JP2015086112A - Method for making aluminum nitride single crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for making aluminum nitride single crystal that enables the quality thereof to be improved..SOLUTION: A method for making an aluminum nitride single crystal 6 uses a single crystal making apparatus 1 including a crucible 10 which stores a raw material 2 and also holds a seed crystal 5 opposite the raw material 2, and an induction coil 50 which is arranged at a periphery of the crucible 10 movably up and down, and heats the crucible 10. The method for making an aluminum nitride single crystal 6 includes a first step of causing the induction coil 50 to be located at a first heating position Pon the side of the seed crystal 5 until the temperature of the crucible 10 reaches a predetermined temperature T, and a second step of moving the induction coil 5 to a second heating position Pon the side of the raw material 2 when the temperature of the crucible 10 reaches the predetermined temperature T.

Description

  The present invention relates to a method for producing an aluminum nitride (AlN) single crystal by a sublimation recrystallization method (an improved Rayleigh method).

  As a method for producing an aluminum nitride single crystal, a so-called sublimation recrystallization method is known in which a raw material is heated and sublimated in a high temperature region, and the sublimation gas is recondensed on a seed crystal provided in a low temperature region (for example, Patent Document 1).

JP 2011-132079 A

  The above-described sublimation recrystallization method requires that a temperature gradient be formed between the raw material and the seed crystal. However, if this temperature gradient is formed even during the temperature raising process, the sublimation of the raw material starts before the temperature of the seed crystal reaches the temperature necessary for single crystal growth, and a large amount of aluminum nitride is formed on the seed crystal. There is a problem that crystals and low-quality aluminum nitride single crystals grow.

  The problem to be solved by the present invention is to provide a method for producing an aluminum nitride single crystal capable of improving the quality.

  [1] A method for producing an aluminum nitride single crystal according to the present invention includes a crucible that contains a raw material and holds a seed crystal so as to face the raw material, and is arranged around the crucible so as to be movable up and down. And heating means for heating the seed crystal side until the temperature of the crucible reaches a predetermined temperature. And a second step of moving the heating means to the second heating position on the raw material side when the temperature of the crucible reaches the predetermined temperature. And

  [2] In the above invention, the heating means includes an induction coil surrounding the crucible, and the first heating position is a position where the induction coil surrounds both the seed crystal and the raw material. The heating position may be a position where the induction coil surrounds the raw material, and the seed crystal may be located outside the induction coil located at the second heating position.

  [3] In the above invention, the predetermined temperature may be 1450 [° C.] to 1550 [° C.].

  [4] In the above invention, in the method for producing an aluminum nitride single crystal, the heating means positioned at the second heating position may be a third between the first heating position and the second heating position. A third step of further moving to the heating position may be provided.

  According to the present invention, by changing the position of the heating means according to the temperature of the crucible, it is possible to suppress a temperature difference between the upper part and the lower part of the crucible during the temperature rising process, Quality can be improved.

FIG. 1 is a schematic configuration diagram of an apparatus for producing an aluminum nitride single crystal according to the first embodiment of the present invention. FIG. 2 is a cross-sectional view showing a modification of the crucible in the first embodiment of the present invention. FIG. 3A and FIG. 3B are views showing a state where the induction coil is located at the first and second heating positions in the first embodiment of the present invention, respectively. FIG. 4A to FIG. 4C are diagrams showing states in which the induction coil is located at the first to third heating positions in the second embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<< first embodiment >>
1 is a schematic configuration diagram of an apparatus for producing an aluminum nitride single crystal according to the present embodiment, FIG. 2 is a cross-sectional view showing a modification of a crucible, and FIGS. It is a figure which shows the state located in the 1st and 2nd heating position, respectively.

  The apparatus 1 for producing an aluminum nitride single crystal in the present embodiment is an apparatus for producing an aluminum nitride single crystal by a sublimation recrystallization method (an improved Rayleigh method). Specifically, the raw material 2 is heated and sublimated in the high temperature region, and the sublimation gas is recondensed on the seed crystal 5 provided in the low temperature region, thereby producing the aluminum nitride single crystal 6.

  As shown in FIG. 1, the single crystal manufacturing apparatus 1 includes a crucible 10 that contains a raw material 2 and holds a seed crystal 5, a crystal growth furnace 20 that contains the crucible 10, and nitrogen in the crystal growth furnace 20. A gas supply device 30 for supplying gas, a decompression device 40 for decompressing the inside of the crystal growth furnace 20, an induction coil 50 disposed outside the crystal growth furnace 20 so as to surround the crucible 10, and the induction coil 50 in the vertical direction The position adjustment device 60 to be moved to the first position, the first and second thermometers 71 and 72 for measuring the temperature of the crucible 10, and the control device 80 for controlling the position adjustment device 60 based on the measurement results of the thermometers 71 and 72. And.

  The crucible 10 includes a container main body 11 having an upper opening 111 and a lid 12 that covers the upper opening 111. The lid 12 is merely placed on the container body 11 and the crucible 10 is introduced into the crystal growth furnace 20 because the crucible 10 has a semi-sealing structure in which fluid can easily enter and exit. The nitrogen gas thus made can flow into the crucible 10.

  The container body 11 has a bottomed cylindrical shape, and the raw material 2 is accommodated therein. Specific examples of the raw material 2 include aluminum nitride powder.

  The lid 12 has a disk shape with an outer diameter larger than the outer diameter of the seed crystal 5, and is placed on the upper end of the container body 11 so as to cover the upper opening 111 of the container body 11. A seed crystal 5 is attached to the lower surface of the lid 12 via an adhesive, and the seed crystal 5 faces the raw material 2 accommodated in the container body 11.

  Specific examples of the seed crystal 5 include, for example, a SiC single crystal, an AlN single crystal, an AlN / SiC single crystal (a single crystal obtained by hetero-growing an AlN single crystal film having a thickness of about 200 to 500 [μm] on the SiC single crystal. Examples thereof include a plate-like or disc-like substrate composed of a crystal). Moreover, as a specific example of the adhesive that bonds the seed crystal 5 to the lid 12, for example, a high temperature adhesive mainly composed of resin, inorganic compound ceramics, or graphite can be exemplified.

  In addition, as shown in FIG. 2, the cover body 12 may be provided with the two cover members 13 and 14, and the above-mentioned adhesive agent becomes unnecessary in this case. Specifically, the first lid member 13 is a ring-shaped member having a through opening 131 having an inner diameter smaller than the outer diameter of the seed crystal 5, and the first lid member 13 is an upper part of the container body 11. It is placed on the container body 11 so as to cover the opening 113. The seed crystal 5 is placed on the first lid member 13 so as to close the through opening 131, and the outer peripheral portion of the seed crystal 5 is held by the first lid member 13. On the other hand, the second lid member 14 is a disk-shaped member having an outer diameter larger than the outer diameter of the seed crystal 5, and is placed on the seed crystal 5 held by the first lid member 13. The seed crystal 5 is sandwiched between the first lid member 13 and the second lid member 14.

  Returning to FIG. 1, the crucible 10 is made of a material having heat resistance during the crystal growth of an aluminum nitride single crystal (about 2000 ° C.). Specifically, the container body 11 and the lid 12 of the crucible 10 are made of graphite, boron nitride, aluminum nitride, gallium nitride, silicon carbide, silicon nitride, molybdenum, tungsten, tantalum, molybdenum carbide, zirconium carbide, tungsten carbide, It is made of at least one material selected from the group consisting of tantalum carbide, molybdenum nitride, zirconium nitride, tungsten nitride, and tantalum nitride.

  In particular, from the viewpoint of preventing contamination to aluminum nitride single crystal 6 (contamination due to solid solution), it is preferable that the aluminum nitride single crystal 6 is composed of a single metal or a nitride or carbide thereof that is greatly different from the ion radius of aluminum. Specifically, among the materials described above, the container body 11 and the lid 12 of the crucible 10 are made of molybdenum, tungsten, tantalum, molybdenum nitride, tungsten nitride, tantalum nitride, molybdenum carbide, tungsten carbide, and tantalum carbide. It is preferably composed of at least one material selected from the group. The contamination of the aluminum nitride single crystal 6 described above occurs when the crucible 10 is etched by the sublimation gas generated from the aluminum nitride and the fine particles are mixed into the aluminum nitride single crystal 6.

The crucible 10 described above is fixed in the crystal growth furnace 20 through fixing means (not shown). The crystal growth furnace 20 is composed of, for example, a double-structured transparent quartz tube, and a gas inlet 21 is provided in the upper part and a gas outlet 22 is provided in the lower part. A gas supply device 30 capable of supplying an inert gas such as nitrogen (N ₂ ) gas is connected to the gas inlet 21. On the other hand, a pressure reducing device 40 such as a vacuum pump is connected to the gas discharge port 22 via a pressure adjusting valve (not shown). By driving the gas supply device 30 and the decompression device 40, the atmosphere in the crystal growth furnace 20 can be adjusted to a predetermined pressure.

  An induction coil 50 is disposed around the crystal growth furnace 20. The induction coil 50 surrounds the crucible 10 in the crystal growth furnace 20, and when the induction coil 50 is energized with a high-frequency current, the crucible 10 self-heats, whereby the raw material 2 and the single crystal 5 have a desired temperature. To be heated. Instead of the induction coil 50, a heating means using resistance heating or infrared heating may be used.

  The induction coil 50 can be moved along the axial direction of the induction coil 50 by the position adjusting means 60. As a specific example of the position adjusting means 60, for example, a linear motion mechanism including a ball screw mechanism or the like can be exemplified. Two thermometers 71 and 72 are arranged outside the crystal growth furnace 20. Specific examples of the first and second thermometers 71 and 72 include a radiation thermometer. The radiation thermometers 71 and 72 detect the temperature of the crucible 10 by measuring the intensity of infrared light and visible light emitted from the crucible 10 through the transparent wall surface of the crystal growth furnace 20.

  The first thermometer 71 is arranged so as to face the upper surface of the lid 12 of the crucible 10 in the crystal growth furnace 20 (upper part of the crucible 10), and can measure the temperature of the upper part of the crucible 10. It is possible. On the other hand, the second thermometer 72 is disposed so as to face the bottom surface of the container body 11 of the crucible 10 in the crystal growth furnace 20 (lower part of the crucible 10), and measures the temperature of the lower part of the crucible 10. It is possible. That is, in this embodiment, the temperature of the seed crystal 5 is measured by the first thermometer 71 and the temperature of the raw material 2 is measured by the second thermometer 72.

The thermometers 71 and 72 are connected to the control device 80, and the control device 80 controls the position adjusting device 60 based on the measurement results of the thermometers 71 and 72. Specifically, when the measurement result is less than a predetermined temperature, the control device 80 controls the position adjustment device 60 so that the induction coil 50 is positioned at the first heating position P ₁ close to the seed crystal 5. To do. On the other hand, when the measurement result reaches a predetermined temperature, the control device 80 adjusts the position so that the induction coil 50 is moved to the second heating position P ₂ closer to the raw material 2 than the first heating position P _1. The device 60 is controlled.

Here, as shown in FIG. 3A, the first heating position P ₁ is a position where the winding portion of the induction coil 50 surrounds both the raw material 2 and the seed crystal 5 in the crucible 10. In contrast, the second heating position P _2, as shown in FIG. 3 (b), the winding portion of the induction coil 50 is the position surrounding the only raw material 2 in the crucible 10, the second heating position In P ₂ , the seed crystal 5 is located outside the winding portion of the induction coil 50. That is, the raw material 2 and the seed crystal 5 are heated to the same extent by the induction coil 50 at the first heating position P ₁ , whereas the raw material 2 is more active than the single crystal 5 at the _second heating position P _2. To be heated.

  Next, the manufacturing method of the aluminum nitride single crystal 6 using the single crystal manufacturing apparatus 1 demonstrated above is demonstrated.

  First, the raw material 2 such as aluminum nitride powder is set in the container body 11 of the crucible 10. Next, the lid body 12 to which the seed crystal 5 is attached is placed on the container body 11. Thereby, the raw material 2 is accommodated in the crucible 10 and the seed crystal 5 is held in the crucible 10 so as to face the raw material 2.

  Next, after the crucible 10 is installed in the crystal growth furnace 20, the decompression device 40 is driven to remove the atmosphere in the crystal growth furnace 20 through the gas discharge port 22, and the inside of the crystal growth furnace 20 is evacuated. .

Next, the gas supply device 30 is driven to introduce nitrogen gas into the crystal growth furnace 20 through the gas introduction port 21 to increase the pressure in the crystal growth furnace 20 to about 700 [torr]. Next, in a state where the induction coil 50 is positioned at the first heating position P ₁ (see FIG. 3A) by the position adjusting device 60, a high-frequency current is applied to the induction coil 50 to cause the crucible 10 to generate heat. Then, the raw material 2 and the seed crystal 5 are heated. In the first heating position P _1, since both the raw material 2 and the seed crystal 5 is encompassed within the winding part of the induction coil 50, the raw material 2 and the seed crystal 5 is heated to the same extent.

Thus, in this embodiment, since the induction coil 50 is positioned at the first heating position P ₁ close to the seed crystal 5 in the temperature rising process, the temperature of the seed crystal 5 is changed before the sublimation of the raw material 2 starts. The temperature can be raised to a temperature required for single crystal growth.

At this time, the upper and lower temperatures of the crucible 10 are respectively measured by the first and second thermometers 71 and 72 described above, and the upper and lower temperatures of the crucible 10 are both set to the first setting. Once at temperature _{T 1,} the control device 80, the induction coil 50 of the first from the heating position _{P 1} second heating position _{P 2} to move in (see FIG. 3 (b)), a position adjusting device 60 Control. The first set temperature _{T 1} of is a sublimation starting temperature of aluminum nitride, specifically 1450 [℃] ~1550 [℃] .

Even after moving to the _second heating position P ₂ , the crucible 10 is further heated by the induction coil 50. At the second heating position P ₂ , only the raw material 2 in the crucible 10 enters the winding portion of the induction coil 50. The seed crystal 5 is surrounded and located outside the winding portion of the induction coil 50. For this reason, the raw material 2 is heated more actively than the single crystal 5. In this state, the lower temperature of the crucible 10 (that is, the temperature of the raw material 2) becomes 1800 [° C.] to 2300 [° C.] (second set temperature T ₂ ), and the upper temperature of the crucible 10 (that is, the temperature of the seed crystal 5). Until the temperature reaches 1700 [° C.] to 2200 [° C.] (second set temperature T ₂ ), the temperature of the crucible 10 is increased by the induction coil 50.

When the temperature of the crucible 10 reaches the second predetermined temperature _{T 2} of the above, depressurizing the crystal growth furnace 20 to 100 [torr] ~600 [torr] by the decompressor 30. Due to this reduced pressure, the growth of the aluminum nitride single crystal 6 starts. Specifically, as shown in the following formulas (1) and (2), the sublimation gas generated from the raw material 2 is seed crystal due to the temperature gradient set between the upper and lower parts of the crucible 10 described above. Then, it is recrystallized on the seed crystal 5 to grow an aluminum nitride single crystal 6.

2AlN (s) → 2Al (g) + N ₂ (g) (1)
2Al (g) + N ₂ (g) → 2AlN (s) (2)

  When the growth of the aluminum nitride single crystal 6 is stopped, nitrogen gas is supplied into the crystal growth furnace 20 from the gas inlet 21 to increase the pressure in the crystal growth furnace 20 to about 700 [torr]. The energization to the induction coil 50 is stopped, and the raw material 2 and the seed crystal 5 are naturally cooled to room temperature.

  As described above, in the present embodiment, by changing the position of the induction coil 50 according to the temperature of the crucible 10, it is possible to suppress the occurrence of a temperature difference between the upper part and the lower part of the crucible 10 during the temperature rising process. The quality of the aluminum nitride single crystal 6 can be improved.

<< Second Embodiment >>
FIG. 4A to FIG. 4C are diagrams showing states in which the induction coil is located at the first to third heating positions in the present embodiment. This embodiment is different from the first embodiment in that the induction coil 50 moves to the _third heating position P ₃ in addition to the first and second heating positions P ₁ and P _2. Is the same as in the first embodiment.

The third heating position P ₃ of, after the temperature of the crucible 10 has reached the second set temperature T ₂ of the above, the upper temperature of the crucible 10 and the lower temperature of the crucible 10 (the temperature of the raw material 2) (seed crystal 5 The temperature is maintained at a temperature difference of about 100 [° C.], and is the optimum coil position during crystal growth. Specifically, heating position _{P 3} of the third, as shown in FIG. 4 (c), FIG. 4 and the first heating position _{P 1} shown in (a), second shown in FIG. 4 (b) It is positioned between the heating position P ₂ of the.

  Next, the manufacturing method of the aluminum nitride single crystal 6 using the single crystal manufacturing apparatus in this embodiment is demonstrated.

  First, as in the first embodiment, the raw material 2 and the seed crystal 5 are set in the crucible 10, the decompression device 40 is driven, and the atmosphere in the crystal growth furnace 20 is removed through the gas discharge port 22. The inside of the growth furnace 20 is evacuated.

Next, the gas supply device 30 is driven to introduce nitrogen gas into the crystal growth furnace 20 through the gas introduction port 21 to increase the pressure in the crystal growth furnace 30 to about 700 [torr]. Next, in a state where the induction coil 50 is positioned at the first heating position P ₁ (see FIG. 4A) by the position adjusting device 60, a high-frequency current is applied to the induction coil 50 to cause the crucible 10 to generate heat. Then, the raw material 2 and the seed crystal 5 are heated. Like the first embodiment, the heating position P ₁ of the first, since both the raw material 2 and the seed crystal 5 is encompassed within the winding part of the induction coil 50, the raw material 2 and the seed crystal 5 Since they are heated to the same extent, the temperature of the seed crystal 5 can be raised to a temperature required for single crystal growth before the sublimation of the raw material 2 starts.

Then, when reaching the set temperature T ₁ of the upper portion and the temperature of the lower are both the first crucible 10, the position adjusting device 60 is an induction coil 50 of the first from the heating position P ₁ second heating position P _{2 (Fig.} 4 (b)). Like the first embodiment, in the second heating position P _2, only the raw material 2 in the crucible 10 is surrounded by the winding part of the induction coil 50, the seed crystal 5 is the winding portion of the induction coil 50 It is located outside. For this reason, the raw material 2 is heated more actively than the single crystal 5. In this state, each raising the temperature of the crucible 10 to a second predetermined temperature T _2.

When the temperature of the crucible 10 reaches the second predetermined temperature _{T 2} of the above, the position adjusting device 60 is an induction coil 50 and the second heating position _{P 2} from the third heating position _{P 3} (see FIG. 4 (c)) And the pressure inside the crystal growth furnace 20 is reduced to 100 [torr] to 600 [torr]. Due to this reduced pressure, the growth of the aluminum nitride single crystal 6 starts. Specifically, as shown in the above formulas (1) and (2), the sublimation gas generated from the raw material 2 is seed crystal due to the temperature gradient set between the upper and lower portions of the crucible 10 described above. Then, it is recrystallized on the seed crystal 5 to grow an aluminum nitride single crystal 6.

  As described above, in the present embodiment, by changing the position of the induction coil 50 according to the temperature of the crucible 10, it is possible to suppress the occurrence of a temperature difference between the upper part and the lower part of the crucible 10 during the temperature rising process. The quality of the aluminum nitride single crystal 6 can be improved.

  The embodiment described above is described for facilitating the understanding of the present invention, and is not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

  For example, a double crucible structure in which the crucible 10 is accommodated in the second crucible may be employed, or a triple crucible structure in which the crucible 10 is accommodated in the second and third crucibles may be employed.

DESCRIPTION OF SYMBOLS 1 ... Single crystal manufacturing apparatus 2 ... Raw material 5 ... Seed crystal 6 ... Aluminum nitride single crystal 10 ... Crucible 11 ... Container body 12 ... Lid body 20 ... Crystal growth furnace 21 ... Gas introduction port 22 ... Gas discharge port 30 ... Gas supply device DESCRIPTION OF SYMBOLS 40 ... Depressurization device 50 ... Induction coil 60 ... Position adjustment device 71, 72 ... Thermometer 80 ... Control device

Claims (4)

A crucible for containing a raw material and holding a seed crystal so as to face the raw material;
A method for producing an aluminum nitride single crystal using a production apparatus, wherein the crucible is arranged around the crucible so as to move up and down, and heating means for heating the crucible,
A first step of positioning the heating means at a first heating position on the seed crystal side until the temperature of the crucible reaches a predetermined temperature;
And a second step of moving the heating means to the second heating position on the raw material side when the temperature of the crucible reaches the predetermined temperature. A method for producing an aluminum nitride single crystal, comprising: A method for producing aluminum nitride according to claim 1,
The heating means includes an induction coil surrounding the crucible,
The first heating position is a position where the induction coil surrounds both the seed crystal and the raw material,
The second heating position is a position where the induction coil surrounds the raw material,
The method for producing an aluminum nitride single crystal, wherein the seed crystal is located outside the induction coil located at the second heating position. A method for producing aluminum nitride according to claim 1 or 2,
The predetermined temperature is 1450 [° C.] to 1550 [° C.]. A method for producing aluminum nitride according to any one of claims 1 to 3,
In the method for producing aluminum nitride, the heating unit positioned at the second heating position is further moved to a third heating position between the first heating position and the second heating position. A method for producing an aluminum nitride single crystal comprising the steps of:

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