JP2009062273A - Structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure which can reduce the dislocation density of a crystal layer of a group III nitride semiconductor. <P>SOLUTION: The structure is provided with: a base substrate; and a chromium nitride film which is formed on the base substrate and has a plurality of triangular pyramid-like fine crystal parts. In each triangular pyramid-like fine crystal part of the chromium nitride film, all inclined faces are each formed with a crystal face of the chromium nitride. The crystal orientation at each inclined face is uniform and the inclined faces are constituted of a ä100} plane group. Further, the bottom face of each fine crystal part of the chromium nitride film is a (111) plane. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a structure.

Conventionally, a method of growing a group III nitride semiconductor crystal on a base substrate through a metal film or a metal nitride film (hereinafter referred to as a metal film or the like) has been proposed (for example, see Patent Document 1). ). In the technique shown in Patent Document 1, a metal film or the like is formed on a base substrate on which a group III nitride layer is formed, and the metal film or the like is subjected to heat treatment, whereby a plurality of through holes are formed on the metal film or the like. A mesh structure distributed in a mesh shape is formed in visual observation. Using the network structure of the metal film or the like as a mask, a group III nitride semiconductor crystal is grown such that the group III nitride exposed in the through-hole of the metal film or the like becomes a nucleation site at the initial stage of growth.
Japanese Patent Laid-Open No. 2005-119921

  However, in the technique disclosed in Patent Document 1, the interval between nucleation sites tends to be random, and the crystal orientation of crystal nuclei tends to be random. As a result, defects are likely to occur in the group III nitride semiconductor crystal, which may increase the dislocation density.

  An object of the present invention is to provide a structure that can reduce the dislocation density of a crystal layer of a group III nitride semiconductor.

  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 structure according to the first aspect of the present invention includes a base substrate and a chromium nitride film formed on the base substrate and having a plurality of triangular pyramid-shaped microcrystalline portions.

  In addition to the characteristics of the structure according to the first aspect of the present invention, the structure according to the second aspect of the present invention further includes a crystal layer formed of a group III nitride semiconductor on the chromium nitride film. It is characterized by that.

  The structure according to the third aspect of the present invention is a multi-twin aggregate having two crystal orientations in addition to the characteristics of the structure according to the first aspect or the second aspect of the present invention. It is characterized by being.

  In addition to the characteristics of the structure according to any one of the first to third aspects of the present invention, the structure according to the fourth aspect of the present invention includes a triangular pyramid-shaped microcrystalline portion of the chromium nitride film, The length of one side is 10 nm or more and 300 nm or less.

  In the structure according to the fifth aspect of the present invention, in addition to the characteristics of the structure according to any one of the first to fourth aspects of the present invention, each microcrystalline portion of the chromium nitride film includes (111 ) The surface is the bottom surface.

  In the structure according to the sixth aspect of the present invention, in addition to the characteristics of the structure according to the fifth aspect of the present invention, each microcrystalline portion of the chromium nitride film has {100} face groups as other facets. It is a surface.

  The structure according to the seventh aspect of the present invention further includes a crystal layer formed of a group III nitride semiconductor on the chromium nitride film in addition to the characteristics of the structure according to the sixth aspect of the present invention. The crystal layer is formed by laterally growing a group III nitride semiconductor from each of the {100} plane groups with each microcrystalline portion of the chromium nitride film as a growth nucleus. .

  In the structure according to the eighth aspect of the present invention, in addition to the characteristics of the structure according to any one of the first aspect to the seventh aspect of the present invention, the underlying substrate may be either a hexagonal system or a pseudo hexagonal system. It is characterized by having such a crystal structure.

  In the structure according to the ninth aspect of the present invention, in addition to the characteristics of the structure according to the eighth aspect of the present invention, the chromium nitride film is laminated on the (0001) surface of the base substrate. It is characterized by.

  In the structure according to the tenth aspect of the present invention, in addition to the characteristics of the structure according to the eighth aspect or the ninth aspect of the present invention, each microcrystalline portion of the chromium nitride film has each side of the bottom surface. It extends along the [10-10] direction, the [01-10] direction, or the [-1100] direction on the (0001) plane of the base substrate.

  In the structure according to the eleventh aspect of the present invention, in addition to the characteristics of the structure according to any one of the first to seventh aspects of the present invention, the base substrate has a cubic crystal structure. Features.

  In the structure according to the twelfth aspect of the present invention, in addition to the characteristics of the structure according to the eleventh aspect of the present invention, the chromium nitride film is laminated on the (111) surface of the base substrate. It is characterized by.

  In the structure according to the thirteenth aspect of the present invention, in addition to the characteristics of the structure according to the eleventh aspect or the twelfth aspect of the present invention, each microcrystalline portion of the chromium nitride film has a base on each side, It extends along any one of the [10-1] direction, the [1-10] direction, and the [01-1] direction.

  According to the present invention, the dislocation density of the crystal layer of the group III nitride semiconductor can be reduced.

  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, the group III nitride semiconductor GaN is described as an example of the crystal layer, but the same applies to other semiconductors. 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 and 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. FIG. 5 is an SEM photograph of the sample surface. FIG. 8 is a photomicrograph of the sample surface. FIG. 6 is a schematic diagram of the surface morphology of the chromium nitride film. FIG. 7 is a diagram showing the crystal orientation of the convex 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 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 as the upper surface 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 to 45 nm, and more preferably a value within a range of 10 nm to 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 further by reducing the pit density of the crystal layer by making it 10 nm or more and 40 nm or less. 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. This shows that the (0001) plane of the base substrate 10 (sapphire) and the (110) plane of the Cr layer 20 are aligned in parallel. 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. The reducing gas containing nitrogen is preferably ammonia or hydrazine. 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, the Cr layer 20 is almost entirely nitrided, and a chromium nitride film 30 having a plurality of triangular pyramid-shaped convex portions 31 on the surface is formed.

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

Further, the length of one side of the triangular pyramid-shaped convex portion varies depending on the thickness of the Cr film before nitriding and the heating temperature condition, but is in the range of 10 nm to 300 nm. By nitriding at a heating temperature of 1040 ° C. or more, the pit density of the surface 50a of the GaN crystal layer 50 described later to be grown thereon is reduced to ^{10 2 ~10 3} / cm 2 level. By nitriding at a heating temperature of 1060 ° C. or higher, the pit density on the surface 50a of the GaN 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. Thereby, it can be seen that the Cr layer 20 is almost entirely nitrided to form the chromium nitride film 30.

  Further, regarding the chromium nitride film, only the peaks on the (111) plane and the (222) plane are observed, and the half-value width is narrowed. Thereby, it can be seen that the chromium nitride film 30 is in a state in which the orientation of the (111) plane is aligned in parallel with 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 convex portions 31 on the surface. It can also be seen that the convex portions 31 of the chromium nitride film 30 have a substantially uniform size and are distributed at substantially uniform intervals. Each convex portion 31 of the chromium nitride film 30 is distributed over substantially the entire surface 10 a of the base substrate 10.

  As shown in FIG. 6, each of the convex portions 31 of the chromium nitride film 30 has a bottom side in any of the [10-10] direction, the [01-10] direction, and the [−1100] direction of the base substrate 10. It extends along the way.

  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 convex portion 31 are formed of {100} surface groups.

  As described above, each convex portion 31 of the chromium nitride film 30 is a single crystal and is a microcrystalline (multi-twin) aggregate having two crystal orientations. 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 convex 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) (see FIG. 7). Different from the white circles shown). Thereby, the atoms (black circles shown in FIG. 7) constituting each convex portion 31 exist stably at positions between sapphire lattices (white circles shown in FIG. 7). Thereby, each convex part 31 becomes a microcrystal (multi-twin) in which patterns of crystal lattices indicated by black circles are repeatedly arranged, and has a plurality of triangular pyramidal convex parts on the surface. And each convex part 31 is extended along any one of a [10-10] direction, a [01-10] direction, and a [-1100] direction, and a side surface 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 convex 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 68 nm or less, and more preferably a value within a range of 15 nm or more and 60 nm or less. Here, the average film thickness of the CrN film can be obtained by measuring unevenness 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 thickness of the chromium nitride film 30 is less than 10 nm, that is, when the thickness of the chromium layer is less than 7 nm, the surface 10a of the base substrate 10 may be partially exposed. ), The GaN buffer layer begins to grow from both the base substrate 10 and the chromium nitride film 30. 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 it may not be possible, or there is a possibility that pits will increase on the surface of GaN after crystal growth in the step of FIG. Further, when the average film thickness of the chromium nitride film 30 exceeds 68 nm, the chromium nitride film 30 does not progress uniformly on the underlying substrate 10 in the above-described heat nitriding process, and the chromium nitride film 30 does not proceed uniformly. 30 tends to be polycrystalline. As a result, GaN grown on the chromium nitride film 30 in the later-described step of FIG. 2A becomes mosaic or polycrystalline, and improvement in crystal quality cannot be expected in the later-described step of FIG. 2B. There is a fear.

  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 triangular pyramid-shaped microcrystals (projections 31) of the chromium nitride film 30 as growth nuclei (as nucleation sites). 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 (convex portions 31) of the chromium nitride film 30 are aligned, when crystals grown from different directions are combined in the lateral growth of the group III nitride, they are caused by in-plane rotation. It is possible to reduce the orientation deviation and the crystal axis deviation (C-axis deviation) in the growth thickness direction. 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 protrusions 31 serving as nucleation sites have a substantially uniform size on the base substrate 10 and are distributed at substantially 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 a result, the structure 1 including the base substrate 10, the chromium nitride film 30, the buffer layer 40, and the crystal layer 50 is formed.

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 one to two orders of magnitude 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. FIG. 8 is a photomicrograph of the sample surface.

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 concave portion 41 corresponding to the convex portion 31 of the chromium nitride film 30 is formed on the back surface of the buffer layer 40. Since the recess 41 has an inverted triangular pyramid shape of several tens of nm to several hundreds of orders, the light extraction efficiency of the light emitting diode can be improved when used in a device. Moreover, since the internal quantum efficiency of the light emitting diode is improved by reducing the crystal defect density, an effect that the overall light emitting efficiency of the light emitting diode is greatly improved can be obtained.

  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.

Comparative example

  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 a reducing gas atmosphere containing nitrogen. The reducing gas containing nitrogen is preferably ammonia or hydrazine. In that case, heating temperature shall be 900 degreeC. Thereby, the vicinity of the surface of the Cr layer 20 is nitrided, and a chromium nitride film 130 having a substantially flat surface 130a is grown.

  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 and the chromium nitride film 130 is grown.

  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.

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

  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.

  According to the SEM photograph of FIG. 11, it can be seen that the chromium nitride film 130 has a flat surface 130a. That is, triangular pyramid-shaped microcrystals (convex portions) 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. Thereby, the structure 100 including the base substrate 10, the Cr layer 20, the chromium nitride film 130, the buffer layer 140, and the crystal layer 150 is formed.

  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. FIG. 12 is a micrograph of the sample surface.

  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 shape of the obtained chromium nitride film changes depending on the temperature (nitriding temperature) at which the Cr layer 20 is nitrided. As a result, the crystallinity of the buffer layer and the crystal layer grown thereon changes. Therefore, a sample was prepared by the same process as that shown in FIGS. Here, when the nitriding temperature (heating temperature in the step shown in FIG. 1C) is changed, the FWHM of the GaN peak is evaluated from the XRD analysis result of the crystal layer, and the SEM photograph or microscope of the crystal layer surface The pit density on the surface of the crystal layer was evaluated from the photograph. The result is shown in FIG. In FIG. 13, the white circle plot represents the change in peak half width, and the black square plot represents the surface pit density. The smaller the peak half-value width, the better the crystallinity.

  From the results shown in FIG. 13, in the heat treatment in a reducing gas atmosphere containing nitrogen, the heating temperature is preferably 1000 ° C. or higher, more preferably 1040 ° C. or higher, and more preferably 1060 ° C. or higher. Is more preferable.

  That is, by nitriding at a heating temperature of 1000 ° C. or more, the Cr layer 20 is almost entirely nitrided, and triangular pyramid-shaped microcrystals (convex parts) are formed on the surface of the chromium nitride film. It can be seen that the pit density on the surface of the crystal layer is reduced by almost one digit as compared with the case where the heating temperature is 900 ° C.

By nitriding at a heating temperature of 1040 ° C. or higher, the pit density on the surface 50a of the crystal layer 50 is reduced to a level of 10 ² to 10 ³ / cm ² . Thereby, it can be estimated that the dislocation density of the crystal layer is lower than when nitriding at a heating temperature of 1000 ° C. or higher.

By nitriding at a heating temperature of 1060 ° C. or higher, the pit density on the surface 50a of the crystal layer 50 is reduced to a few / cm ² level. Thereby, it can be estimated that the dislocation density of the crystal layer is further reduced as compared with the case of nitriding at a heating temperature of 1040 ° C. or higher.

  As described above, it is considered that the dislocation density of the crystal layer is reduced as the heating temperature is higher because the irregularity of the triangular pyramid shape is eliminated. 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.

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 convex 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 nitriding temperature and crystallinity.

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 (7)

A base substrate;
A chromium nitride film formed on the base substrate and having a plurality of triangular pyramid-shaped microcrystalline portions;
With
Each of the triangular pyramid-shaped microcrystalline portions of the chromium nitride film has a structure in which all inclined surfaces are formed of a crystal plane of chromium nitride. 2. The structure according to claim 1, wherein each of the microcrystalline portions of the triangular pyramid shape of the chromium nitride film has a uniform crystal orientation on each inclined surface. 3. The structure according to claim 1, wherein each of the microcrystalline portions of the chromium nitride film has a {100} plane group in all inclined surfaces. 4. The structure according to claim 1, wherein each microcrystalline portion of the chromium nitride film has a (111) plane as a bottom surface. 5. 5. The structure according to claim 1, wherein the chromium nitride film has a continuous surface formed by a bottom surface of each microcrystalline portion. 6. 6. The structure according to claim 1, wherein the chromium nitride film is formed so as to cover the base substrate so that an upper surface of the base substrate is not exposed. The structure according to any one of claims 1 to 6, further comprising a crystal layer formed of a group III nitride semiconductor on the chromium nitride film.