melt can be greatly reduced. Therefore, it is possible to stably grow a high quality sapphire single crystal.

  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, both the degassing treatment and the melting of the raw material are continuously performed in the molybdenum crucible, but the present invention is not limited to such a case. After performing the degassing process in advance, the sapphire raw material may be transferred to a chamber and put into a molybdenum crucible, and only the raw material may be melted in the molybdenum crucible.

  In the above embodiment, both the molybdenum crucible emptying step and the sapphire raw material degassing step are performed, but the molybdenum crucible emptying step may be omitted.

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

  As Example 1, the relationship between the generation of hardly soluble substances and the hydrogen concentration was examined. First, a molybdenum crucible having a diameter of 200 mm and a height of 225 mm was prepared, and was baked in an Ar atmosphere (trace hydrogen atmosphere) containing various trace amounts of hydrogen before the sapphire raw material was added thereto. The trace hydrogen atmosphere at this time was 7 conditions (samples A to G) of 5 ppm, 10 ppm, 0.1 vol%, 0.5 vol%, 1 vol%, 3 vol%, and 5 vol%.

  Next, a predetermined amount of the sapphire raw material was put into the crucible after baking and melted by a resistance heating method without performing degassing treatment. A high-purity alumina powder (average particle size 100 μm) manufactured by Sumika was used as a raw material. During the melting, the atmosphere in the chamber was set to 100% Ar. Thereafter, the surface of the sapphire melt was observed through a light-reducing filter from a viewing window provided in the chamber, and the diameter of the hardly soluble matter floating on the surface of the melt was measured. The results are shown in Table 1. Finally, the seed crystal was brought into contact with the melt, and the crystal diameter was increased to a predetermined diameter while controlling the heater power.

  As is clear from Table 1, a large amount of hardly soluble substances were generated at a hydrogen concentration of 5 ppm, and the diameter became 100 mm. As a result, the subsequent stable crystal growth could not be performed, and the crystal quality deteriorated. When the hydrogen concentration was 10 ppm, the effect of suppressing the hardly soluble material by hydrogen was obtained, and the diameter was greatly reduced to 15 mm. When the hydrogen concentration was further increased, the diameter of the hardly soluble material gradually decreased, and in 1 to 3%, the diameter decreased to 5 mm. In the case where the hydrogen concentration is very high, if there is an inflow of air into the chamber, there is a risk that hydrogen will burn violently, which is very dangerous. Therefore, in this embodiment, the upper limit of the hydrogen concentration is set to 5%. .

  In Example 2, the crucible was baked in a trace hydrogen atmosphere with a hydrogen concentration of 3 vol%, and then degassed in an Ar 100% atmosphere before the raw material melting step. The degassing temperature was carried out for 8 conditions in steps of 100 ° C. from 400 ° C. to 1100 ° C. (samples H to O). Thereafter, in the same manner as in Example 1, the surface of the sapphire melt was observed from a viewing window through a neutral density filter, and the diameter of the hardly soluble matter floating on the surface of the melt was measured. The results are shown in Table 2. Finally, the seed crystal was brought into contact with the melt, and the crystal diameter was increased to a predetermined diameter while controlling the heater power.

  As is clear from Table 2, when the degassing temperature was 400 ° C. (sample H), the effect of suppressing hardly dissolved substances was not obtained. Moreover, when the degassing temperature was 1100 ° C. (sample O), the amount of hardly dissolved substances increased. This is probably because the adsorbed impurity gas reacted with the molybdenum crucible to generate molybdenum oxide, which promoted the generation of hardly soluble substances.

  As a comparative example, a predetermined amount of sapphire raw material was put into a molybdenum crucible that was not baked and melted by a resistance heating method without performing degassing treatment. During melting, the inside of the chamber was set to an Ar 100% atmosphere (sample P). Thereafter, in the same manner as in Example 1, the surface of the sapphire melt was observed from a viewing window through a neutral density filter, and the diameter of the hardly soluble matter floating on the surface of the melt was measured. The results are shown in Table 3. Finally, the seed crystal was brought into contact with the melt, and the crystal diameter was increased to a predetermined diameter while controlling the heater power.

  As can be seen from Table 3, with the conventional raw material melting method (without crucible empty baking and without degassing treatment), a hardly soluble material having a diameter of 100 mm was generated, making it difficult to deposit the seed crystal.

  As described above, from the results of Examples 1 and 2 and the comparative example, the hydrogen concentration during baking is preferably 10 ppm or more and 5 vol% or less, and the degassing temperature is preferably in the range of 500 ° C. or more and 1000 ° C. or less, As a result, it was found that the effect of suppressing hardly dissolved substances can be obtained.

DESCRIPTION OF SYMBOLS 10 Sapphire single crystal manufacturing apparatus 11 Chamber 12 Support rotating shaft 13 Support stand 14 Molybdenum crucible 15 Resistance heater 16 Support shaft rotating mechanism 17 Viewing window 18 Seed bar 19 Lifting mechanism 20 Sapphire single crystal 21 Sapphire melt 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 31 Oxygen meter

Claims (4)

A degassing step of degassing the sapphire raw material by heat-treating the surface of the sapphire raw material at a temperature of 500 ° C. or higher and 1000 ° C. or lower in a vacuum inert atmosphere chamber ;
A melting step of obtaining a sapphire melt by melting the sapphire raw material in a molybdenum crucible;
And a pulling step of obtaining a sapphire single crystal by pulling up a seed crystal immersed in the sapphire melt. 2. The method for producing a sapphire single crystal according to claim 1, wherein in the degassing step , the degassing process is continued until the oxygen concentration in the exhaust gas discharged from the chamber becomes 0.1 ppm or less.   3. The method for producing a sapphire single crystal according to claim 1, wherein the process from degassing to melting of the sapphire raw material is continuously performed in the molybdenum crucible. A chamber;
A molybdenum crucible for supporting the sapphire raw material in the chamber;
A heater for heating the molybdenum crucible;
An oxygen concentration meter for measuring the oxygen concentration in the exhaust gas discharged from the chamber;
A control unit for controlling the heater,
The controller is
After the sapphire raw material is put into the molybdenum crucible, the heater is controlled so that the temperature in the chamber is maintained in the first temperature range, and the sapphire raw material is degassed, and the degassing The oxygen concentration in the exhaust gas during the process is monitored by the oxygen concentration meter, and after the oxygen concentration becomes a predetermined level or less, the temperature in the chamber is higher than the first temperature range. The apparatus for producing a sapphire single crystal is characterized in that the power of the heater is increased so as to reach a temperature and melting of the sapphire raw material is started.

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