JP2013237600A - Method for growing aluminum nitride crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for sublimating and growing an AlN crystal, by which a seed crystal can be held without using a holder or an adhesive, and falling of a grown aluminum nitride (AlN) crystal into a growth vessel and leakage of a raw material to the outside of the growth vessel can be prevented.SOLUTION: A method for growing an AlN crystal 24 includes: sublimating a raw material 25 filled on the high temperature part side in a growth vessel 21 constituted of a cylindrical vessel body 20, whose one end side is opened and the other end side is closed, and a cap body 22 for closing an opening part; and depositing the sublimated raw material 25 on a seed crystal 23 arranged on the low temperature part side in the growth vessel. The method is characterized by: using a seed crystal having such a size that the outer peripheral edge of the seed crystal protrudes to the outside from the opening edge part of the opening part of the cylindrical vessel body to cover the opening part of the cylindrical vessel body; at the same time, closing the opening part of the cylindrical vessel body by superposing a cap body having such a size that the cap body protrudes to the outside from the outer peripheral edge of the seed crystal on the rear surface side of the seed crystal; and sublimating the raw material to grow an AlN crystal on the surface side opposite to the rear surface side of the seed crystal.

Description

  The present invention relates to a method for growing an aluminum nitride crystal by sublimating a raw material charged on a high temperature portion side in a growth vessel and depositing it on a seed crystal disposed on a low temperature portion side in the growth vessel to grow an aluminum nitride crystal. In particular, the seed crystal can be easily held without using any special holding member or adhesive, and the phenomenon that the grown aluminum nitride crystal falls into the growth vessel together with the seed crystal can be avoided. The present invention relates to a method for growing an aluminum nitride crystal that can improve confidentiality (sealing property) and avoid leakage of raw materials outside the growth vessel.

  Aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN) and mixed 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. In particular, it is well known that GaN and GaInN mixed crystals have made significant progress as blue (white) light emitting device materials. The basis for the development of GaN-based materials is an epitaxial growth technology using a sapphire single crystal as a substrate material, and a device technology such as p-type doping.

  However, when trying to form more efficient light-emitting elements and laser diodes in the ultraviolet and deep ultraviolet regions where the wavelength is shorter than that of blue, using the sapphire single crystal substrate, which is currently mainstream, has limitations in terms of material properties, Homoepitaxial growth, that is, it is necessary to use the same kind of material as AlN or GaN for the substrate. The reason for this is that when a semiconductor material is used as a device, it is necessary to form a thin film structure as well as a nitride semiconductor, but it is the characteristics of the base substrate material that greatly affects the quality of the thin film. . In order to realize a high-quality device, it is necessary to grow a high-quality thin film single crystal. For this purpose, it is the best method to use the same type of substrate having the same lattice constant and thermal expansion coefficient.

  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. In fact, a GaN free-standing substrate (a substrate obtained by growing a GaN thick film by vapor deposition and peeling the seed substrate and the growth layer after growth) has already been developed for the practical use of blue laser diodes. Has been put to practical use.

  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 crystals has been actively conducted. Development of an AlN single crystal substrate, which is the same type of substrate, is considered indispensable.

  By the way, there are sublimation growth method, solution growth method, chloride vapor phase growth method (HVPE method), metalorganic vapor phase crystal growth method (MOVPE method), 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 a GaN substrate, since it is difficult to obtain a bulk single crystal, it is currently necessary to rely on a self-supporting substrate technology based on a thick film growth using the HVPE method or the like. Since the material 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, in the AlN single crystal growth by the sublimation method, it is difficult to obtain an AlN single crystal substrate to be a seed crystal. Therefore, as shown in Non-Patent Document 1, an AlN thick film is grown on a SiC substrate in advance. A method of obtaining a thicker bulk AlN single crystal by using a grown AlN film separated from SiC as an AlN single crystal substrate (seed) is used. That is, a method is used in which a raw material is sublimated in a growth vessel composed of a vessel body and a lid, and AlN crystals are deposited on an AlN single crystal substrate (seed).

  Here, SiC or AlN used as a seed crystal (seed) needs to be arranged on the low temperature side facing the raw material arranged on the high temperature side in the growth vessel. In general, a seed crystal (seed) is attached to the lid using an adhesive. And in the sublimation growth method of SiC mentioned above, many examinations are made about the adhesive agent for making the graphite which comprises the said lid hold | maintain a SiC seed crystal reliably (for example, patent document 3), and after crystal growth In addition to preventing the fall of crystals, it is an important technique for preventing the occurrence of crystal defects such as micropipes due to sublimation on the back side of the crystal.

  By the way, when an AlN single crystal is grown by a sublimation growth method, graphite constituting the growth vessel lacks suitability for Al gas reactivity and Al gas permeability. It is necessary to configure the growth vessel using carbide, nitride or the like. Then, it is necessary to bond SiC or AlN as a seed crystal to a lid made of a refractory metal such as tantalum carbide or tungsten, but since there is no appropriate adhesive, the bonding strength is weak and the grown AlN single unit is not suitable. There was a problem that the crystal easily dropped into the growth vessel together with the seed crystal. There is also a problem that the crystallinity of the crystal to be grown deteriorates due to the difference in thermal expansion coefficients of the lid, the adhesive, and the seed crystal.

  To deal with these problems, Patent Document 4 discloses a method of holding a seed crystal without using an adhesive, using a seed crystal holding member having a through opening smaller than the outer diameter of the seed crystal substrate. However, refractory metals such as tantalum carbide used as the growth vessel and holding member have poor shape accuracy and may be deformed during crystal growth. In this case, due to inaccuracy and deformation, the sealing of the growth vessel is impaired, and there is a problem that production efficiency decreases due to sublimation leakage of the raw material, the seed crystal itself disappears due to sublimation, and defects are easily introduced. Furthermore, there has been a problem that the cost of the growth vessel is increased by using the seed crystal holding member.

JP 2006-511432 A (1st page) Japanese Patent Laid-Open No. 10-53495 (first page) Japanese Patent No. 3680531 (pages 1 to 3) JP 2011-1332079 A (first page)

Yu.N.Makarov et.al, Journal of Crystal Growth 310 (2008) 881

  The present invention has been made paying attention to such problems, and the problem is that the seed crystal can be easily held without using a special seed crystal holding member or an adhesive, and has been grown. Providing a sublimation growth method for aluminum nitride crystals that can avoid the phenomenon of aluminum crystals falling into the growth vessel together with the seed crystal, and improve the confidentiality (sealing property) of the growth vessel and avoid leakage of raw materials outside the growth vessel. There is to do.

That is, the invention according to claim 1
The raw material filled on the high temperature part side in the growth vessel composed of a cylindrical vessel body that is open at one end and closed at the other end and a lid that closes the open part is sublimated, and the low temperature part in the growth vessel In the method for growing an aluminum nitride crystal, the aluminum nitride crystal is grown by being deposited on a seed crystal arranged on the side,
Covering the open part of the cylindrical container body with a seed crystal having a size that the outer peripheral edge protrudes outward from the open edge of the open part of the cylindrical container body, and externally from the outer peripheral edge of the seed crystal. A lid with a size that protrudes toward the back is overlaid on the back side of the seed crystal, the open part of the cylindrical container body is closed, and the raw material filled on the high temperature part side in the growth container is sublimated to seed crystal An aluminum nitride crystal is grown on the surface side opposite to the back side.

Next, the invention according to claim 2
In the growth method of the aluminum nitride crystal of Claim 1,
A filling layer is formed between the seed crystal and the lid body overlapped on the back side thereof,
The invention according to claim 3
In the growth method of the aluminum nitride crystal of Claim 1 or 2,
The cylindrical container body and the lid are made of at least one material selected from tantalum carbide and tungsten,
The invention according to claim 4
In the growth method of the aluminum nitride crystal of Claim 1 or 2,
The seed crystal is selected from silicon carbide, silicon carbide having an aluminum nitride single crystal layer formed on the surface in advance, and aluminum nitride,
The invention according to claim 5
In the growth method of the aluminum nitride crystal in any one of Claims 1-4,
The seed crystal has a thickness of 1 mm or more.

The method for growing an aluminum nitride crystal according to the present invention includes:
Cover the open part of the cylindrical container body with a seed crystal having a size that the outer peripheral edge protrudes outward from the open edge of the open part of the cylindrical container body, and outward from the outer peripheral edge of the seed crystal. A lid with a size that protrudes to the back is overlaid on the back side of the seed crystal to close the open part of the cylindrical container body, and the raw material filled on the high temperature part side in the growth container is sublimated to An aluminum nitride crystal is grown on the surface side opposite to the back side.

  And in the state where the outer peripheral edge of the seed crystal protrudes outward from the open edge portion of the cylindrical container body, the inner vicinity region of the outer peripheral edge of the seed crystal is in the open edge portion of the cylindrical container body. Since it is locked, the seed crystal can be easily held without using a special seed crystal holding member or an adhesive.

  In addition, since the lid is overlapped on the back side of the seed crystal with the outer periphery of the lid projecting outward from the outer periphery of the seed crystal, the entire back side of the seed crystal is Since it is covered with the lid, it is possible to prevent disappearance of sublimation on the back side of the seed crystal. Therefore, the grown aluminum nitride crystal does not fall into the growth vessel together with the seed crystal, and can be recovered without damaging the aluminum nitride crystal.

  Further, the inner vicinity region of the outer periphery of the seed crystal is locked to the open edge of the cylindrical container body, and the inner vicinity region of the outer periphery of the seed crystal in contact with the open edge of the cylindrical container body is cylindrical. Heated by heat transfer from the open edge of the container body, the temperature becomes high, and disappearance due to sublimation is more than that in other areas, so a cylindrical shape is formed in the area near the inside of the seed crystal in contact with the open edge. A recess is formed along the open edge shape of the container body. And since the open edge part of a cylindrical container main body fits into this recessed part and the clearance gap produced between a cylindrical container main body and a seed crystal will be closed, the confidentiality (sealing property) of a growth container improves. Thus, sublimation leakage of the raw material to the outside of the growth vessel is reduced, and the crystallinity and growth efficiency of the aluminum nitride crystal can be improved.

Explanatory drawing which shows the growth method of the aluminum nitride crystal by the conventional sublimation growth method by which a seed crystal is hold | maintained at the cover body of a growth container using an adhesive agent. Explanatory drawing which shows the growth method of the aluminum nitride crystal concerning this invention. Explanatory drawing which shows the growth method of the aluminum nitride crystal which concerns on the modification of this invention. Explanatory drawing which shows the growth method of the aluminum nitride crystal which concerns on the other modification of this invention.

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

  First, FIG. 1 is an explanatory view showing a growth method of an aluminum nitride crystal according to a conventional example in which a seed crystal is held on a lid of a growth vessel using an adhesive.

  As shown in FIG. 1, the growth vessel 1 has a cylindrical vessel body 10 made of tantalum carbide or the like whose one end is opened and the other end is closed, and a lid made of tantalum carbide or the like for closing the open portion of the vessel body 10. The temperature distribution of the high temperature part 7 and the low temperature part 8 is formed in the growth container 1 by the heating device 9 arranged in the vicinity of the outer periphery of the growth container 1. Further, the raw material 6 is filled on the high temperature portion 7 side of the growth vessel 1, and the seed crystal 4 is disposed on the low temperature portion 8 side of the growth vessel 1. The seed crystal 4 is held by being bonded to the lid 12 using the adhesive 3 as described above. And the said raw material 6 with which the high temperature part 7 side of the growth container 1 was sublimated, AlN was deposited on the seed crystal 4 arrange | positioned at the low temperature part 8 side of the growth container 1, and the growth crystal 5 is made to grow. is there.

  Next, FIG. 2 is an explanatory view showing a method for growing an aluminum nitride crystal according to the present invention.

  The growth vessel 21 of the present invention also has a cylindrical vessel body 20 made of tantalum carbide having one end opened and the other end closed, as shown in FIG. 2, and a carbonized vessel that closes the open portion of the vessel body 20. And a lid 22 made of tantalum or the like.

  In the AlN crystal growth method according to the present invention, as shown in FIG. 2, a seed crystal 23 having such a size that the outer peripheral edge protrudes outward from the open edge of the open portion of the cylindrical container body 20 is used. In the state where the outer peripheral edge of the seed crystal 23 is protruded outward from the open edge of the cylindrical container body 20 as shown in FIG. The main body 20 is locked to the open edge. Further, as shown in FIG. 2, a lid body 22 having a size that the outer circumferential edge protrudes outward from the outer circumferential edge of the seed crystal 23 is used, and the outer circumferential edge of the lid body 22 is shown in FIG. In addition, the lid 22 is overlaid on the back side (back side) of the seed crystal 23 in a state where the seed crystal 23 protrudes outward from the outer peripheral edge of the seed crystal 23, and the open portion of the container body 20 is interposed via the seed crystal 23. Is closed by the lid 22.

  And in the growth method of the AlN crystal which concerns on this invention, the raw material 25 with which the high temperature part side of the growth container 21 was sublimated, the said back side (back side) of the seed crystal 23 arrange | positioned at the low temperature part side of the growth container 21 is carried out. The growth crystal 24 is grown by depositing AlN on the opposite surface side (the side facing the inside of the growth vessel 21).

  About the cylindrical shape of the said cylindrical container main body 20, even if a cross section is circular shape (namely, cylindrical shape), a cross section may be a rectangular shape, and is arbitrary. Further, the planar shape of the lid body 22 is arbitrary, for example, a circular shape or a rectangular shape according to the cylindrical shape of the cylindrical container body 20. Further, the cross-sectional shape of the lid body 22 is not particularly limited. For example, as shown by a reference numeral 22B in FIG. 3, a convex piece extending downward along the outer peripheral edge of the lid body is provided. The structure may be such that the side surface of the seed crystal 23 disposed on the lower surface side of the lid body is protected.

  Also, as shown in FIG. 4, in order to prevent the sublimation on the back side of the seed crystal 23 by making the gap between the lid 22 and the seed crystal 23 as small as possible, a packed layer 26 made of, for example, a carbon-based compound or the like is used. It is also suitable to provide. The packed layer 26 can be formed by, for example, using a resin composition in which graphite fine particles having an average particle diameter of 1 μm are dispersed in a phenol resin and heat-treating the resin composition at 80 ° C. to 200 ° C.

  Next, in the method for growing an aluminum nitride crystal according to the present invention shown in FIGS. 2 to 4, it is preferable that the cylindrical container body and the lid are made of at least one material selected from tantalum carbide and tungsten. . In this case, the tantalum carbide may be carbonized on the surface of tantalum or may be entirely made of tantalum carbide, and the effect of the present invention is not limited by the manufacturing method and dimensions of the cylindrical container body and lid. .

  In the method for growing an aluminum nitride crystal according to the present invention shown in FIGS. 2 to 4, the seed crystal is preferably silicon carbide, silicon nitride having an aluminum nitride single crystal layer previously formed on the surface, or aluminum nitride. is there. The seed crystal production method, orientation, dimensions, surface state, and the like may be appropriately selected according to the dimensions and growth of the target AlN crystal, and the effects of the present invention are not limited thereto.

  Furthermore, in the method for growing an aluminum nitride crystal according to the present invention shown in FIGS. 2 to 4, the thickness of the seed crystal used is preferably 1 mm or more. The reason is that when a thin seed crystal of less than 1 mm is used, the seed crystal itself may not be able to hold the seed crystal and the grown AlN crystal due to the disappearance of sublimation of the seed crystal itself.

  In addition, although the sublimation method was demonstrated using FIGS. 1-4, various kinds, such as the heating method in the growth method (sublimation growth method) of the aluminum nitride crystal concerning this invention, a raw material, atmospheric gas kind, pressure, temperature, time, etc. It is clear that the effect is not limited by the growth conditions.

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

  The aluminum nitride crystal growth method according to this embodiment is an example using the structure of FIG. 4 in which a filling layer is provided between the lid and the seed crystal.

  As the cylindrical container body 20, a cylindrical tantalum carbide having a diameter of 47 mmφ, a height of 80 mm, and a thickness of 1 mm with one end opened and the other end closed was used. Further, as the seed crystal 23, the growth surface side (side on which the aluminum nitride crystal is deposited) is a mirror surface by mechanical chemical polishing, and the c-plane 6H having a thickness of 2 mm and a diameter of 50 mm with the back surface opposite to the growth surface side as a lapping surface. -A SiC substrate was used. Further, a tantalum carbide plate having a thickness of 2 mm and a diameter of 60 mm is used as the lid body 22, and a slight gap is generated between the lid body 22 and the seed crystal 23 due to the planar accuracy of the tantalum carbide lid body. A filling layer 26 made of a carbon compound was formed between the seed crystal 23 and the seed crystal 23.

  The packed layer 26 is formed by heat-treating a resin composition in which graphite fine particles having an average particle diameter of 1 μm are dispersed in a thermosetting phenol resin at 80 ° C. to 200 ° C. Further, AlN polycrystalline powder was used as the raw material 25.

  In the sublimation growth of an aluminum nitride (AlN) crystal, the above-described dimensions are set inside a graphite susceptor set in a quartz container that can be evacuated and supplied with high-purity nitrogen gas using high-frequency induction heating as a heating method. The material composition (the composition shown in FIG. 4) was filled.

  The growth atmosphere of the aluminum nitride (AlN) crystal is high-purity nitrogen 101 kPa, the graphite susceptor is heated by high-frequency induction heating, and the upper part of the growth vessel 21 in which the seed crystal 23 is arranged is 1700 ° C. to 1800 ° C. The portion of the growth vessel 21 in which 25 was disposed was set to 1850 ° C. to 1950 ° C. on the high temperature side, and AlN crystals were grown for 10 to 50 hours.

  The obtained AlN crystal (growth crystal 24) is grown as a single crystal with a diameter of about 30 mm and a thickness of about 1 to 5 mm on the center portion of the SiC substrate which is the seed crystal 23. It could be recovered without falling into the growth vessel 21.

  Further, the grown AlN single crystal (growth crystal 24) was relatively transparent, the half-value width of the X-ray rocking curve was about 100 seconds, and the crystallinity was also good.

  In addition, a region near the inside of the seed crystal 23 in contact with the open edge of the cylindrical container body 20 has a thickness reduced by about 0.5 to 1 mm due to disappearance of sublimation from a region not in contact with the open edge. It was observed that a recess along the open edge shape of the cylindrical container body 20 was formed in a region near the inner side of 23. This phenomenon is caused by the heat transfer from the open edge of the cylindrical container body 20 in which the region near the inside of the seed crystal 23 that has been in contact with the open edge of the cylindrical container body 20 is located on the high temperature portion side of the growth container 21. As a result of the heating, the temperature becomes higher than the other region, and the concave portion along the open edge shape of the cylindrical container body 20 is formed by sublimation disappearance. And since the open edge part of the cylindrical container main body 20 fits into this recessed part, and the clearance gap produced between the cylindrical container main body 20 and the seed crystal 23 will be closed, the confidentiality (sealing of the growth container 21). This improves the sublimation leakage of the raw material to the outside of the growth vessel 21 and improves the crystallinity and growth efficiency of the aluminum nitride crystal.

[Comparative example]
The aluminum nitride crystal growth method according to this comparative example is an example using the structure of FIG. 1 that holds a seed crystal on the back side of the lid using an adhesive.

  That is, the diameter of the seed crystal 4 is 40 mm, and an adhesive made of a carbon-based compound as the adhesive 3 (a resin in which graphite fine particles having an average particle diameter of 1 μm are dispersed in a thermosetting phenol resin as in the filling layer 26 of the example. The aluminum nitride crystal is grown under the same configuration and growth conditions as in the example except that the composition is affixed to the lid body 12.

  In the comparative example, due to insufficient adhesion between the seed crystal 4 and the lid 12, the seed crystal 4 and the grown AlN crystal are grown at a high temperature inside the growth vessel 1 at a rate of about 50% during or after the growth. As a result, the fallen object stuck to the raw material 6 and sublimated and disappeared, and an AlN single crystal could not be obtained.

  Further, when the seed crystal 4 and the grown AlN crystal can be recovered after the growth without dropping, the obtained AlN crystal is about 25 mm in diameter and about 0.00 mm in thickness at the center portion of the SiC substrate as the seed crystal. A single crystal was grown to 5 to 3 mm, and when compared with the example, a tendency to be thin with respect to the thickness of the growing AlN single crystal was confirmed. Moreover, when compared with the Examples, there was a tendency to be somewhat inferior in terms of crystallinity and transparency, which is considered to be due to the thin growth film thickness.

  According to the present invention, the seed crystal can be easily held without using a special seed crystal holding member or adhesive, and the phenomenon that the grown aluminum nitride crystal falls into the growth vessel together with the seed crystal can be avoided. Since the confidentiality (sealing property) of the growth vessel is improved and leakage of the raw material to the outside of the growth vessel can be avoided, a high-quality AlN substrate having characteristics suitable as an AlGaN-based semiconductor device substrate is manufactured at a high yield and at a low cost. It becomes possible. 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 3 Adhesive 4 Seed crystal 5 Growth crystal (AlN crystal)
6 Raw material 7 High temperature part 8 Low temperature part 9 Heating device 10 Tubular container body 12 Lid body 20 Tubular container body 21 Growth container 22 Lid 22B Lid 23 Seed crystal 24 Growth crystal (AlN crystal)
25 Raw material 26 Packed bed

Claims (5)

The raw material filled on the high temperature part side in the growth vessel composed of a cylindrical vessel body that is open at one end and closed at the other end and a lid that closes the open part is sublimated, and the low temperature part in the growth vessel In the method for growing an aluminum nitride crystal, the aluminum nitride crystal is grown by being deposited on a seed crystal arranged on the side,
Covering the open part of the cylindrical container body with a seed crystal having a size that the outer peripheral edge protrudes outward from the open edge of the open part of the cylindrical container body, and externally from the outer peripheral edge of the seed crystal. A lid with a size that protrudes toward the back is overlaid on the back side of the seed crystal, the open part of the cylindrical container body is closed, and the raw material filled on the high temperature part side in the growth container is sublimated to seed crystal A method for growing an aluminum nitride crystal, comprising growing an aluminum nitride crystal on a surface side opposite to the back surface side of the above.   The method for growing an aluminum nitride crystal according to claim 1, wherein a filling layer is formed between the seed crystal and the lid body overlapped on the back side thereof.   The method for growing an aluminum nitride crystal according to claim 1 or 2, wherein the material of the cylindrical container body and the lid is at least one selected from tantalum carbide and tungsten.   The method for growing an aluminum nitride crystal according to claim 1 or 2, wherein the seed crystal is selected from silicon carbide, silicon carbide having an aluminum nitride single crystal layer formed on the surface in advance, and aluminum nitride.   The method for growing an aluminum nitride crystal according to any one of claims 1 to 4, wherein the seed crystal has a thickness of 1 mm or more.

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