JP4236121B2 - Manufacturing method of semiconductor substrate - Google Patents

Description

  The present invention relates to a semiconductor substrate manufacturing method and a semiconductor substrate.

Conventionally, as shown in Non-Patent Document 1, a chromium (Cr) layer is prepared using a metal source by the MBE method, and the Cr layer is nitrided with an N2 plasma source, and the average film thickness is 20 nm or less. There is a technique for forming a chromium nitride (CrN) layer.
Li Asahi and 7 others, “Growth of GaN using low temperature CrxN buffer layer by MBE”, Proceedings of the Japan Society of Applied Physics, page 364

  In the technique of Non-Patent Document 1, a chromium nitride film is formed by nitriding a Cr layer with N 2 plasma at a temperature of 500 ° C. to 600 ° C. At this time, when the buffer layer and the group III nitride semiconductor crystal layer are grown on the chromium nitride film, the crystallinity of the group III nitride semiconductor crystal layer may be deteriorated.

  The objective of this invention is providing the manufacturing method of a semiconductor substrate which can improve the crystallinity of the crystal layer of a group III nitride semiconductor, and a semiconductor substrate.

  In addition, as a group III nitride semiconductor, Ga and In type semiconductors can be cited. Group III nitride semiconductors are, for example, GaN-based, AlGaN-based, and AlInGaN-based, but are not limited thereto.

  The method for manufacturing a semiconductor substrate according to the first aspect of the present invention includes a chromium layer film forming step of forming a chromium layer on an underlying substrate with an average layer thickness of 7 nm or more and less than 45 nm, and the chromium layer at 1000 ° C. or more. And a nitriding step of nitriding at a temperature to form a chromium nitride film.

  The method for manufacturing a semiconductor substrate according to the second aspect of the present invention includes a chromium layer forming step of forming a chromium layer on an underlying substrate with an average layer thickness of 7 nm or more and less than 45 nm, and the chromium layer at 1000 ° C. or more. A nitriding step of nitriding at a temperature to form a chromium nitride film and a crystal layer growing step of growing a group III nitride semiconductor crystal layer on the chromium nitride film are provided.

  In addition to the characteristics of the semiconductor substrate manufacturing method according to the first aspect or the second aspect of the present invention, the method for manufacturing a semiconductor substrate according to the third aspect of the present invention includes the step of forming the chromium substrate in the base substrate. The chromium layer is formed on either the hexagonal system or pseudo-hexagonal system (0001) plane or cubic (111) plane.

  In addition to the characteristics of the method of manufacturing a semiconductor substrate according to any one of the first to third aspects of the present invention, the method for manufacturing a semiconductor substrate according to the fourth aspect of the present invention includes, in the chromium layer film forming step, The chromium layer is formed with an average layer thickness of 10 nm or more and 40 nm or less.

  According to a fifth aspect of the present invention, there is provided a method for manufacturing a semiconductor substrate, comprising: etching the chromium nitride film in addition to the characteristics of the method for manufacturing a semiconductor substrate according to any one of the first to fourth aspects of the present invention. The method further includes a separation step of separating the group III nitride semiconductor crystal from the base substrate.

  A semiconductor substrate according to a sixth aspect of the present invention includes a base substrate, a chromium nitride film having an average thickness of 10 nm or more and less than 68 nm formed on the base substrate, and a group III nitride on the chromium nitride film. And a crystal layer formed of a physical semiconductor.

  The semiconductor substrate according to the seventh aspect of the present invention is characterized in that, in addition to the characteristics of the semiconductor substrate according to the sixth aspect of the present invention, the chromium nitride film has an average film thickness of 15 nm or more and less than 60 nm. .

  According to the present invention, the crystallinity of the crystal layer can be improved.

  In this specification, the “film” may be a continuous film or a discontinuous film. The “film” represents a state where the film is formed with a thickness.

  A method for manufacturing a semiconductor substrate according to an embodiment of the present invention will be described with reference to FIGS. In the following description, a group III nitride semiconductor GaN will be described as an example of the crystal layer. As will be described later, considering that the crystal layer is used as a free-standing substrate and applied to a diode or the like, the group III nitride semiconductor used as the material of the crystal layer is preferably GaN.

  1 to 2 are process cross-sectional views illustrating a method for manufacturing a semiconductor substrate according to an embodiment of the present invention. 3 and 4 are XRD (X-Ray Diffraction) charts. 5 and 8 are SEM photographs obtained by photographing the sample surface. FIG. 6 is a schematic diagram of the surface morphology. FIG. 7 is a diagram showing the crystal orientation of the microcrystalline portion of the chromium nitride film.

  In the step shown in FIG. 1A, a base substrate 10 is prepared. The base substrate 10 is formed of a single crystal of sapphire. The upper surface 10a of the base substrate 10 is a (0001) plane of sapphire single crystal. A single crystal of sapphire has a trigonal (pseudo hexagonal) crystal structure.

  Note that the base substrate may be formed of a material other than sapphire as long as the material has any one of a hexagonal crystal system, a pseudo hexagonal crystal system, and a cubic crystal system. When the base substrate is a cubic system, the (111) plane is used in the following description.

  In the step shown in FIG. 1B, a Cr (chrome) layer 20 is formed on the upper surface 10 a of the base substrate 10. That is, the Cr layer 20 is formed on the (0001) plane of the sapphire crystal. Specifically, first, the base substrate 10 is cleaned by a normal semiconductor substrate cleaning method (degreasing by organic cleaning, removal of contaminants / particles by acid / alkali / pure water cleaning), and the cleanliness of the surface 10a. Secure. Next, a Cr layer 20 is formed by forming a metal Cr film on the surface 10a in which cleanliness is ensured by sputtering in an inert gas atmosphere, for example, an Ar gas atmosphere.

  Here, the average layer thickness of the Cr layer 20 is preferably a value within a range of 7 nm or more and less than 45 nm, and more preferably a value of 10 nm or more and less than 40 nm. By making the average layer thickness of the Cr layer 7 nm or more and less than 45 nm, it becomes possible to grow a crystalline layer having good crystallinity, and by making the average layer thickness 10 nm or more and less than 40 nm, the pit density of the crystal layer can also be reduced. Is possible.

  The Cr layer 20 may be formed by chemical vapor deposition (CVD) using an alkyl compound containing metal or chloride, or may be formed by metal organic chemical vapor deposition (MOCVD). Alternatively, the film may be formed by vacuum (thermal) vapor deposition.

  When the XRD analysis of the sample obtained in this step is performed, for example, the result shown in FIG. 3 is obtained. In FIG. 3, the vertical axis indicates the peak intensity (arbitrary unit), and the horizontal axis indicates the diffraction angle 2θ. Thus, it can be seen that the (110) -oriented Cr layer 20 is grown on the (0001) plane of the base substrate 10 (sapphire). The Cr layer 20 is a metal having a body-centered cubic structure.

  In the step shown in FIG. 1C, the base substrate 10 on which the Cr layer 20 is formed is transferred to an apparatus for growing GaN crystals. Then, the base substrate 10 on which the Cr layer 20 is formed is heat-nitrided in a reducing gas atmosphere containing nitrogen. At that time, the heating temperature is preferably 1000 ° C. or higher (1273 K or higher), more preferably 1040 ° C. or higher, further preferably 1060 ° C. or higher. By nitriding at a heating temperature of 1000 ° C. or higher, a chromium nitride film 30 having a Cr layer 20 having a plurality of triangular pyramid-shaped microcrystalline portions 31 on the surface is formed.

  Here, the composition of the chromium nitride film 30 is preferably CrN.

By nitriding at a heating temperature of 1040 ° C. or higher, the pit density on the surface 50a of the crystal layer 50 described later is reduced to a level of 10 ² to 10 ³ / cm ² . By nitriding at a heating temperature of 1060 ° C. or higher, the pit density on the surface 50a of the crystal layer 50 described later is reduced to a few / cm ² level. This is probably because the higher the heating temperature, the more the irregular shape of the triangular pyramid is resolved.

  However, if the temperature is excessively high, there is a problem of deterioration of the members of the apparatus due to an increase in thermal load, and problems such as mutual thermal diffusion between the formed chromium nitride film and the base substrate occur. 1300 degrees C or less is preferable.

  When the XRD analysis of the sample obtained in this step is performed, for example, the result shown in FIG. 4 is obtained. FIG. 4 is an XRD chart for the sample shown in FIG. In FIG. 4, the vertical axis indicates the peak intensity (arbitrary unit), and the horizontal axis indicates the diffraction angle 2θ. In the XRD chart of FIG. 4, sapphire peaks and CrN peaks are observed, but no Cr peaks are observed. As a result, it can be seen that most of the Cr layer 20 is nitrided to form the chromium nitride film 30.

  Further, regarding CrN, only the peaks of the (111) plane and the (222) plane are observed, and the half-value width is narrow. Thereby, it can be seen that the chromium nitride film 30 is in a (111) plane orientation on the (0001) plane of the sapphire substrate.

  When the surface of the sample obtained in this step is observed with an SEM, for example, the result shown in FIG. 5 is obtained. FIG. 5 is an SEM photograph of the sample surface.

  According to the SEM photograph of FIG. 5, it can be seen that the chromium nitride film 30 has a plurality of triangular pyramid-shaped microcrystalline portions 31 on the surface. Further, the microcrystalline portions 31 of the chromium nitride film 30 are distributed over substantially the entire surface 10 a of the base substrate 10.

  As shown in FIG. 6, each microcrystalline portion 31 of the chromium nitride film 30 has bottom sides in the [10-10] direction, the [01-10] direction, and the [−1100] direction of the base substrate 10. It extends along either.

  Further, a cross section of the sample obtained in the step shown in FIG. As a result, it was found that the three side surfaces (facet surfaces other than the bottom surface) of each microcrystalline portion 31 were formed of {100} plane groups.

  Thus, each microcrystalline portion 31 of the chromium nitride film 30 is individually a single crystal. As shown in FIG. 5 and FIG. 6, the direction of the base of the triangular pyramid has two kinds of crystal orientations (multi-twin) rotated in the plane of 180 °. Therefore, the grown group III nitride semiconductor crystal becomes a single crystal, so there is no problem. That is, as shown in FIG. 7, the lattice spacing of the microcrystalline portions 31 of the chromium nitride film 30 (the spacing of the black circles of the equilateral triangular portion shown in FIG. 7) is the lattice spacing of the base substrate 10 (sapphire) (FIG. 7). Different from the white circle interval shown in FIG. Thereby, the atoms (black circles shown in FIG. 7) constituting each microcrystalline portion 31 are stably present at positions between sapphire lattices (white circles shown in FIG. 7). Thereby, each microcrystal part 31 becomes a microcrystal (multi-twin) in which patterns of crystal lattices indicated by black circles are repeatedly arranged. The chromium nitride film 30 has a plurality of triangular pyramid-shaped microcrystalline portions 31 on the surface. Each microcrystalline portion 31 has a base extending on the (0001) plane of the base substrate 10 along any one of the [10-10] direction, the [01-10] direction, and the [-1100] direction, and the side surfaces thereof It becomes {100} face group. Thereby, the crystal orientation deviation due to the in-plane rotation of the microcrystals becomes extremely small. The direction from the center of gravity of the bottom surface of each microcrystal portion 31 toward the upper end is perpendicular to the (0001) plane of the base substrate, that is, the orientation parallel to the C axis of the sapphire crystal.

  Here, the average film thickness of the chromium nitride film 30 is preferably a value within a range of 10 nm or more and less than 75 nm, and more preferably a value of 15 nm or more and less than 60 nm. Here, the average film thickness of the chromium nitride film can be obtained by measuring irregularities with a cross-sectional TEM, and it was confirmed that it corresponds to 1.5 times the average layer thickness of the Cr layer before nitriding. .

  When the average film thickness of the chromium nitride film 30 is less than 15 nm, that is, when the Cr layer thickness is less than 10 nm, the surface 10a of the base substrate 10 is partially exposed, and in the step of FIG. The GaN buffer layer starts to grow from both the base substrate 10 and the chromium nitride film 30, but the buffer layer grown from the base substrate remains during the growth of the chromium nitride film. As a result, the crystal orientation differs between the GaN buffer layer grown from the base substrate 10 and the GaN buffer layer grown from the chromium nitride film 30, so that an improvement in crystal quality is expected in the process of FIG. There is a possibility that pits on the surface of the GaN layer increase. Further, when the average film thickness of the chromium nitride film 30 is 75 nm or more, that is, when the average layer thickness of the Cr layer is 50 nm or more, the solid phase of the chromium nitride film 30 on the base substrate 10 in the above-described thermal nitriding treatment. Epitaxial growth does not proceed uniformly, and the chromium nitride film 30 tends to be mosaic or polycrystalline. Thereby, the GaN grown on the chromium nitride film 30 in the process of FIG. 2A to be described later becomes a mosaic or polycrystalline, and the GaN grown in the process of FIG. There is a possibility that improvement in crystal quality cannot be expected because it becomes polycrystalline.

  Note that the step shown in FIG. 1B and the step shown in FIG. 1C may be performed by the same apparatus or different apparatuses. It is preferable to perform without opening to the atmosphere between the step shown in FIG. 1B and the step shown in FIG.

  Next, in the step shown in FIG. 2A, the base substrate temperature is lowered to 900 ° C., and a buffer layer 40 of group III nitride (for example, GaN) is formed by HVPE. The layer thickness of the buffer layer 40 is about 10 μm, for example.

  Here, the buffer layer 40 grows laterally from each of the {100} facet plane groups, with the microcrystal (microcrystal portion 31) of the triangular pyramid-shaped chromium nitride film 30 as a growth nucleus (as a nucleation site). . Thereby, it is possible to suppress the dislocation (threading dislocation) generated at the interface (growth interface) between the chromium nitride film 30 and the buffer layer 40 from propagating upward. The triangular pyramid shape is not limited to those having an acute angle or having a straight line on one side, but generally refers to a triangular pyramid shape. It also includes an object whose shape is artificially processed or made into a polyhedron during the growth process.

  In addition, since the crystal orientations of the microcrystals (microcrystal part 31) of the chromium nitride film 30 are aligned, in-plane rotation occurs when crystals grown from different directions are combined in the lateral growth of the group III nitride. Misalignment due to, and crystal axis misalignment (C axis misalignment) in the growth thickness direction can be reduced. As a result, the crystallographic orientations can be merged, so that the occurrence of group III nitride dislocations can be suppressed in the portion where the crystals grown from different directions merge.

  Further, the microcrystalline portions 31 that are nucleation sites have a uniform size on the base substrate 10 and are distributed at uniform intervals. Thereby, since the buffer layer 40 grows in a uniform direction on the chromium nitride film 30, the occurrence of dislocation can be suppressed also from this point.

  In the step shown in FIG. 2B, the temperature of the base substrate is raised to 1040 ° C., and the GaN crystal layer 50 is grown. The thickness of the crystal layer 50 during the growth is, for example, about 10 μm.

As described above, since the crystal layer 50 is grown on the buffer layer 40 in which dislocations are reduced, the dislocation density of the crystal layer 50 is reduced to 10 ⁷ to 10 ⁸ / cm ² . That is, the dislocation density is reduced by 1 to 2 digits compared to the so-called low temperature buffer layer technology.

  When the surface of the sample obtained in this step is observed with a microscope, for example, the result shown in FIG. 8 is obtained.

According to the micrograph of FIG. 8, it can be seen that the surface 50a of the crystal layer 50 has almost no pits. That is, the surface pit density is reduced to 0 to 10 ² / cm ² . That is, when a method using a metal buffer layer (for example, a method using Al, Au, Ag, Ni, Ti, Cu disclosed in JP-A-2002-284600 is used, the surface pit density is 10 ⁴ to 10 ⁵ / cm. Compared with ² ), the surface pit density of the epitaxially grown film can be reduced by 3 to 4 digits or more. As a result, the yield is not reduced due to the pits. It is also estimated that the dislocation density in the crystal layer 50 can be reduced.

  In the step shown in FIG. 2C, the chromium nitride film 30 is selectively etched using a chemical solution. The GaN substrate SB can be separated from the base substrate 10. That is, the GaN substrate SB can be obtained as a free-standing substrate. Here, the substrate SB includes the buffer layer 40 and the crystal layer 50.

  As a secondary effect, a microcrystalline portion 41 corresponding to the microcrystalline portion 31 of the chromium nitride film 30 is formed on the back surface of the buffer layer 40. Since the microcrystalline portion 41 has an inverted triangular pyramid shape on the order of several tens to several hundreds nm, the light extraction efficiency of the light emitting diode can be improved when used in a device. In addition, since the crystal defects are reduced, the internal quantum efficiency of the light emitting diode is also improved, so that the light emitting efficiency of the light emitting diode is improved overall.

  An excellent semiconductor element can be obtained by further laminating a group III-based nitride semiconductor layer on the buffer layer 40 to obtain an element structure.

  Next, a method for manufacturing a semiconductor substrate according to a comparative example will be described with reference to FIGS. Below, it demonstrates centering on a different part from the manufacturing method of the semiconductor substrate which concerns on embodiment of this invention, and abbreviate | omits description about the same part.

  In the step shown in FIG. 9A, the base substrate 10 on which the Cr layer 20 is formed is transferred to an apparatus for growing GaN crystals. Then, the base substrate 10 on which the Cr layer 20 is formed is heat-nitrided in an ammonia-containing gas atmosphere. In that case, heating temperature shall be 900 degreeC. Thereby, the vicinity of the surface of the Cr layer 20 is nitrided, and the chromium nitride film 130 having the flat surface 130a is formed.

  Here, the average film thickness of the chromium nitride film 130 is, for example, 5 nm.

  When the XRD analysis of the sample obtained in this step is performed, for example, the result shown in FIG. 10 is obtained. FIG. 10 is an XRD chart for the sample shown in FIG. In FIG. 10, the vertical axis indicates the peak intensity (arbitrary unit), and the horizontal axis indicates the diffraction angle 2θ. In the XRD chart of FIG. 10, not only sapphire peaks and CrN peaks but also Cr peaks are observed. Thereby, it can be seen that the Cr layer 20 is partially nitrided to form the chromium nitride film 130.

  For CrN, only the peaks on the (111) plane and the (222) plane are observed, and the full width at half maximum is widened. Thereby, it can be seen that the chromium nitride film 130 is in a state in which the orientation of the (111) plane varies with respect to the (0001) plane of the sapphire substrate.

  When the surface of the sample obtained in this step is observed by SEM, for example, the result shown in FIG. 11 is obtained. FIG. 11 is an SEM photograph of the sample surface.

  From the SEM photograph of FIG. 11, it can be seen that the chromium nitride film 130 has a substantially flat surface 130a. That is, triangular pyramid-shaped microcrystals (microcrystal parts) are not formed on the surface 130 a of the chromium nitride film 130.

  Next, in the step shown in FIG. 9B, the GaN buffer layer 140 is formed by the HVPE method with the substrate temperature kept at 900.degree. The layer thickness of the buffer layer 140 is, for example, about 10 μm.

  Here, the buffer layer 140 is grown on the flat surface 130 a of the chromium nitride film 130. Thereby, dislocations generated at the interface (growth interface) between the chromium nitride film 130 and the buffer layer 140 are likely to propagate upward.

  Further, since the crystal orientation of the chromium nitride film 130 varies, when the crystals of the buffer layer 140 grown thereon are combined, the orientation misalignment due to in-plane rotation and the crystal axis misalignment in the growth thickness direction (C axis) Is likely to occur. As a result, coalescence may occur in a state where the crystal orientation varies, so dislocations are likely to occur in the portion where crystals grown from different directions merge.

  Even if atomic level flatness is ensured with respect to the surface 130a of the chromium nitride film 130, there is a lattice irregularity between GaN and CrN, so that high-density dislocations tend to occur at the growth interface. Further, since the growth does not involve lateral growth, there is a possibility that the dislocation density cannot be reduced.

  In the step shown in FIG. 9C, the substrate temperature is raised to 1040 ° C. to grow the GaN crystal layer 150. The thickness of the crystal layer 150 during growth is, for example, about 10 μm.

  As described above, since the crystal layer 150 is grown on the buffer layer 140 where dislocation is likely to occur, the dislocation density of the crystal layer 150 tends to increase.

  When the surface of the sample obtained in this step is observed with a microscope, for example, the result shown in FIG. 12 is obtained.

  According to the micrograph of FIG. 12, it can be seen that many pits are generated on the surface 150a of the crystal layer 150. As a result, the yield may be reduced due to the pits. It is also estimated that the dislocation density in the crystal layer 150 is high.

  As described above, the crystallinity of the buffer layer and the crystal layer grown on the chromium nitride film varies depending on the film thickness of the chromium nitride film. Therefore, a sample was prepared by the same process as that shown in FIGS. 1 to 2C (the process shown in FIG. 1C was performed at a nitriding temperature of 1000 ° C. and a nitriding time of 30 minutes). Here, an experiment was conducted to evaluate the peak half-value width of the XRD analysis of the crystal layer when the thickness of the Cr layer was changed. The result is shown in FIG. Further, according to the same process as that shown in FIGS. 1 to 2C, the Cr layer is almost entirely nitrided to form a chromium nitride film. From the average thickness evaluation result by cross-sectional TEM observation, it has been found that the average thickness is 1.5 times the initial Cr film thickness. Since this coincides with the layer thickness obtained by the specific gravity of the chromium nitride film with respect to the Cr layer, the layer thickness of the initial Cr layer was converted to the film thickness of the chromium nitride film. The result is shown in FIG. In FIGS. 13 and 14, the black triangle plot represents the change in peak half-value width of the (0002) plane of GaN, and the black square plot represents the change in peak half-value width of the (10-11) plane of GaN. Represents. Moreover, the result of having observed the sample surface at this time with a microscope is shown in FIGS.

  The results shown in FIGS. 13 to 22 are, as will be described below, the average layer thickness of the Cr layer 20 is preferably a value within a range of 7 nm or more and less than 50 nm, and preferably a value of 10 nm or more and 40 nm or less. It is further preferable. The average film thickness of the chromium nitride film 30 is preferably a value within the range of 10 nm or more and less than 75 nm, and more preferably 15 nm or more and less than 60 nm. That is, by nitriding the Cr layer to a thickness of 10 nm or more and 40 nm or less, the average thickness of the chromium nitride film 30 becomes a value of 15 nm or more and 60 nm or less, and a triangular pyramid shape is formed on the surface of the chromium nitride film. The microcrystalline portion is suitably formed. Thereby, the crystallinity of the crystal layer of the group III nitride semiconductor grown thereon is improved, and the pit density on the surface of the crystal layer is reduced (see FIGS. 13 and 14).

  Here, when the average film thickness of the chromium nitride film 30 is less than 10 nm (when the average layer thickness of the Cr layer 20 is less than 7 nm), the surface 10a of the base substrate 10 may be partially exposed. In the step 2 (a), the GaN buffer layer starts to grow from both the base substrate 10 and the chromium nitride film 30. Thereby, since the crystal orientation differs between the GaN buffer layer grown from the base substrate 10 and the GaN buffer layer grown from the chromium nitride film 30, the crystal quality is not improved in the step of FIG. 2B, the number of pits increases on the surface of GaN after crystal growth in the step of FIG. 2B (see FIGS. 15 and 16). When the average film thickness of the chromium nitride film 30 exceeds 75 nm (when the average layer thickness of the Cr layer 20 exceeds 50 nm), the chromium nitride film 30 is formed on the base substrate 10 in the above-described heat nitriding process. The solid phase epitaxial growth does not proceed uniformly, and the chromium nitride film 30 tends to be mosaic or polycrystalline. As a result, the GaN grown on the chromium nitride film 30 in the step of FIG. 2A becomes polycrystalline, and the GaN grown in the step of FIG. 2B also becomes mosaic or polycrystalline, improving the crystal quality. Cannot be expected (see FIG. 20 and FIG. 21).

Process sectional drawing which shows the manufacturing method of the semiconductor substrate which concerns on embodiment of this invention. Process sectional drawing which shows the manufacturing method of the semiconductor substrate which concerns on embodiment of this invention. XRD chart of the sample. XRD chart of the sample. SEM photograph of the sample surface. Schematic diagram of surface morphology. The figure which shows the crystal orientation of the microcrystal part of a chromium nitride film | membrane. A photomicrograph of the sample surface. Process sectional drawing which shows the manufacturing method of the semiconductor substrate which concerns on the comparative example of this invention. XRD chart of the sample. SEM photograph of the sample surface. A photomicrograph of the sample surface. The figure which shows the relationship between the average layer thickness of Cr layer, and crystallinity. The figure which shows the relationship between the average film thickness of a chromium nitride film | membrane, and crystallinity. A photomicrograph of the sample surface (Cr layer thickness: 5 nm). A micrograph of the sample surface (Cr layer thickness: 7 nm). A photomicrograph of the sample surface (Cr layer thickness: 14 nm). A photomicrograph of the sample surface (Cr layer thickness: 20 nm). A micrograph of the sample surface (Cr layer thickness: 25 nm). A photomicrograph of the sample surface (Cr layer thickness: 35 nm). A photomicrograph of the sample surface (Cr layer thickness: 45 nm). A photomicrograph of the sample surface (Cr layer thickness: 50 nm).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Base substrate 20 Cr layer 30,130 Chromium nitride film 40,140 Buffer layer 50,150 Crystal layer

Claims (6)

A chromium layer forming step of forming a chromium layer on the base substrate with an average layer thickness of 7 nm or more and less than 45 nm;
A nitriding step of nitriding the chromium layer at a temperature of 1000 ° C. or higher to form a chromium nitride film;
A crystal layer growth step of growing a crystal layer of a group III nitride semiconductor on the chromium nitride film;
A method for manufacturing a semiconductor substrate, comprising: In the chromium layer forming step, the chromium layer is formed on either the hexagonal system or pseudo-hexagonal system (0001) plane or cubic (111) plane of the base substrate. A method for manufacturing a semiconductor substrate according to claim 1 . Wherein the chromium layer deposition step, the method for manufacturing a semiconductor substrate according to claim 1 or 2, characterized in that deposition of the chromium layer with an average layer thickness of more than 40nm or less 10 nm. The semiconductor substrate according to any one of claims 1 to 3, characterized in that the chromium nitride film is etched in the group III nitride semiconductor crystal, further comprising a separation step of separating from said starting substrate Manufacturing method. Wherein the nitriding step, a method of manufacturing a semiconductor substrate according to claim 1, any one of 4, wherein <br/> forming said chromium nitride film in less than an average thickness of 10nm or more 68 nm. The method for manufacturing a semiconductor substrate according to claim 5 , wherein, in the nitriding step, the chromium nitride film is formed with an average film thickness of 15 nm or more and less than 60 nm.