JP2010163302A - Growth container and method for growing aluminum nitride crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a growth container which is made of tantalum and from which Al being a raw material component hardly leaks to outside at a growth temperature, and to provide a method for growing an aluminum nitride crystal by a sublimation growth method applying the container. <P>SOLUTION: The growth container 20 is used in the sublimation growth method in which a raw material 23 filled in the high temperature part side of the container is sublimed and deposited on the low temperature part side in the container, for growing an aluminum nitride crystal. The growth container 20 is constituted of: a container body (crucible) 22 whose one end side is opened, in which the raw material 23 is filled, and which is made of tantalum; and a cap body 21 which covers the opening part of the container body 22 and is made of tantalum. The edge part of the opening part of the container body 22 and a surface 24 being in contact with the cap body 21 are each made of tantalum, and the surface 25 of the inner wall of a space formed by the container body 22 and the cap body 21 covering the opening part is made of tantalum. In the method for growing an aluminum nitride crystal by a sublimation growth method, the growth container 20 is applied. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sublimation growth method for producing an aluminum nitride (AlN) crystal by sublimating a raw material filled on a high temperature portion side in a container and depositing it on a low temperature portion side in the container. The present invention relates to a growth container made of tantalum in which Al as a component hardly leaks out of the container, and a method for growing aluminum nitride crystals by a sublimation growth method to which the growth container is applied.

  Aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), and mixed crystal semiconductor crystals thereof are called group III nitride semiconductors, and the band gap ranges from 0.8 eV for InN to 6.4 eV for AlN. It can be applied as a material for light emitting devices in the infrared, visible, and deep ultraviolet regions over a wide range. In particular, it is well known that GaN and GaInN mixed crystal semiconductor crystals have made great progress as materials for blue and white light emitting elements.

  In recent years, it has attracted attention as a semiconductor material for high-frequency devices and high-power devices because of its high dielectric breakdown strength, thermal conductivity, and electron saturation speed.

  The group III nitride semiconductor crystal is manufactured by epitaxial growth on a sapphire single crystal substrate processed into a substrate shape.

  However, if an attempt is made to form a more efficient light-emitting element in the ultraviolet and deep ultraviolet region, which has a wavelength shorter than that of blue, there is a limit in material properties if epitaxial growth is performed on the sapphire single crystal substrate, and homoepitaxial growth, that is, AlN It is necessary to use the same kind of material such as GaN for the substrate. This is because when a semiconductor material is used as a device, it is necessary to form a thin film structure by epitaxial growth on a substrate as well as a nitride semiconductor. Because it is a characteristic. That is, in order to realize a high-quality device, it is necessary to grow a high-quality thin film single crystal. For that purpose, it is the best method to use the same type of substrate that has the same lattice constant and thermal expansion coefficient as the thin film. .

  Also, the characteristics required for the substrate vary depending on the type of device to be manufactured. In the case of a light emitting device, it is desirable that the substrate material itself has a light transmission characteristic that does not absorb light emitted from the device layer so that light can be efficiently extracted outside. In addition, when heat generation of the device becomes a problem due to high output, it is necessary to efficiently dissipate heat through the substrate, and a substrate material having high thermal conductivity is desirable. Actually, for the practical use of blue laser diodes, a GaN free-standing substrate (GaAs or sapphire substrate is already used as a seed substrate, and a GaN thick film is grown on this seed substrate by vapor phase growth. A substrate obtained by peeling off the seed substrate and the growth layer) has been developed and marketed. Furthermore, for the development of next-generation devices in the deep ultraviolet region, which is a short wavelength region, the development of epitaxial growth technology and device technology for AlGaN mixed crystal semiconductor crystals is active. For practical application of these, high-quality AlN The development of single crystal substrates is considered essential.

  The AlN single crystal growth method includes sublimation growth method, solution growth method, hydride vapor phase growth method (HVPE method), metalorganic vapor phase crystal growth method (MOVPE method), and molecular beam epitaxial method (MBE method). Various methods have been studied for practical use of device substrates. On the other hand, in the case of the GaN substrate, since it is difficult to obtain a bulk single crystal, it is currently necessary to rely on the above-mentioned free-standing substrate technology by thick film growth using the HVPE method or the like. Since different types such as sapphire must be used as a seed substrate, there is a limit in terms of quality and cost such as generation of cracks and dislocation density. On the other hand, AlN has a great advantage that a relatively fast growth rate can be realized by a sublimation growth method, and a bulk single crystal can be grown. The sublimation growth method is in the stage of practical application as a SiC single crystal growth technique, and AlN single crystal growth is also considered to be a very advantageous method in terms of high quality and cost, represented by low dislocation density. Therefore, as shown in Patent Document 1 and Patent Document 2, earnest research has been conducted.

  However, AlN single crystal growth by the sublimation growth method requires a high temperature of 2000 ° C. or more as the growth temperature, and the growth containers that can be used are limited due to the strong reactivity of Al. As for the growth container for single crystal growth, as shown in Patent Document 1 and Patent Document 3, a growth container having a sealed structure using tungsten is used to prevent the permeation of Al. It is a material that is difficult to process and very expensive. For this reason, as shown in Non-Patent Document 1, a crucible is made in advance with tantalum, which is a material that is easier and cheaper to process than tungsten, and tantalum carbide is formed on the surface to react with Al. Attempts have been made to suppress it. However, even if such a growth vessel is used, it takes much time to completely seal the vessel, such as performing electron beam welding in a vacuum atmosphere in advance, and this increases costs. Thus, after filling with the AlN raw material, measures such as attaching a lid with a structure to reduce the gap are taken so that the growth vessel has a sealed structure as much as possible, but it is difficult to achieve a completely sealed structure. At a temperature of 2000 ° C. or more suitable as a growth temperature, Al vapor leaks out of the growth vessel, causing problems such as contamination of the growth furnace and hindering reproducibility of growth.

JP 2006-511432 A (1st page) Japanese Patent Laid-Open No. 10-53495 (first page) Special table 2005-519841 (first page)

E.N.Mokhov et.al, Journal of Crystal Growth 281 (2005) 93

  The present invention has been made paying attention to such problems, and the problem is to provide a growth container made of tantalum, in which the raw material component Al hardly leaks out of the container at the growth temperature. An object of the present invention is to provide a method for growing an aluminum nitride crystal by a sublimation growth method to which a growth vessel is applied.

That is, the invention according to claim 1
In the growth container used for the sublimation growth method in which the raw material filled on the high temperature part side in the container is sublimated and precipitated on the low temperature part side in the container to grow an aluminum nitride crystal.
Consists of a tantalum container body that is open at one end and filled with the raw material, and a tantalum lid that covers the open part of the container body, and an open edge and a lid of the container body. The contact surfaces are each composed of tantalum, and the inner wall surface of the space formed by the container body and the lid covering the open portion is composed of tantalum carbide,
The invention according to claim 2
In the method of growing aluminum nitride crystals,
An aluminum nitride crystal is produced by a sublimation growth method to which the growth vessel according to claim 1 is applied.

  The growth container according to the invention of claim 1 is composed of a tantalum container body that is open at one end side and filled with a raw material, and a tantalum lid that covers the open part of the container body, And the contact surface of the open edge part of a container main body and a cover body is each comprised with tantalum, and the inner wall surface of the space formed with a container main body and the cover body which covers this open part is comprised with tantalum carbide. It is characterized by.

  And since the contact surface of the open edge part of a container main body and a cover body is each comprised with tantalum, under growth temperature, the area | region where the said open edge part and a cover body contact, and tantalum and Al which is a raw material Since the reaction with the steam causes the open edge and the lid to adhere, the gap between the open edge and the lid is closed, and the growth vessel composed of the vessel body and the lid has a sealed structure, Crystal growth of aluminum nitride crystals can be performed in a state in which leakage of Al vapor to the outside of the growth vessel is prevented, and the inner wall surface of the space formed by the vessel body and the lid that covers this open portion Since it is composed of tantalum carbide, it is possible to perform crystal growth of an aluminum nitride crystal in a state where the reaction between the growth vessel and Al is suppressed.

  Therefore, instability of crystal growth such as composition fluctuation caused by leakage of Al to the outside of the growth vessel is prevented, so that high-quality AlN crystals can be efficiently grown, and into the growth furnace. Since the contamination of Al vapor can be reduced, the stability of the temperature environment in the growth furnace is improved.

Explanatory drawing which shows the sublimation growth method of an aluminum nitride crystal. Explanatory drawing which shows schematic structure of the growth container which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described in more detail.

  First, a sublimation growth method is used for growing aluminum nitride according to the present invention. As shown in FIG. 1, the sublimation growth method provides a temperature distribution in which a high temperature portion 6 and a low temperature portion 7 are provided in the growth vessel 1 by the heating device 2, and the raw material 5 filled on the high temperature portion 6 side. Is grown on the seed crystal 3 disposed on the low temperature part 7 side to produce the grown crystal 4. In FIG. 1, reference numeral 8 indicates a growth direction.

  As shown in FIG. 2, the growth container 20 according to the present invention includes a tantalum container body 22 that is open at one end and filled with the raw material 23, and a tantalum lid that covers the open portion of the container body 22. 21, the lid body 21 is disposed on the low temperature side of the growth furnace and has a region for growing crystals, and the container body 22 has a space for filling the raw material 23. Further, the contact surface 24 between the open edge portion of the container body 22 and the lid body 21 is made of tantalum, and the inner wall surface 25 of the space formed by the container body 22 and the lid body 21 covering the open portion is tantalum carbide. It consists of

  Using the container body 22 and the lid body 21 thus prepared, the lid body 21 is placed on the open portion of the container body 22 filled with the AlN raw material 23, and each container body 22 is made of tantalum. After adjusting the position so that the contact surface 24 of the open edge of the lid and the lid 21 are in contact with each other, the temperature is raised to the growth temperature in a heating apparatus of the growth furnace (see reference numeral 2 in FIG. 1) to grow AlN crystals. Do. At this time, Al vapor leaks because there is a gap between the container body 22 and the lid body 21 in the temperature rising process, but in the region where the tantalum is exposed (contact surface 24), the reaction between tantalum and the Al vapor gradually occurs. When the growth temperature is finally reached, the open edge of the container body 22 and the lid 21 are bonded by the reaction of tantalum and Al vapor via the region (contact surface 24), and the growth container 20 is reached. Has a sealed structure.

  Once the growth vessel 20 has a sealed structure, the growing Al vapor does not leak to the outside of the growth vessel 20, and the inner wall surface 25 of the growth vessel 20 is composed of tantalum carbide that does not react with Al vapor. Therefore, the sublimation growth of AlN can be performed in a state where the formation of reactants that inhibit the crystal growth of AlN is suppressed.

  Accordingly, since instability of crystal growth such as composition fluctuation caused by leakage of Al to the outside of the growth vessel 20 is prevented, it becomes possible to efficiently grow high quality AlN crystals, and further, in the growth furnace. Therefore, the stability of the temperature environment in the growth furnace can be improved.

  In addition, although the sublimation growth method was demonstrated using FIG. 1 and FIG. 2, the shape and shape of the growth container which consists of a tantalum, the method and conditions of forming a tantalum carbide in the inner wall surface of the space formed with a container main body and a cover body, Methods and conditions for providing a region where tantalum carbide is formed and a region where tantalum carbide is not formed (that is, the contact surface between the open edge of the container body where tantalum is exposed and the lid), heating method in sublimation growth method, raw material It is clear that the effects of the present invention are not limited by the presence or absence, the type of atmospheric gas, pressure, temperature, various growth conditions such as time, and the like.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, the technical content of this invention is not limited at all by the following Examples.

  This embodiment is an example using a growth vessel having the shape shown in FIG.

  That is, as shown in FIG. 2, the growth vessel 20 has a tantalum vessel body (crucible) 22 having an outer diameter of 50 mmφ, a height of 75 mm, and a thickness of 3 mm having a circular open portion on one end side, and the open portion. It is composed of a lid 21 made of tantalum having a circular convex surface to be inserted and having a thickness of 3 mm and a diameter of 50 mmφ. In addition, the ring-shaped contact surface 24 of the lid 21 in contact with the open edge of the container body (crucible) 22 has a width of 3 mm and a thickness of 2 mm.

  Then, after filling the container body (crucible) 22 with graphite and placing the lid body 21 so that the convex surface of the lid body 21 is fitted into the open part of the container body (crucible) 22, A growth vessel 20 composed of a vessel body (crucible) 22 and a lid 21 was filled into a graphite vessel.

  The growth vessel 20 set in this way and the graphite filled in the vessel are heated to 2200 ° C. by high frequency induction heating in an atmosphere of 7 kPa of argon gas, held for 6 hours, and then cooled, thereby cooling the vessel body ( A tantalum carbide layer is formed on the inner wall surface 25 of the space formed by the container body (crucible) 22 and the lid body 21 covering the open portion except for the contact surface 24 between the crucible) 22 and the lid body 21. It was. In addition, the area | region (ring-shaped contact surface 24) of the cover body 21 in which a tantalum carbide layer is not formed is 3 mm in outer periphery width, 2 mm in thickness, and the open edge part of the container main body (crucible) 22 in which a tantalum carbide layer is not formed. The width is also 3 mm.

  Next, in sublimation growth of AlN crystals, high-frequency induction heating is used as a heating method, and carbonization is performed beforehand in the graphite susceptor set in a quartz container capable of evacuation and supply of high-purity nitrogen gas by the above-described method. An AlN single crystal was grown by arranging a growth vessel in which a tantalum layer was formed. An AlN polycrystalline powder was used as the raw material 23 and filled in a container body (crucible) 22. In addition, an AlN single crystal substrate (seed crystal) having a thickness of 1 mm and a diameter of 25 mm was set on the inner side of the lid 21 and the main surface orientation was c-plane and the surface was processed into a mirror surface by chemical polishing.

  The growth atmosphere of the AlN crystal is high-purity nitrogen 101 kPa, the graphite susceptor is heated by high-frequency induction heating, the portion where the seed crystal of the lid 21 is placed is kept at 2100 ° C. as the low temperature side, and the container body (crucible) The portion where 22 raw materials 23 were arranged was held at 2200 ° C. on the high temperature side, and AlN crystals were grown for 80 hours.

  Immediately after reaching the growth temperature, the occurrence of scattered matter due to the leakage of Al vapor was observed, but the occurrence of the scattered matter disappeared within a few hours. And it cooled to room temperature after completion | finish of growth.

  The container body (crucible) 22 after the growth of the AlN crystal and the portion of the lid 21 where the tantalum is exposed on the surface (that is, the contact surface 24) are completely welded by reaction with the Al vapor, and the growth container is sealed. Therefore, an AlN crystal was obtained by cutting the growth vessel.

  The obtained AlN crystal has a cylindrical shape with a diameter of about 30 mm and a thickness of about 10 mm, and there is a part of the crystal around the outer periphery of the crystal, but the other part is a single crystal and is colored. There were few good quality bulk AlN single crystals.

[Comparative Example 1]
AlN was formed under the same conditions as in Example 1 except that a growth vessel in which a tantalum carbide layer was formed on the vessel body (crucible) 22 and the portion of the lid 21 where tantalum was exposed on the surface (that is, the contact surface 24) was applied. Crystal sublimation growth was performed.

  And in this comparative example 1, generation | occurrence | production of the scattering material resulting from the leakage of Al vapor | steam was continuously observed through the growth after reaching growth temperature.

  The state of the container body (crucible) 22 and the lid 21 after the growth of the AlN crystal was almost the same as that before the growth, and the container body (crucible) 22 and the lid 21 could be easily removed.

  The obtained AlN crystal has a columnar shape with a diameter of about 20 mm and a thickness of about 5 mm. The growth amount is smaller than that of Example 1, and the outer peripheral portion is also polycrystallized and yellow coloring is observed. It was.

  According to the present invention, a high-quality AlN substrate having characteristics suitable as an AlGaN-based semiconductor device substrate can be manufactured efficiently and at low cost. The obtained AlN substrate has industrial applicability for use in manufacturing devices such as light-emitting elements and high-frequency high-power electronic elements in the deep ultraviolet region.

DESCRIPTION OF SYMBOLS 1 Growth container 2 Heating device 3 Seed crystal 4 Growth crystal 5 Raw material 6 High temperature part 7 Low temperature part 8 Growth direction 20 Growth container 21 Lid 22 Container body (crucible)
23 Raw material 24 Contact surface 25 Inner wall surface

Claims (2)

In the growth container used for the sublimation growth method in which the raw material filled on the high temperature part side in the container is sublimated and precipitated on the low temperature part side in the container to grow an aluminum nitride crystal.
Consists of a tantalum container body that is open at one end and filled with the raw material, and a tantalum lid that covers the open part of the container body, and an open edge and a lid of the container body. A growth vessel characterized in that each contact surface is made of tantalum, and an inner wall surface of a space formed by the vessel body and a lid covering the open portion is made of tantalum carbide.   A method for growing an aluminum nitride crystal, comprising producing an aluminum nitride crystal by a sublimation growth method to which the growth vessel according to claim 1 is applied.

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