JP2015096457A - Single crystal production device and single crystal production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a single crystal production device capable of producing a high quality single crystal by preventing impurity contamination to a crystal under an optimized growth condition.SOLUTION: A single crystal production device 1 includes: a growth crucible 21 for accommodating a material 40 inside; and an outside crucible 22 arranged outside of the growth crucible 21. A gas flow passage 66 for passing nitrogen gas for dilution and ventilation between the growth crucible 21 and the outside crucible 22 is formed in the outside crucible 22. The single crystal production device 1 includes: a gas supply source 63 which supplies gas from a gas introduction port 60 formed in the outside crucible 22 to the gas flow passage 66, and which exhausts gas in the gas flow passage 66 from the gas discharge port 67 formed in the outside crucible 22 to outside; and a coil 30 for heating and sublimating the material 40 accommodated in the growth crucible 21.

Description

  The present invention relates to a single crystal manufacturing apparatus and a single crystal manufacturing method, and more particularly to an apparatus and a method for manufacturing a single crystal using a sublimation method.

  Aluminum nitride (AlN), which is a kind of group III-V nitride semiconductor, has the widest band gap among direct transition semiconductors, and is expected as a next-generation material. By using aluminum nitride, an optical device with a short wavelength that emits light with a wavelength of 210 nm, for example, can be produced. In addition to an optical device, it is possible to manufacture a power device having advantages such as high breakdown voltage, low on-resistance, and small deterioration in characteristics under a high temperature environment. However, at present, a method for producing an aluminum nitride wafer of quality that contributes to the production of an aluminum nitride device has not been established, and early realization is expected.

  By the way, as a method for producing a single crystal, a pulling method for growing a bulk crystal from a melt, a sublimation method for growing from a vapor phase, a hydride vapor phase growth method (HVPE method), a metal organic chemical vapor deposition method (MOCVD method). Etc. are known. Since aluminum nitride has a high nitrogen dissociation pressure in the vicinity of the melting point, a sublimation method is mainly used as a method for producing an aluminum nitride single crystal.

  In this sublimation method, a crucible which is a growth vessel is heated to form a temperature difference between the upper and lower portions of the crucible, the raw material charged into the lower portion of the crucible is sublimated, and the sublimation gas is heated to a relatively high temperature. This is a method of growing a crystal by recrystallization in a growth part at the top of a low crucible. Among these sublimation methods, a method using a seed crystal is called an improved Rayleigh method, and the nucleation process of crystal growth can be controlled by using the seed crystal. In this method, the gas sublimated from the raw material is transported by diffusion and condensed in a supersaturated state on the seed crystal at a lower temperature than the raw material.

  Here, in order to produce a high-quality single crystal, it is necessary to optimize the growth conditions. In general, the crystal growth conditions vary greatly depending on the structure and material of the crucible. The optimum growth conditions are also obtained by combining the above. For example, when a crystal is grown inside a graphite crucible, carbon is mixed as an impurity in the crystal. Therefore, by placing a crucible made of tantalum carbide inside the graphite crucible, the graphite crucible can be used as a heating element. It has been proposed to grow a crystal inside a tantalum carbide crucible (see, for example, Patent Document 1).

  However, when a plurality of crucibles are combined, impurities generated by thermal etching or the like are likely to accumulate between the crucibles. When these impurities enter the growth crucible, a large amount of impurities are mixed into the crystal, and the quality of the produced single crystal may be significantly deteriorated.

International Publication No. 2010/122801

  The present invention has been made in view of such problems of the prior art, and can produce a high-quality single crystal by preventing impurities from being mixed into the crystal under optimized growth conditions. An object is to provide a single crystal manufacturing apparatus and a single crystal manufacturing method.

  According to the first aspect of the present invention, there is provided a single crystal manufacturing apparatus capable of manufacturing a high quality single crystal by preventing impurities from being mixed into the crystal under optimized growth conditions. This single crystal manufacturing apparatus includes a growth crucible that accommodates a raw material therein, and an outer crucible arranged outside the growth crucible. The outer crucible is formed with a gas flow path for circulating a gas for dilution ventilation between the growth crucible and the outer crucible. The single crystal manufacturing apparatus supplies the gas from a gas inlet formed in the outer crucible to the gas flow path and supplies the gas to the dilution ventilation in the gas flow path from a gas discharge port formed in the outer crucible. A dilution ventilation section for discharging the gas to the outside, and a heating section for heating and sublimating the raw material stored in the growth crucible.

  According to the second aspect of the present invention, there is provided a single crystal manufacturing method capable of manufacturing a high-quality single crystal by preventing impurities from being mixed into the crystal under optimized growth conditions. In this single crystal manufacturing method, a raw material is accommodated in a growth crucible, and a seed crystal is disposed so as to face the raw material accommodated in the growth crucible. A gas for dilution ventilation is supplied from a gas inlet formed in an outer crucible disposed outside the growth crucible to a gas flow path formed between the growth crucible and the outer crucible, and the outer crucible is supplied. The raw material contained in the growth crucible is heated and sublimated while discharging the gas in the gas flow path to the outside from the gas discharge port formed on the seed crystal. Precipitate.

  According to the present invention, since the gas for dilution ventilation is caused to flow through the gas flow path formed between the growth crucible and the outer crucible, impurities generated by thermal etching or the like are externally caused by the gas flow in the gas flow path. Can be discharged. Thereby, impurities mixed in the inside of the growth crucible are suppressed, so that a high-purity single crystal can be grown in the growth crucible.

  Here, it is preferable to supply the gas to the gas flow path so that the flow rate of the gas at the gas discharge port is 15 cm / s or more. Further, nitrogen gas or inert gas can be used as the gas for dilution ventilation.

  According to the present invention, it is possible to manufacture a high-quality single crystal by preventing impurities from being mixed into the crystal under optimized growth conditions.

It is sectional drawing which shows typically the single crystal manufacturing apparatus in one Embodiment of this invention. It is a bottom view of the outer crucible in the single crystal manufacturing apparatus of FIG. It is the III-III sectional view taken on the line of FIG. It is a top view of the outer crucible in the single crystal manufacturing apparatus of FIG.

  Hereinafter, an embodiment of a single crystal manufacturing apparatus according to the present invention will be described in detail with reference to FIGS. 1 to 4. 1 to 4, the same or corresponding components are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a cross-sectional view schematically showing a single crystal manufacturing apparatus 1 according to an embodiment of the present invention. As shown in FIG. 1, the single crystal manufacturing apparatus 1 in the present embodiment is wound around a crystal growth furnace 10, a crystal growth part 20 disposed in an internal space 11 of the crystal growth furnace 10, and the periphery of the crystal growth furnace 10. And a coil 30 to be rotated.

  The crystal growth unit 20 includes a growth crucible 21, an outer crucible 22 disposed outside the growth crucible 21, a heat insulating material 23 that covers the outside of the outer crucible 22, and a support unit 24 that supports these members. The The growth crucible 21 has a main body 25 that contains aluminum nitride (AlN) as a raw material 40 and a lid 26 that seals the main body 25.

  The growth crucible 21 is formed of a material having a melting point higher than that of the crystal to be grown. For example, the growth crucible 21 can be formed from a metal, nitride, carbide, nitride alloy, carbide alloy, or the like having a melting point higher than that of the crystal to be grown. In particular, when producing a single crystal of aluminum nitride, the growth crucible 21 is formed from graphite (C), tantalum (Ta), tungsten (W), alloys thereof, tantalum carbide (TaC), tungsten carbide (WC), or the like. It is preferable to do. These materials can be preferably used because they have low reactivity with growing crystals and are excellent in heat resistance at high temperatures. The outer crucible 22 is made of, for example, graphite (C), tantalum (Ta), tungsten (W), alloys thereof, tantalum carbide (TaC), tungsten carbide (WC), or the like.

  A seed crystal mounting unit 50 is fixed to the lower surface of the lid 26 of the growth crucible 21. A seed crystal 51 can be placed on the lower surface of the seed crystal placement unit 50, and the seed crystal 51 placed on the seed crystal placement unit 50 is a raw material 40 accommodated in the growth crucible 21. It comes to oppose. As the seed crystal 51, for example, aluminum nitride or silicon carbide can be used. A substrate on which a buffer layer is grown can also be used as the seed crystal 51. The main surface of the seed crystal 51 is preferably mirror-polished by CMP or the like, and not only the main surface but also the back side thereof may be mirror-polished by CMP or the like.

  FIG. 2 is a bottom view of the outer crucible 22. As shown in FIG. 2, a gas inlet 60 for introducing a gas for dilution ventilation is formed in the center of the bottom surface 22 </ b> A of the outer crucible 22. As shown in FIG. 1, a hole 61 is formed in the heat insulating material 23 at a position corresponding to the gas inlet 60, and a flow path 62 communicating with the hole 61 of the heat insulating material 23 is formed inside the support portion 24. Is formed. The flow path 62 is connected to a gas supply source 63 that supplies dilution ventilation gas such as nitrogen gas or inert gas.

  As shown in FIG. 1, a floor surface 22B is formed inside the outer crucible 22 above the bottom surface 22A, and the growth crucible 21 is disposed on the floor surface 22B. A space 64 is formed between the bottom surface 22A and the floor surface 22B.

  3 is a cross-sectional view taken along line III-III in FIG. As shown in FIG. 3, a plurality of communication holes 65 are formed on the floor surface 22B of the outer crucible 22 at predetermined intervals. As shown in FIG. 1, a gas flow path 66 is formed above the floor surface 22 </ b> B for circulating the diluted ventilation gas between the outer crucible 22 and the growth crucible 21.

  FIG. 4 is a top view of the outer crucible 22. As shown in FIG. 4, a gas discharge port 67 for discharging the diluted ventilation gas introduced into the gas flow channel 66 is formed on the upper surface 22 </ b> C of the outer crucible 22. In the example shown in FIG. 4, a plurality of gas discharge ports 67 are formed on the upper surface 22 </ b> C of the outer crucible 22 with a predetermined interval.

  In this way, diluted ventilation gas such as nitrogen gas or inert gas from the gas supply source 63 flows into the flow path 62 of the support 24, the hole 61 of the heat insulating material 23, the gas inlet 60 of the outer crucible 22, the space 64, and The gas is supplied to the gas flow channel 66 through the communication port 65, and is further discharged to the internal space 11 of the crystal growth furnace 10 from the hole formed in the heat insulating material 23 through the gas discharge port 67. That is, the gas supply source 63 in the present embodiment supplies the diluted ventilation gas from the gas introduction port 60 of the outer crucible 22 to the gas flow channel 66 and the gas in the gas flow channel 66 from the gas discharge port 67 of the outer crucible 22. It functions as a dilution ventilation part that discharges the outside.

  As shown in FIG. 1, the crystal growth furnace 10 is formed with a gas inlet 12 for introducing a gas used for growing a single crystal into an internal space 11, and this gas inlet 12 is connected to a gas supply source 13. Has been. As a result, a gas such as nitrogen gas or inert gas is introduced into the internal space 11 of the crystal growth furnace 10 from the gas supply source 13 through the gas inlet 12. The crystal growth furnace 10 is also provided with a gas discharge port 14, which is connected to a vacuum pump 15. Thus, the gas supplied from the gas supply source 13 to the internal space 11, the gas for dilution ventilation discharged from the gas discharge port 67 through the gas flow channel 66 between the outer crucible 22 and the growth crucible 21 described above. The gas generated in the internal space 11 of the crystal growth furnace 10 is discharged through the gas discharge port 14. Thus, by adjusting the gas supply from the gas supply source 13 and the gas supply source 63 and the pressure reduction by the vacuum pump 15, the internal space 11 of the crystal growth furnace 10 is adjusted to a desired pressure.

  A high frequency power source (not shown) is connected to the coil 30, and when a high frequency current is passed through the coil 30, an induced current is generated in the outer crucible 22 and the growth crucible 21, thereby heating the raw material 40 in the growth crucible 21. And sublimated. As described above, the coil 30 in this embodiment functions as a heating unit that heats and sublimates the raw material 40 accommodated in the main body 25 of the growth crucible 21. The coil 30 is configured to be movable relative to the growth crucible 21 by a moving mechanism (not shown).

  A radiation thermometer (not shown) is arranged outside the crystal growth furnace 10 so that the temperature of the lower part of the main body 25 of the growth crucible 21 and the upper part of the lid 26 can be measured by this radiation thermometer. It has become. Based on these measured temperatures, the current supplied to the coil 30 is controlled so that the temperature in the growth crucible 21 has a desired distribution.

  In the single crystal manufacturing apparatus 1 having such a configuration, first, the raw material 40 is accommodated in the main body portion 25 of the growth crucible 21, and the seed crystal 51 is placed and fixed on the seed crystal placement portion 50. Then, the main body 25 of the growth crucible 21 is sealed with the lid body 26, and the internal space 11 of the crystal growth furnace 10 is evacuated using the vacuum pump 15 to reduce the pressure in the internal space 11. Subsequently, for example, nitrogen gas is supplied from the gas supply source 13 to the internal space 11 of the crystal growth furnace 10 to make the internal space 11 a nitrogen gas atmosphere. Thereby, the growth of the single crystal 52 can be performed in an atmosphere of high-purity nitrogen gas.

  Further, for example, nitrogen gas is supplied from the gas supply source 63 to the gas flow path 66 so that a flow of nitrogen gas is formed in the gas flow path 66 between the growth crucible 21 and the outer crucible 22. At this time, the flow rate of nitrogen gas from the gas supply source 63 is adjusted so that the flow rate of nitrogen gas at the gas discharge port 67 is preferably 15 cm / s or more, more preferably 30 cm / s or more.

  The raw material 40 in the growth crucible 21 is heated to, for example, about 2000 ° C. by flowing a high-frequency current through the coil 30 and sublimated. At this time, the coil 30 is moved with respect to the growth crucible 21 based on the temperature of the lower portion of the main body portion 25 of the growth crucible 21 and the upper portion of the lid body 26 detected by the radiation thermometer, and the main body portion 25 of the growth crucible 21. The seed crystal 51 on the seed crystal mounting unit 50 is adjusted to be lower in temperature than the raw material 40 accommodated in the container. At this time, the temperature of the growth surface of the single crystal 52 is preferably 1700 ° C. to 2300 ° C., and the pressure in the internal space 11 of the crystal growth furnace 10 is 13.3 kPa (100 Torr) to 101.3 kPa (760 Torr). Is preferred.

  As described above, the temperature of the seed crystal 51 on the seed crystal mounting unit 50 is lower than that of the raw material 40 accommodated in the main body 25 of the growth crucible 21, so that the sublimation gas of the raw material 40 is discharged from the main body 25. It is transferred onto the seed crystal 51, and a single crystal 52 is deposited on the seed crystal 51 and recrystallized. At this time, nitrogen gas from the gas supply source 63 is always supplied to the gas passage 66 between the growth crucible 21 and the outer crucible 22, and the gas passage 66 is diluted and ventilated. Accordingly, impurities generated by thermal etching or the like in the heat insulating material 23, the outer crucible 22, and the growth crucible 21 are exhausted to the outside of the crystal growth unit 20 by the flow of nitrogen gas in the gas flow channel 66. Thereby, since impurities mixed in the inside of the growth crucible 21 are suppressed, the growth of the aluminum nitride single crystal 52 is performed in a high purity nitrogen gas atmosphere. Therefore, high-purity aluminum nitride single crystal 52 can be grown on seed crystal 51. After the growth, a single crystal substrate can be obtained by cutting and polishing the single crystal 52.

  The aluminum nitride single crystal 52 was manufactured using the single crystal manufacturing apparatus 1 according to the embodiment described above. First, an aluminum nitride seed crystal having a plane orientation (0001) and a thickness of about 500 μm and a diameter of 60 mm was prepared as the seed crystal 51. A crucible made of a tantalum carbide sintered body was used as the growth crucible 21, and a tungsten crucible was used as the outer crucible 22. Aluminum nitride powder as a raw material 40 was accommodated in the main body 25 of the growth crucible 21. The seed crystal 51 was fixed to the seed crystal placement unit 50 with an adhesive and held on the seed crystal placement unit 50. At this time, the main surface of the seed crystal 51 was made to face the raw material 40 (aluminum nitride powder) accommodated in the main body portion 25. The heat insulating material 23 was made of carbon, and a quartz chamber was used as the crystal growth furnace 10.

  After evacuating the internal space 11 of the crystal growth furnace 10 using the vacuum pump 15, nitrogen gas is supplied from the gas supply source 13 to the internal space 11 of the crystal growth furnace 10, and the internal space 11 is set to 53.4 kPa (400 Torr). Of nitrogen atmosphere. Before the single crystal growth step, the growth crucible 21 was heated at 1000 ° C. for 1 hour to clean the surface of the seed crystal 51.

  Next, the raw material 40 in the growth crucible 21 was heated by passing a high-frequency current through the coil 30, and an aluminum nitride single crystal 52 was grown on the seed crystal 51 by a sublimation method. The growth conditions were a growth surface temperature of 2200 ° C., a pressure in the internal space 11 of the crystal growth furnace 10 of 53.4 kPa (400 Torr), and a growth time of 50 hours. The temperature of the seed crystal 51 was set to be about 50 ° C. lower than the temperature of the raw material 40. The difference between the temperature of the seed crystal 51 and the temperature of the raw material 40 was adjusted by moving the coil 30 with respect to the growth crucible 21.

  In this state, the aluminum nitride single crystal 52 was grown while supplying nitrogen gas from the gas supply source 63 to the gas flow channel 66. At this time, the supply amount of nitrogen gas was changed so that the flow rates of nitrogen gas at the gas outlet 67 were 8 cm / s, 15 cm / s, and 30 cm / s, respectively. After growing the single crystal 52, the growth crucible 21 was cooled to room temperature at a rate of about 100 K / h, and the single crystal 52 of aluminum nitride was taken out.

  It was confirmed by micro Raman scattering measurement whether carbon was mixed as an impurity in the obtained single crystal 52. Whether or not carbon as an impurity is mixed can be easily determined based on whether or not a peak derived from mixing of carbon is confirmed in microscopic Raman scattering measurement. Table 1 shows the results.

  As can be seen from Table 1, when the flow rate of nitrogen gas at the gas outlet 67 was 15 cm / s or more, it was confirmed that the amount of impurities mixed was below the detection limit of micro Raman. Thus, it was found that a high-purity single crystal 52 can be obtained by adjusting the supply amount of nitrogen gas so that the flow rate of nitrogen gas at the gas discharge port 67 is 15 cm / s or more.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and it goes without saying that the present invention may be implemented in various forms within the scope of the technical idea.

  For example, in the above-described embodiment, the example in which the seed crystal placement unit 50 is provided as a member different from the lid 26 has been described, but the lower surface of the lid 26 itself may be used as the seed crystal placement unit 50. it can. In the above-described embodiment, the example in which the raw material 40 is sublimated by high-frequency heating using the coil 30 has been described. However, the heating method of the raw material 40 is not limited to this, and the raw material 40 is heated by resistance heating, for example. May be.

  Further, in the embodiment described above, an example in which nitrogen gas is introduced into the internal space 11 of the crystal growth furnace 10 and the gas flow channel 66 between the growth crucible 21 and the outer crucible 22 has been described. In the case of producing a crystal, an inert gas such as argon gas may be introduced instead of nitrogen gas, or a gas obtained by mixing an inert gas such as argon gas with nitrogen gas may be introduced. Furthermore, in the above-described embodiment, the gas supplied from the gas supply source 13 and the gas supplied from the gas supply source 63 are the same, but they may be different.

  In the above-described embodiment, the example in which the two crucibles of the growth crucible 21 and the outer crucible 22 are used as the crucible has been described. However, the present invention is not limited to this. The present invention can also be applied when three or more crucibles are used in combination.

DESCRIPTION OF SYMBOLS 1 Single crystal manufacturing apparatus 10 Crystal growth furnace 11 Internal space 12 Gas introduction port 13 Gas supply source 14 Gas discharge port 15 Vacuum pump 20 Crystal growth part 21 Growth crucible 22 Outer crucible 22A Bottom 22B Floor 22C Top 23 Insulation 24 Support part 25 Main Body 26 Lid 30 Coil 40 Raw Material 50 Seed Crystal Placement Part 51 Seed Crystal 52 Single Crystal 60 Gas Inlet 61 Hole 62 Channel 63 Gas Supply Source 64 Space 65 Communication Hole 66 Gas Channel 67 Gas Exhaust Port

Claims (6)

A growth crucible containing raw materials inside,
An outer crucible disposed outside the growth crucible, wherein an outer crucible in which a gas flow path for flowing a gas for dilution ventilation is formed between the growth crucible and the outer crucible;
The gas is supplied to the gas channel from a gas inlet formed in the outer crucible, and the dilution ventilation gas in the gas channel is discharged to the outside from a gas outlet formed in the outer crucible. A dilution ventilation section;
A heating unit for heating and sublimating the raw material stored in the growth crucible;
A single crystal manufacturing apparatus.   2. The single crystal manufacturing apparatus according to claim 1, wherein the dilution ventilation unit supplies the gas to the gas flow path so that a flow rate of the gas at the gas discharge port is 15 cm / s or more.   The single crystal manufacturing apparatus according to claim 1 or 2, wherein the gas for dilution ventilation is nitrogen gas or inert gas. The raw material is stored inside the growth crucible,
A seed crystal is arranged so as to face the raw material stored in the growth crucible,
A gas for dilution ventilation is supplied to a gas flow path formed between the growth crucible and the outer crucible from a gas inlet formed in an outer crucible disposed outside the growth crucible, and the outer crucible is supplied. A single crystal of the raw material is formed on the seed crystal by heating and sublimating the raw material stored in the growth crucible while discharging the gas in the gas flow path to the outside from the gas discharge port formed in Deposit,
A method for producing a single crystal.   The single crystal manufacturing apparatus according to claim 4, wherein the gas is supplied to the gas flow path so that a flow rate of the gas at the gas discharge port is 15 cm / s or more.   The single crystal manufacturing apparatus according to claim 4 or 5, wherein nitrogen gas or inert gas is used as the gas for dilution ventilation.

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