JP2011057468A - Crucible, method for producing aluminum nitride single crystal, and aluminum nitride single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crucible which has improved durability and restrains mixing of impurities into an AlN single crystal. <P>SOLUTION: The crucible 1 is used for producing an aluminum nitride single crystal by a vapor deposition method, and includes an inside crucible 10, an inner lid 20 for holding a seed crystal so that the seed crystal opposes to the bottom wall of the inside crucible 10, and an outside crucible 30 arranged to surround the inside crucible 10 and the inner lid 20. The outside crucible 30 includes an outside crucible body 31 formed from carbon and a coating layer 32 covering the inner wall of the outside crucible body 31 and formed of a high-melting point material. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a crucible, a method for producing an aluminum nitride single crystal, and an aluminum nitride single crystal, and more specifically, a crucible capable of reducing contamination of impurities in the production of an aluminum nitride single crystal, and reducing contamination of impurities. The present invention relates to a method for producing an aluminum nitride single crystal that can be used, and an aluminum nitride single crystal with reduced contamination of impurities.

  Aluminum nitride (AlN) single crystal is very useful as a material for forming various semiconductor devices such as light-emitting elements, electronic elements, and semiconductor sensors because of its excellent semiconductor characteristics. In order to efficiently produce a high-performance semiconductor device, it is important to produce an AlN single crystal having a large diameter and excellent crystallinity.

  As a method for producing an AlN crystal, a sublimation method, HVPE (Hydride Vapor Phase Epitaxy) method, MBE (Molecular Beam Epitaxy) method, MOCVD (Metal Organic Chemical VD) Various vapor deposition methods such as chemical vapor deposition) are employed. Among these methods, the sublimation method is preferably used because an AlN single crystal having a small half width of X-ray diffraction and excellent crystallinity can be obtained and the growth rate is high. Here, the sublimation method refers to a method of growing a crystal by once sublimating a raw material and then solidifying it again.

  In the production of an AlN single crystal by a sublimation method, a compound semiconductor substrate made of a compound semiconductor such as AlN or silicon carbide (SiC) is used as a seed crystal substrate. Since the AlN seed crystal and SiC seed crystal have good lattice constant matching with the AlN single crystal to be grown and are excellent in heat resistance, the seed crystal composed of AlN or SiC is used for the production of the AlN single crystal by the sublimation method. A substrate is considered suitable.

  In order to improve the crystallinity of the AlN single crystal, it is necessary to reduce impurities mixed in the AlN single crystal. Further, in the growth of the AlN single crystal by the sublimation method as described above, in order to increase the growth rate and obtain a high quality AlN single crystal, it is necessary to grow the AlN single crystal at a high temperature of 2000 ° C. or higher, for example. . Therefore, the durability of the crucible used for manufacturing AlN is also a problem. Various studies have been made on many issues such as reduction of impurities and improvement of durability of crucibles used for manufacturing, and various proposals have been made (for example, see Patent Documents 1 to 3).

JP 2006-27988 A JP 2007-308364 A International Publication No. 03/081730 Pamphlet

  However, as described in Patent Document 1, in the method of mixing carbon in the raw material and removing oxygen present in the AlN raw material, the ratio of carbon to be mixed in accordance with the amount of oxygen contained in the AlN raw material is set. There is a problem that control is necessary and the control is difficult. Moreover, although the durability of the crucible is improved by the configuration disclosed in Patent Document 2, in this configuration, there is a problem that impurities such as carbon are mixed into the AlN single crystal from a member such as a heat insulating material existing outside. Furthermore, when a crucible containing a tungsten crystal that expands due to absorption of aluminum is employed as in Patent Document 3, it is difficult to control the expansion, and there remains a problem in lowering the mechanical strength when used multiple times. As described above, in the conventional method for producing an AlN single crystal using a crucible, there remain problems in suppressing the mixing of impurities into the AlN single crystal and improving the durability of the crucible.

  Therefore, an object of the present invention is to provide a crucible that can improve the durability and suppress the mixing of impurities into the AlN single crystal. In addition, another object of the present invention is to provide an AlN single crystal manufacturing method capable of suppressing the mixing of impurities into the AlN single crystal while improving the durability of the crucible, and the AlN single crystal in which the mixing of impurities is suppressed. To provide crystals.

  The crucible according to the present invention is a crucible used for producing an aluminum nitride single crystal by a vapor phase growth method. The crucible includes an inner crucible, a holding member that holds the seed crystal so as to face the bottom wall of the inner crucible, and an outer crucible arranged so as to surround the inner crucible and the holding member. The outer crucible includes an outer crucible body made of carbon and a coating layer made of a high melting point material that covers the inner wall of the outer crucible body.

  The crucible of the present invention has a double structure in which an inner crucible in which an AlN single crystal is to be grown is surrounded by an outer crucible. And when an outer crucible main body consists of carbon, even when it is used in multiple times, high mechanical strength is maintained and high durability is ensured. The outer crucible body made of carbon is covered with a coating layer made of a high melting point material. Therefore, it is suppressed that the carbon which comprises an outer crucible main body mixes as an impurity in the AlN single crystal which grows in an inner crucible. Further, since the inner crucible is surrounded by such an outer crucible, impurities from the member arranged outside such as a heat insulating material arranged outside the crucible during the growth of the AlN single crystal into the inner crucible. Intrusion (such as carbon) is suppressed. As described above, according to the crucible of the present invention, it is possible to provide a crucible capable of achieving improvement in durability and suppressing mixing of impurities into the AlN single crystal.

  Preferably, in the crucible, the outer crucible is made of tantalum (Ta), covers the coating layer formed on the inner bottom wall of the outer crucible body, and at least the surface opposite to the coating layer is carbonized. A bottom wall protective layer and a side wall protective layer made of tantalum (Ta), covering the coating layer formed on the inner side wall of the outer crucible body, and having a carbonized surface at least on the opposite side of the coating layer. In addition.

  In the coating layer made of the high melting point material, a minute hole called a microcrack may be formed at a high temperature. And the carbon which comprises an outer crucible main body is discharge | released from the said micro crack, and there exists a possibility that it may mix as an impurity in the AlN single crystal which grows in an inner crucible. On the other hand, by arranging a bottom wall protective layer and a side wall protective layer made of Ta as a lining on the coating layer, and carbonized on the surface, mixing of carbon into the AlN single crystal is more reliably suppressed. be able to.

  In the crucible, the refractory material constituting the coating layer is preferably tantalum carbide (TaC) or tungsten carbide (WC). TaC and WC which are excellent in heat resistance and can form a dense film are suitable as materials constituting the coating layer.

  In the crucible, the thickness of the coating layer is preferably 0.1 μm or more and 1 mm or less. By setting the thickness of the coating layer in such a range, it is possible to form a coating layer that is not easily damaged even when used multiple times.

In the crucible, preferably, the absolute value of the difference between the thermal expansion coefficient of the outer crucible body and the thermal expansion coefficient of the coating layer is 30 × 10 ⁻⁶ K ⁻¹ or less in a temperature range of room temperature to 3000 ° C.

If the absolute value of the difference in coefficient of thermal expansion between the outer crucible body and the coating layer is large, the stress acting on the interface between the outer crucible body and the coating layer will increase due to the thermal cycle of multiple use, and the durability of the coating layer will increase. Decreases. And as a result of examination by the present inventor, by setting the absolute value of the difference in thermal expansion coefficient to 30 × 10 ⁻⁶ K ⁻¹ or less in a temperature range of room temperature to 3000 ° C., the coating layer has high durability. It turns out that it can be granted. Therefore, with the above configuration, high durability of the coating layer can be ensured.

  In the crucible, the inner crucible may be a sintered body made of tantalum (Ta) and carbon (C). In this case, the molar ratio of carbon to tantalum in the sintered body is preferably 0.001 or more and 0.11 or less.

  When the inner crucible is a sintered body made of Ta and C, according to the study by the present inventor, when the molar ratio of C to Ta exceeds 0.11, the release of C from the inner crucible causes AlN single crystal It has been found that carbon is mixed in as impurities, and polycrystals may be mixed in part of the AlN single crystal due to this. Moreover, when the said molar ratio exceeded 0.11, it also turned out that durability of an inner side crucible falls. On the other hand, it was revealed that the durability of the inner crucible also decreased when the molar ratio was less than 0.001. Therefore, from the viewpoint of improving the crystallinity of the AlN single crystal and ensuring the durability of the inner crucible, the molar ratio is preferably 0.001 or more and 0.11 or less.

  In the crucible, the inner crucible may be a sintered body of boron nitride (BN). In this case, the thickness of the sintered body is preferably 100 μm or more and 30 mm or less.

  By forming the inner crucible from a sintered body of BN, a chemically stable inner crucible can be easily produced at a relatively low cost. And by making the thickness of a sintered compact into the said range, while ensuring sufficient durability of an inner side crucible, a high quality AlN single crystal can be grown.

  The method for producing an aluminum nitride single crystal according to the present invention is a method for producing an aluminum nitride single crystal using the crucible of the present invention. The method for producing an aluminum nitride single crystal includes a step of supplying an aluminum nitride raw material into the inner crucible, a step of holding a seed crystal in a holding member so as to face the raw material, and an inner crucible in the outer crucible. And a step of sublimating the raw material and growing an aluminum nitride single crystal on the seed crystal.

  According to the method for producing an aluminum nitride single crystal of the present invention, an AlN single crystal grows by adopting a crucible that achieves an improvement in durability and suppresses mixing of impurities into the AlN single crystal. Impurities can be prevented from being mixed into the AlN single crystal while improving the durability of the crucible.

  The aluminum nitride single crystal according to the present invention is produced by the above-described method for producing an aluminum nitride single crystal of the present invention. According to the aluminum nitride single crystal of the present invention, it is possible to provide a high-quality AlN single crystal in which the manufacturing cost is reduced due to the high durability of the crucible used for manufacturing and the mixing of impurities is suppressed. .

  As is clear from the above description, according to the crucible of the present invention, it is possible to provide a crucible that can improve the durability and suppress the mixing of impurities into the AlN single crystal. Moreover, according to the manufacturing method of the AlN single crystal of this invention, mixing of the impurity to an AlN single crystal can be suppressed, improving the durability of a crucible. Furthermore, according to the AlN single crystal of the present invention, an AlN single crystal in which mixing of impurities is suppressed can be provided.

It is a schematic sectional drawing which shows the structure of a crucible. It is a flowchart which shows the outline of the manufacturing method of an AlN single crystal. It is a schematic sectional drawing for demonstrating the manufacturing method of an AlN single crystal. It is a schematic sectional drawing for demonstrating the manufacturing method of an AlN single crystal.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  First, the structure of the crucible in one embodiment of the present invention will be described. Referring to FIG. 1, a crucible 1 in the present embodiment is a crucible used for manufacturing an aluminum nitride single crystal by a vapor phase growth method. The crucible 1 surrounds the inner crucible 10, the inner lid 20 as a holding member capable of holding the seed crystal so as to face the bottom wall of the inner crucible 10, and the inner crucible 10 and the inner lid 20. The outer crucible 30 is provided.

  The inner crucible 10 has, for example, a cylindrical outer shape and a shape in which a cylindrical space is formed inside. Moreover, as a raw material of the inner crucible 10, for example, a sintered body made of Ta and C can be employed. In this case, the molar ratio of C to Ta in the sintered body is preferably 0.001 or more and 0.11 or less.

  The inner lid 20 has a disk shape, and can fit into the opening of the inner crucible 10 to form a space for growing an AlN single crystal in the inner crucible 10. The inner lid 20 has a structure in which, for example, the surface of an inner lid body 21 made of C is covered with a coating layer 22 made of TaC. The seed crystal can be held on the holding surface 20 </ b> A facing the bottom wall of the inner crucible 10 in the inner lid 20.

  The outer crucible 30 has, for example, a cylindrical outer shape and a shape in which a cylindrical space is formed in which the inner crucible 10 into which the inner lid 20 is fitted can be stored. The outer crucible 30 includes an outer crucible body 31 made of C and a coating layer 32 made of a high melting point material that covers the inner wall of the outer crucible body 31. More specifically, the outer crucible body 31 is made of, for example, a C bulk material. And as a high melting-point material which comprises the coating layer 32, TaC and WC are employable, for example.

  Furthermore, the crucible 1 has a disc shape and includes an outer lid 40 that closes a space in which the inner crucible 10 is accommodated by being fitted into an opening of the outer crucible 30. The outer lid 40 has a structure in which, for example, the surface of an outer lid main body 41 made of C is covered with a coating layer 42 made of TaC.

  Thus, the crucible 1 has a double structure in which the inner crucible 10 is surrounded by the outer crucible 30. And since the outer crucible main body 31 consists of carbon, even when it is used in multiple times, high mechanical strength is maintained and high durability is ensured. In addition, since the outer crucible body 31 is covered with the coating layer 32, it is suppressed that C constituting the outer crucible body 31 is mixed as impurities into the AlN single crystal grown in the inner crucible 10. Since the inner crucible 10 is surrounded by the outer crucible 30 as described above, intrusion of impurities such as C from the outside into the inner crucible 10 during the growth of the AlN single crystal is suppressed. As a result, the crucible 1 is a crucible that can improve the durability and suppress the mixing of impurities into the AlN single crystal.

  Further, the outer crucible 30 of the crucible 1 in the present embodiment is made of Ta, covers the coating layer 32 formed on the inner bottom wall of the outer crucible body 31, and is at least on the side opposite to the coating layer 32. The bottom wall protective layer 33 in which the region 33A including the surface is carbonized and the coating layer 32 made of Ta and formed on the inner side wall of the outer crucible body 31 cover at least the opposite side of the coating layer 32 The region 34A including the surface further includes a carbonized side wall protective layer 34.

  The formation of the bottom wall protective layer 33 and the side wall protective layer 34 is not essential in the present invention. However, since the outer crucible 30 includes the bottom wall protective layer 33 and the side wall protective layer 34, the coating layer 32 is formed. Mixing of carbon into the AlN single crystal due to microcracks that can be formed can be suppressed. Here, in the bottom wall protective layer 33 and the side wall protective layer 34, only the regions 33A and 34A including the surface opposite to the coating layer 32 are carbonized as shown in FIG. May be metal Ta, or the entire region of the bottom wall protective layer 33 and the side wall protective layer 34 may be TaC.

  In the crucible 1, the thickness of the coating layer 32 is preferably 0.1 μm or more and 1 mm or less. Thereby, the coating layer 32 which is hard to be damaged even if used multiple times can be formed.

In the crucible 1, the absolute value of the difference between the thermal expansion coefficient (linear expansion coefficient) of the outer crucible body 31 and the thermal expansion coefficient of the coating layer 32 is 30 × 10 ⁻⁶ in the temperature range of room temperature to 3000 ° C. It is preferable that it is below K- ¹ . Thereby, the stress at the interface between the outer crucible main body 31 and the coating layer 32 generated in the thermal cycle by multiple use can be sufficiently reduced, and the durability of the coating layer 32 can be improved.

  The inner crucible 10 may be a sintered body of boron nitride (BN). In this case, the thickness of the sintered body is preferably 100 μm or more and 30 mm or less. Thereby, while ensuring sufficient durability of the inner crucible 10, a high quality AlN single crystal can be grown.

  Next, an example of a method for producing an AlN single crystal using the crucible 1 in the present embodiment will be described with reference to FIGS. Referring to FIG. 2, in the method of manufacturing an AlN single crystal in the present embodiment, first, a raw material supply step is performed as a step (S10). In this step (S <b> 10), referring to FIG. 3, a raw material 70 such as aluminum nitride powder or sintered body is supplied into the inner crucible 10.

  Next, a seed crystal arranging step is performed as a step (S20). In this step (S20), a seed substrate 80 as a seed crystal is attached to the holding surface 20A of the inner lid 20 so as to face the raw material 70. As this seed substrate 80, a SiC substrate, an AlN substrate, or the like can be employed. Then, with the seed substrate 80 held, the inner lid 20 is fitted into the inner crucible 10 so as to close the opening of the inner crucible 10. As a result, the seed substrate 80 is held by the inner lid 20 so as to face the raw material 70, and a space in which the AlN single crystal is to be grown surrounded by the inner crucible 10 and the inner lid 20 is formed.

  Next, an inner crucible charging step is performed as a step (S30). In this step (S30), the inner crucible 10 to which the inner lid 20 is attached in the step (S20) is charged into the outer crucible 30. Thereafter, the outer lid 40 is fitted into the outer crucible 30 so as to close the opening of the outer crucible 30.

  Next, a heat insulating material arrangement | positioning process is implemented as process (S40). In this step (S40), the entire crucible 1 configured by combining the outer crucible 30 and the outer lid 40 in the step (S30) is covered with the heat insulating material 50.

  And a crystal growth process is implemented as process (S50). In this step (S50), the crucible 1 is heated, so that the raw material 70 is sublimated and an aluminum nitride single crystal grows on the seed substrate 80. Specifically, referring to FIG. 3, crucible 1 covered with heat insulating material 50 in step (S <b> 40) is arranged at a position surrounded by, for example, induction heating coil 60. The crucible 1 is heated when a high-frequency current is passed through the induction heating coil 60. At this time, for example, a gas such as nitrogen gas is supplied into the crucible 1 at a predetermined flow rate, and the inside of the crucible 1 is controlled to a predetermined pressure. As a result, the raw material 70 is sublimated, and the gaseous raw material 70 is crystallized on the seed substrate 80. Thereby, an AlN single crystal 90 grows on the seed substrate 80 as shown in FIG. With the above procedure, the manufacturing method of the AlN single crystal in the present embodiment is completed.

  According to the method for producing an AlN single crystal in the present embodiment, the crucible 1 capable of achieving improvement in durability and suppressing the mixing of impurities into the AlN single crystal is employed to grow the AlN single crystal. Therefore, it is possible to suppress the mixing of impurities into the AlN single crystal while improving the durability of the crucible. The manufactured AlN single crystal 90 is a high-quality AlN single crystal in which manufacturing costs are reduced and mixing of impurities is suppressed.

  An experiment was conducted to confirm the effect of the coating layer in the outer crucible of the crucible of the present invention. The experimental procedure is as follows.

  First, in order to produce a crucible having the same configuration as the crucible 1 described in the above embodiment, (1) production of the outer crucible and (2) production of the inner crucible were performed in the following procedure.

(1) Production of outer crucible First, a base material made of a carbon bulk material having a shape corresponding to the shape of the outer crucible is prepared, and a coating layer made of TaC is formed on the entire surface by spraying the base material. did. The base material has a coefficient of thermal expansion (linear expansion coefficient) of 8.0 × 10 ⁻⁶ K ⁻¹ , and the coating layer has a coefficient of thermal expansion of 7.1 × 10 ⁻⁶ K ⁻¹ . The absolute value was 0.9 × 10 ⁻⁶ K ⁻¹ . The film thickness of the coating layer was 100 μm.

  Next, a bottom plate made of Ta was arranged so as to cover the bottom wall inside the outer crucible on which the coating layer was formed, and a lining made of Ta was arranged so as to cover the side wall inside the outer crucible. The thickness of the bottom plate was 1 mm, and the thickness of the lining was 100 μm. Here, considering that the bottom plate and the lining expand due to carbonization, the dimensions of the bottom plate and the lining are given an appropriate margin with respect to the inner dimensions of the outer crucible. After that, a cylindrical carbon bulk material was disposed so as to face the bottom plate and the lining. Then, in an atmosphere adjusted so that the pressure becomes 90 kPa while supplying nitrogen gas at a flow rate of 100 sccm, the outer crucible is heated to 2000 ° C. by induction heating with a high-frequency coil so that the surface of the bottom plate and the lining is removed. Carbonized to form a bottom wall protective layer and a side wall protective layer. Thereafter, it was confirmed visually and with a stereomicroscope that the bottom wall protective layer and the side wall protective layer were in close contact with the bottom wall and the side wall of the outer crucible, respectively. The production of the outer crucible was completed by the above procedure.

For comparison, an outer crucible in which the formation of the coating layer was omitted was also produced.
(2) Production of inner crucible First, Ta powder and C powder were mixed so that the molar ratio [C] / [Ta] of C to Ta was 0.01. And the camphor powder which is a sintering auxiliary agent was added, it mixed with acetone, and the mixed powder was obtained by making it dry.

  Next, 5 kg of the above mixed powder was prepared and solidified into a cylindrical shape by CIP (Cold Isostatic Press) to obtain a cylindrical molded body. The pressing conditions were such that a pressure of 400 MPa was applied isotropically to the rubber container charged with the mixed powder. Furthermore, the cylindrical molded body was formed into a processed molded body having an inner crucible shape having an outer diameter of 70 mm, an inner diameter of 60 mm, a height of 70 mm, and a bottom thickness of 10 mm.

  Next, the processed molded body was heated and sintered by induction heating using a high frequency coil. In the sintering, the above-mentioned processed compact is inserted into a crucible made of carbon, and the temperature of the crucible is 2300 ° C. in an atmosphere adjusted to a pressure of 80 kPa while supplying nitrogen gas at a flow rate of 100 sccm and argon gas at a flow rate of 300 sccm. This was carried out by heating and holding for 20 hours. With the above procedure, the production of the inner crucible was completed. The obtained inner crucible was shrunk by the sintering, and had an outer diameter of 68 mm, an inner diameter of 58 mm, a height of 68 mm, and a bottom thickness of 8 mm. Further, the surface of the obtained inner crucible was observed visually, with a stereomicroscope, an optical microscope, and an SEM (Scanning Electron Microscope), and it was confirmed that there were no cracks, chips, or holes.

  Next, (3) AlN single crystal was grown using the crucible including the inner crucible and the outer crucible produced by the above procedure.

(3) Growth of AlN single crystal First, the raw material powder of AlN is put into the inner crucible produced in (1) above, and the inner lid with the SiC seed substrate having a diameter of 2 inches attached to the holding surface is used as the inner crucible. Was fitted into the opening. Next, this was inserted into the outer crucible produced in (2) above, and the crucible was completed by fitting the outer lid, and then the whole was covered with a heat insulating material. And the crystal growth by the sublimation method was implemented by induction heating using the high frequency coil, and the AlN crystal was grown on the SiC seed substrate affixed on the holding surface of the inner lid. The heating conditions were 1800 ° C. and 100 hours. At this time, the pressure was 90 kPa while supplying nitrogen gas at a flow rate of 300 sccm.

  Thereafter, an AlN crystal grown on the SiC seed crystal was collected, and the crystal was evaluated visually, using an optical microscope, SEM, and an X-ray diffractometer. The evaluation results are shown in Table 1.

  Referring to Table 1, when a crucible in which a coating layer made of TaC was formed on the outer crucible was used, the obtained AlN crystal was subjected to measurement of the half-value width of the rocking curve by an X-ray diffractometer and wide-angle scanning. The full width at half maximum was 45 arcsec, and only the (0002) plane, (0004) plane, and (0006) plane were measured by wide-angle scanning. Further, it was confirmed by visual observation that the crystal surface was in a mirror state, and flat step flow growth was confirmed by an optical microscope and SEM. From this, it was confirmed that an AlN single crystal having good crystallinity can be produced by using a crucible in which a coating layer made of a high melting point material such as TaC is formed on the outer crucible.

  On the other hand, when the same evaluation was performed on the AlN crystal obtained when the crucible without the formation of the outer crucible coating layer was used, it was found that there were many irregularities and uniform and flat crystal growth could not be realized. .

  From the above experimental results, it was confirmed that it is effective to form a coating layer made of a high melting point material such as TaC or AlN on the outer crucible in order to obtain an AlN single crystal having good crystallinity. This is presumably because the formation of a coating layer made of a high-melting-point material suppressed the scattering of impurities such as carbon from the outer crucible body, and the contamination of AlN with impurities was reduced.

  An experiment was conducted to confirm the relationship between the thickness of the coating layer in the outer crucible of the crucible of the present invention and the durability of the coating layer. The experimental procedure is as follows.

  First, an outer crucible on which a coating layer made of TaC was formed by the same procedure as in (1) of Example 1 was prepared, and an inner crucible was prepared by the same procedure as (2). Then, an AlN single crystal was grown in the same procedure as in (3) of Example 1 above, and the presence or absence of damage such as peeling, cracking or chipping of the coating layer was investigated. Further, the quality of the obtained AlN single crystal was confirmed in the same manner as in Example 1. Furthermore, the growth of the AlN single crystal, the confirmation of the damage of the coating layer, and the quality confirmation of the AlN single crystal were repeated. The results of the experiment are shown in Table 2.

  Table 2 shows the thickness of the coating layer and the number of times that an AlN single crystal could be produced without causing damage to the coating layer. Referring to Table 2, when the thickness of the coating layer was 0.01 μm, the coating layer was not damaged until the 15th crystal growth, and a good AlN single crystal could be produced. As a result of the crystal growth, peeling occurred in a part of the coating layer, and polycrystals were partially mixed in the obtained AlN single crystal. In addition, when the thickness of the coating layer was 10 mm, the coating layer was not damaged until the 17th crystal growth, and a good AlN single crystal could be produced. Cracking and chipping occurred, and polycrystals were partially mixed in the obtained AlN single crystal.

  On the other hand, when the thickness of the coating layer was 0.1 μm to 1 mm, the coating layer was not damaged even during the 20th crystal growth, and a good AlN single crystal could be produced.

  From this, in order to improve the durability of the coating layer, it was confirmed that the thickness of the coating layer is preferably 0.1 μm or more and 1 mm or less.

  An experiment was conducted to confirm the influence of the difference in thermal expansion coefficient between the outer crucible body and the coating layer on the durability of the coating layer in the outer crucible of the crucible of the present invention. The experimental procedure is as follows.

First, an outer crucible on which a coating layer made of TaC was formed in the same procedure as (1) of Example 1 was prepared. At this time, the absolute value of the difference in coefficient of thermal expansion between the coating layer and the outer crucible body in the range of room temperature to 3000 ° C. is changed to 0-50 × 10 ⁻ by changing the specification of carbon that is the base material of the outer crucible. ^The variation was in the range of ⁶ K ⁻¹ . The thickness of the coating layer was 100 μm. And after heating up from the room temperature to 2500 degreeC with respect to the said outer crucible, the heat cycle which cools to room temperature was given, and the presence or absence of the damage in a coating layer was confirmed. And the durability of the coating layer was confirmed by repeating this. The experimental results are shown in Table 3.

Table 3 shows, for each coating layer material, the absolute value of the difference in thermal expansion coefficient between the coating layer and the outer crucible body and the number of times that the thermal cycle could be given without causing damage to the coating layer. It is displayed. Referring to Table 3, when the absolute value of the difference in thermal expansion coefficient exceeds 30 × 10 ⁻⁶ K ⁻¹ , no damage occurred in the coating layer until the 15th thermal cycle, Damage to the coating layer occurred during thermal cycling. On the other hand, when the absolute value of the difference in thermal expansion coefficient was 30 × 10 ⁻⁶ K ⁻¹ or less, the coating layer was not damaged even after the 20th thermal cycle.

From this, the absolute value of the difference between the thermal expansion coefficient of the outer crucible body and the thermal expansion coefficient of the coating layer is 30 × 10 ⁻⁶ K ⁻¹ or less in the temperature range of room temperature to 3000 ° C. It was confirmed that the durability of the layer could be improved.

  When the inner crucible of the crucible of the present invention is a sintered body made of Ta and C, an experiment was conducted to confirm the influence of the composition of the sintered body on the durability of the inner crucible. The experimental procedure is as follows.

  First, an inner crucible composed of a sintered body made of Ta and C was produced in the same procedure as in (2) of Example 1 above. At this time, the value of [C] / [Ta], which is the molar ratio of C to Ta, was changed in the range of 0.0001 to 0.15. And the AlN single crystal was produced in the procedure similar to the said Example 1, and the quality (crystallinity) was confirmed. The inner crucible was subjected to the same heat cycle as in Example 3 50 times, and the durability was confirmed by investigating the occurrence of breakage. The experimental results are shown in Table 4.

  Referring to Table 4, by setting the value of [C] / [Ta] to 0.11 or less, the durability of the inner crucible is improved and a single crystal having good crystallinity with no polycrystals is obtained. It turns out that it is obtained. On the other hand, when the value of [C] / [Ta] is less than 0.001, the durability of the inner crucible is lowered, and it was confirmed that the value of [C] / [Ta] is preferably 0.001 or more. .

  From this, it was found that the molar ratio is preferably 0.001 or more and 0.11 or less from the viewpoint of improving the crystallinity of the AlN single crystal and ensuring the durability of the inner crucible.

  When the inner crucible of the crucible of the present invention is a sintered body of boron nitride, an experiment was conducted to confirm the influence of the thickness of the sintered body on the durability of the inner crucible and the crystallinity of the resulting AlN single crystal. It was. The experimental procedure is as follows.

  First, an outer crucible was produced in the same procedure as in Example 1 (1). On the other hand, the inner crucible was prepared by preparing and molding a commercially available BN solid. The outer diameter of the inner crucible was 70 mm, the inner diameter was 60 mm, the height was 70 mm, and the bottom thickness was 10 mm.

  Then, AlN single crystals were grown in the same procedure as in (3) of Example 1 above, and the quality (crystallinity) of the obtained AlN single crystals was confirmed in the same manner as in Example 1. Further, the growth of the AlN single crystal was repeated 10 times, and then the presence or absence of damage in the inner crucible was investigated. The results of the experiment are shown in Table 5.

  Referring to Table 5, by setting the thickness of the BN sintered body constituting the inner crucible to 30 mm or less, the durability of the inner crucible is improved and a single crystal having good crystallinity with no polycrystals is obtained. It turns out that it is obtained. On the other hand, when the thickness of the BN sintered body is less than 100 μm, the durability of the inner crucible is lowered, and therefore it can be said that the thickness is preferably 100 μm or more. Further, by making the inner crucible made of a BN sintered body, a chemically stable inner crucible can be produced relatively easily and inexpensively.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The crucible, the method for producing an aluminum nitride single crystal, and the aluminum nitride single crystal of the present invention can be particularly advantageously applied to the production of an aluminum nitride single crystal and the aluminum nitride single crystal that are required to reduce impurity contamination.

  1 crucible, 10 inner crucible, 20 inner lid, 20A holding surface, 21 inner lid body, 22 coating layer, 30 outer crucible, 31 outer crucible body, 32 coating layer, 33 bottom wall protective layer, 34 sidewall protective layer, 40 outer Lid, 41 outer lid body, 42 coating layer, 50 heat insulating material, 60 induction heating coil, 70 raw material, 80 seed substrate, 90 AlN single crystal.

Claims (9)

A crucible used for producing an aluminum nitride single crystal by a vapor phase growth method,
An inner crucible,
A holding member that holds the seed crystal so as to face the bottom wall of the inner crucible;
An outer crucible arranged to surround the inner crucible and the holding member;
The outer crucible is
An outer crucible body made of carbon;
A crucible covering an inner wall of the outer crucible body and including a coating layer made of a high melting point material. The outer crucible is
A bottom wall protective layer made of tantalum, covering the coating layer formed on the inner bottom wall of the outer crucible body, and carbonized at least on the surface opposite to the coating layer;
The side wall protective layer made of tantalum, covering the coating layer formed on the inner side wall of the outer crucible body, and having a carbonized surface at least opposite to the coating layer. The crucible described.   The crucible according to claim 1 or 2, wherein the high melting point material constituting the coating layer is tantalum carbide or tungsten carbide.   The crucible according to any one of claims 1 to 3, wherein the coating layer has a thickness of 0.1 µm or more and 1 mm or less. The absolute value of the difference between the thermal expansion coefficient of the outer crucible body and the thermal expansion coefficient of the coating layer is 30 × 10 ⁻⁶ K ⁻¹ or less in a temperature range of room temperature to 3000 ° C. 5. The crucible according to any one of the above.   The inner crucible is a sintered body made of tantalum and carbon, and the molar ratio of carbon to tantalum in the sintered body is 0.001 or more and 0.11 or less. The crucible described. The inner crucible is a sintered body of boron nitride,
The crucible according to claim 1, wherein the sintered body has a thickness of 100 μm or more and 30 mm or less. A method for producing an aluminum nitride single crystal using the crucible according to any one of claims 1 to 7,
Supplying an aluminum nitride raw material into the inner crucible;
Holding the seed crystal on the holding member so as to face the raw material;
Charging the inner crucible into the outer crucible;
And a step of growing the aluminum nitride single crystal on the seed crystal while sublimating the raw material.   An aluminum nitride single crystal produced by the method for producing an aluminum nitride single crystal according to claim 8.

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