JP2020008497A - Gallium nitride crystal substrate and crystal evaluation method thereof - Google Patents

Abstract

A gallium nitride crystal substrate having high crystal quality and a crystal evaluation method for the gallium nitride crystal substrate capable of evaluating the crystal quality thereof in detail are provided.
The gallium nitride crystal substrate has at least one main surface, and the main surface is a surface having an off angle from (0001) of 0 ° or more and 2 ° or less, and uses a small divergence angle incident X-ray. In the X-ray diffraction measurement, <0001> and the φ axis are adjusted so as to coincide with each other, and in the φ scan pattern measurement using the φ axis as the rotation axis at the incident angle ω and the diffraction angle 2θ for the 0001 symmetric forbidden Bragg reflection, The ratio of the intensity of the first reference X-ray multiple diffraction peak derived from at least (1-100) and (-1101) to the ground intensity is 500 or more, and at least (02- 21) and the ratio of the intensities of the second reference multiple diffraction peaks derived from (0-220) is 0.18 or more.
[Selection diagram] FIG.

Description

  The present invention relates to a gallium nitride crystal substrate and a crystal evaluation method thereof.

  Japanese Patent Application Laid-Open No. 2013-203653 (Patent Document 1) discloses a method for producing a high-quality group III nitride crystal in which warpage is small and cracks are suppressed. Production of a group III nitride crystal including a step of obtaining a group III nitride seed substrate by performing a heat treatment and a step of forming a group III nitride crystal film on the group III nitride seed substrate to obtain a group III nitride crystal A method is disclosed.

  Japanese Patent Application Laid-Open No. 2006-071354 (Patent Literature 2) discloses a method of evaluating the crystal quality of a surface layer of a group III nitride crystal by using an X-ray diffraction method in a direction from a crystal surface to a depth direction. This is a method for evaluating the crystallinity of the crystal surface layer by evaluating the change in the crystallinity, wherein X is continuously adjusted so as to satisfy a diffraction condition (a diffraction condition by Bragg reflection) with respect to one crystal lattice plane of the crystal. By irradiating the crystal with X-rays while changing the line penetration depth, at least one of the variation of the half-width of the plane spacing and the half-width of the diffraction peak in the diffraction profile of the crystal lattice plane and the half-width of the rocking curve is measured. A method for evaluating the crystallinity of a crystal surface layer to be evaluated is disclosed.

  In addition, Katsuhiko Inaba, "Evaluation of GaN material by high-resolution X-ray diffraction method", Rigaku Journal, 44 (2), 2013, pp. 7-15 (Non-Patent Document 1) discloses GaN grown on a sapphire substrate. It discloses that forbidden reflection, which is considered to be derived from multiple reflection of a lattice plane that is not parallel to the surface, is observed in a high resolution X-ray diffraction ω-2θ scan of a thin film. Furthermore, J. Blasing and A. Krost, “X-ray multiple diffraction (Umweganregung) in wurtzite-type GaN and ZnO epitaxial layers”, phys.stat.sol., (A) 201, No. 4, 2004, pp. R17-R20 (Non-Patent Document 2) discloses that a diffraction peak is observed in a φ scan at ω-2θ of forbidden (0001) reflection of X-ray diffraction for a GaN thin film grown on a silicon substrate. .

JP 2013-203653 A JP 2006-071354 A

Katsuhiko Inaba, "Evaluation of GaN material by high resolution X-ray diffraction method", Rigaku Journal, 44 (2), 2013, pp. 7-15. J. Blasing and A. Krost, “X-ray multiple diffraction (Umweganregung) in wurtzite-type GaN and ZnO epitaxial layers”, phys.stat.sol., (A) 201, No. 4, 2004, pp.R17- R20

  Even if the gallium nitride crystal obtained by the method for manufacturing a group III nitride crystal disclosed in Japanese Patent Application Laid-Open No. 2013-203653 (Patent Document 1), the crystal quality is deteriorated when processing into a gallium nitride crystal substrate. There is a problem. Further, in the industry, in order to manufacture a semiconductor device with higher characteristics, development of a gallium nitride crystal substrate having higher crystal quality is required.

  Further, a method for evaluating the crystallinity of a crystal surface layer disclosed in Japanese Patent Application Laid-Open No. 2006-071354 (Patent Document 2) discloses a method of evaluating crystal quality such as uniform distortion, non-uniform distortion, and plane misorientation in a surface layer of a gallium nitride crystal. It is useful as an index for evaluating. However, there is a demand in the industry for the development of an evaluation method for evaluating the crystal quality of a gallium nitride crystal substrate having high crystal quality in more detail.

  Also, Katsuhiko Inaba, "Evaluation of GaN material by high-resolution X-ray diffraction method", Rigaku Journal, 44 (2), 2013, pp. 7-15 (Non-Patent Document 1), and J. Blasing and A. Krost, " X-ray multiple diffraction (Umweganregung) in wurtzite-type GaN and ZnO epitaxial layers ”, phys.stat.sol., (A) 201, No.4, 2004, pp.R17-R20 (Non-Patent Document 2) The diffraction peaks appearing in the ω-2θ scan and the φ scan in the obtained X-ray diffraction are not linked to a detailed evaluation of the crystal quality of the gallium nitride crystal substrate.

  In view of the above situation, an object of the present invention is to provide a gallium nitride crystal substrate having a high crystal quality and a crystal evaluation method for a gallium nitride crystal substrate capable of evaluating the crystal quality in detail.

  A gallium nitride crystal substrate according to one embodiment of the present invention is a gallium nitride crystal substrate having at least one main surface, wherein the main surface is a surface having an off angle from a (0001) plane of 0 ° or more and 2 ° or less. In an X-ray diffraction measurement using a small divergence incident X-ray parallel beam, a gallium nitride crystal substrate is arranged so that a main surface is exposed on a biaxially tilted sample table, and the normal to the (0001) plane is < The 0001> axis and the φ axis coincide with each other, and the [1-100] direction is adjusted to be the direction of φ = 0 °, and the φ axis at the incident angle ω and the diffraction angle 2θ for the 0001 symmetric forbidden Bragg reflection is adjusted. In the measurement of φ from −180 ° to 180 ° in the φ scan pattern measurement with the rotation axis as, the X-ray multiple diffraction pattern appearing by the multiple diffraction of X-rays in the crystal has φ from −180 ° to −60 °. , -60 And three 120 ° rotationally symmetric peak regions having a three-fold rotational symmetry that repeats every 120 ° from 90 ° to 60 ° and from 60 ° to 180 °, each 120 ° rotationally symmetric peak region being the φ of that region A region including the line indicating the angle of φ at the center of the range and the plane including the <0001> axis are mirrored surfaces, and have − and + regions that have mirror symmetry with respect to each other. And the -L region and the -R region having anti-symmetry with respect to the line indicating the angle of φ at the center and the intersection of the <0001> axis, and each + region is located at the center of the range of φ of that region. And a + L region and a + R region having a reciprocal symmetry with respect to a line indicating the angle of φ and the intersection of the <0001> axes. Each of the -L region, each -R region, each + L region, and each + R region Background in at least one of the regions The first reference peak intensity ratio, which is the ratio of the intensity of the first reference X-ray multiple diffraction peaks derived from at least (1-100) and (-1101) to the intensity, is 500 or more, and the first reference X-ray multiple diffraction peak is The second reference peak intensity ratio, which is the ratio of the intensity of the second reference multiple diffraction peaks derived from at least (02-21) and (0-220) with respect to the intensity of, is 0.18 or more.

  A gallium nitride crystal substrate according to one embodiment of the present invention is a gallium nitride crystal substrate having at least one main surface, wherein the main surface has an off angle of 0 ° or more and 2 ° or less from a (000-1) plane. In an X-ray diffraction measurement using a small-divergence incident X-ray parallel beam, a gallium nitride crystal substrate is arranged such that a main surface is exposed on a biaxially tilted sample table, and a (000-1) plane method is used. The <0001> axis which is a line coincides with the φ axis, and the [1-100] direction is adjusted to be the direction of φ = 0 °, and the incident angles ω and 000 for the 000-1 symmetric forbidden Bragg reflection are adjusted. In the measurement of φ from −180 ° to 180 ° in the φ scan pattern measurement using the φ axis as the rotation axis at the diffraction angle 2θ, the X-ray multiple diffraction pattern appearing by the multiple diffraction of X-rays in the crystal has φ of −180. ° to -60 ° Comprising three 120 ° rotationally symmetric peak regions having a threefold rotational symmetry that repeats every 120 ° from 60 ° to 60 ° and from 60 ° to 180 °, each 120 ° rotational symmetric peak region being A plane including the line indicating the angle of φ in the center of the range of φ and the plane including the <0001> axis is a mirror plane, and has − and + areas having mirror symmetry with respect to each other. A line indicating the angle of φ in the center of the range and a -L region and a -R region having a reciprocal symmetry with respect to the intersection of the <0001> axis, and each + region has a range of φ of the region. And a + L region and a + R region having a reciprocal symmetry with respect to a line indicating the angle of φ at the center and the intersection of the <0001> axes, and each -L region, each -R region, each + L region, and In at least one region of each + R region, The first reference peak intensity ratio, which is the ratio of the intensity of the first reference X-ray multiple diffraction peaks derived from at least (1-100) and (-1101) to the land intensity, is 750 or more; The second reference peak intensity ratio, which is the ratio of the intensity of the second reference multiple diffraction peaks derived from at least (02-21) and (0-220) to the peak intensity, is less than 0.18.

  A gallium nitride crystal substrate according to one embodiment of the present invention is a gallium nitride crystal substrate having two main surfaces, wherein one main surface has an off angle of 0 ° or more and 2 ° or less from a (0001) plane. And the other main surface is a surface having an off angle from the (000-1) plane of 0 ° or more and 2 ° or less, and in the X-ray diffraction measurement using a small divergence angle incident X-ray parallel beam for each main surface. A gallium nitride crystal substrate is arranged on the biaxially tilted sample stage such that each main surface is exposed, and the <0001> axis, which is the normal to the (0001) plane and the (000-1) plane, and the φ axis are aligned with each other. And the [1-100] direction is adjusted so that φ = 0 °. When the main surface is a surface whose off angle from the (0001) plane is 0 ° or more and 2 ° or less, 0001 symmetry forbidden. For Bragg reflection, when the main surface is a surface whose off angle from the (000-1) plane is 0 ° or more and 2 ° or less. Is the multiplexing of X-rays in the crystal in the φ scan pattern measurement from -180 ° to 180 ° with the φ axis as the rotation axis at the incident angle ω and the diffraction angle 2θ for the 000-1 symmetric forbidden Bragg reflection. The X-ray multiple diffraction pattern appearing by diffraction has a three-fold rotational symmetry where φ repeats every 120 ° from −180 ° to −60 °, from −60 ° to 60 °, and from 60 ° to 180 °. Two 120 ° rotationally symmetric peak regions, each 120 ° rotationally symmetric peak region being mirrored to each other with a plane including the line indicating the angle of φ in the center of the range of φ and the <0001> axis as the mirror plane. A-region and a + region having symmetry are provided. Each-region has a reciprocal symmetry with respect to an intersection of a line indicating the angle of φ in the center of the range of φ of the region and the <0001> axis. You A + L region having a -L region and a -R region, each + region having a reciprocal symmetry with respect to an intersection of a line indicating an angle of φ at the center of a range of φ of the region and an <0001> axis. And a + R region, in at least one of each of the -L region, each of the -R region, each of the + L region, and each of the + R region, being derived from at least (1-100) and (-1101) on two main surfaces. The value of the second reference peak intensity ratio, which is the ratio of the intensity of the second reference multiple diffraction peak derived from at least (02-21) and (0-220) to the intensity of the first reference X-ray multiple diffraction peak, is different from each other; The principal surface giving a larger second reference peak intensity ratio is a surface having an off angle from the (0001) plane of 0 ° or more and 2 ° or less.

  The crystal evaluation method for a gallium nitride crystal substrate according to one embodiment of the present invention has at least one main surface, and the main surface has an off angle of at least one of a (0001) plane and a (000-1) plane of 0. A method for evaluating a crystal of a gallium nitride crystal substrate having a surface of not less than 2 ° and not more than 2 ° by X-ray diffraction measurement using a small-divergence incident X-ray parallel beam, wherein a main surface is placed on a biaxially inclined sample stage. The gallium nitride crystal substrate is arranged so as to be exposed, the <0001> axis, which is the normal to the (0001) plane and the (000-1) plane, matches the φ axis, and the [1-100] direction is φ. = 0 °, and when the main surface is a surface whose off angle from the (0001) plane is 0 ° or more and 2 ° or less, the main surface is (000- 1) When the off angle from the surface is 0 ° or more and 2 ° or less Performing a φ scan pattern measurement with the φ axis as a rotation axis at an incident angle ω and a diffraction angle 2θ for the 000-1 symmetric forbidden Bragg reflection, the X-ray multiple diffraction peak obtained from the φ scan pattern measurement. From the magnitude of the first reference peak intensity ratio, which is the ratio of the intensity of the first reference X-ray multiple diffraction peaks derived from at least (1-100) and (-1101) to the height of symmetry and the background intensity, Evaluate the crystal quality of the gallium crystal substrate.

  According to the above, it is possible to provide a gallium nitride crystal substrate having a high crystal quality and a crystal evaluation method for the gallium nitride crystal substrate capable of evaluating the crystal quality in detail.

FIG. 1 is a schematic view illustrating an example of an X-ray parallel beam method used for a gallium nitride crystal substrate crystal evaluation method according to one embodiment of the present invention. FIG. 2 is a schematic diagram illustrating an example of an incident-side setting of an X-ray diffractometer used for the gallium nitride crystal substrate crystal evaluation method according to one embodiment of the present invention. FIG. 3 is a schematic view showing an example of the setting of the light receiving side of the X-ray diffraction apparatus used for the method for evaluating the crystal of a gallium nitride crystal substrate according to one embodiment of the present invention. FIG. 4A is a plan photograph showing an example of a biaxially tilted sample stage of an X-ray diffractometer used for the gallium nitride crystal substrate crystal evaluation method according to one embodiment of the present invention. FIG. 4B is a side view photograph showing an example of a biaxially tilted sample stage of the X-ray diffractometer used for the gallium nitride crystal substrate crystal evaluation method according to one embodiment of the present invention. FIG. 5 is a schematic diagram illustrating an example of 0002 symmetric Bragg reflection in the crystal evaluation method for a gallium nitride crystal substrate according to one embodiment of the present invention. FIG. 6 is a schematic diagram illustrating an example of 0001 symmetric forbidden Bragg reflection in the method for evaluating a gallium nitride crystal substrate according to one embodiment of the present invention. FIG. 7 is a schematic view showing an example of the (0001) plane and the (000-1) plane of the gallium nitride crystal substrate. FIG. 8 is a schematic view showing an example of the (0002) plane and the (000-2) plane of the gallium nitride crystal substrate. FIG. 9 is a schematic diagram showing the arrangement of gallium atoms and nitrogen atoms on a gallium nitride crystal substrate. FIG. 10 is a schematic plan view showing a crystal orientation and a region of a gallium nitride crystal in the method for evaluating the crystal quality of a gallium nitride crystal substrate according to one embodiment of the present invention. FIG. 11 is a schematic diagram illustrating an example of a φ scan in a region where each φ of the 0002 symmetric Bragg reflection and the 000-2 symmetric Bragg reflection of the gallium nitride crystal substrate according to one embodiment of the present invention is from −180 ° to 180 °. It is. FIG. 12 shows 360 ° X-ray multiplexing in a region where φ is from −180 ° to 180 ° when the main surface is substantially (0001) in the φ scan pattern measurement of the gallium nitride crystal substrate according to one embodiment of the present invention. It is the schematic which shows an example of a diffraction pattern on a vertical axis | shaft by a logarithmic scale. FIG. 13 shows 360 ° X-ray multiplexing in a region where φ is from −180 ° to 180 ° when the main surface is substantially (0001) plane in the φ scan pattern measurement of the gallium nitride crystal substrate according to one embodiment of the present invention. It is the schematic which shows an example of a diffraction pattern on a vertical axis | shaft by a square root scale. FIG. 14 shows 360 ° X in a region where φ is from −180 ° to 180 ° when the main surface is substantially (000-1) in the φ scan pattern measurement of the gallium nitride crystal substrate according to one embodiment of the present invention. It is the schematic which shows an example of a line multiple diffraction pattern on a vertical axis | shaft by a square root scale. FIG. 15 shows X-rays in the A- _L region when the main surface is substantially (0001) plane and substantially (000-1) plane in the φ scan pattern measurement of the gallium nitride crystal substrate according to one embodiment of the present invention. It is the schematic which shows an example of a multiple diffraction pattern. FIG. 16 shows X-rays in the _AR region when the main surface is substantially (0001) plane and substantially (000-1) plane in the φ scan pattern measurement of the gallium nitride crystal substrate according to one embodiment of the present invention. It is the schematic which shows an example of a multiple diffraction pattern. FIG. 17 shows X-rays in the A _{+ L} region when the main surface is substantially (0001) plane and substantially (000-1) plane in the φ scan pattern measurement of the gallium nitride crystal substrate according to one embodiment of the present invention. It is the schematic which shows an example of a multiple diffraction pattern. FIG. 18 shows X-rays in the A _{+ R} region when the main surface is substantially (0001) plane and substantially (000-1) plane in the φ scan pattern measurement of the gallium nitride crystal substrate according to one embodiment of the present invention. It is the schematic which shows an example of a multiple diffraction pattern.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

  [1] A gallium nitride crystal substrate according to an embodiment of the present invention is a gallium nitride crystal substrate having at least one main surface, wherein the main surface has an off angle from the (0001) plane of 0 ° or more and 2 ° or less. In the X-ray diffraction measurement using a small-divergence incident X-ray parallel beam, a gallium nitride crystal substrate is arranged so that the main surface is exposed on a biaxially inclined sample stage, and the method of (0001) plane The <0001> axis which is a line coincides with the φ axis, and the [1-100] direction is adjusted to be the direction of φ = 0 °, and the incident angle ω and the diffraction angle for the 0001 symmetric forbidden Bragg reflection are adjusted. In the measurement from φ of −180 ° to 180 ° in the φ scan pattern measurement using the φ axis as the rotation axis at 2θ, the X-ray multiple diffraction pattern that appears due to the multiple diffraction of X-rays in the crystal has a φ of −180 °. -60 ° With three 120 ° rotationally symmetric peak regions having a three-fold rotational symmetry that repeats every 120 ° from −60 ° to 60 ° and from 60 ° to 180 °, each 120 ° rotationally symmetric peak region comprising: The region including a line indicating the angle of φ in the center of the range of φ in the region and the plane including the <0001> axis is a mirror surface, and has − and + regions that have mirror symmetry with respect to each other. A line indicating the angle of φ at the center of the range of φ of the region and a -L region and a -R region having anti-rotational symmetry with respect to the intersection of the <0001> axis are provided. A line indicating the angle of φ at the center of the range of φ and a + L region and a + R region having a reciprocal symmetry with respect to an intersection of the <0001> axis are provided, each of -L region, each -R region, and each + L region. Region and at least one of the + R regions. The first reference peak intensity ratio, which is the ratio of the intensity of the first reference X-ray multiple diffraction peaks derived from at least (1-100) and (-1101) to the background intensity, is 500 or more; The second reference peak intensity ratio, which is the ratio of the intensity of the second reference multiple diffraction peaks derived from at least (02-21) and (0-220) to the peak intensity, is 0.18 or more. The gallium nitride crystal substrate of the present embodiment is different from a conventional gallium nitride crystal substrate in an X-ray multiple diffraction pattern having a main surface whose off angle from the (0001) plane (Ga plane) is 0 ° or more and 2 ° or less. In comparison, the crystal quality is high because it has high symmetry and a large first reference peak intensity ratio.

  [2] A gallium nitride crystal substrate according to an embodiment of the present invention is a gallium nitride crystal substrate having at least one main surface, wherein the main surface has an off angle of 0 ° or more from the (000-1) plane. ° or less, and in X-ray diffraction measurement using a small divergence angle incident X-ray parallel beam, the gallium nitride crystal substrate is arranged so that the main surface is exposed on the biaxially tilted sample stage, and the method of the main surface The <0001> axis which is a line coincides with the φ axis, and the [1-100] direction is adjusted to be the direction of φ = 0 °, and the incident angles ω and 000 for the 000-1 symmetric forbidden Bragg reflection are adjusted. In the measurement of φ from −180 ° to 180 ° in the φ scan pattern measurement using the φ axis as the rotation axis at the diffraction angle 2θ, the X-ray multiple diffraction pattern appearing by the multiple diffraction of X-rays in the crystal has φ of −180. ° to −60 °, − Comprising three 120 ° rotationally symmetric peak regions having a threefold rotational symmetry that repeats every 120 ° from 0 ° to 60 ° and from 60 ° to 180 °, each 120 ° rotationally symmetric peak region being A plane including the line indicating the angle of φ in the center of the range of φ and the plane including the <0001> axis is a mirror plane, and has − and + areas having mirror symmetry with respect to each other. A line indicating the angle of φ in the center of the range and a -L region and a -R region having a reciprocal symmetry with respect to the intersection of the <0001> axis, and each + region has a range of φ of the region. And a + L region and a + R region having a reciprocal symmetry with respect to a line indicating the angle of φ at the center and the intersection of the <0001> axes, and each -L region, each -R region, each + L region, and In at least one region of each + R region, The first reference peak intensity ratio, which is the ratio of the intensity of the first reference X-ray multiple diffraction peaks derived from at least (1-100) and (-1101) to the laser beam intensity, is 750 or more; The second reference peak intensity ratio, which is the ratio of the intensity of the second reference multiple diffraction peaks derived from at least (02-21) and (0-220) to the peak intensity, is less than 0.18. The gallium nitride crystal substrate of the present embodiment has a conventional gallium nitride crystal in an X-ray multiple diffraction pattern having a main surface whose off angle from the (000-1) plane (N plane) is 0 ° or more and 2 ° or less. Compared with the substrate, the crystal quality is high because it has high symmetry and a large first reference peak intensity ratio.

  [3] A gallium nitride crystal substrate according to one embodiment of the present invention is a gallium nitride crystal substrate having two main surfaces, wherein one main surface has an off angle of 0 ° or more and 2 ° from a (0001) plane. And the other main surface is a surface having an off angle from the (000-1) plane of 0 ° or more and 2 ° or less, and X using a small divergence angle incident X-ray parallel beam for each main surface. In the X-ray diffraction measurement, a gallium nitride crystal substrate was placed on a biaxially tilted sample stage such that each main surface was exposed. The <0001> axis, which is the normal to the (0001) plane and the (000-1) plane, and φ When the axis is aligned and the [1-100] direction is adjusted so that φ = 0 °, and the main surface is a surface whose off angle from the (0001) plane is 0 ° or more and 2 ° or less. Is the 0001 symmetric forbidden Bragg reflection, with the main surface having an off angle from the (000-1) plane of 0 ° or more and 2 ° or less In the case of the surface of に お け る, in the measurement of φ from −180 ° to 180 ° in the φ scan pattern measurement using the φ axis as the rotation axis at the incident angle ω and the diffraction angle 2θ for the 000-1 symmetric forbidden Bragg reflection, The X-ray multiple diffraction pattern appearing by the multiple diffraction of X-rays at 3 rotations every 120 ° from φ of −180 ° to −60 °, −60 ° to 60 °, and 60 ° to 180 ° It comprises three 120 ° rotationally symmetric peak regions with symmetry, each 120 ° rotationally symmetric peak region reflecting a plane containing a line indicating the central φ angle of the range of φ of the region and the <0001> axis. The surface includes a-region and a + region having mirror symmetry with respect to each other, and each-region rotates with respect to each other about an intersection of a line indicating the angle of φ in the center of the range of φ of the region and the <0001> axis. It has a -L region and a -R region having symmetry, and each + region has a reciprocal symmetry with respect to an intersection of a line indicating an angle of φ at the center of a range of φ of the region and the <0001> axis. And at least one of the -L region, the -R region, the + L region, and the + R region, at least (1-100) and (-1101) on the two main surfaces. )), A value of a second reference peak intensity ratio, which is a ratio of at least the intensity of the second reference multiple diffraction peak derived from (02-21) and (0-220) to the intensity of the first reference X-ray multiple diffraction peak. Are different from each other, and the main surface giving a larger second reference peak intensity ratio is a surface having an off angle from the (0001) plane of 0 ° or more and 2 ° or less. The gallium nitride crystal substrate of the present embodiment has an X-ray multiple diffraction pattern having a main surface whose off angle from the (0001) plane (Ga plane) is 0 ° or more and 2 ° or less and the (000-1) plane (N In any of the X-ray multiple diffraction patterns having a main surface having an off angle of 0 ° or more and 2 ° or less from (surface), since the X-ray multiple diffraction pattern has higher symmetry than a conventional gallium nitride crystal substrate, High crystal quality. In addition, the gallium nitride crystal substrate of the present embodiment has an off-state from the (0001) plane (Ga plane) based on the magnitude of the two second reference peak intensity ratios obtained from the X-ray multiple diffraction patterns of the two main planes. Since the principal surface whose angle is 0 ° or more and 2 ° or less is determined, the polarity can be determined without breaking the gallium nitride crystal substrate.

  [4] The crystal evaluation method for a gallium nitride crystal substrate according to one embodiment of the present invention has at least one main surface, and the main surface is formed from at least one of a (0001) plane and a (000-1) plane. A method for evaluating a crystal of a gallium nitride crystal substrate having an off angle of 0 ° or more and 2 ° or less by X-ray diffraction measurement using a small divergence angle incident X-ray parallel beam, comprising: The gallium nitride crystal substrate is arranged such that the main surface is exposed to the substrate, the [0001] axis, which is the normal to the (0001) plane and the (000-1) plane, and the φ axis coincide with each other, and [1-100 Adjusting the direction so that the direction is φ = 0 °, and, when the main surface is a surface whose off angle from the (0001) plane is 0 ° or more and 2 ° or less, the 0001 symmetric forbidden Bragg reflection is applied to the main surface. Has an off angle from the (000-1) plane of 0 ° or more and 2 ° or less Performing a φ scan pattern measurement with the φ axis as a rotation axis at an incident angle ω and a diffraction angle 2θ for a 000-1 symmetric forbidden Bragg reflection in the case of a surface, The magnitude of the first reference peak intensity ratio, which is the ratio of the intensity of the first reference X-ray multiple diffraction peak derived from at least (1-100) and (-1101) to the height of symmetry and background intensity of the multiple diffraction peaks. Therefore, the quality of the crystal of the gallium nitride crystal substrate is evaluated. In the method for evaluating a gallium nitride crystal substrate according to the present embodiment, in the X-ray diffraction measurement using a small divergence incident X-ray parallel beam, the higher the symmetry of the X-ray multiple diffraction peak obtained from the φ scan pattern measurement, the higher the symmetry. Also, as the first reference peak intensity ratio is larger, the crystal quality of the gallium nitride crystal substrate is higher, and the crystal quality of the gallium nitride crystal substrate can be evaluated in detail.

  [5] In the method for evaluating a crystal of a gallium nitride crystal substrate, at least the (02-21) and (0-220) of the second reference multiple diffraction peak with respect to the intensity of the first reference X-ray multiple diffraction peak on the main surface. The polarity of the crystal of the gallium nitride crystal substrate can be evaluated from the magnitude of the second reference peak intensity ratio, which is the intensity ratio. Such a crystal evaluation method for a gallium nitride crystal substrate determines the polarity of the gallium nitride crystal substrate without destroying the gallium nitride crystal substrate based on the magnitude of the second reference peak intensity ratio obtained from the X-ray multiple diffraction pattern of the main surface. it can.

  [6] In the above-described method for evaluating a crystal of a gallium nitride crystal substrate, the off-angle from the (0001) plane of the main surface when the second reference peak intensity ratio on the main surface is 0.18 or more is 0 ° or more and 2 ° or less. The main surface when the second reference peak intensity ratio on the main surface is less than 0.18 can be evaluated as a surface having an off angle from the (000-1) plane of 0 ° or more and 2 ° or less. Specifically, such a crystal evaluation method for a gallium nitride crystal substrate includes a method in which, when the second reference peak intensity ratio obtained from the X-ray multiple diffraction pattern of the main surface is 0.18 or more, the main surface is set to the (0001) plane. Is evaluated as a plane (polar plane) having an off angle from 0 ° to 2 °, and when the second reference peak intensity ratio obtained from the X-ray multiple diffraction pattern of the main plane is less than 0.18, the main plane Is evaluated as a plane (polar plane) having an off angle from the (000-1) plane of 0 ° or more and 2 ° or less, whereby the polarity can be determined without breaking the gallium nitride crystal substrate.

  [7] In the method for evaluating a crystal of a gallium nitride crystal substrate, the gallium nitride crystal substrate has two main surfaces, and at least (02-21) and the intensity of the first reference X-ray multiple diffraction peak on the two main surfaces. The values of the second reference peak intensity ratios, which are the ratios of the intensities of the second reference multiple diffraction peaks derived from (0-220), are different from each other, and the main surface giving the larger second reference peak intensity ratio is shifted from the (0001) plane. Can be evaluated as a surface having an off angle of 0 ° or more and 2 ° or less. According to such a crystal evaluation method for a gallium nitride crystal substrate, the plane (polarity) whose off angle from the (0001) plane is 0 ° or more and 2 ° or less is determined based on the magnitude of the two second reference peak intensity ratios obtained for the two principal planes. Since the main surface (plane) can be determined, the polarity can be determined without breaking the gallium nitride crystal substrate.

[Details of Embodiment of the Present Invention]
Embodiments of the present invention will be described below in detail with reference to the drawings. First, a crystal evaluation method for a GaN (gallium nitride) crystal substrate will be described, and then a GaN crystal substrate having a high crystal quality and a high polarity evaluated by the crystal evaluation method will be described. In the specification, the claims and the drawings of the present application, for a GaN crystal that is a hexagonal crystal, a specific crystal plane is represented by (hkil), and a set of equivalent crystal planes is defined as {hkil} based on crystal symmetry. Expressed by Also, a specific direction is represented by [hkill], and a set of equivalent directions is represented by <hkill> from the symmetry of the crystal. Here, h, k, i, and 1 are Miller indices. Here, there is a relationship of i = − (h + k). Usually, the Miller index is represented by 0, a natural number, and a number with a bar above the natural number. In the present specification and the drawings, a natural number with a bar is represented by adding a minus sign before the natural number. . For example, the notation of (11-20) is read as a crystal plane of "Ichi Ichi ni / Bar Zero", and the notation of [1-100] is expressed in the direction of "Ichi Ichi / Bar Zero Zero". Read.

<Embodiment 1: Crystal evaluation method of GaN crystal substrate>
Referring to FIGS. 1 to 3, the crystal evaluation method for a GaN crystal substrate of the present embodiment has at least one main surface, and the main surface is at least one of a (0001) plane and a (000-1) plane. A crystal of a GaN crystal substrate having an off angle of 0 ° or more and 2 ° or less (hereinafter, referred to as “at least one of a (0001) plane and a (000-1) plane”) from the incident side 0.5 mm x 0.5 mm, 0.8 mm x 0.8 mm, 1.5 mm x 0.8 mm, and 3.0 mm x 0.8 mm using an X-ray capillary lens (divergence angle 0.3 °) Using a small divergence incident X-ray parallel beam of CuKα ₁ monochromatic X-rays whose X-ray intensity was changed by changing the irradiation area by a cross slit, a 0.27 ° slit for reflectance measurement was provided on the light receiving side. .27 ° collimator and graphite flat This is a method of evaluating by X-ray diffraction measurement using a plate monochromator. In some cases, the measurement of the X-ray multiple diffraction peak is performed by removing the 0.27 ° slit on the light receiving side in order to increase the intensity of X-rays.

  Referring to FIGS. 4 to 10, 12 and 13, the GaN crystal substrate is arranged on the biaxially tilted sample stage such that the main surface is exposed, and the (0001) plane and the (000-1) plane are measured. A step of adjusting the <0001> axis, which is a line, to coincide with the φ axis, and adjusting the [1-100] direction to the direction of φ = 0 °, and setting the main surface to an off angle from the (0001) plane. Is 0 ° or more and 2 ° or less (hereinafter referred to as “substantially (0001) plane”), the off angle of the main surface from the (000-1) plane is 0 ° or more and 2 ° with respect to 0001 symmetric forbidden Bragg reflection. In the following planes (hereinafter referred to as “substantially (000-1) plane”), the φ scan pattern measurement using the φ axis as a rotation axis at the incident angle ω and the diffraction angle 2θ for the 000-1 symmetric forbidden Bragg reflection is performed. Performing the steps. Further, referring to FIGS. 13 to 18, the X-ray multiple diffraction peak obtained from the φ scan pattern measurement has at least the (1-100) and (−1101) derived from (1-100) with respect to the height of symmetry and background intensity. The quality of the crystal of the GaN crystal substrate is evaluated from the magnitude of the first reference peak intensity ratio, which is the ratio of the intensity of the one reference X-ray multiple diffraction peak.

  The crystal evaluation method for a GaN crystal substrate according to the present embodiment is the same as the crystal evaluation method for a GaN crystal substrate according to the embodiment, except that the X-ray diffraction measurement using a small-divergence incident X-ray parallel beam is performed from the φ scan pattern measurement. The higher the symmetry of the obtained X-ray multiple diffraction peak and the higher the first reference peak intensity ratio, the higher the crystal quality of the GaN crystal substrate, and the more the quality of the crystal of the GaN crystal substrate can be evaluated.

  In the method for evaluating the crystal quality of a GaN crystal substrate according to the present embodiment, a GaN crystal having at least one main surface and at least one of a substantially (0001) plane and a substantially (000-1) plane is used. In the X-ray diffraction measurement of the substrate, in addition to the large diffraction peak due to the 0002 symmetric Bragg reflection or the 000-2 symmetric Bragg reflection, the 0001 symmetric forbidden Bragg reflection and the 000-1 symmetric forbidden Bragg reflection determined from the structure factor indicated by the annihilation law This utilizes a diffraction peak observed at least at one of the reflection positions. Such diffraction is multiple diffraction on two or more strong crystal planes inside the crystal that are not parallel to the crystal surface, and is also referred to as Umweganregung (detour) diffraction. Such multiple diffraction is particularly well observed as the single crystal approaches a perfect crystal. Also, since the atoms of the crystal structure of the single crystal material are not a rigid sphere model in the theoretical calculation but have an atomic cloud extending in the direction of atomic bonding, the fact that the structural factor is not zero means that the background is Probable cause. Such a background area is an area where the above-mentioned multiple diffraction of X-rays has not occurred. In such multiple diffraction measurement, it is necessary to set the GaN crystal substrate using a biaxially tilted sample stage in order to match the <0001> axis of the GaN crystal substrate with the φ axis which is the rotation axis of the GaN crystal substrate. It is.

  The present inventors have proposed a φ scan with the [0001] axis as the rotation axis at the incident angle ω and the diffraction angle 2θ of 0001 symmetric forbidden Bragg reflection or 000-1 symmetric forbidden Bragg reflection using a small-divergence incident X-ray parallel beam. In the pattern measurement, the crystal quality inside the vicinity of the main surface of the GaN crystal substrate is measured by using the X-ray multiple diffraction peak observed by the multiple diffraction of X-rays on the crystal plane not parallel to the surface of the crystal inside the vicinity of the crystal surface. The crystal evaluation method of the GaN crystal substrate of the present embodiment for destructive evaluation has been completed.

  According to the method for evaluating a crystal of a GaN crystal substrate of the present embodiment, multiple diffraction of X-rays occurs on an internal crystal plane near the crystal surface depending on the rotation angle φ of φ scan with the <0001> axis as the rotation axis. It is suitable for evaluating uniformity in the crystal plane near the surface of the crystal substrate.

  In a conventional evaluation method of the crystal quality of a GaN crystal substrate, which uses the half-width of the diffraction peak due to 0002 symmetric Bragg reflection of the ω rocking curve in the ω-2θ measurement, the crystal in the depth direction from the main surface is used. Focusing on the structure, the incident angle ω of the 0002 symmetric Bragg reflection is 17.2833 °. On the other hand, in the crystal evaluation method of the GaN crystal substrate of the present embodiment, the incident angle ω of the 0001 symmetric forbidden Bragg reflection is 8.5428 °, and the incident angle is approximately half or less of the incident angle of the 0002 symmetric Bragg reflection. Because of this, the sample transmission thickness of X-rays on the main surface is reduced to approximately half, and the evaluation of crystal quality close to the main surface (that is, the crystal surface) becomes possible. It is considered preferable. Further, since the incident X-ray is a point-focused parallel beam having a dot shape of 0.5 mm × 0.5 mm, 0.8 mm × 0.8 mm, 1.5 mm × 0.8 mm, or 3.0 mm × 0.8 mm. By moving the measurement location in the plane, the in-plane uniformity and the like of the crystal structure in the plane near the main surface can be evaluated nondestructively.

(Structure setting of X-ray diffractometer)
The X-ray diffractometer can detect monochromatic X-rays with a monochromator, and is not particularly limited except that a parallel beam with a small divergence angle is used. It is preferable to use a goniometer method. The optical axis of the X-ray is fixed, and the incident angle ω, the diffraction angle (reflection angle) 2θ, the coordinates x, y, z of the GaN crystal substrate position, the rotation angle φ of the GaN crystal substrate, the tilt angle χ of the GaN crystal substrate, etc. Is set.

(Use of small divergence angle incident X-ray parallel beam)
In the crystal evaluation method of the GaN crystal substrate of the present embodiment, the φ scan pattern measurement with the [0001] axis of at least one of 0001 symmetric forbidden Bragg reflection and 000-1 symmetric forbidden Bragg reflection as a rotation axis is performed. Since it is necessary to reduce the divergence angle of the incident X-rays of the X-ray diffraction apparatus, a parallel beam method as shown in FIG. 1 is used.

(Setting of the incident side of the X-ray diffractometer)
Referring to FIGS. 1 and 2, in the parallel beam method, in order to obtain a parallel beam of X-rays, at least one of an X-ray capillary lens and a monocapillary is used in addition to the X-ray tube. In the parallel beam method using an X-ray capillary lens, a beam diameter of 0.3 mm × 0.3 mm is obtained, and in the parallel beam method using a monocapillary, a beam diameter of 0.1 mm is obtained. The divergence angle of X-rays is the same regardless of whether an X-ray capillary lens or a monocapillary is used, and the intensity of X-rays decreases when a monocapillary is used. Therefore, a parallel beam method using an X-ray capillary lens is preferable. . In the present embodiment, a point-focus Cu X-ray tube is operated at a voltage of 45 kV and a current of 40 mA as the X-ray tube. Further, the irradiation area is changed using a cross slit of 0.5 mm × 0.5 mm, 0.8 mm × 0.8 mm, 1.5 mm × 0.8 mm, and 3.0 mm × 0.8 mm using an X-ray capillary lens. As a result, a small divergence angle incident X-ray parallel beam whose X-ray intensity is changed is obtained. Here, there are a width W and a height H in the opening of the cross slit, the width W corresponds to the irradiation length of the X-ray in the lateral direction of the sample surface, and the height H is the spread of the X-ray in the vertical direction of the sample surface. And the open area W × H of the cross slit corresponds to the X-ray irradiation area. Since the X-ray capillary lens is formed by bundling mono-capillary lenses, the divergence angle of the parallel X-ray beam is the same even if the irradiation area changes, and does not affect the multiple diffraction. In the present embodiment, although a CuKa ₁ monochromatic X-ray by placing a graphite flat monochromator (CuKa ₁ monochromatic X-ray spectrometer for selection) on the light receiving side, CuKa ₁ monochromatic X-rays for selection on the incident side Can also be arranged.

The value of φ at which multiple diffraction peaks occur depends on the wavelength of X-rays and the reflecting surface of 0001 symmetric forbidden Bragg reflection or 000-1 symmetric forbidden Bragg reflection. In addition to CuKα ₁ (wavelength: 1.54 °), CuKβ (wavelength: 1.39 °) without a Ni filter can also be used.

(Setting on the light receiving part side of the X-ray diffractometer)
Referring to FIGS. 1 and 3, in order to detect a diffracted X-ray having a small divergence angle of the incident X-ray, a 0.27 ° collimator and a 0.27 ° slit for reflectance measurement are also used on the light receiving side. Although the above-mentioned slit is necessary for axially setting the GaN crystal substrate, the above-mentioned slit may be removed for the purpose of increasing the X-ray intensity for measuring the X-ray multiple diffraction peak. Further, since it is necessary to select a CuKa ₁ monochromatic X-rays, using a parallel plate graphite monochromator CuKa ₁ monochromatic X-ray for selection. By inserting the slits behind the collimator and cutting the X-rays spread in the horizontal direction, the intensity of the X-rays detected by the light receiving unit is reduced. By inserting the slit, the intensity of the X-ray to be detected is reduced, but mixing of the scattered X-ray is prevented. In the case of placing a CuKa ₁ monochromatic X-ray spectrometer for selection on the incident side may be omitted parallel plate graphite monochromator CuKa ₁ monochromatic X-ray for selection.

  When CuKβ is used as the X-ray source, a charge-coupled device (CCD) type high-speed semiconductor array detector (X′Celerator) that does not use a monochromator is used on the light receiving side.

(Sample stage setting of X-ray diffractometer)
A biaxially inclined sample stage is used as the sample stage. Referring to FIGS. 4A and 4B, the biaxially tilted sample stage is such that a part of the sample stage has a two-layer structure, and the tilt angles in the x-axis and y-axis directions are adjusted with the center at the lower side of the upper layer as a fulcrum. Screws of Sx and Sy are attached to each negative side of the x-axis and y-axis, and a fixed point with a spring is attached to the lower part of each positive side of the x-axis and the y-axis so that the normal direction of the upper surface of the sample table can be adjusted. A sample stage that can be adjusted. The GaN crystal substrate is cut out from a GaN crystal to have a normal direction and a crystal plane of a main surface (a surface having an off angle of 0 ° or more and 2 ° or less from a (0001) plane or a (000-1) plane) ( The normal direction of the (0001) plane or the (000-1) plane does not always match, and the φ axis, which is the rotation axis of the sample stage, and the (0001) of the GaN crystal substrate attached to the upper layer of the sample stage. ) Plane and (000-1) plane) do not necessarily coincide with the <0001> axis. However, by adjusting the biaxial inclination of the upper layer portion in the x-axis direction and the y-axis direction using the above-mentioned Sx and Sy screws (also referred to as “axis setting of the GaN crystal substrate”, the same applies hereinafter), The φ axis of the table and the <0001> axis, which is the normal to the (0001) plane and the (000-1) plane of the GaN crystal substrate attached to the upper layer of the biaxially inclined sample table, can be matched. it can.

(Step of arranging and adjusting a GaN crystal substrate on a biaxially inclined sample stage)
First, in the step of arranging the GaN crystal substrate on the biaxially inclined sample stage, the GaN crystal substrate is arranged on the upper layer of the biaxially inclined sample stage so that its main surface is exposed.

  The GaN crystal substrate arranged so that the main surface is exposed on the upper layer portion of the biaxially tilted sample stage is moved along the <0001> axis and the φ axis which are the normals of the (0001) plane and the (000-1) plane. There is no particular limitation on the step of adjusting the orientation so that it is the same and the [1-100] direction is set to the direction of φ = 0 °, but the following steps are preferred from the viewpoint of efficient adjustment.

First, 0002 symmetric Bragg reflection and 000-2 symmetric Bragg reflection of a GaN crystal substrate having at least one main surface and the main surface being at least one of a substantially (0001) plane and a substantially (000-1) plane The detector is installed at at least one of the diffraction positions of the reflection (the incident angle ω is 17.2833 °, the diffraction angle 2θ is 34.5666 °, and the tilt angle の of the GaN crystal substrate is 0.0 °). The value of the axis is determined in advance, the ω rocking curve that changes the incident angle ω of the 0002 symmetric Bragg reflection or the 000-2 symmetric Bragg reflection at φ = 0 ° for adjustment in the x-axis direction is measured, and the maximum peak position ω Record _max0 .

Next, at φ = 180 °, the ω rocking curve of the 0002 symmetric Bragg reflection or the 000-2 symmetric Bragg reflection is measured in the same manner as described above, and the maximum peak position ω _max180 is recorded. Sx is adjusted so that the difference Δω _x = ω _max0 −ω _max180 becomes a value of 0.001 ° or less (adjustment of the x-axis). A z-axis scan is performed to determine an accurate z-axis value at the peak position (adjustment of the z-axis).

Then, for adjustment in the y-axis direction, the ω rocking curve of the 0002 symmetric Bragg reflection or the 000-2 symmetric Bragg reflection was measured at φ = 90 ° and φ = 270 ° in the same manner as described above, and the position of the maximum peak was measured. the difference Δω _y = _ω max90 -ω max270 between omega _Max90 and omega _Max270 to adjust the Sy so that the value of 0.001 ° or less (the adjustment of y-axis). An accurate z-axis value is determined at the peak position by performing z-axis scanning (adjustment of z-axis: change of z-value).

  As described above, the adjustment of the x-axis and the z-axis and the adjustment of the y-axis and the z-axis are repeated several times, and the crystal plane of the GaN crystal substrate (for example, The normal direction of the (0001) plane or the (000-1) plane) is made to coincide with the φ axis. At this time, the offset value of ω is determined so that the value of ω corresponds to the 2θ angle of 0002 symmetric Bragg reflection or 000-2 symmetric Bragg reflection. In this state, in order to optimize the tilt angle χ (Chi) of the biaxially tilted sample stage, χ scan is performed, and the offset value of χ is determined.

  Next, in order to make the rotation angle φ of the φ axis coincide with the azimuth of the <0001> axis, the diffraction position of the 10-11 asymmetric Bragg reflection (incident angle ω is 18.4370 °, diffraction angle 2θ is 36.8740, The detector is set at an angle ６１ of 61.96 °), φ scan is performed, and the position of the peak generated in the [1-100] direction is set to φ = 0 ° to determine the offset value of φ.

  The coincidence between the <0001> axis and the φ axis adjusted as described above can be confirmed as follows. That is, referring to FIG. 11, φ scan is performed over 360 ° from −180 ° to 180 ° at the peak position of diffraction angle 2θ of 0002 symmetric Bragg reflection of the GaN crystal substrate. At the peak position of the diffraction angle 2θ of the 000-2 symmetric Bragg reflection of the GaN crystal substrate, φ scan is performed over 360 ° from -180 ° to 180 °. The ideal result of these φ scans is that the peak intensity is uniform with φ. However, actually, pulsation occurs due to the accuracy of adjusting the coincidence between the <0001> axis and the φ axis. Since the width of the pulsation (the width of the minimum value with respect to the maximum value) is caused by the crystal structure near the main surface even after the above-described axis setting of the GaN crystal substrate, the pulsation width should be small (for example, the maximum value). On the other hand, 25% or less, preferably 20% or less, more preferably 15% or less) indicates the uniformity of the crystal of the GaN crystal substrate.

(Measurement of forbidden Bragg reflection)
Referring to FIG. 6, in the step of performing the φ scan pattern measurement using the <0001> axis of the 0001 symmetric forbidden Bragg reflection as the rotation axis, when the rotation angle φ of the GaN crystal substrate is scanned from −180 ° to 180 °, A highly symmetric diffraction pattern appears (see FIGS. 12 and 13). 5 and FIG. 6, the incident angle ω in the 0002 symmetric Bragg reflection measurement is 17.2833 °, whereas the incident angle ω in the 0001 symmetric forbidden Bragg reflection measurement is 8.5428 °, which is almost half. Therefore, the crystal quality near the crystal surface can be known in detail.

  FIG. 5 describes the relationship between the incident angle ω, the diffraction angle 2θ, and the φ axis with respect to the 0002 symmetric Bragg reflection on the (0002) plane, but 000 in the (000-2) plane on the opposite side of the (0002) plane. The incident angle ω, the diffraction angle 2θ, and the φ axis for the -2 symmetric Bragg reflection have the same relationship. When the crystal of the GaN crystal substrate is uniform and uniform, as shown in FIG. 11, the 000-2 symmetric Bragg reflection is larger than the 0002 symmetric Bragg reflection, the former has a maximum intensity of 37344 cps, and the latter has a maximum intensity of 35714 cps. Larger than.

  FIG. 6 describes the relationship between the incident angle ω, the diffraction angle 2θ, and the φ-axis for the 0001 symmetric forbidden Bragg reflection on the (0001) plane, and 000− in the (000-1) plane on the opposite side of the (0001) plane. The incident angle ω, the diffraction angle 2θ, and the φ axis for one symmetric forbidden Bragg reflection have a similar relationship.

(Evaluation of crystal quality of GaN crystal substrate)
The crystal quality near the main surface, which is the crystal surface, is determined based on at least (1-100) and (-1100) relative to the symmetry and background intensity of the X-ray multiple diffraction peak obtained from the φ scan pattern measurement. Evaluation is made from the magnitude of the first reference peak intensity ratio, which is the ratio of the multiple diffraction peak intensities. Here, a GaN crystal substrate having a higher crystal quality has a higher symmetry of the X-ray multiple diffraction peak and a higher first reference peak intensity ratio. Therefore, the symmetry of the X-ray multiple diffraction peak is higher and the first reference peak is higher. It is evaluated that the higher the intensity ratio, the higher the crystal quality of the GaN crystal substrate.

(Relationship between forbidden Bragg reflection measurement and crystal structure of GaN crystal substrate)
The relationship between the φ scan pattern measurement using the [0001] axis of the 0001 symmetric forbidden Bragg reflection or the 000-1 symmetric forbidden Bragg reflection as the rotation axis and the crystal structure of the GaN crystal substrate will be described below.

(1) Crystal Structure of GaN Crystal Substrate The GaN crystal forming the GaN crystal substrate has a hexagonal wurtzite crystal structure. As for the lattice constants, a (a ₁ = a ₂ = a ₃ ) is 0.31891 nm and c is 0.51855 nm. The (0001) plane and (000-1) plane shown in FIG. 7 (together, the {0001} plane (c plane)) shown in FIG. 7 and the (0002) plane and (000-2) plane shown in FIG. (They include the {0002} plane (referred to as (c / 2) plane).) Fig. 8 shows the arrangement of Ga atoms and N atoms in the crystal lattice. The crystal substrate has a polarity in the <0001> axis (c-axis) direction based on the crystal structure and the arrangement of Ga atoms and N atoms, where the (0001) plane is a Ga plane composed of Ga atoms and (000). -1) The plane is an N plane composed of N atoms.

(2) Relationship between X-ray incident direction and crystal orientation on GaN crystal substrate The GaN crystal forming the GaN crystal substrate has a hexagonal wurtzite-type crystal structure, and has a space group no. It has a six-fold antisymmetry of 186 P6 ₃ mc, but has three-fold rotational symmetry in a plane perpendicular to the c-axis. Therefore, when the [1-100] direction is made to coincide with the direction of φ = 0 °, the GaN crystal substrate has a crystal orientation shown in FIG. A region A (a region where φ is −60 ° to 60 °), a B region (a region where φ is 60 ° to 180 °) and a C region (a region where φ is −180 ° to −60 °) Divide into regions.

The A region is an A _- region (a region where φ is from −60 ° to 0 °) and A ₊ which have a mirror symmetry with respect to a plane including a line indicating φ = 0 ° and a plane including the <0001> axis. It is divided into regions (regions where φ is from 0 ° to 60 °). The B region is a B ₋ region (a region where φ is from 60 ° to 120 °) and a B ₊ region having a mirror symmetry with respect to each other with a plane including a line indicating φ = 120 ° and a plane including the <0001> axis as a mirror plane. (Region where φ is from 120 ° to 180 °). The C region is a C _- region (a region in which φ is from −180 ° to −120 °) having a mirror symmetry with respect to a plane including a line indicating φ = −120 ° and a plane including the <0001> axis as a mirror plane. C ₊ region (region where φ is from −120 ° to −60 °).

The A _- region further includes an A- _L region (a region where φ is from -60 ° to -30 °) which has anti-symmetry with respect to the intersection of the line indicating φ = −30 ° and the <0001> axis. And an _AR region (φ is from −30 ° to 0 °). The A ₊ region includes an A _{+ L} region (a region where φ is from 0 ° to 30 °) and an A _{+ R} region having anti-rotational symmetry with respect to the line indicating φ = 30 ° and the intersection of the <0001> axis. (Φ is from 30 ° to 60 °). B _- area further, phi = 90 ° line and shows the <0001> and B _-L regions having mutually times antisymmetry around the intersection of the axis (region from phi is 60 ° to 90 °) B _{- R} region (φ is from 90 ° to 120 °). B ₊ area further, phi = 150 ° line and shows the <0001> B _{+ L} region having mutually times antisymmetry around the intersection of the axis (phi a region to 150 ° from 120 °) and B _{+ R} region (φ is from 150 ° to 180 °). The C _- region further has a C- _L region (a region in which φ is from -180 ° to -150 °) having anti-symmetry with respect to a line indicating φ = −150 ° and an intersection of the <0001> axis. And a _CR region (φ is from −150 ° to −120 °). The C ₊ region is further a C _{+ L} region (a region where φ is from -120 ° to -90 °) having anti-symmetry with respect to a line indicating φ = −90 ° and an intersection of the <0001> axis. And a C _{+ R} region (φ is from −90 ° to −30 °). In this manner, the crystal plane perpendicular to the c-axis has a φ of −180 ° to 180 °, a C _−L region, a C _−R region, a C _{+ L} region, a C _{+ R} region, an A _−L region, and an A region. _The region is divided into twelve divided regions: a _-R region, an A _{+ L} region, an A _{+ R} region, a B _-L region, a B _-R region, a B _{+ L} region, and a B _{+ R} region.

In the φ scan pattern measurement, φ is a C- _L region from −180 ° to −150 °, a C− _R region from −150 ° to −120 °, a C _{+ L} region from −120 ° to −90 °, C _{+ R} region from −90 ° to −60 °, A _−L region from −60 ° to −30 °, A _−R region from −30 ° to 0 °, A ₊ from 0 ° to 30 ° _L region, A _{+ R} region from 30 ° to 60 °, B _-L region from 60 ° to 90 °, B _-R region from 90 ° to 120 °, B _{+ L} region from 120 ° to 150 ° , And when divided into 12 segmented regions of 30 ° from the B _{+ R} region from 150 ° to 180 °, at least two regions of each segmented region are derived from a predetermined plurality of crystal planes arbitrarily specified. Reference X-ray multiple diffraction peaks (eg, a first reference derived from at least (1-100) and (-1101)) X-ray multiple diffraction peaks derived from another predetermined plurality of crystal planes arbitrarily specified other than the reference peak for the peak intensity of the X-ray multiple diffraction peak (for example, X-rays other than the first reference X-ray multiple diffraction peak) It is preferable to evaluate the crystal quality of the GaN crystal substrate from the small variation in the contrast peak intensity ratio, which is the ratio of the peak intensities (multiple diffraction peaks). Here, the variation of the contrast peak intensity ratio refers to any one of the variance, the standard deviation, and the range (difference between the maximum value and the minimum value) of the corresponding contrast peak intensity ratio in at least two regions of each of the divided regions. It can be a value. According to such a method for evaluating a crystal of a GaN crystal substrate, the smaller the variation in the relative peak intensity ratio, the higher the crystal quality of the GaN crystal substrate, and the more detailed the crystal quality of the GaN crystal substrate can be evaluated.

Referring to FIGS. 12 to 14, a GaN crystal substrate having a substantially (0001) plane or a substantially (000-1) plane as a main surface appears in a measurement where φ in the X-ray incident direction is from −180 ° to 180 °. A typical X-ray multiple diffraction pattern has three rotation symmetries that repeat every 120 ° from φ from −180 ° to −60 °, from −60 ° to 60 °, and from 60 ° to 180 °. It has a 120 ° rotationally symmetric peak region (A region, B region, and C region). Each 120 ° rotationally symmetric peak region (A region, B region, or C region) is the angle of φ (φ = 0 °, φ = 120 °, or φ = −120 °) at the center of the range of φ in that region. Area (A _- area, B _- area, or C _- area) and + area (A ₊ area, B ₊ area) having mirror symmetry with respect to each other, with the plane including , Or C ₊ region). Each -region (A _- region, B _- region, or C _- region) is the central φ angle (φ = −30 °, φ = 90 °, or φ = −150 °) of the range of φ in that region. -L region (A- _L region, B- _L region, or C- _L region) and -R region (A- _R region, B _-R region or C _-R region). Each + region (A ₊ region, B ₊ region, or C ₊ region) has a central φ angle (φ = 30 °, φ = 150 °, or φ = −90 °) of the range of φ of the region. The + L region (A _{+ L} region, B _{+ L} region, or C _{+ L} region) and the + R region (A _{+ R} region, B _{+ R} ) which have anti-symmetry with respect to the intersection of the line shown and the [0001] axis. Region or C _{+ R} region). Here, “symmetry” in the symmetry and the mirror symmetry relationship of the X-ray multiple diffraction pattern refers to a position where the positions of the background region (region where X-ray multiple diffraction does not occur) and the X-ray multiple diffraction peak region are symmetric. , And does not mean that the number and intensity of each X-ray multiple diffraction peak in the X-ray multiple diffraction peak region are symmetric.

  FIG. 12 and FIG. 13 show X-ray multiple diffraction patterns in φ scan of φ from −180 ° to 180 ° for 0001 symmetric forbidden Bragg reflection of a GaN crystal substrate having a substantially (0001) main surface. Here, FIG. 12 shows the intensity on the vertical axis on a logarithmic scale, and FIG. 13 shows the intensity on the vertical axis on a square root scale. FIG. 14 shows an X-ray multiple diffraction pattern in a φ scan from −180 ° to 180 ° for 000-1 symmetric forbidden Bragg reflection of a GaN crystal substrate having a substantially (000-1) principal plane, and the vertical axis represents the vertical axis. Are shown on a square root scale. Referring to FIGS. 12 to 14, regardless of whether the main surface of the GaN crystal substrate is substantially the (0001) plane or the substantially (000-1) plane, φ is from −180 ° to 180 °. The background intensity of the X-ray multiple diffraction pattern in the scan is uniform. Thus, by using the biaxially inclined sample stage, the <0001> axis of the GaN crystal substrate can be made to coincide with the φ axis, which is the rotation axis of the GaN crystal substrate, with high accuracy, and the precision of the GaN crystal substrate can be improved. It can be seen that crystal evaluation is possible.

Referring to FIGS. 13 to 18, when the A _{+ R} region shown in FIG. 18 the basic division area, A _{+ L} area shown in FIG. 17 is anti-basic division times in the relationship A _{+ R} region and times antisymmetric an area, a _-R area shown in FIG. 16 is a basic partitioned area movies with times anti mirrors symmetrical relationship mirroring and a _{+ L} region, a _-L region shown in FIG. 15 a _{+ R} region and mirror This is a reflection basic division area having a reflection symmetry relationship. Considering such symmetry, the two X-ray multiple diffraction peak groups present in the A _{+ R} region (FIG. 18) are represented as mp1 and mp2, and the two X-ray diffraction peak groups existing in the A _{+ L} region (FIG. 17) The group of X-ray multiple diffraction peaks can be represented as mp1 ′ and mp2 ′ by attaching a “′” symbol indicating anti-symmetry to mp1 and mp2. A _-R area two multiple peaks present in the (FIG. 16) is assigned the "() m" symbol showing the mirror-symmetrical to mp1 'and mp2', (mp1 ') m and (mp2') It can be expressed as m. The two X-ray multiple diffraction peak groups present in the A- _L region (FIG. 15) are marked with "() m" indicating the reflection symmetry of mp1 and mp2, and have (mp1) m and (mp2) m It can be expressed as.

  Referring to FIG. 15 to FIG. 18, for each of the above-described divided regions of the GaN crystal substrate having a substantially (0001) main surface and the Ga crystal substrate having a substantially (000-1) main surface, mp1 and the above A maximum of six X-ray multiple diffraction peaks in the group of X-ray multiple diffraction peaks corresponding to the symmetry relationship, and a maximum of eight X-ray multiple diffraction peaks in the group of multiple X-ray diffraction peaks corresponding to the above-mentioned symmetry relationship, in total Up to 14 X-ray multiple diffraction peaks are seen. From this fact, in the actual X-ray multiple diffraction measurement of a GaN crystal substrate, it is conceivable that the number of X-ray multiple diffraction peaks may decrease due to the overlap or lack of some X-ray multiple diffraction peaks. In the case of a crystal having no defect theoretically derived from the structure), it is considered that 14 X-ray multiple diffraction peaks exist.

  Referring to FIGS. 15 to 18, for a GaN crystal substrate having a substantially (0001) main surface and a Ga crystal substrate having a substantially (000-1) main surface, respective X-ray multiplexing in the above-described basic division region is performed. The positions of the diffraction peak groups are in good agreement. Here, that the positions of the respective X-ray multiple diffraction peak groups are in good agreement means that the difference in the number of peaks of each of the X-ray multiple diffraction peak groups having a symmetrical relationship is two or less, and It means that the difference between the positions of the peaks in a certain X-ray multiple diffraction peak group exceeds 2 ° and two or less. Here, the fact that the positions of the respective X-ray multiple diffraction peak groups are in good agreement means that the GaN crystal substrate has high symmetry. That is, the symmetry of the GaN crystal substrate is evaluated by the degree of coincidence of the positions of the respective X-ray multiple diffraction peak groups of the GaN crystal substrate, and the degree of coincidence of the respective X-ray multiple diffraction peak groups of the GaN crystal substrate is large. As the GaN crystal substrate becomes higher, the symmetry is higher and the crystal quality is higher.

Indexing of X-ray multiple diffraction peaks of mp1 and mp2 in the A _{+ R} region of a GaN crystal substrate having a substantially (0001) plane as a main surface, the position, peak intensity ratio, and multiple diffraction types (at least two The diffraction surface is shown in Table 1. For indexing of X-ray multiple diffraction peaks and identification of multiple diffraction types, see J. Blasing and A. Krost, “X-ray multiple diffraction (Umweganregung) in wurtzite-type GaN and ZnO epitaxial layers”, phys. sol., (a) 201, No. 4, 2004, pp. R17-R20 (Non-Patent Document 2). P1 to P3 and P5 to P10 in the indexing peak column in Table 1 indicate the indexing peaks shown in the above literature. In the above-mentioned document, a multiple diffraction type indicating at least two diffraction planes each participating in X-ray multiple diffraction is assigned to the indexing peak.

  In the above document, in the GaN crystal substrate of the present embodiment, the peak No. derived from at least (1-100) and (-1101) having the maximum peak intensity in the range of 360 ° scan in many cases. The X-ray multiple diffraction peak of 8 is indexed as P6. Further, in the GaN crystal substrate of the present embodiment, an indexing peak P4 not found at present is also described. In the indexing peak P4, φ is almost the same as the indexing peak P5 (φ is smaller than P5 by 0.002 °), and the multiple diffraction type is (02-22) / (0-22-1). Have been. Here, in the range of φ of 30 °, only 10 X-ray multiple diffraction peaks are obtained in the above-mentioned document, but in the present embodiment, 14 X-ray multiple diffraction peaks are found. . In the above document, multiple reflections were calculated by Bragg reflection from two crystal planes. However, actual multiple reflections may be caused by two or more crystal planes, and a new peak is generated by two or more crystal planes. It is considered to occur.

  The peak No. derived from at least the above (1-100) and (-1101) shown in Table 1. Since the X-ray multiple diffraction peak of No. 8 has the maximum peak intensity in many cases, it is considered to be the most effective peak for evaluating the crystal quality of the GaN crystal substrate, and is referred to as a first reference X-ray multiple diffraction peak (S1). . The crystal quality of the GaN crystal substrate depends on the magnitude of the first reference peak intensity ratio (S1 / BG ratio), which is the ratio of the intensity of the first reference X-ray multiple diffraction peak (S1) to the background (BG) intensity. Is evaluated, and the higher the first reference peak intensity ratio, the higher the crystal quality.

  Here, as for the intensity of the X-ray multiple diffraction peak, the intensity value at the peak of the peak is read. That is, the intensity of the first standard X-ray multiple diffraction peak (S1) is the intensity value of the peak of the peak, and the intensity of the second standard X-ray multiple diffraction peak (S2) described later is the intensity value of the peak of the peak. is there. The intensity of the X-ray multiple diffraction peak is hardly changed in the range of 1 second to 50 seconds for the measurement time for each step of φ of 0.02 °, and the measurement of the X-ray multiple diffraction peak is intended to shorten the measurement time. For example, 3 seconds.

  The background intensity is measured with an accuracy of 2 digits or more by increasing the measurement time for each step of a flat portion between the first reference X-ray multiple diffraction peak (S1) and the second reference X-ray multiple diffraction peak (S2). A value of a certain intensity is read (specifically, an average value of a plurality of points is taken). In order to set the accuracy of the background intensity measurement to two digits or more, the range between the first reference X-ray multiple diffraction peak (S1) and the second reference X-ray multiple diffraction peak (S2) is measured for each step. Is set to 10 seconds or more (preferably in the range of 15 seconds to 50 seconds) to measure the background (BG) intensity.

(Evaluation of polarity of GaN crystal substrate)
Referring to FIGS. 15 to 18, in each of the basic divided regions, the intensity of 14 X-ray multiple diffraction peaks on the substantially (0001) main surface of the GaN crystal substrate is substantially the same as that of the same GaN crystal substrate (000-1). The differences from the intensities of the 14 X-ray multiple diffraction peaks on the main surface of ()) differ between the X-ray multiple diffraction peaks having the corresponding symmetry. For example, among X-ray multiple diffraction peaks having relatively high intensity, peak No. 8, the first reference X-ray multiple diffraction peak (S1) is substantially (000) in comparison with a substantially (0001) plane (that is, a substantially Ga plane; a plane having an off angle from the Ga plane of 0 ° or more and 2 ° or less; the same applies hereinafter). -1) plane (that is, substantially N-plane; a plane having an off angle from the N-plane of 0 ° or more and 2 ° or less, the same applies hereinafter), while the peak intensity becomes extremely high. In the X-ray multiple diffraction peak of No. 7, the peak intensity on the substantially (0001) plane and the peak intensity on the substantially (000-1) plane are substantially the same. Therefore, the peak Nos. Derived from at least (02-21) and (0-220) shown in Table 1. 7 as the second reference X-ray multiple diffraction peak (S2), the polarity of the GaN crystal substrate depends on the intensity of the first reference X-ray multiple diffraction peak (S1). It is evaluated based on the magnitude of the second reference peak intensity ratio (S2 / S1 ratio), which is the ratio of the intensity of the diffraction peak (S2). Specifically, when the second reference peak intensity ratio is 0.18 or more, preferably 0.20 or more, the main surface at that time is evaluated as a substantially (0001) plane (ie, a substantially Ga plane). You. When the second reference peak intensity ratio is less than 0.18, preferably 0.16 or less, the principal surface at that time is evaluated as a substantially (000-1) plane (that is, a substantially N plane).

  In addition, for a GaN crystal substrate having two main surfaces, a main surface of a substantially (0001) plane and a main surface of a substantially (000-1) plane, the X-ray multiple diffraction peaks of one main surface and the other main surface are used. When the values of the obtained second reference peak intensity ratios are different from each other, the principal surface giving the larger second reference peak intensity ratio is evaluated as substantially (0001) (that is, substantially Ga surface).

(Evaluation of crystal quality considering polarity of GaN crystal substrate)
As described above, the crystal quality of the GaN crystal substrate is evaluated by the magnitude of the first reference peak intensity ratio (the intensity ratio of the first reference X-ray multiple diffraction peak to the background intensity). In the case of a GaN crystal substrate, even if the crystal quality is almost the same, the intensity of the first reference X-ray multiple diffraction peak on the substantially (0001) plane (substantially Ga plane) main surface is substantially (000) due to its polarity. -1) The intensity of the first reference X-ray multiple diffraction peak on the main surface (substantially N surface) is different. Therefore, in consideration of the polarity, the GaN crystal substrate has a first reference peak intensity ratio of 500 or more when the main surface is substantially (0001) plane (substantially Ga plane) and / or the main surface has substantially (000-1). ) Plane (substantially N plane), the crystal quality is high when the first reference peak intensity ratio is 750 or more, and the first reference peak intensity ratio when the main surface is substantially (0001) plane (substantially Ga plane) is 650. The crystal quality is higher when the first reference peak intensity ratio is 950 or more when the above and / or the main surface is substantially (000-1) plane (substantially N plane), and the main surface is substantially (0001) plane (substantially Ga plane). Surface), the crystal quality is further improved when the first reference peak intensity ratio is 800 or more and / or when the main surface is substantially (000-1) plane (substantially N plane). It is evaluated as high. Here, the first reference peak intensity ratio and the second reference peak intensity ratio are determined by a 0.5 mm × 0.5 mm cross slit using an X-ray capillary lens (divergence angle: 0.3 °) on the incident side. Using the obtained CuKα ₁ monochromatic X-ray, a small divergence incident X-ray parallel beam, a 0.27 ° collimator (without a 0.27 ° slit) and a graphite flat plate monochromator for reflectance measurement are used on the light receiving side. It should be obtained in the X-ray diffraction measurement.

  In the case of a crystal having polarity, such as a GaN crystal substrate, with respect to the structure factor that determines the intensity of X-ray Bragg reflection, the structure factor F (h, k, l) is not equal to F (-h, -k, -l) for the other polar plane (for example, the (000-1) plane which is the N plane). In evaluating the quality and polarity of the crystal, a ratio obtained by dividing the intensity of the X-ray multiple diffraction peak by the background intensity is used. In the intensity of the X-ray multiple diffraction peak, a difference in intensity due to the above-described difference in the structure factor appears. . In the case of a GaN crystal substrate, the (0001) plane is a Ga plane (polar plane), and the (000-1) plane is an N plane (polar plane). Since the intensity of the X-ray multiple diffraction peak corresponding to such a polar plane is determined, it is necessary to perform crystal evaluation by specifying the polar plane. In other words, even for crystals of the same type and quality, if the polar planes to be evaluated are different, the intensity of the X-ray multiple diffraction peak to be evaluated is different. Therefore, it is necessary to determine a reference value for each polar plane to be evaluated.

  The crystal quality can be determined to be high quality as the intensity of the X-ray diffraction peak is larger and the half-width of the X-ray diffraction peak is smaller. Therefore, the X-ray diffraction peak intensity in the symmetric Bragg reflection and the X-ray diffraction in the symmetric forbidden Bragg reflection can be determined. It is possible to use line multiplex diffraction peak intensity and the like. Also in the case of the X-ray diffraction peak intensity in the symmetric Bragg reflection, the normal line (for example, the <0001> axis) of the crystal plane (for example, the (0001) plane, the (000-1) plane) using the biaxially inclined sample stage. When the crystal and the rotation axis (φ axis) of the crystal are made to coincide with each other, the intensity corresponding to the polarity can be measured. However, the X-ray diffraction peak in symmetric Bragg reflection is easily affected by the surface state of the main surface, and the intensity of the peak is different if the crystal state of one main surface is different from that of the other main surface.

  When the intensity of the X-ray multiple diffraction peak is used, as described above, the peak No. depending on the polarity is used. 8 (at least the first reference X-ray multiple diffraction peak (S1) derived from (1-100) and (-1101)) and the peak No. 8 independent of polarity. 7 peaks (at least a second reference multiple diffraction peak (S2) derived from (02-21) and (0-220)), and a second reference to the intensity of the first reference X-ray multiple diffraction peak (S1). The polarity can be determined from the second reference peak intensity ratio (S2 / S1 ratio), which is the intensity ratio of the multiple diffraction peaks (S2). In this case, even if the crystal states of the one main surface and the other main surface are different, there is an advantage that the polarity can be determined without any problem because the X-ray multiple diffraction is a phenomenon inside the crystal. Therefore, the evaluation method using the intensity of the X-ray multiple diffraction peak is expected to be widely applicable to polar crystals other than the GaN crystal substrate.

<Embodiment 2: GaN crystal substrate>
[Embodiment 2-1]
Referring to FIG. 13 and FIGS. 15 to 18, the GaN crystal substrate of the present embodiment is a GaN crystal substrate having at least one main surface, and the main surface is substantially (0001) plane (that is, (0001) plane). Off-angle from the surface of 0 ° or more and 2 ° or less). In X-ray diffraction measurement using a small divergence incident X-ray parallel beam, a GaN crystal substrate is arranged so that a main surface is exposed on a biaxially tilted sample stage, and <0001> is a normal line of a (0001) plane. Axis is aligned with the φ axis, and the [1-100] direction is adjusted so that φ = 0 °, and the φ axis at the incident angle ω and the diffraction angle 2θ for the 0001 symmetric forbidden Bragg reflection is rotated. In the measurement in which φ is −180 ° to 180 ° in the φ scan pattern measurement with the axis as the axis, the X-ray multiple diffraction pattern that appears due to the multiple diffraction of X-rays in the crystal has φ ranging from −180 ° to −60 °, − It comprises three 120 ° rotationally symmetric peak regions with a triple rotational symmetry that repeats every 60 ° from 60 ° to 60 ° and from 60 ° to 180 °. Each of the 120 ° rotationally symmetric peak regions is a-region and a + region that have mirror symmetry with respect to each other, with a plane including the line indicating the angle of φ in the center of the range of φ and the <0001> axis as a mirror plane. Is provided. Each − region includes a line indicating the angle of φ at the center of the range of φ of the region and a −L region and a −R region having anti-rotational symmetry about the intersection of the <0001> axis. Each + region includes a line indicating the angle of φ in the center of the range of φ of the region and a + L region and a + R region having anti-rotational symmetry about an intersection of the <0001> axis. First reference X-ray multiple diffraction peaks derived from at least (1-100) and (-1101) with respect to the background intensity in at least one of the -L region, -R region, + L region, and + R region. The first reference peak intensity ratio, which is the ratio of the intensity of the first reference X-ray multiple diffraction peak, is at least 500, and the second reference multiple diffraction peak derived from at least (02-21) and (0-220) with respect to the intensity of the first reference X-ray multiple diffraction peak. Is a second reference peak intensity ratio of 0.18 or more. The GaN crystal substrate of the present embodiment has a higher symmetry and a larger first reference peak intensity compared to a conventional GaN crystal substrate in an X-ray multiple diffraction pattern having a substantially (0001) plane (substantially Ga plane) as a main surface. And the crystal quality is high.

Here, the first reference peak intensity ratio and the second reference peak intensity ratio are determined by a 0.5 mm × 0.5 mm cross slit using an X-ray capillary lens (divergence angle: 0.3 °) on the incident side. Using the obtained CuKα ₁ monochromatic X-ray, a small divergence incident X-ray parallel beam, a 0.27 ° collimator (without a 0.27 ° slit) and a graphite flat plate monochromator for reflectance measurement are used on the light receiving side. It should be obtained in the X-ray diffraction measurement.

  Here, "symmetry" in the rotational symmetry and the mirror symmetry of the X-ray multiple diffraction pattern means that the position of the multiple peak region is symmetric, and each X-ray in the multiple diffraction peak region is not symmetric. It does not mean that the position and intensity of the line multiple diffraction peak are symmetric. That is, a high symmetry of the GaN crystal substrate means that the positions of the X-ray multiple diffraction peak groups having a symmetrical relationship are in good agreement, and specifically, the respective X-ray multiple diffraction peak groups having a symmetrical relationship. Means that the difference in the number of peaks is 2 or less, and that the difference between the positions of the peaks in each symmetric X-ray multiple diffraction peak group exceeds 2 ° is 2 or less.

  In the GaN crystal substrate whose main surface is a substantially (0001) plane (that is, a substantially Ga plane) in the present embodiment, the first reference peak intensity ratio is 500 or more, preferably 650 or more from the viewpoint of high crystal quality. And more preferably 800 or more. From the viewpoint of clearly determining the polarity of the crystal, the second reference peak intensity ratio is 0.18 or more, preferably 0.20 or more.

In the crystal evaluation of the GaN crystal substrate of the present embodiment, the principal surface is a substantially {0001} plane (substantially a Ga surface), and an X-ray capillary lens is used on the incident side and a W0.5 mm × H0.5 mm cross slit is used. Using a point-focused CuKα ₁ monochromatic X-ray small divergence incident X-ray parallel beam, a GaN crystal substrate is arranged on a biaxially tilted sample stage such that the main surface is exposed, and is a normal to the (0001) plane. The <0001> axis is matched with the φ axis, and the [1-100] direction is adjusted so that φ = 0 °, and a 0.27 ° collimator (0) for reflectance measurement is provided on the light receiving side. In the X-ray diffraction measurement using a .27 ° slit and a graphite flat plate monochromator, the incident angle ω and the diffraction angle 2θ of the 0001 symmetric forbidden Bragg reflection (that is, the incident angle ω: 8.5428 ° and the diffraction angle 2θ: 7.0856 °) with the <0001> axis as the rotation axis, from the viewpoint of obtaining a detailed and accurate X-ray multiple diffraction pattern, the measurement φ angle step is 0.02 ° and the angle range of φ to be measured. Is performed under measurement conditions in a range of 1 second to 50 seconds in each step.

The GaN crystal substrate having a substantially (0001) plane (substantially Ga plane) in the present embodiment is preferably a free-standing substrate. Since such a GaN crystal substrate is a free-standing substrate having high crystal quality, it is suitably used for manufacturing semiconductor devices. Here, the GaN crystal substrate preferably has a thickness of 250 μm or more in order to be a free-standing substrate.
In the present embodiment, the GaN crystal substrate whose main surface is substantially (0001) plane (substantially Ga plane) preferably has a thickness of 250 μm or more, more preferably 300 μm or more, and still more preferably 400 μm or more. Since such a GaN crystal substrate is a substrate having a high crystal quality and a thickness of 250 μm or more, it is suitably used for manufacturing a semiconductor device. Further, the diameter of the GaN crystal substrate of the present embodiment is preferably 50 mm or more, more preferably 75 mm or more, and even more preferably 100 mm or more. Since such a GaN crystal substrate is a substrate having a high crystal quality and a diameter of 50 mm or more, it is suitably used for manufacturing a semiconductor device. Although 2 inches is exactly 50.8 mm, a substrate having a diameter of 50 mm may be called a 2 inch substrate in the art.

(Manufacturing method of GaN crystal substrate)
The method of manufacturing a GaN crystal substrate having a substantially (0001) plane (substantially Ga plane) according to the present embodiment includes a step of growing a GaN crystal on a base substrate, and a step of growing the grown GaN crystal in a nitrogen gas atmosphere. The method includes a step of performing heat treatment twice or more under high temperature and high pressure conditions of not less than 1 ° C. and not less than 1800 atm, and a step of processing the heat-treated GaN crystal into a GaN crystal substrate. In the method of manufacturing a GaN crystal substrate according to the present embodiment, a GaN crystal substrate having high crystal quality can be obtained by processing a GaN crystal that has been heat-treated twice or more under high-temperature and high-pressure conditions of 900 ° C. or higher and 1800 atm or higher.

  The heat treatment of the grown GaN crystal at least twice is performed in a nitrogen atmosphere at a processing temperature of 900 ° C. or higher from the viewpoint of improving the crystal quality of a GaN crystal substrate obtained by processing the GaN crystal after the heat treatment. , Preferably at a temperature of at least 1000 ° C., and a processing pressure of at least 1800 atm, preferably at least 2,000 atm. Further, from the specifications of the manufacturing apparatus, the processing temperature is preferably 1200 ° C. or lower, and the processing pressure is preferably 2000 atm or lower.

[Embodiment 2-2]
Referring to FIGS. 14 to 18, the GaN crystal substrate of the present embodiment is a GaN crystal substrate having at least one main surface, and the main surface is substantially (000-1) plane (that is, (000-1) ) Plane from 0 ° to 2 °). In the X-ray diffraction measurement using the small divergence incident X-ray parallel beam, the GaN crystal substrate is arranged so that the main surface is exposed on the biaxially tilted sample stage, and the normal to the (000-1) plane is < The 0001> axis and the φ axis coincide with each other, and the [1-100] direction is adjusted to be the direction of φ = 0 °, and the incident angle ω and the diffraction angle 2θ for the 000-1 symmetric forbidden Bragg reflection are adjusted. In the measurement of φ in the range of −180 ° to 180 ° in the φ scan pattern measurement using the φ axis as the rotation axis, the X-ray multiple diffraction pattern that appears due to the multiple diffraction of X-rays in the crystal has a φ of −180 ° to −60 °. And three 120 ° rotationally symmetric peak regions with a threefold rotational symmetry that repeats every 120 ° from −60 ° to 60 ° and from 60 ° to 180 °. Each of the 120 ° rotationally symmetric peak regions is a-region and a + region that have mirror symmetry with respect to each other, with a plane including the line indicating the angle of φ in the center of the range of φ and the <0001> axis as a mirror plane. Is provided. Each − region includes a line indicating the angle of φ at the center of the range of φ of the region and a −L region and a −R region having anti-rotational symmetry about the intersection of the <0001> axis. Each + region includes a line indicating the angle of φ in the center of the range of φ of the region and a + L region and a + R region having anti-rotational symmetry about an intersection of the <0001> axis. First reference X-ray multiple diffraction peaks derived from at least (1-100) and (-1101) with respect to the background intensity in at least one of the -L region, -R region, + L region, and + R region. The first reference peak intensity ratio, which is a ratio of the intensity of the first reference X-ray multiple diffraction peak, is at least 750, and the second reference multiple diffraction peak derived from at least (02-21) and (0-220) with respect to the intensity of the first reference X-ray multiple diffraction peak. Is less than 0.18. The GaN crystal substrate of the present embodiment has higher symmetry and a larger first reference peak intensity ratio in the X-ray multiple diffraction pattern having the (0001) plane (Ga plane) as a main surface, as compared with the conventional GaN crystal substrate. Therefore, the crystal quality is high.

Here, the first reference peak intensity ratio and the second reference peak intensity ratio are determined by a 0.5 mm × 0.5 mm cross slit using an X-ray capillary lens (divergence angle: 0.3 °) on the incident side. Using the obtained CuKα ₁ monochromatic X-ray, a small divergence incident X-ray parallel beam, a 0.27 ° collimator (without a 0.27 ° slit) and a graphite flat plate monochromator for reflectance measurement are used on the light receiving side. It should be obtained in the X-ray diffraction measurement.

  Here, “symmetric” and “GaN” in the rotational symmetry and the mirror symmetry of the X-ray multiple diffraction pattern on the GaN crystal substrate whose main surface is substantially the (000-1) plane (that is, substantially the N plane) are used. The meaning of “the crystal substrate has high symmetry” is the same as in the case of the GaN crystal substrate having the substantially (0001) plane (substantially Ga plane) in Embodiment 2-1 and will not be repeated here.

  In the GaN crystal substrate having a substantially (000-1) plane (substantially N plane) in the present embodiment, the first reference peak intensity ratio is 750 or more, preferably 950, from the viewpoint of high crystal quality. Or more, more preferably 1100 or more. Further, from the viewpoint of clearly defining the polarity of the crystal, the second reference peak intensity ratio is less than 0.18, and preferably 0.16 or less.

  In the crystal evaluation of the GaN crystal substrate whose main surface is substantially (000-1) plane (substantially N plane) in the present embodiment, the main surface of Embodiment 2-1 is substantially (0001) plane (substantially Ga plane). Since it is similar to the case of the GaN crystal substrate, it will not be repeated here. In addition, the advantage of the GaN crystal substrate whose main surface is a substantially (000-1) plane (substantially N plane) of the present embodiment being a self-standing substrate, its thickness and its diameter are also described in Embodiment 2-1. This is the same as the case of a GaN crystal substrate having a substantially (0001) plane (substantially Ga plane), and thus will not be repeated here. In the method of manufacturing a GaN crystal substrate whose main surface is substantially (000-1) plane (substantially N plane) according to the present embodiment, the main surface of Embodiment 2-1 is substantially (0001) plane (substantially Ga plane). Since it is similar to the case of the GaN crystal substrate, it will not be repeated here.

[Embodiment 2-3]
Referring to FIGS. 13 to 18, the GaN crystal substrate of the present embodiment is a GaN crystal substrate having two main surfaces, and one main surface is substantially (0001) plane (that is, from the (0001) plane). The off angle is a surface of 0 ° or more and 2 ° or less), and the other main surface is substantially a (000-1) surface (that is, a surface having an off angle of 0 ° or more and 2 ° or less from a (000-1) surface). is there. In X-ray diffraction measurement using a small divergence incident X-ray parallel beam for each main surface, a GaN crystal substrate is arranged on a biaxially tilted sample stage such that each main surface is exposed, and the (0001) plane and the ( The <0001> axis, which is the normal to the 000-1) plane, is aligned with the φ axis, and the [1-100] direction is adjusted so that φ = 0 °. ) Plane, for 0001 symmetric forbidden Bragg reflection, and when the main surface is substantially (000-1) plane, for 000-1 symmetric forbidden Bragg reflection. In the scan pattern measurement in which φ is from −180 ° to 180 °, the X-ray multiple diffraction pattern that appears due to the multiple diffraction of X-rays in the crystal has φ of −180 ° to −60 ° and −60 ° to 60 °. Up to ° and 60 ° With three 120 ° rotational symmetry peak region having a 3-fold rotational symmetry repeats every 120 ° until et 180 °. Each of the 120 ° rotationally symmetric peak regions is a-region and a + region that have mirror symmetry with respect to each other, with a plane including the line indicating the angle of φ in the center of the range of φ and the <0001> axis as a mirror plane. Is provided. Each − region includes a line indicating the angle of φ at the center of the range of φ of the region and a −L region and a −R region having anti-rotational symmetry about the intersection of the <0001> axis. Each + region includes a line indicating the angle of φ in the center of the range of φ of the region and a + L region and a + R region having anti-rotational symmetry about an intersection of the <0001> axis. First reference X-ray multiple diffraction derived from at least (1-100) and (-1101) on two main surfaces in at least one region of each -L region, each -R region, each + L region, and each + R region. The value of the second reference peak intensity ratio, which is the ratio of the intensity of the second reference multiple diffraction peaks derived from at least (02-21) and (0-220) to the peak intensity, is different from each other, and is larger than the second reference peak intensity. The principal surface giving the ratio is a substantially (0001) surface. The GaN crystal substrate of the present embodiment has a conventional GaN crystal in both an X-ray multiple diffraction pattern having a substantially (0001) plane as a main surface and an X-ray multiple diffraction pattern having a substantially (000-1) plane as a main surface. Compared with a crystal substrate, it has higher symmetry, and thus has higher crystal quality. Further, the GaN crystal substrate of the present embodiment has a substantially (0001) plane (substantially Ga plane) (polarity) based on the magnitude of the two second reference peak intensity ratios obtained from the X-ray multiple diffraction patterns of the two main surfaces. Since the main surface is determined, the polarity can be determined without breaking the GaN crystal substrate.

  Regarding the meaning of “symmetry” and “high symmetry of the GaN crystal substrate” in the rotational symmetry and the mirror symmetry of the X-ray multiple diffraction pattern in the GaN crystal substrate of the present embodiment, the crystal evaluation is substantially (0001) plane. Is the same as the case of the GaN crystal substrate in which the main surface of the embodiment 2-1 is a substantially (0001) plane (substantially Ga plane). Since the main surface of 2-2 is similar to the case of a GaN crystal substrate having a substantially (000-1) plane (substantially N plane), it will not be repeated here. Regarding the thickness and diameter of the GaN crystal substrate of this embodiment, the main surface of Embodiment 2-1 is a substantially (0001) plane (substantially Ga surface) and the main surface of Embodiment 2-2. Is similar to the case of a GaN crystal substrate having a substantially (000-1) plane (substantially N plane), and thus will not be repeated here. The method for manufacturing a GaN crystal substrate according to the present embodiment is the same as that of the GaN crystal substrate having the substantially (0001) plane (substantially Ga plane) in Embodiment 2-1 and will not be repeated here.

(Example 1)
1. Preparation of GaN Crystal Substrate A template having a main surface with an off angle of 0 ° or more and 2 ° or less from a (0001) plane on which GaN was grown on a sapphire substrate having a diameter of 76 mm by MOCVD (metal organic chemical vapor deposition). A substrate was prepared and used as a base substrate, placed on a substrate holder made of SiC coated with 85 mm in diameter and 20 mm in thickness, and placed in a reactor of an HVPE (hydride vapor phase epitaxy) apparatus. After heating the inside of the reactor to 1020 ° C., GaCl gas generated by reacting HCl gas with Ga and NH ₃ gas were supplied into the reactor. In the GaN layer growth process on such an undersubstrate, the reactor temperature is maintained at 1020 ° C. for 29 hours, the growth pressure is set to 1.01 × 10 ⁵ Pa, and the partial pressure of GaCl gas is set to 6.52 × 10 5 ^The pressure was ² Pa, the partial pressure of NH ₃ gas was 7.54 × 10 ³ Pa, and the partial pressure of HCl gas was 3.55 × 10 ¹ Pa. After the GaN layer growth step was completed, the temperature in the reactor was lowered to room temperature to obtain a GaN crystal. The obtained GaN crystal was grown using the (0001) plane as a crystal growth surface, and the thickness measured by a stylus-type film thickness meter was 3.5 mm.

  The obtained GaN crystal is processed on both its outer periphery and both the front (front) surface (the surface on the crystal growth surface side) and the back surface (the surface opposite to the crystal growth surface) (specifically, both surfaces are parallelized). And processed flat) to remove the affected layer (processed strained layer), and then heat-treated twice. For the heat treatment, a hot isostatic press (HIP) device made by Kobe Steel was used. The conditions of the two heat treatments were each set to 1200 ° C. for 20 hours in a nitrogen atmosphere at 2000 atm. After the above two heat treatments, the GaN crystal is collected from the HIP device, and both the front (front) surface and the back surface are polished to a mirror surface, and the work-altered layer (work strain layer) is removed on both surfaces. The substrate was processed into a GaN crystal substrate having a diameter of 2 inches (50.8 mm) and a thickness of 400 μm.

2. X-Ray Diffraction of GaN Crystal Substrate (1) Arrangement and Adjustment of GaN Crystal Substrate on Biaxial Tilt Sample Stage The above GaN crystal is placed on the biaxial tilt sample stage of an X-ray diffractometer (PANALYTICAL X'Pert MRD manufactured by Spectris Co., Ltd.). The substrate was arranged such that the main surface on the crystal growth surface side was exposed. The (0001) plane is obtained by adjusting the x-axis, the y-axis, and the z-axis to determine the offset value of the incident angle ω, the offset value of the tilt angle χ, and the offset value of the rotation angle φ. The <0001> axis, which is the normal line of the (000-1) plane, and the φ axis coincide with each other, and the [1-100] direction was adjusted so that φ = 0 °. Such adjustment, the small divergence angle incident X-ray parallel beam (incident side: Point focus for CuKa ₁ rays CuX ray tube operated at voltages 45kV and current 40mA the generated, divergence angle 0.3 ° X-ray capillary X-ray parallel beam obtained using a lens and a cross slit of width W 0.5 mm × height H 0.5 mm, light receiving side: 0.27 ° collimator (no 0.27 ° slit provided) and graphite plate monochromator, Xe proportional counter).

(2) Measurement of X-ray multiple diffraction peak of GaN crystal substrate Using the above small divergence incident X-ray parallel beam, measurement φ angle step is 0.02 °, and each step is performed according to the angle range of measurement φ. Under the measurement conditions in which the measurement time is in the range of 1 second to 50 seconds, at the position of 0001 symmetric forbidden Bragg reflection or 000-1 symmetric forbidden Bragg reflection (incident angle ω: 8.5428 °, diffraction angle 2θ: 17.0856 °). Φ scan was measured. X-ray multiple diffraction peaks similar to those in FIGS. 13 and 15 to 18 were measured. The main X of the A region (a region where φ is −60 ° to 60 °, that is, a region composed of four divided regions of an A _−L region, an A _−R region, an A _{+ L} region, and an A _{+ R} region) The results for the line multiple diffraction peaks are summarized in Tables 2 and 3.

The difference in the number of peaks of each of the symmetrical X-ray multiple diffraction peak groups in the four divided regions of the A- _L region, the A- _R region, the A _{+ L} region, and the A _{+ R} region is two or less. In addition, since the difference between the positions of the peaks of the respective X-ray multiple diffraction peak groups having a symmetrical relationship was more than 2 ° and not more than two, the positions of the respective X-ray multiple diffraction peak groups matched well. Thus, the symmetry of the GaN crystal substrate was high. Further, referring to Tables 2 and 3, the first reference X-ray with respect to the background (BG) intensity in four divided regions of the A _-L region, the A _-R region, the A ₊ region _L and the A _{+ R} region. The first reference peak intensity ratio (S1 / BG ratio), which is the ratio of the intensity of the multiple diffraction peaks (S1), was extremely high at 766 to 1161, and the crystal quality was evaluated to be extremely high. Further, the second reference X-ray multiple diffraction peak with respect to the intensity of the first reference X-ray multiple diffraction peak (S1) in four divided regions of the _AL region, the _AR region, the A _{+ L} region, and the A ₊ region _R. The second reference peak intensity ratio (S2 / S1 ratio), which is the intensity ratio of (S2), is 0.207 to 0.232, which is 0.18 or more. It was evaluated as a (0001) plane (that is, a substantially Ga plane) (polar plane).

3. Formation of Epitaxial Layer on GaN Crystal Substrate and Photoluminescence Measurement On the main surface of the GaN crystal substrate, a 3 μm-thick GaN layer was grown as an epitaxial layer by MOCVD. The photoluminescence emission intensity of the grown epitaxial layer was measured, and the results are summarized in Table 6.

(Example 2)
A GaN crystal substrate similar to that of Example 1 was produced. Except that the obtained GaN crystal substrate was placed on a biaxially inclined sample stage with the main surface on the side opposite to the crystal growth surface being exposed, the (0001) plane and the The <0001> axis, which is the normal line of the (000-1) plane, is aligned with the φ axis, and the [1-100] direction is adjusted so that φ = 0 °, as in the first embodiment. The X-ray multiple diffraction peak was measured under the following conditions. X-ray multiple diffraction peaks similar to those in FIGS. 14 to 18 were measured. The main X of the A region (a region where φ is −60 ° to 60 °, that is, a region composed of four divided regions of an A _−L region, an A _−R region, an A _{+ L} region, and an A _{+ R} region) The results for the line multiple diffraction peaks are summarized in Tables 4 and 5.

The difference in the number of peaks of each of the symmetrical X-ray multiple diffraction peak groups in the four divided regions of the A- _L region, the A- _R region, the A _{+ L} region, and the A _{+ R} region is two or less. In addition, since the difference between the positions of the peaks of the respective X-ray multiple diffraction peak groups having a symmetrical relationship was more than 2 ° and not more than two, the positions of the respective X-ray multiple diffraction peak groups matched well. Thus, the symmetry of the GaN crystal substrate was high. Further, referring to Tables 4 and 5, the first reference X-ray with respect to the background (BG) intensity in four divided regions of the A _-L region, the A _-R region, the A _{+ L} region, and the A _{+ R} region. The first reference peak intensity ratio (S1 / BG ratio), which is the ratio of the intensities of the multiple diffraction peaks (S1), was extremely high at 1188 to 1287, and the crystal quality was evaluated to be extremely high. Further, the second reference X-ray multiple diffraction peak with respect to the intensity of the first reference X-ray multiple diffraction peak (S1) in four divided regions of the A _-L region, the A _-R region, the A _{+ L} region, and the A _{+ R} region. The second reference peak intensity ratio (S2 / S1 ratio), which is the intensity ratio of (S2), is 0.144 to 0.159 and less than 0.18, and is opposite to the crystal growth surface of the present example. The main surface was evaluated to be a substantially (000-1) surface (that is, a substantially N surface).

(Reference Example 1)
A GaN crystal substrate was manufactured in the same manner as in Example 1 except that the heat treatment was not performed twice after the crystal growth. Regarding the obtained GaN crystal substrate, the (0001) plane and the (0001) plane were formed in the same manner as in Example 1 except that the main surface on the side opposite to the crystal growth plane was exposed and arranged on the biaxially inclined sample stage. The <0001> axis, which is the normal line of the (000-1) plane, is aligned with the φ axis, and the [1-100] direction is adjusted so that φ = 0 °, as in the first embodiment. The X-ray multiple diffraction peak was measured under the following conditions. This is the ratio of the intensity of the first reference X-ray multiple diffraction peak (S1) to the background (BG) intensity in four divided regions of the A- _L region, the A- _R region, the A _{+ L} region, and the A _{+ R} region. The first reference peak intensity ratio (S1 / BG ratio) was 320 to 400, which was less than 500, and it was evaluated that the crystal quality was not high. Further, the second reference X-ray multiple diffraction peak with respect to the intensity of the first reference X-ray multiple diffraction peak (S1) in four divided regions of the A _-L region, the A _-R region, the A _{+ L} region, and the A _{+ R} region. The second reference peak intensity ratio (S2 / S1 ratio), which is the intensity ratio of (S2), is 0.34 to 0.41 and 0.18 or more. The (0001) plane (that is, the substantially Ga plane) was evaluated.

  Further, a GaN layer having a thickness of 3 μm was grown as an epitaxial layer on the main surface of the GaN crystal substrate by MOCVD. The photoluminescence emission intensity of the grown epitaxial layer was measured, and the results are summarized in Table 6.

(Reference Example 2)
A GaN crystal substrate similar to that of Reference Example 1 was produced. Except that the obtained GaN crystal substrate was placed on a biaxially inclined sample stage with the main surface on the side opposite to the crystal growth surface being exposed, the (0001) plane and the The <0001> axis, which is the normal line of the (000-1) plane, is aligned with the φ axis, and the [1-100] direction is adjusted so that φ = 0 °, as in the first embodiment. The X-ray multiple diffraction peak was measured under the following conditions. This is the ratio of the intensity of the first reference X-ray multiple diffraction peak (S1) to the background (BG) intensity in four divided regions of the A- _L region, the A- _R region, the A _{+ L} region, and the A _{+ R} region. The first reference peak intensity ratio (S1 / BG ratio) was 375 to 550 and less than 750, and it was evaluated that the crystal quality was not high. Further, in four basic divisional regions of the A _-L region, the A _-R region, the A _{+ L} region and the A _{+ R} region, the second reference X-ray multiple diffraction with respect to the intensity of the first reference X-ray multiple diffraction peak (S1) is performed. The second reference peak intensity ratio (S2 / S1 ratio), which is the ratio of the intensity of the peak (S2), is 0.15 to 0.16 and less than 0.18, and is the side opposite to the crystal growth surface of the present example. Was evaluated to be a substantially (000-1) plane (that is, a substantially N plane).

  Referring to Table 6, the epitaxial layer grown on the main surface (that is, substantially (0001) plane (substantially Ga plane)) of the GaN crystal substrate of Reference Example 1 in which the crystal quality was not as high It was found that the luminescence intensity was low and the epitaxial layer was low in crystal quality. On the other hand, the epitaxial layer grown on the main surface (that is, the substantially (0001) plane (substantially Ga plane)) of the GaN crystal substrate of Example 1, which was confirmed to have extremely high crystal quality, has a photoluminescent property. It was found that the epitaxial layer had high emission intensity and high crystal quality.

  As described above, the crystal evaluation using the X-ray multiple diffraction peak in the 0001 symmetrical forbidden Bragg reflection or the 000-1 symmetrical forbidden Bragg reflection (that is, the first symmetry of the X-ray multiple diffraction peak, the first relative to the background (BG) intensity) The ratio of the intensity of the reference X-ray multiple diffraction peak (S1) (S1 / BG ratio), and the ratio of the intensity of the second reference X-ray multiple diffraction peak (S2) to the intensity of the first reference X-ray multiple diffraction peak (S1). (S2 / S1 ratio), etc., the crystal quality and polarity of the GaN crystal substrate with high crystal quality could be evaluated in detail.

  It should be understood that the embodiments and examples disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the embodiments and examples described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 Peak No. , S1 first reference X-ray multiplexing diffraction peaks, S2 second reference X-ray multiplexing diffraction _{peaks, A, A -, A +} , A -L, A -R, A + L, A + R, B, B -, _{B +, B -L, B -R} , B + L, B + R, C, C -, C +, C -L, C -R, C + L, C + R region, omega incident angle, 2 [Theta] diffraction Fold angle, χ angle, φ rotation angle.

Claims (7)

A gallium nitride crystal substrate having at least one major surface,
The main surface is a surface having an off angle from the (0001) plane of 0 ° or more and 2 ° or less,
In the X-ray diffraction measurement using a parallel beam of small divergence incident X-rays, the gallium nitride crystal substrate is arranged so that the main surface is exposed on a biaxially inclined sample stage, and is a normal line of the (0001) plane. The <0001> axis and the φ axis are aligned, and the [1-100] direction is adjusted so that the φ = 0 ° direction.
In the measurement of φ from −180 ° to 180 ° in the φ scan pattern measurement using the φ axis as the rotation axis at the incident angle ω and the diffraction angle 2θ for the 0001 symmetrical forbidden Bragg reflection, the multiple diffraction of X-rays in the crystal is performed. The resulting X-ray multiple diffraction pattern has three 120-fold rotational symmetries that repeat every 120 ° from φ from −180 ° to −60 °, from −60 ° to 60 °, and from 60 ° to 180 °. ° Rotationally symmetric peak area,
Each of the 120 ° rotationally symmetric peak regions is a − region and a + region having a mirror symmetry with respect to each other, with a plane including the line indicating the angle of φ in the center of the range of φ and the <0001> axis as a mirror plane. With
Each of the-regions includes a line indicating the angle of φ in the center of the range of φ of the region and -L regions and -R regions having anti-symmetrical symmetry with respect to the intersection of the <0001> axis,
Each of the + regions includes a line indicating the angle of φ in the center of the range of φ of the region and a + L region and a + R region having anti-rotational symmetry with respect to an intersection of the <0001> axis,
In at least one of the -L region, each -R region, each + L region, and each + R region, a first reference X derived from at least (1-100) and (-1101) with respect to background intensity. A first reference peak intensity ratio, which is a ratio of the intensity of the line multiplex diffraction peak, is 500 or more;
A second reference peak intensity ratio, which is a ratio of at least the intensity of the second reference multiple diffraction peak derived from (02-21) and (0-220) to the intensity of the first reference X-ray multiple diffraction peak, is 0.18 or more. A gallium nitride crystal substrate. A gallium nitride crystal substrate having at least one major surface,
The main surface is a surface having an off angle from the (000-1) plane of 0 ° or more and 2 ° or less,
In X-ray diffraction measurement using a parallel beam of small divergence incident X-rays, the gallium nitride crystal substrate is arranged on a biaxially inclined sample stage so that the main surface is exposed, and a normal to a (000-1) plane is set. Is adjusted so that the <0001> axis coincides with the φ axis, and the [1-100] direction is the direction of φ = 0 °.
Multiplexing of X-rays in the crystal in the measurement of φ in the range of −180 ° to 180 ° in the φ scan pattern measurement using the φ axis as the rotation axis at the incident angle ω and the diffraction angle 2θ for the 000-1 symmetric forbidden Bragg reflection The X-ray multiple diffraction pattern appearing by diffraction has a three-fold rotational symmetry where φ repeats every 120 ° from −180 ° to −60 °, from −60 ° to 60 °, and from 60 ° to 180 °. With two 120 ° rotationally symmetric peak regions,
Each of the 120 ° rotationally symmetric peak regions is a − region and a + region having a mirror symmetry with respect to each other, with a plane including the line indicating the angle of φ in the center of the range of φ and the <0001> axis as a mirror plane. With
Each of the-regions includes a line indicating the angle of φ in the center of the range of φ of the region and -L regions and -R regions having anti-symmetrical symmetry with respect to the intersection of the <0001> axis,
Each of the + regions includes a line indicating the angle of φ in the center of the range of φ of the region and a + L region and a + R region having anti-rotational symmetry with respect to an intersection of the <0001> axis,
In at least one of the -L region, each -R region, each + L region, and each + R region, a first reference X derived from at least (1-100) and (-1101) with respect to background intensity. A first reference peak intensity ratio, which is a ratio of the intensity of the line multiplex diffraction peak, is 750 or more;
A second reference peak intensity ratio, which is a ratio of at least the intensity of the second reference multiple diffraction peak derived from (02-21) and (0-220) to the intensity of the first reference X-ray multiple diffraction peak, is less than 0.18. A gallium nitride crystal substrate. A gallium nitride crystal substrate having two main surfaces,
One of the principal surfaces is a surface having an off angle from the (0001) plane of 0 ° or more and 2 ° or less, and the other principal surface has an off angle of 0 ° or more and 2 ° or less from the (000-1) plane. Plane
In X-ray diffraction measurement using a small divergence incident X-ray parallel beam on each of the main surfaces, the gallium nitride crystal substrate is arranged on a biaxially inclined sample stage such that the main surfaces are exposed, and (0001) The <0001> axis, which is the normal line of the) plane and the (000-1) plane, is aligned with the φ axis, and the [1-100] direction is adjusted to be the direction of φ = 0 °,
When the main surface is a surface having an off angle of 0 ° or more and 2 ° or less from the (0001) plane, the main surface has an off angle of 0 ° or more and 2 ° from the (000-1) plane for 0001 symmetric forbidden Bragg reflection. When the surface is less than or equal to 000-1 symmetrical forbidden Bragg reflection, in the φ scan pattern measurement with the φ axis as the rotation axis at the incident angle ω and the diffraction angle 2θ at the diffraction angle 2θ, in the measurement from −180 ° to 180 °, The X-ray multiple diffraction pattern appearing by the multiple diffraction of X-rays in the crystal repeats every 120 ° from φ ranging from −180 ° to −60 °, from −60 ° to 60 °, and from 60 ° to 180 °. Comprising three 120 ° rotationally symmetric peak regions with rotational symmetry,
Each of the 120 ° rotationally symmetric peak regions is a − region and a + region having a mirror symmetry with respect to each other, with a plane including the line indicating the angle of φ in the center of the range of φ and the <0001> axis as a mirror plane. With
Each of the-regions includes a line indicating the angle of φ in the center of the range of φ of the region and -L regions and -R regions having anti-symmetrical symmetry with respect to the intersection of the <0001> axis,
Each of the + regions includes a line indicating the angle of φ in the center of the range of φ of the region and a + L region and a + R region having anti-rotational symmetry with respect to an intersection of the <0001> axis,
In at least one of the -L region, the -R region, the + L region, and the + R region, the first derived from at least (1-100) and (-1101) on the two main surfaces. The value of the second reference peak intensity ratio, which is the ratio of the intensity of the second reference multiple diffraction peak derived from at least (02-21) and (0-220) to the intensity of the reference X-ray multiple diffraction peak, is different from each other and is larger. The gallium nitride crystal substrate, wherein the main surface giving the second reference peak intensity ratio is a surface having an off angle from the (0001) plane of 0 ° or more and 2 ° or less. A gallium nitride crystal substrate having at least one main surface, wherein the main surface is a surface having an off angle of at least 0 ° and not more than 2 ° from at least one of a (0001) plane and a (000-1) plane. A method of evaluating by X-ray diffraction measurement using a small divergence angle incident X-ray parallel beam,
The gallium nitride crystal substrate is arranged on the biaxially tilted sample stage such that the main surface is exposed, and the <0001> axis, which is a normal to the (0001) plane and the (000-1) plane, and the φ axis are aligned with each other. And adjusting the [1-100] direction so that φ = 0 °.
When the main surface is a surface having an off angle of 0 ° or more and 2 ° or less from the (0001) plane, the main surface has an off angle of 0 ° or more and 2 ° from the (000-1) plane for 0001 symmetric forbidden Bragg reflection. At a plane of less than or equal to 000-1 symmetrical forbidden Bragg reflection, at an incident angle ω and a diffraction angle 2θ, performing a φ scan pattern measurement with the φ axis as a rotation axis,
Ratio of the intensity of the first reference X-ray multiple diffraction peak derived from at least (1-100) and (-1101) to the height of symmetry and background intensity of the X-ray multiple diffraction peak obtained from the φ scan pattern measurement A gallium nitride crystal substrate crystal evaluation method, wherein the quality of the gallium nitride crystal substrate crystal is evaluated from the magnitude of the first reference peak intensity ratio.   A second reference peak intensity ratio, which is a ratio of the intensity of the second reference multiple diffraction peak derived from at least (02-21) and (0-220) to the intensity of the first reference X-ray multiple diffraction peak on the main surface. The crystal evaluation method for a gallium nitride crystal substrate according to claim 4, wherein the polarity of the crystal of the gallium nitride crystal substrate is evaluated based on the size.   When the second reference peak intensity ratio on the main surface is 0.18 or more, the main surface is evaluated as a surface having an off angle from the (0001) plane of 0 ° or more and 2 ° or less, and The gallium nitride according to claim 5, wherein the main surface when the second reference peak intensity ratio is less than 0.18 is evaluated as a surface having an off angle from the (000-1) plane of 0 ° or more and 2 ° or less. Crystal evaluation method for crystal substrate. The gallium nitride crystal substrate has two main surfaces,
A second reference peak intensity which is a ratio of at least the intensity of the second reference multiple diffraction peak derived from (02-21) and (0-220) to the intensity of the first reference X-ray multiple diffraction peak on the two main surfaces. The ratio values are different from each other,
The crystal evaluation method for a gallium nitride crystal substrate according to claim 5, wherein the main surface providing the larger second reference peak intensity ratio is evaluated as a surface having an off angle from the (0001) plane of 0 ° or more and 2 ° or less. .