JP2012121772A - Method for producing nitride semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a nitride semiconductor substrate suppressible of a fissure or crack in a thick film layer in the growth process of the thick film layer.SOLUTION: This method for producing the nitride semiconductor substrate comprises: forming a ground substrate 3 by providing a ground layer comprising a nitride semiconductor on a substrate 2; forming a metal film on the ground layer of the ground substrate 3; then heat-treating the ground substrate 3 in an atmosphere containing hydrogen gas or hydrogen-containing compound gas to form voids in the ground layer and also form micropores in the metal layer; growing a nitride semiconductor on the micropore-formed metal film to form a thick film layer 5; and peeling off the thick film layer 5 from the ground substrate 3 to obtain the nitride semiconductor substrate 1, where the used substrate 2 has a diameter larger than that of the nitride semiconductor substrate 1 and the thick film layer 5 is grown at the central portion of the ground substrate 3.

Description

  The present invention relates to a method for manufacturing a nitride semiconductor substrate used for epitaxial growth of an ultraviolet to blue semiconductor laser, a short wavelength light emitting diode or the like.

  Si (silicon) substrates and GaAs (gallium arsenide) substrates, which are already widely used as semiconductor growth substrates, are produced by cutting a large ingot in which a bulk crystal is grown from a melt mainly by a pulling method, These substrates are stably produced with few dislocations and defects.

  On the other hand, since a nitride semiconductor substrate is difficult to grow like a silicon substrate or a gallium arsenide substrate, a single crystal sapphire substrate or a SiC substrate has been used as a substrate for growing a nitride semiconductor. I came.

  However, since the sapphire substrate has a large lattice constant different from that of GaN, which is a nitride semiconductor, a GaN single crystal film cannot be obtained by directly growing GaN on the sapphire substrate. For this reason, a method has been devised in which an AlN or GaN buffer layer is first grown on a sapphire substrate at a relatively low temperature, lattice strain is relaxed by this low temperature growth buffer layer, and then GaN is grown thereon.

  By using this low-temperature grown nitride layer as a buffer layer, epitaxial growth of a single crystal of GaN has become possible, but even with this method, GaN after growth is still affected by the large shift in the lattice constant of the substrate and crystal. Has innumerable defects. This defect is expected to be a major obstacle to performance and reliability in manufacturing GaN-based laser light-emitting diodes (LD) and high-intensity light-emitting diodes (LEDs).

  For the reasons described above, the appearance of a GaN free-standing substrate that does not cause a lattice shift between the substrate and the crystal is eagerly desired. For example, various methods such as HVPE (Hydride Vapor Phase Epitaxy) method, ultra-high temperature and high pressure method, and flux method have been tried. Among them, the development of GaN free-standing substrate by HVPE method is the most advanced. As a result, the nitride semiconductor substrate has been attracting attention as a material for increasing the output and efficiency of blue-violet laser light-emitting diodes (LDs) and blue light-emitting diodes (LEDs).

  The most practical application as a GaN free-standing substrate is a method in which a GaN layer with a reduced dislocation density is epitaxially grown on the underlying substrate thickly, and this GaN thick film layer is peeled off from the underlying substrate and used as a GaN free-standing substrate. .

  Specifically, after forming a Ti film as an intermediate layer for peeling on a base substrate in which a GaN base layer is formed on a sapphire substrate, the substrate is heated under a mixed atmosphere of hydrogen gas and ammonia gas, thereby A void (void) is formed in the ground layer, and the Ti film is formed into a TiN film having micropores, a GaN thick film layer is grown on the TiN film, the GaN thick film layer is peeled off from the sapphire substrate, and warpage is small. A method for producing a low-defect GaN free-standing substrate is disclosed (for example, see Patent Document 2).

JP-A-5-55143 JP 2008-290919 A

  As described above, in the manufacture of a conventional nitride semiconductor substrate, a thick film of nitride semiconductor is grown on what is called a base substrate, and the nitride semiconductor of the thick film is peeled off. The quality of the end portion viewed from the surface is unstable and is affected by this. In the thick film growth process, cracks and cracks are generated particularly from the outer periphery of the substrate, and the yield tends to decrease.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a nitride semiconductor substrate capable of suppressing the occurrence of cracks and cracks during the thick film growth process.

  The present invention was devised to achieve the above object, and a base substrate made of a nitride semiconductor is formed on a base material to form a base substrate, and a metal film is formed on the base layer of the base substrate Then, the base substrate is heat-treated in an atmosphere containing hydrogen gas or a hydrogen-containing compound gas, thereby forming voids in the base layer and forming micropores in the metal film, thereby forming the micropores. In the method of manufacturing a nitride semiconductor substrate, a nitride semiconductor substrate is obtained by growing a nitride semiconductor on the metal film to form a thick film layer, and then peeling the thick film layer from the base substrate. As a method for manufacturing a nitride semiconductor substrate, a substrate having a diameter larger than that of the nitride semiconductor substrate is used, and the thick film layer is grown at the center of the base substrate.

  The thick film layer may be grown in the region of the metal film where the micropores are formed.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the nitride semiconductor substrate which can suppress that a crack and a crack generate | occur | produce in a thick film growth process can be provided.

(A)-(f) is a figure explaining the manufacturing method of the nitride semiconductor substrate which concerns on 1st embodiment of this invention. (A)-(g) is a figure explaining the manufacturing method of the nitride semiconductor substrate which concerns on 2nd embodiment of this invention.

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

  1 and 2 are views for explaining a method of manufacturing a nitride semiconductor substrate according to the first and second embodiments of the present invention. Hereinafter, although the case where GaN is grown as a nitride semiconductor will be described, the nitride semiconductor is not limited to this.

  First, the first embodiment of the present invention will be described with reference to FIG. First, as shown to Fig.1 (a), the sapphire substrate 2 as a base material is prepared.

  As the sapphire substrate 2, a substrate having a diameter larger than the diameter of the nitride semiconductor substrate 1 to be manufactured (the diameter before the outer diameter processing is performed, that is, the diameter of the thick film layer 5 described later) is used. If the diameter of the sapphire substrate 2 is D and the diameter of the nitride semiconductor substrate 1 to be manufactured is d, the ratio d / D is preferably 0.89 or less. This is because the crack generation ratio can be reduced to 15% or less by setting the ratio d / D to 0.89 or less.

  Thereafter, a base layer made of GaN is formed on the sapphire substrate 2 by MOCVD (metal organic chemical vapor deposition) to form a base substrate, and a metal is formed on the base layer of the base substrate by vacuum deposition. A film (FIG. 1B) is formed, and then the base substrate 3 is heat-treated in an atmosphere containing hydrogen gas or a hydrogen-containing compound gas. Note that the formation method of the base layer and the metal film is not limited to the MOCVD method or the vacuum evaporation method.

  In this embodiment, a Ti film is formed as a metal film, and heat treatment is performed in a mixed atmosphere of hydrogen gas and ammonia gas, whereby voids are formed in the base layer and the Ti film that is the metal film is formed. Fine holes were formed to form a mesh-like TiN film (TiN nanonet). Reference numeral 4 in FIG. 1C indicates a void generation region (region in which fine holes are uniformly formed) in the metal film. Micropores are also formed in the metal film at the outer region of the void generation region 4, that is, at the end portion of the base substrate 3, but the micropores formed in this region are not uniform. In order to avoid the formation of the thick film layer 5, a mask 6 is formed on the outer peripheral portion so that a diameter smaller than the diameter of the base substrate 3 is exposed (FIG. 1D). Note that the metal material used for the metal film and the atmosphere of the heat treatment are not limited thereto.

  Thereafter, as shown in FIG. 1E, GaN is grown on the exposed metal film to form a thick film layer 5. The thick film layer 5 can be formed by, for example, the HVPE method. The thick film layer 5 is formed in the central portion of the base substrate 3 and in a region where the fine holes of the metal film are uniformly formed (in the void generation region 4).

  The diameter of the thick film layer 5 and the position where the thick film layer 5 is grown may be adjusted according to the formation width of the mask 6.

  After forming the thick film layer 5, as shown in FIG. 1 (f), the thick film layer 5 is peeled from the base substrate 3 to form an outer diameter process or an orientation flat (OF). When the machining is performed, a GaN free-standing substrate that is the nitride semiconductor substrate 1 is obtained.

  A method for manufacturing a nitride semiconductor substrate according to the second embodiment of the present invention will be described with reference to FIG.

  On the sapphire substrate 2 (FIG. 2 (a)) having a diameter larger than that of the nitride semiconductor substrate 1 to be manufactured, a base layer made of GaN is formed by MOCVD (metal organic chemical vapor deposition) to form a base substrate. At the same time, a Ti film is formed as a metal film on the underlayer by a vacuum deposition method (FIG. 2B).

  Next, a mask 6 is formed on the outer periphery of the metal film deposited on the base substrate 3 (FIG. 2C), and heat treatment is performed in a mixed atmosphere of hydrogen gas and ammonia gas to generate voids in the base layer. Micropores are formed in the Ti film, which is a metal film (FIG. 2D). The reason why the mask 6 is put on the outer periphery of the base substrate 3 is to selectively form voids in the central portion of the base substrate 3 while avoiding unstable portions at the end portions of the base layer.

  Thereafter, a second mask 7 is formed on the outer periphery of the void generation region 4 (FIG. 2E), and the GaN thick film layer 5 is grown on the exposed portion by the HVPE method (FIG. 2F). The grown GaN thick film layer 5 is peeled from the base substrate 3 and subjected to outer diameter processing, high-precision OF processing, and chamfering processing to obtain a GaN free-standing substrate that is the nitride semiconductor substrate 1 (FIG. 2G).

  Note that the formation method of the base layer and the metal film, the material of the metal film, and the heat treatment method are not limited to the above.

  As described above, in the method for manufacturing a nitride semiconductor substrate according to the present invention, the base material 2 having a diameter larger than the diameter of the nitride semiconductor substrate 1 is used, and the thick film layer 5 is formed at the center of the base substrate 3. To grow.

  As a result, it becomes possible to grow the thick film layer 5 while avoiding the end portion of the base substrate 3, that is, the unstable region of the base layer and the gap, and the thick film layer 5 is grown in the growth process (thick film growth process). It is possible to greatly suppress cracks and cracks in the thick film layer 5 that cause a large failure.

  In the present invention, since the thick film layer 5 is grown in the region (void generation region 4) in which the fine holes of the metal film are uniformly formed, cracks and cracks in the thick film layer 5 can be further suppressed.

  In the present invention, the so-called void formation exfoliation method (Yuichi OSHIMA et al., Japanese Journal of Applied Physics, Vol. 42 (2003), pp. L1-L3) as described above can be suitably used. However, the present invention is not limited to this, and the MOHVPE method (organometallic chloride vapor phase growth method) and the MOCVD method can also be employed.

  As described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  In order to obtain a nitride semiconductor substrate 1 having a diameter of 50.8 mm (2 inches), first, a c-plane sapphire single crystal substrate (sapphire substrate 2) having a diameter of 62 mm (2.5 inches) is prepared (FIG. 1A). A 300 nm thick GaN thin film (underlayer) was grown thereon using a metal organic chemical vapor deposition (MOCVD) apparatus.

  After forming the GaN thin film (underlying layer), a Ti thin film (metal film) was deposited to a thickness of 20 nm using a vacuum evaporator (FIG. 1B). Thereafter, a heat treatment was performed at 1060 ° C. for 30 minutes in a mixed atmosphere of ammonia and hydrogen to generate a network of TiN nanonets and a large number of voids at the Ti / GaN interface (FIG. 1C).

A mask 6 is formed on the outer periphery of the base substrate 3 on which the void is formed so that a diameter smaller than the void generation region 4 is exposed. In this case, a mask 6 is formed on the outer periphery so that a diameter of about 55 mm is exposed at the center of the void generation region 4 (FIG. 1D), and the thickness is determined using a hydride vapor phase epitaxy (HVPE) apparatus. A 300 μm thick GaN thick film (thick film layer 5) was grown at 1060 ° C. (FIG. 1E). The raw materials used for the growth are NH ₃ and GaCl. Moreover, the GaCl partial pressure and NH ₃ partial pressure in the supply gas were 8 × 10 ⁻³ atm (about 0.81 kPa) and 8 × 10 ⁻² atm (about 8.1 kPa), respectively. Growth was performed at normal pressure, and N ₂ was used as a carrier gas.

  By forming and growing a mask 6 on the circumference so that a diameter of about 55 mm is exposed at the center of the void generation region 4, the GaN thick film (thick film layer 5) selectively generates voids. Formed in part.

  This GaN thick film (thick film layer 5) is easily peeled off from the HVPE-GaN (thick film layer 5) / Ti (metal film) interface, and is subjected to outer diameter processing, high-precision OF processing, and chamfering. A nitride semiconductor substrate 1 having a diameter of 50.8 mm (2 inches) could be obtained (FIG. 1F).

  Similarly, 20 nitride semiconductor substrates 1 were produced and the number of cracks generated was investigated. Further, as a conventional example, 20 nitride semiconductor substrates were produced using a sapphire substrate having the same diameter as that of the GaN thick film (thick film layer 5), and the number of cracks generated was examined. The test results are shown in Table 1.

  In Table 1, the “diameter ratio between the void region of the metal film and the sapphire substrate” means that the diameter of the nitride semiconductor substrate to be manufactured (the diameter before outer diameter processing, that is, the diameter of the thick film layer 5) d, It is a ratio d / D with the diameter D of the sapphire substrate 2 which is a base material.

  As shown in Table 1, cracks occurred in 12 out of 20 sheets in the conventional example, and the crack generation rate was very high at 60%. However, in the example of the present invention, cracks occurred in 3 out of 20 sheets. It can be seen that the crack generation rate is 15%, which is suppressed to 1/4 of the conventional one. It can also be seen that the crack generation ratio can be made 15% or less by setting the ratio d / D to 0.89 or less.

  As described above, according to the present invention, it is possible to reduce the crack generation ratio and improve the yield as compared with the prior art.

1 Nitride semiconductor substrate 2 Sapphire substrate (base material)
3 Substrate (after metal film formation)
4 Void generation region 5 Thick film layer 6 Mask 7 Second mask

Claims (2)

A base layer made of a nitride semiconductor is provided on a base material to form a base substrate, a metal film is formed on the base layer of the base substrate, and then the base layer in an atmosphere containing hydrogen gas or a hydrogen-containing compound gas By heat-treating the substrate, voids are formed in the underlayer and fine holes are formed in the metal film, and a nitride semiconductor is grown on the metal film in which the fine holes are formed to form a thick film layer. Then, in the method for manufacturing a nitride semiconductor substrate, the thick film layer is peeled from the base substrate to obtain a nitride semiconductor substrate.
As the base material, one having a diameter larger than the diameter of the nitride semiconductor substrate is used,
The method for producing a nitride semiconductor substrate, wherein the thick film layer is grown at a central portion of the base substrate.   The method for manufacturing a nitride semiconductor substrate according to claim 1, wherein the thick film layer is grown in a region in which the fine holes are uniformly formed in the metal film.