JP2018024539A - C PLANE GaN SUBSTRATE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new C plane GaN substrate used for manufacturing a nitride semiconductor device and a bulk nitride semiconductor crystal, and a method for manufacturing the same.SOLUTION: A method for manufacturing a C plane GaN substrate 10 comprises: arranging a pattern mask having a periodic opening pattern provided on the polar surface of a GaN seed and composed of a linear opening; forming a gap between a GaN crystal and the pattern mask by ammonothermally growing the GaN crystal through the pattern mask; and growing the GaN crystal in a C axis direction; and processing the GaN crystal to obtain the C plane GaN substrate 10. In the C plane GaN substrate 10, when an X ray incident surface is parallel to each line segment when ω scanning on virtual line segments LS1 and LS2 drawn on the main surface of the C plane GaN substrate 10 and having a length of 40 mm and the XRC of (004) reflection is measured at an interval of 1 mm, the maximum value of FWHM of XRC among all measurement points is less than 30 arcsec and a difference between the maximum value and minimum value of peak angles of the XRC is less than 0.2°.SELECTED DRAWING: Figure 3

Description

  The present invention mainly relates to a C-plane GaN substrate.

GaN (gallium nitride) is a kind of III-V group compound semiconductor and has a wurtzite crystal structure belonging to the hexagonal system.
In recent years, GaN single crystal substrates have attracted attention as semiconductor substrates for nitride semiconductor devices.
Nitride semiconductors are also called nitride-based III-V compound semiconductors, III-nitride compound semiconductors, GaN-based semiconductors, and the like, including GaN, and part or all of GaN gallium in other periodic tables. Includes compounds substituted with Group 13 elements (B, Al, In, etc.).

One of the highly useful GaN single crystal substrates is a C-plane GaN substrate. The C-plane GaN substrate is a GaN single crystal substrate having a main surface parallel to the C-plane or slightly inclined from the C-plane.
The C-plane GaN substrate has a gallium polar surface that is the main surface on the [0001] side and a nitrogen polar surface that is the main surface on the [000-1] side. It is currently mainly gallium polar surfaces that are used to form nitride semiconductor devices.
Examples of producing a C-plane GaN substrate from a GaN single crystal grown by an ammonothermal method have been reported (Non-patent Documents 1 and 2).

In Patent Document 1, a GaN crystal is grown by an ammonothermal method on a C-plane GaN substrate provided with a stripe pattern mask. NH ₄ F (ammonium fluoride) is used alone as a mineralizer, and a GaN crystal film with a thickness of 160 to 580 μm having a flat upper surface has grown through a pattern mask. It is not clear whether the pattern mask was formed on the gallium polar surface or the nitrogen polar surface.

In Patent Document 2, a GaN single crystal is grown by an ammonothermal method on a C-plane GaN substrate provided with a stripe pattern mask on a nitrogen polar surface. NH ₄ F and NH ₄ I (ammonium iodide) are used in combination as mineralizers, and the GaN crystal does not coreless after passing through the pattern mask until the c-axis size reaches the order of millimeters [ It has grown in the [000-1] direction.
Non-Patent Document 3 reports the growth rate of GaN crystals when various ammonium halide mineralizers are used in the ammonothermal method.

JP 2014-1111527 A JP 2014-208571 A

R.Dwilinski, R.Doradzinski, J.Garczynski, LPSierzputowski, A.Puchalski, Y.Kanbara, K.Yagi, H.Minakuchi, H.Hayashi, “Excellent crystallinity of truly bulk ammonothermal GaN”, Journal of Crystal Growth 310 (2008) 3911-3916 R.Dwilinski, R.Doradzinski, J.Garczynski, L.Sierzputowski, R.Kucharski, M.Zajac, M. Rudzinski, R.Kudrawiec, J.serafnczuk, W.Strupinski, “Recent achievements in AMMONO-bulk method”, Journal of Crystal Growth 312 (2010) 2499-2502 Quanxi Bao, Makoto Saito, Kouji Hazu, Kentaro Furusawa, Yuji Kagamitani, Rinzo Kayano, Daisuke Tomida, Kun Qiao, Tohru Ishiguro, Chiaki Yokoyama, Shigefusa F. Chichibu, “Ammonothermal Crystal Growth of GaN Using an NH4F Mineralizer”, Crystal Growth & Design 4158-4161 (2013) 13

The object of the present invention includes providing a novel C-plane GaN substrate that can be preferably used in the manufacture of nitride semiconductor devices, bulk nitride semiconductor crystals, and the like.
The object of the present invention also includes providing a novel method for producing a C-plane GaN substrate.

Embodiments of the present invention include the following.
[1] A C-plane GaN substrate capable of drawing at least one first line segment, which is a virtual line segment having a length of 40 mm, satisfying at least one of the following conditions (A1) and (B1) on the main surface:
(A1) On the first line segment, when the X-ray incident surface at the time of each ω scan is parallel to the first line segment and (004) XRC of reflection is measured at intervals of 1 mm, between all measurement points The XRC FWHM maximum is less than 30 arcsec;
(B1) On the first line segment, when the X-ray incident surface at the time of each ω scan is parallel to the first line segment and (004) XRC of reflection is measured at intervals of 1 mm, between all measurement points The difference between the maximum value and the minimum value of the XRC peak angle is less than 0.2 °.
[2] The C-plane GaN substrate according to [1], wherein the first line segment satisfies the condition (A1). [3] The C-plane GaN substrate according to [2], wherein the first line segment satisfies the following condition (A2) in addition to the condition (A1): (A2) On the first line segment obtained from the XRC measurement The average XRC FWHM among all the measurement points is less than 20 arcsec.
[4] The C-plane GaN substrate according to [2], wherein the first line segment satisfies the following condition (A3) in addition to the condition (A1): (A3) On the first line segment obtained from the XRC measurement The mean and standard deviation of XRC FWHM between all measurement points is less than 12 arcsec and less than 5 arcsec, respectively.
[5] On the main surface on which the first line segment can be drawn, at least one second line segment that is a virtual line segment having a length of 40 mm that satisfies at least one of the following conditions (C1) and (D1) can be drawn. The C-plane GaN substrate according to any one of [1] to [4]:
(C1) The second line segment is orthogonal to at least one of the first line segments, and on the second line segment, the X-ray incident surface at the time of each ω scan is made parallel to the second line segment. (004) When the XRC of reflection is measured at 1 mm intervals, the maximum value of FWHM of XRC between all measurement points is less than 30 arcsec;
(D1) The second line segment is orthogonal to at least one of the first line segments, and the X-ray incident surface at the time of each ω scan is parallel to the second line segment on the second line segment. When the XRC of (004) reflection is measured at 1 mm intervals, the difference between the maximum value and the minimum value of the peak angle of XRC between all measurement points is less than 0.2 °.
[6] The C-plane GaN substrate according to [5], wherein the second line segment satisfies the condition (C1). [7] The C-plane GaN substrate according to [6], wherein the second line segment satisfies the following condition (C2) in addition to the condition (C1): (C2) On the second line segment obtained from the XRC measurement The average XRC FWHM among all the measurement points is less than 20 arcsec.
[8] The C-plane GaN substrate according to [6], wherein the second line segment satisfies the following condition (C3) in addition to the condition (C1): (C3) On the second line segment obtained from the XRC measurement The mean and standard deviation of XRC FWHM between all measurement points is less than 12 arcsec and less than 5 arcsec, respectively.
[9] The C-plane GaN substrate according to any one of [1] to [8], which has a plurality of dislocation arrays arranged periodically on the main surface.
[10] The C-plane GaN substrate according to [9], wherein the dislocation array is two-dimensionally arranged on the main surface.
[11] The C-plane GaN substrate according to [10], wherein the arrangement of the plurality of dislocation arrays on the main surface has periodicity in two or more directions.
[12] The C-plane GaN substrate according to any one of [1] to [11], wherein the concentrations of Li, Na, K, Mg, and Ca are less than 1 × 10 ¹⁶ atoms / cm ³ .
[13] The C-plane GaN substrate according to [12], containing F.
[14] The C-plane GaN substrate according to [13] above, which contains one or more halogens selected from Cl, Br and I in addition to F.
[15] The C-plane GaN substrate according to [14], containing F and I.
[16] The C-plane GaN substrate according to any one of [1] to [15], wherein the H concentration is 5 × 10 ¹⁷ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less.
[17] The C-plane GaN substrate according to any one of [1] to [16], comprising a GaN crystal having an infrared absorption peak at 3140 to 3200 cm ⁻¹ belonging to a gallium vacancy-hydrogen complex.
[18] The C-plane GaN according to any one of [1] to [17], wherein the sizes in the [1-100] direction, the [10-10] direction, and the [01-10] direction are all 45 mm or more. substrate.
[19] The C-plane GaN substrate according to any one of [1] to [18], which has a disc shape and a diameter of 45 mm or more.
[20] The C-plane GaN substrate according to any one of [1] to [19], which has a gallium polar surface whose orientation is within 5 ° from [0001].
[21] including a step of preparing the C-plane GaN substrate according to any one of [1] to [20] and a step of epitaxially growing one or more nitride semiconductors on the prepared C-plane GaN substrate. A method for manufacturing a nitride semiconductor device.
[22] A step of preparing the C-plane GaN substrate according to any one of [1] to [20] and a step of epitaxially growing one or more types of nitride semiconductors on the prepared C-plane GaN substrate. Epitaxial substrate manufacturing method.
[23] Bulk nitriding comprising: preparing the C-plane GaN substrate according to any one of [1] to [20]; and epitaxially growing a nitride semiconductor crystal on the prepared C-plane GaN substrate Of manufacturing a semiconductor crystal.
[24] A GaN layer bonded substrate comprising the steps of: preparing the C-plane GaN substrate according to any one of [1] to [20]; and bonding the prepared C-plane GaN substrate to a different composition substrate. Manufacturing method.

[25] A first step of preparing a GaN seed having a nitrogen polar surface; and a step of disposing a pattern mask on the nitrogen polar surface of the GaN seed, the pattern mask comprising a periodic opening comprising a linear opening A second step in which an opening pattern is provided; a mono-thermal growth of a GaN crystal through the pattern mask on the nitrogen polar surface of the GaN seed, between the GaN crystal and the pattern mask. Includes a third step in which a gap is formed; and a fourth step in which the GaN crystal is processed to obtain a C-plane GaN substrate.
[26] The manufacturing method according to [25], wherein the periodic opening pattern is a stripe pattern.
[27] The manufacturing method according to [26], wherein a pitch between the linear openings is 1 mm or more. [28] In the second step, the pattern mask is arranged so that the longitudinal direction of the linear opening forms an angle of 12 ° ± 5 ° with respect to the direction of the line of intersection between the nitrogen polar surface and the M plane The manufacturing method according to any one of [25] to [27].
[29] The manufacturing method according to [25], wherein the periodic opening pattern includes an intersection.
[30] The manufacturing method according to [29], wherein the arrangement of the intersecting portions in the periodic opening pattern is two-dimensional.
[31] The manufacturing method according to [30], wherein the pattern mask includes the intersecting portion with a number density of 1 cm ⁻² or more.
[32] The [30] or [30], wherein all the non-openings included in the unit pattern of the pattern mask are square or hexagonal, and the pattern mask does not include linear openings arranged at a pitch of less than 1 mm. 31].
[33] The manufacturing method according to [32], wherein the pattern mask includes linear openings arranged at a pitch of 10 mm or less.
[34] The pattern mask includes linear openings arranged at a pitch of 2 mm or less and linear openings arranged at a pitch of more than 2 mm, or linear openings arranged at a pitch of 3 mm or less; [32] including linear openings arranged at a pitch exceeding 3 mm, or linear openings arranged at a pitch of 4 mm or less and linear openings arranged at a pitch exceeding 4 mm. The manufacturing method as described in.
[35] The manufacturing method according to [34], wherein the pattern mask includes linear openings arranged at a pitch exceeding 4 mm.
[36] The periodic opening pattern is a square lattice pattern, and in the second step, a first linear opening and a second linear opening having different longitudinal directions are provided in the pattern mask. 35].
[37] The manufacturing method according to [36], wherein one of the pitch between the first linear openings and the pitch between the second linear openings is 1.5 times or more of the other.
[38] In the second step, the pattern is formed such that the longitudinal direction of at least a part of the linear opening forms an angle of 12 ° ± 5 ° with respect to the direction of the line of intersection between the nitrogen polar surface and the M plane. The manufacturing method according to any one of [29] to [37], wherein a mask is arranged.
[39] In the second step, the longitudinal direction of the portion of the linear opening occupying 50% or more of the total extension is 12 ° ± 5 ° with respect to the direction of the line of intersection between the nitrogen polar surface and the M plane. The manufacturing method according to any one of [29] to [37], wherein the pattern mask is arranged so as to form an angle.
[40] In the second step, the pattern is formed such that the longitudinal direction in all the portions of the linear opening forms an angle of 12 ° ± 5 ° with respect to the direction of the line of intersection between the nitrogen polar surface and the M plane. The manufacturing method according to any one of [29] to [37], wherein a mask is arranged.
[41] The manufacturing method according to any one of [25] to [40], wherein in the third step, a void is formed between the GaN crystal and the pattern mask.
[42] The manufacturing method according to [41], wherein in the third step, a GaN crystal is grown so that no through hole remains above the non-opening portion of the pattern mask.
[43] The [25] to [42] above, wherein the mineralizer used in the third step contains at least one ammonium halide selected from NH ₄ Cl, NH ₄ Br and NH ₄ I and NH ₄ F. ] The manufacturing method in any one of.
[44] The production method according to [43], wherein the mineralizer used in the third step includes NH ₄ I and NH ₄ F.
[45] The production method according to any one of [25] to [44], wherein the GaN crystal contains F and I.
[46] Any of [25] to [45], wherein the GaN seeds have a size in the [1-100] direction, [10-10] direction, and [01-10] direction that are all 45 mm or more. Manufacturing method.
[47] Any of [25] to [46], wherein the GaN crystal has a size in the [1-100] direction, [10-10] direction, and [01-10] direction that are all 45 mm or more. Manufacturing method.
[48] [1-100] direction, [10-10] direction and [01-] of the C-plane GaN substrate
10] The manufacturing method according to any one of [25] to [47], wherein the size in the direction is 45 mm or more.
[49] The manufacturing method according to any one of [25] to [48], wherein the fourth step includes a sub-step of slicing the GaN crystal parallel or substantially parallel to the C plane.

According to one embodiment, a novel C-plane GaN substrate that can be preferably used for manufacturing a nitride semiconductor device, a bulk nitride semiconductor crystal, or the like is provided.
According to another embodiment, a novel method for manufacturing a C-plane GaN substrate is provided.

FIG. 1 shows an example of the shape of a C-plane GaN substrate according to an embodiment, FIG. 1 (a) is a perspective view, and FIG. 1 (b) is a side view. 2A to 2C are perspective views showing shapes that the C-plane GaN substrate according to the embodiment may have. FIG. 3 is a plan view of the C-plane GaN substrate according to the embodiment. FIG. 4 is a flowchart of the C-plane GaN substrate manufacturing method according to the embodiment. FIG. 5A is a perspective view showing the GaN seed, and FIG. 5B is a perspective view showing the GaN seed after the pattern mask is arranged on the nitrogen polar surface. FIG. 6 is a plan view showing a part of the GaN seed on the nitrogen polar surface side after the pattern mask is arranged. FIG. 7 is a plan view showing a part of the GaN seed on the nitrogen polar surface side after the pattern mask is arranged. FIGS. 8A to 8D are plan views of GaN seeds in which a pattern mask is disposed on a nitrogen polar surface, respectively. FIGS. 9E to 9H are plan views of GaN seeds in which a pattern mask is disposed on the nitrogen polar surface, respectively. FIGS. 10 (i) to 10 (l) are plan views of GaN seeds in which a pattern mask is arranged on the nitrogen polar surface, respectively. FIGS. 11A to 11F are plan views each showing a part of a pattern mask arranged on the nitrogen polar surface of the GaN seed. FIGS. 12A to 12F are plan views each showing a part of a pattern mask arranged on the nitrogen polar surface of the GaN seed. FIGS. 13A to 13E are cross-sectional views showing a process of growing a GaN crystal. FIG. 14A is a plan view showing a portion of the GaN seed on the nitrogen polar surface side after the pattern mask in which the linear openings form continuous intersections is arranged, and FIG. FIG. 15 is a plan view showing a GaN crystal in an initial growth stage grown through the pattern mask shown in FIG. FIG. 15A is a plan view showing a part of the GaN seed on the nitrogen polar surface side after the pattern mask in which the linear openings form discontinuous intersections is arranged, and FIG. FIG. 16 is a plan view showing a GaN crystal in an initial growth stage grown through the pattern mask shown in FIG. FIG. 16 shows a crystal growth apparatus that can be used for the growth of GaN crystals by the ammonothermal method. FIGS. 17A and 17B are cross-sectional views each showing a position where the GaN crystal is sliced.

In the GaN crystal, the crystal axis parallel to [0001] and [000-1] is the c axis, <10−
The crystal axis parallel to 10> is called the m-axis, and the crystal axis parallel to <11-20> is called the a-axis. The crystal plane orthogonal to the c-axis is referred to as C-plane (C-plane), the crystal plane orthogonal to the m-axis is referred to as M-plane (M-plane), and the crystal plane orthogonal to the a-axis is referred to as A-plane.
In the following, when referring to crystal axes, crystal planes, crystal orientations, etc., the crystal axes, crystal planes, crystal orientations, etc. of GaN crystals are meant unless otherwise specified.
Embodiments of the present invention will be described below with reference to the drawings as appropriate.

1. C-plane GaN substrate One embodiment of the present invention relates to a C-plane GaN substrate.
1.1. Shape and Size The C-plane GaN substrate of the embodiment has the shape of a plate having a main surface on one side and a main surface on the opposite side, and the thickness direction is parallel or substantially parallel to the c-axis. . One of the two main surfaces is a gallium polar surface and the other is a nitrogen polar surface. There is no particular limitation on the shape of the main surface.
FIG. 1 illustrates the shape of the C-plane GaN substrate of the embodiment, in which FIG. 1 (a) is a perspective view and FIG. 1 (b) is a side view.
Referring to FIG. 1, the C-plane GaN substrate 10 has a disk shape, and the shape of a gallium polar surface 11 that is a main surface on the [0001] side and a shape of a nitrogen polar surface 12 that is a main surface on the [000-1] side. Is round. The gallium polar surface 11 and the nitrogen polar surface 12 are connected via a side surface 13.

2A to 2C are perspective views illustrating other shapes that the C-plane GaN substrate of the embodiment may have. 2, the same reference numerals as those in FIG. 1 are given to the components corresponding to those shown in FIG. 1 (the same applies to FIG. 3 described later).
2A to 2C, the main surfaces (gallium polar surface 11 and nitrogen polar surface 12) of the C-plane GaN substrate 10 have a quadrangular shape, a hexagonal shape, and an octagonal shape, respectively.
Area of the main surface having the C-plane GaN substrate according to the embodiment, preferably at 15cm ² or more, 15cm ² 50cm or more than ^2, 50cm ² or more 100cm less than ^2, 100cm ² or more 200cm less than ^2, 200cm ² or more 350 cm ² less, 350 cm ² or more 500cm less than ^2, and the like 500cm ² or more 750cm less than ^2.

In the C-plane GaN substrate of the embodiment, the orientation of the gallium polar surface is within 10 ° from [0001]. This means that the angle between the normal vector of the gallium polar surface and [0001] is within 10 °.
When the normal vector of the gallium polar surface is inclined from [0001], the preferable inclination direction is within a range of ± 10 ° from either the m-axis direction or the a-axis direction, but is not limited thereto.
In the C-plane GaN substrate of the embodiment, the orientation of the gallium polar surface is preferably within 5 ° from [0001], more preferably within 2 °, and may be within 1 °. In the C-plane GaN substrate of the embodiment, the orientation of the nitrogen polar surface is within 10 ° from [000-1], preferably within 5 °, more preferably within 2 °, more preferably within 1 °. It may be.
When the normal vector of the nitrogen polar surface is inclined from [0001], the preferable inclination direction is within a range of ± 10 ° from either the m-axis direction or the a-axis direction, but is not limited thereto.
Although not limited, the gallium polar surface and the nitrogen polar surface are preferably parallel to each other.

When the C-plane GaN substrate of the embodiment has a disk shape, the diameter is preferably 45 mm or more and 305 mm or less. The diameters are typically 45-55 mm (about 2 inches), 95-105 mm (about 4 inches), 145-155 mm (about 6 inches), 195-205 mm (about 8 inches), 295-305 mm (about 12 inches).
When the C-plane GaN substrate of the embodiment has a rectangular main surface, the vertical and horizontal sizes of the main surface are preferably 5 cm or more and 15 cm or less.
The thickness of the C-plane GaN substrate according to the embodiment is preferably 100 μm or more, 150 μm or more and less than 250 μm, 250 μm or more and less than 300 μm, 300 μm or more and less than 400 μm, 400 μm or more and less than 500 μm, 500 μm or more and less than 750 μm, 750 μm or more and less than 1 mm, It may be 1 mm or more and less than 2 mm, 2 mm or more and less than 5 mm. Although there is no upper limit in particular in this thickness, it is usually 20 mm or less.

In the C-plane GaN substrate of the embodiment, the boundary between the gallium polar surface and the side surface may be chamfered. The same applies to the boundary between the nitrogen polar surface and the side surface.
The C-plane GaN substrate according to the embodiment has various markings as required, such as an orientation flat or notch for displaying the crystal orientation, and an index flat for facilitating discrimination between the gallium polar surface and the nitrogen polar surface. Can be provided.

1.2. Crystallinity On the main surface of the C-plane GaN substrate according to the embodiment, a first line that is a virtual line segment having a length of 40 mm that satisfies at least one of the following conditions (A1) and (B1), preferably both: You can draw at least one minute.
(A1) On the first line segment, when the X-ray incident surface at the time of each ω scan is parallel to the first line segment and (004) XRC of reflection is measured at intervals of 1 mm, between all measurement points The maximum value of the XRC FWHM is less than 30 arcsec.
(B1) On the first line segment, when the X-ray incident surface at the time of each ω scan is parallel to the first line segment and (004) XRC of reflection is measured at intervals of 1 mm, between all measurement points The difference between the maximum value and the minimum value of the XRC peak angle is less than 0.2 °.

XRC here is an X-ray rocking curve (or X-ray diffraction rocking curve). In XRC measurement of a GaN crystal, CuKα is usually used as a radiation source.
FWHM (Full Width at Half Maximum) of XRC is an index generally used in crystal quality evaluation.
The difference between the maximum value and the minimum value of the XRC peak angle in the condition (B1) is an index representing how much the direction of the c-axis varies on the first line segment.

In a preferred example, the first line segment satisfies the following condition (A2) in addition to the condition (A1).
(A2) The average FWHM of XRC between all measurement points on the first line segment obtained from the XRC measurement is less than 20 arcsec.
In a more preferred example, the first line segment satisfies the following condition (A3) in addition to the condition (A1).
(A3) The XRC FWHM average and standard deviation between all measurement points on the first line segment obtained from the XRC measurement are less than 12 arcsec and less than 5 arcsec, respectively.

In the C-plane GaN substrate of the embodiment, the first line segment only needs to be drawn on at least one of a gallium polar surface and a nitrogen polar surface. In some cases, one of the main surfaces is roughened and may not be suitable for XRC measurement. In a substrate whose both main surfaces are finished so that XRC measurement is possible, if a first line segment can be drawn on one main surface, the first line segment can often be drawn on the other main surface.
Of the first line segments that can be drawn on the main surface of the C-plane GaN substrate according to the embodiment, at least one of the first line segments preferably passes through the center (center of gravity) of the main surface, but is not limited thereto.

In the C-plane GaN substrate of the embodiment, a virtual line having a length of 40 mm satisfying at least one of the following conditions (C1) and (D1), preferably both, on the main surface capable of drawing the first line segment. It is desirable to be able to draw at least one second line segment that is a minute.
(C1) The second line segment is orthogonal to at least one of the first line segments, and on the second line segment, the X-ray incident surface at the time of each ω scan is made parallel to the second line segment. When the XRC of (004) reflection is measured at 1 mm intervals, the maximum value of the FWHM of XRC between all measurement points is less than 30 arcsec.
(D1) The second line segment is orthogonal to at least one of the first line segments, and on the second line segment, the X-ray incident surface at the time of each ω scan is made parallel to the second line segment. When the XRC of (004) reflection is measured at 1 mm intervals, the difference between the maximum value and the minimum value of the peak angle of XRC between all measurement points is less than 0.2 °.

In a preferred example, the second line segment satisfies the following condition (C2) in addition to the condition (C1).
(C2) The average FWHM of XRC between all measurement points on the second line segment obtained from the XRC measurement is less than 20 arcsec.
In a more preferred example, the second line segment satisfies the following condition (C3) in addition to the condition (C1).
(C3) The average and standard deviation of the XRC FWHM between all measurement points on the second line segment obtained from the XRC measurement are less than 12 arcsec and less than 5 arcsec, respectively.
Of the second line segments that can be drawn on the main surface of the C-plane GaN substrate of the embodiment, it is desirable that at least one passes through the center (center of gravity) of the main surface, but the present invention is not limited thereto.

FIG. 3 shows an example of a C-plane GaN substrate that can draw two line segments respectively corresponding to the first line segment and the second line segment on the main surface.
The C-plane GaN substrate 10 shown in FIG. 3 has a disk shape, and its diameter is in the range of 45 to 55 mm. A line segment LS1 corresponding to the first line segment and a line segment LS2 corresponding to the second line segment can be drawn on the gallium polar surface 11 of the C-plane GaN substrate 10.
Each of the line segment LS1 and the line segment LS2 orthogonal to each other has a length of 40 mm, and both pass through the approximate center of the gallium polar surface 11. Each of the line segment LS1 and the line segment LS2 intersects the other line segment at its midpoint.

On the line segment LS1, the X-ray incident surface in each ω scan is parallel to the line segment LS1, and (004) XRC of reflection can be measured at intervals of 1 mm. When the X-ray incident surface is parallel to the line segment LS1, the incident direction of X-rays to the C-plane GaN substrate 10 is parallel to a plane that includes the line segment LS1 and is perpendicular to the C plane.
The maximum value of FWHM of XRC between 40 measurement points on the line segment LS1 obtained from such XRC measurement is less than 30 arcsec, preferably less than 25 arcsec, more preferably less than 20 arcsec.
The average FWHM of XRC between the 40 measurement points is preferably less than 20 arcsec, more preferably less than 16 arcsec, more preferably less than 12 arcsec.
More preferably, the XRC FWHM mean and standard deviation between the 40 measurement points is less than 12 arcsec and less than 5 arcsec, respectively.
The difference between the maximum value and the minimum value of the XRC peak angle between the 40 measurement points is preferably less than 0.2 °, more preferably less than 0.15 °, and more preferably less than 0.1 °. .

On the line segment LS2, the XRC-FWHM of the (004) reflection can be measured at intervals of 1 mm with the X-ray incident surface at the time of each ω scan parallel to the line segment LS2. When the X-ray incident surface is parallel to the line segment LS2, the incident direction of X-rays to the C-plane GaN substrate 10 is parallel to a plane that includes the line segment LS2 and is perpendicular to the C plane.
The maximum value of FWHM of XRC between 40 measurement points on the line segment LS2 obtained from such XRC measurement is less than 30 arcsec, preferably less than 25 arcsec, more preferably less than 20 arcsec.
The average FWHM of XRC between the 40 measurement points is preferably less than 20 arcsec, more preferably less than 16 arcsec, more preferably less than 12 arcsec.
More preferably, the XRC FWHM mean and standard deviation between the 40 measurement points is less than 12 arcsec and less than 5 arcsec, respectively.
The difference between the maximum value and the minimum value of the XRC peak angle between the 40 measurement points is preferably less than 0.2 °, more preferably less than 0.15 °, and more preferably less than 0.1 °. .

1.3. Dislocation Array The C-plane GaN substrate according to the embodiment may have a group of dislocations arranged in a line, that is, a dislocation array on the main surface. The dislocation here is an end point of threading dislocation (edge dislocation, spiral dislocation, and mixed dislocation).
A plurality of dislocation arrays may be periodically arranged on the main surface of the C-plane GaN substrate according to the embodiment. The arrangement of the plurality of dislocation arrays may be two-dimensional, and may have periodicity in two or more directions.
The existence, shape, arrangement, etc. of dislocation arrays on the main surface of the C-plane GaN substrate can be confirmed with an optical microscope if the main surface is etched under appropriate conditions and etch pits are formed at the end points of threading dislocations. Is possible. The confirmation may be performed on at least one of a gallium polar surface and a nitrogen polar surface.
For example, in the case of a gallium polar surface, etching is performed for 1 hour or more using 89% sulfuric acid heated to 270 ° C. as an etchant to form etch pits corresponding to all types of threading dislocations existing on the surface. be able to.
The reason why the C-plane GaN substrate according to the embodiment may have a plurality of dislocation arrays periodically arranged on the main surface is described later in the manufacture of the C-plane GaN substrate, for example. When the C-plane GaN substrate manufacturing method of the item is used or the GaN seed used for manufacturing the GaN substrate is described later in 2. It is a case where it manufactures with the C surface GaN substrate manufacturing method of term.

1.4. Impurities The concentration of various impurities in the GaN crystal is determined by SIMS (Secondary Ion Mass Spectrometry).
) Is generally measured. The impurity concentration mentioned below is a value at a portion where the depth from the crystal surface is 1 μm or more as measured by SIMS.
The C-plane GaN substrate of the embodiment includes NH ₄ F, NH ₄ Cl (ammonium chloride), NH ₄ Br
It may preferably include GaN crystals grown ammonothermally in Pt (platinum) capsules using ammonium halides such as (ammonium bromide) and NH ₄ I as mineralizers. In such GaN crystals, unless added intentionally, alkali metals such as Li (lithium), Na (sodium) and K (potassium), and alkaline earth metals such as Mg (magnesium) and Ca (calcium). The concentration of each element may be less than 1 × 10 ¹⁶ atoms / cm ³ .

GaN crystals grown ammonothermally using ammonium halide as a mineralizer can contain halogens derived from the mineralizer. For example, a GaN crystal grown by an ammonothermal method using NH ₄ F as a mineralizer is 5 × 10 ¹⁴ atoms / cm ³ or more and 1 × 10 ^1.
F (fluorine) may be contained at a concentration of less than ⁶ atoms / cm ³ , 1 × 10 ¹⁶ atoms / cm ³ or more and less than 1 × 10 ¹⁷ atoms / cm ³ .
As the present inventors have confirmed through experiments, the concentration of I (iodine) in GaN crystals grown ammonothermally using NH ₄ F and NH ₄ I as mineralizers is usually 1 × 10 ¹⁶ atoms / cm ³

GaN crystals grown ammonothermally using ammonium halide as a mineralizer can contain H (hydrogen) at a concentration of 5 × 10 ¹⁷ atoms / cm ³ or more. The hydrogen concentration in the GaN crystal is usually 10 ²¹ atoms / cm ³ or less, 5 × 10 ²⁰ atoms / cm ³ or less, 1 × 10 ²⁰ atoms / cm ³ or less, or 5 × 10 ¹⁹ atoms / cm ³ or less. possible.
A monothermally grown GaN crystal generally has an infrared absorption peak attributed to a gallium vacancy-hydrogen complex 3140-3200c.
m ^-1 . In the GaN crystal grown by the HVPE method or the Na flux method, such an infrared absorption peak is not observed.

1.5. Use (1) Nitride Semiconductor Device The C-plane GaN substrate of the embodiment can be preferably used for manufacturing a nitride semiconductor device.
Usually, one or more types of nitride semiconductors are epitaxially grown on a C-plane GaN substrate to form an epitaxial substrate having a device structure. As the epitaxial growth method, a vapor phase method such as MOCVD method, MBE method, pulse vapor deposition method and the like suitable for forming a thin film can be preferably used, but is not limited thereto.
The device structure is formed on the main surface where the first line segment can be drawn.
After a semiconductor process including etching and application of a structure such as an electrode or a protective film is performed, the epitaxial substrate is divided into a nitride semiconductor device chip.

Specific examples of nitride semiconductor devices that can be manufactured using the C-plane GaN substrate of the embodiment include light-emitting devices such as light-emitting diodes and laser diodes, rectifiers, bipolar transistors, field-effect transistors, and HEMTs (High Electron Mobility Transistors). Electronic devices, temperature sensors, pressure sensors, radiation sensors, semiconductor sensors such as visible-ultraviolet light detectors, solar cells, and the like.
In addition, the C-plane GaN substrate of the embodiment is a SAW (Surface Acoustic Wave) device,
The present invention can also be applied to applications such as vibrators, resonators, oscillators, MEMS (Micro Electro Mechanical System) parts, voltage actuators, and electrodes for artificial photosynthesis devices.

(2) Seed The C-plane GaN substrate of the embodiment can be preferably used for production of bulk nitride semiconductor crystals, particularly bulk GaN crystals.
Specifically, in the growth of bulk nitride semiconductor crystals by various methods, the C-plane GaN substrate of the embodiment can be used as a seed.
Bulk nitride semiconductor crystal growth methods include HVPE (hydride vapor phase epitaxy), ammonothermal and Na flux methods, THVPE (Tri-Halide Vapor Phase Epitaxy), and OVPE (Oxide Vapor Phase Epitaxy). A method or the like can also be preferably used.
The THVPE method is a vapor phase growth method of a nitride semiconductor crystal using a group 13 element trichloride such as GaCl ₃ and a nitrogen-containing compound such as NH ₃ as raw materials. Reference can be made to WO2015 / 037232. In manufacturing a bulk GaN crystal using the THVPE method, a GaN crystal is epitaxially grown on the nitrogen polar surface of the C-plane GaN substrate of the embodiment.
The OVPE method is a GaN vapor phase growth method using Ga ₂ O and NH ₃ as raw materials. For details, see, for example, M. Imade, et al., Journal of Crystal Growth, 312 (2010) 676-679. You can refer to it.

(3) GaN layer bonded substrate In one example, a GaN layer bonded substrate can be manufactured using the C-plane GaN substrate of the embodiment.
The GaN layer bonded substrate is a composite substrate having a structure in which a GaN layer is bonded to a different composition substrate having a chemical composition different from that of GaN, and can be used for manufacturing a light emitting device and other semiconductor devices. As the different composition substrate, sapphire substrate, AlN substrate, SiC substrate, ZnSe substrate, Si substrate, ZnO substrate, ZnS substrate, quartz substrate, spinel substrate, carbon substrate, diamond substrate, Ga ₂ O ₃ substrate, ZrB ₂ substrate, Mo Examples include a substrate, a W substrate, and a ceramic substrate.
JP, 2006-210660, A JP, 2011-44665, etc. can be referred to for details, such as a structure of a GaN layer bonded substrate, a manufacturing method, and an application.

The GaN layer bonded substrate typically has a step of implanting ions in the vicinity of the main surface of the GaN substrate, a step of bonding the main surface side of the GaN substrate to a different composition substrate, and an ion-implanted region. As described above, the GaN substrate is cut into two parts to form a GaN layer bonded to the different composition substrate in this order.
As a method of manufacturing a GaN layer bonded substrate that does not perform ion implantation, after a GaN substrate is bonded to a different composition substrate, the GaN substrate is mechanically cut to form a GaN layer bonded to the different composition substrate. Has been developed.
Whichever method is used, when the C-plane GaN substrate of the embodiment is used as a material, a GaN layer bonded substrate having a structure in which a GaN layer separated from the C-plane GaN substrate is bonded to a different composition substrate Is obtained.

2. C-plane GaN substrate manufacturing method One embodiment of the present invention is related with a C-plane GaN substrate manufacturing method.
FIG. 4 is a flowchart of the C-plane GaN substrate manufacturing method according to the embodiment. This method includes the following steps S1 to S3 which are sequentially executed.
S1: preparing a GaN seed having a nitrogen polar surface.
S2: A step of placing a pattern mask on the nitrogen polar surface of the GaN seed prepared in step S1.
S3: A step of growing a GaN crystal in an ammonothermal manner on the nitrogen polar surface of the GaN seed prepared in Step S1 through the pattern mask arranged in Step S2.
S4: processing the GaN crystal grown in step S3 to obtain a C-plane GaN substrate.
Details of steps S1 to S4 will be described below.

(1) Step S1
In step S1, a GaN seed having a nitrogen polar surface is prepared.
A preferred GaN seed is a C-plane GaN substrate obtained by processing a bulk GaN crystal grown by the HVPE method or the acidic ammonothermal method. It may be manufactured by the method described in the section. In the C-plane GaN substrate, the main surface on the [0001] side is a gallium polar surface, and the main surface on the [000-1] side is a nitrogen polar surface.
The orientation of the nitrogen polar surface of the GaN seed is preferably within 2 ° from [000-1], more preferably within 1 ° from [000-1].
Area of the N-polar surface of the GaN seed is preferably not 15cm ² or more, 15cm ² 50cm or more than ^2, 50cm ² or more 100cm less than ^2, 100cm ² or more 200cm less than ^2,
200 cm ² or more 350cm less than ^2, 350cm ² or more 500cm less than ^2, and the like 500cm ² or more 750cm less than ^2.

When the nitrogen polar surface of the GaN seed is circular, its diameter is preferably 45 mm or more. The diameters are typically 45-55 mm (about 2 inches), 95-105 mm (about 4 inches), 145-155 mm (about 6 inches), 195-205 mm (about 8 inches), 295-305 mm (about 12 inches).
For example, when the GaN seed is a C-plane GaN substrate having a diameter of 50 mm, the thickness is preferably 300 μm or more. There is no particular upper limit to the thickness of the GaN seed, but it is usually 20 mm or less.

The size of the GaN seed is determined in consideration of the size of the GaN crystal to be grown in the subsequent step S3.
For example, when a C-plane GaN substrate having a size of 45 mm in all the [1-100] direction, [10-10] direction, and [01-10] direction is to be cut out from a GaN crystal to be grown, Must be grown so that the sizes in the [1-100] direction, the [10-10] direction, and the [01-10] direction are all 45 mm or more. In order to grow a GaN crystal whose sizes in the [1-100] direction, the [10-10] direction, and the [01-10] direction are all 45 mm, the [1-100] direction, [10− 10] and [01-10] are preferably 45 mm or more in size.
The nitrogen polar surface of the GaN seed is usually planarized by polishing or grinding. Preferably, the damaged layer introduced by the planarization process is removed from the nitrogen polar surface by CMP (Chemical Mechanical Polishing) and / or etching.

(2) Step S2
In step S2, a pattern mask is placed on the nitrogen polar surface of the GaN seed prepared in step S1.
The material forming the surface of the pattern mask is preferably a platinum group metal, that is, a metal selected from Ru (ruthenium), Rh (rhodium), Pd (palladium), Os (osmium), Ir (iridium) and Pt (platinum). Particularly preferred is Pt (platinum). The pattern mask may be a single layer film made of a platinum group metal or an alloy thereof, but is preferably a platinum group as a surface layer on an underlayer made of a metal having better adhesion to a GaN crystal than the platinum group metal. It is a multilayer film formed by laminating metal layers. Examples of the material for the underlayer include, but are not limited to, W (tungsten), Mo (molybdenum), Ti (titanium), and alloys containing one or more selected from these.

The pattern mask is provided with a periodic opening pattern composed of linear openings. An example will be described with reference to FIGS.
FIG. 5A is a perspective view showing a GaN seed. The GaN seed 20 is a disc-shaped C-plane GaN substrate, and has a gallium polar surface 21, a nitrogen polar surface 22, and side surfaces 23.
FIG. 5B is a perspective view showing the GaN seed 20 after the pattern mask 30 is formed on the nitrogen polar surface 22. The pattern mask 30 is provided with a plurality of linear openings 31 arranged in parallel to each other. The periodic opening pattern formed by the linear openings 31 is a stripe pattern.
FIG. 6 is a plan view showing a part of the GaN seed 20 on the nitrogen polar surface 22 side after the pattern mask 30 is arranged.
Referring to FIG. 6, a plurality of linear openings 31 are provided in the pattern mask 30 in parallel with each other at a constant pitch P, and the nitrogen polar surface 22 of the GaN seed is exposed inside each linear opening. The pitch means the distance between the center lines between adjacent parallel linear openings across the non-opening portion of the pattern mask.

In order to reduce dislocation defects inherited from the GaN seed 20 by the GaN crystal grown in the subsequent step S3, it is advantageous that the line width W of the linear opening 31 is narrow. Therefore, the line width W is preferably 0.5 mm or less, more preferably 0.2 mm or less, and more preferably 0.1 mm or less.
From the viewpoint of manufacturing efficiency, it is preferable that the line width W of the linear opening 31 is appropriately wide. This is because the growth rate in the initial stage is higher when the GaN crystal is grown in the subsequent step S3. Therefore, the line width W is preferably 5 μm or more, more preferably 20 μm or more, and more preferably 40 μm or more.
In order to reduce dislocation defects inherited from the GaN seed 20 by the GaN crystal grown in the subsequent step S3, it is advantageous that the pitch P between the linear openings 31 is large. Accordingly, the pitch P is preferably 1 mm or more, more preferably 2 mm or more, more preferably 3 mm or more, and more preferably 4 mm or more.

The larger the pitch P between the linear openings 31 is, the longer it takes to close the through hole formed above the non-opening portion of the pattern mask when the GaN crystal is grown in the subsequent step S3. Therefore, from the viewpoint of production efficiency, the pitch P is preferably 10 mm or less, and can be 4 mm or less, 3 mm or less, and further 2 mm or less.
When the direction of intersection between the nitrogen polar surface 22 and the M plane [(1-100) plane, (10-10) plane or (01-10) plane] in the GaN seed 20 is defined as a reference direction, the linear opening 31 The angle θ formed by the longitudinal direction of the reference and the reference direction is preferably 12 ° ± 5 °. The angle θ may be 12 ° ± 3 °, 12 ° ± 2 ° or 12 ° ± 1 °. When the linear openings are oriented in this way, the through holes generated above the non-opening portions of the pattern mask are easily blocked when the GaN crystal is grown in the subsequent step S3.

The pattern mask may be provided with a periodic opening pattern that includes linear openings and includes intersecting portions. An example will be described with reference to FIG.
FIG. 7 is a plan view showing a part of the GaN seed 20 on the nitrogen polar surface 22 side after the pattern mask 30 is formed.
The pattern mask 30 is provided with a linear opening 31, and the nitrogen polar surface 22 of the GaN seed is exposed inside the linear opening 31.
There are two types of linear openings provided in the pattern mask 30, that is, a first linear opening 311 and a second linear opening 312 having different longitudinal directions. The plurality of first linear openings 311 and the plurality of second linear openings 312 constitute a square lattice pattern.
The pitch P ₁ between the first linear openings 311 and the pitch P ₂ between the second linear openings 312 are constant. The pitch means the distance between the center lines between the linear openings adjacent to each other across the non-opening portion of the pattern mask.
The pitch P ₁ and the pitch P ₂ may be the same, but the present inventors have found that the pitch P ₁ and the pitch P ₂ are different from each other in the later step S3. When the crystal is grown, the through hole generated above the non-opening portion of the pattern mask tends to be easily blocked. Therefore, _{one of the} pitches P ₁ and P ₂ is preferably 1.5 times or more of the other and more preferably 2 times or more.

The square lattice pattern provided in the pattern mask 30 includes an intersection K formed between the first linear opening 311 and the second linear opening 312. As will be described later, it is advantageous to provide an intersection in the opening pattern in order to promote the closure of the through-hole generated above the non-opening of the pattern mask when the GaN crystal is grown in the subsequent step S3. . From this point of view, the number density of the intersections included in the pattern mask is preferably 1 cm ⁻² or more.
On the other hand, in order to increase the number density of the intersections, it is necessary to increase the density of the linear openings,
And considering that the dislocation defects that the GaN crystal grown in the subsequent step S3 takes over from the GaN seed increases as the density of the linear openings is increased, the number density of the intersecting portion is preferably 20 cm ⁻² or less. Preferably it is 15 cm- ² or less, More preferably, it is 10 cm- ² or less.

For the orientation of the first linear opening 311 and the second linear opening 312, it is convenient to express one of the directions of intersection of the nitrogen polar surface 22 and the M plane as the first reference direction and the other as the second reference direction. It is. For example, when the first reference direction is the direction of the line of intersection between the nitrogen polar surface 22 and the (1-100) plane, the second reference direction is the (10-10) plane or the (01-10) plane and the nitrogen polarity. The direction of the line of intersection with the surface 22.
In one of the preferred examples, at least an angle θ ₁ formed by the longitudinal direction of the first linear opening 311 and the first reference direction and an angle θ ₂ formed by the longitudinal direction of the second linear opening 312 and the two reference directions are at least. One can be 12 ° ± 5 °.
When the total extension of the first linear opening 311 is equal to or greater than the total extension of the second linear opening 312, it is preferable that at least the angle θ ₁ is 12 ° ± 5 °. In other words, the longitudinal direction in the portion of 50% or more of the total extension of the linear opening 31 may form an angle of 12 ° ± 5 ° with respect to the direction of the line of intersection between the nitrogen polar surface of the GaN seed and the M plane. preferable.
In a more preferred example, both the angle θ ₁ and the angle θ ₂ are 12 ± 5 °, that is, the longitudinal direction in all parts of the linear opening 31 is the direction of the line of intersection between the nitrogen polar surface of the GaN seed and the M plane. Is at an angle of 12 ± 5 °.
The angles θ ₁ and θ ₂ may be 12 ± 3 °, 12 ± 2 °, 12 ± 1 °.
When the linear openings are oriented as described above, the through holes generated above the non-opening portions of the pattern mask are easily closed when the GaN crystal is grown in the subsequent step S3.

It does not prevent one or both of the angles θ ₁ and θ _{2 from being} less than 7 °. In one example, one or both of the angles θ ₁ and θ ₂ may be ± 3 °, ± 2 °, ± 1 °, or the like. According to what the inventors have found, when the longitudinal direction of the linear opening is oriented substantially parallel to the M-plane of the GaN seed, when the GaN crystal is grown in the subsequent step S3, it penetrates in the crystal. There is an effect that the dislocation is bent in the lateral direction.
Angle theta ₁₂ formed by the first linear opening and second linear apertures, for example, less than 30 ° or 45 °, may be a 45 ° or 75 ° or less than 75 ° to 90 °. The angle theta ₁₂ is, 60 ° ± 10 °, 60 ° ± 5 °, 60 ° ± 3 °, may be 60 ° ± 1 ° and the like.

For GaN crystal grown in step S3 a later reduce the dislocation defect to take over from the GaN seed 20, better line width W ₂ of the line width W ₁ and the second linear opening 312 of the first linear opening 311 is narrower It is advantageous. Accordingly, the line widths W ₁ and W ₂ are each preferably 0.5 mm or less, more preferably 0.2 mm or less, and even more preferably 0.1 mm or less.
From the viewpoint of production efficiency, the line width W ₂ of the line width W ₁ and the second linear opening 312 of the first linear opening 311 preferably has reasonably wide. This is because the growth rate in the initial stage is higher when the GaN crystal is grown in the subsequent step S3. Accordingly, the line widths W ₁ and W ₂ are each preferably 5 μm or more, more preferably 20 μm or more, and even more preferably 40 μm or more.

In order to reduce dislocation defects inherited from the GaN seed 20 by the GaN crystal grown in the subsequent step S3, the pitch P ₁ between the first linear openings 311 and the pitch P ₂ between the second linear openings 312 are larger. It is advantageous. Accordingly, the pitches P ₁ and P ₂ are preferably 1 mm or more, more preferably 2 mm or more, more preferably 3 mm or more, and more preferably 4 mm or more.
The larger the pitches P ₁ and P _{2, the} longer it takes to close the through-hole formed above the non-opening portion of the pattern mask when the GaN crystal is grown in the subsequent step S3. Therefore, from the viewpoint of manufacturing efficiency, it is preferable that at least one of the pitches P ₁ and P ₂ is 10 mm or less. In one example, one or both of the pitches P ₁ and P ₂ may be 4 mm or less, 3 mm or less, and further 2 mm or less.
In a preferred example, only _{one of} pitches P ₁ and P ₂ can be set to 4 mm or less, 3 mm or less, or 2 mm or less in consideration of both reduction of dislocation defects to be inherited and improvement of manufacturing efficiency.

The periodic opening pattern that can be provided in the pattern mask disposed on the nitrogen polar surface of the GaN seed in step S2 is not limited to the above-described stripe pattern or square lattice pattern.
Each of the drawings included in FIGS. 8 to 10 is a plan view of the GaN seed 20 after the pattern mask 30 is arranged on the nitrogen polar surface 22 and illustrates various periodic opening patterns that can be provided in the pattern mask. However, the opening pattern that can be adopted is not limited to these.
In FIG. 8A, the linear openings 31 form a zigzag stripe opening pattern.
In FIG. 8B, the linear openings 31 form a kind of lattice pattern.
In FIG.8 (c), the linear opening 31 forms the inclined brick lattice pattern.
In FIG. 8D, a square lattice pattern in which the linear openings 31 are inclined is formed.

In FIG. 9 (e), the linear openings 31 form a herringbone lattice pattern.
In FIG. 9F, the linear openings 31 form a lattice pattern in which an inclined brick lattice and an inclined square lattice are compromised.
In FIG. 9G, the linear openings 31 form a triangular lattice pattern.
In FIG. 9 (h), the linear openings 31 form a flat honeycomb lattice pattern.

In FIG. 10 (i), the linear openings 31 form a Bishamon turtle shell lattice pattern.
In each of FIGS. 10J and 10K, the linear openings 31 form a cubic pattern.
In FIG. 10 (l), the linear openings 31 form a Y-shaped pattern.

In any of the examples shown in FIGS. 8 to 10, the periodic opening pattern included in the pattern mask 30 includes an intersection. Several types of intersections are shown in FIGS. 11 (a) to 11 (f) and FIGS. 12 (a) to 12 (f).
In this specification, a crossing portion in which two or more linear openings having different longitudinal directions are connected is referred to as a continuous crossing portion, including those shown in FIGS. 11 (a) to (f).
Unless otherwise specified, the intersections referred to in this specification include not only continuous intersections but also discontinuous intersections exemplified in FIGS. 12A to 12F. A discontinuous intersection can be regarded as an intersection formed by adding a change that disconnects the connection between the linear openings to the continuous intersection.
The distance between two linear openings separated by a non-opening at a discontinuous intersection is 300 μm or less, preferably 200 μm or less.

8 to 10, in all examples except FIG. 8B, the arrangement of the intersections included in the periodic opening pattern is two-dimensional.
If the periodic opening pattern includes an intersection, the through-hole generated above the non-opening portion of the pattern mask is easily blocked when the GaN crystal is grown in the subsequent step S3. This effect is remarkable when the arrangement of the intersections in the periodic opening pattern is two-dimensional, and becomes more remarkable by increasing the number density of the intersections.
For this reason, the arrangement of the intersections in the periodic opening pattern is preferably two-dimensional, and the number density of the intersections included in the pattern mask at that time is preferably 1 cm ⁻² or more. However, it is necessary to increase the density of the linear openings in order to increase the number density of the intersections, and as the density of the linear openings is increased, the GaN crystal grown in the subsequent step S3 takes over from the GaN seed. Considering that the number of dislocation defects increases, the number density at the intersection is preferably 20 cm ⁻² or less, more preferably 15 cm ⁻² or less, and more preferably 10 cm ⁻² or less.

A preferred design regarding the orientation, line width, and pitch of the linear opening when the various periodic opening patterns shown in FIGS. 8 to 10 are provided in the pattern mask is as follows.
It is preferable that at least a part of the linear opening has an angle of 12 ± 5 ° with respect to the direction of the line of intersection between the nitrogen polar surface of the GaN seed and the M plane. More preferably, in the portion that occupies 50% or more of the total extension of the linear opening, and in all the portions of the linear opening, the longitudinal direction is the intersection of the nitrogen polar surface of the GaN seed and the M plane. And an angle of 12 ± 5 ° with respect to the direction.
The line width of the linear opening is preferably 0.5 mm or less, more preferably 0.2 mm or less, more preferably 0.1 mm or less, and preferably 5 μm or more, More preferably, it is 20 μm or more, and more preferably 40 μm or more. The line width need not be the same in all portions of the linear opening.

When the non-openings included in the unit pattern of the pattern mask are all quadrangular or all hexagonal, the following can be said with respect to the pitch between the linear openings.
From the viewpoint of reducing dislocation defects that the GaN crystal grown on the GaN seed takes over from the GaN seed, the pattern mask preferably does not include a linear opening arranged at a pitch of less than 1 mm, and arranged at a pitch of less than 2 mm. More preferably, it does not include the linear openings arranged at a pitch of less than 3 mm, more preferably does not include the linear openings arranged at a pitch of less than 4 mm, and more preferably does not include the linear openings arranged at a pitch of less than 4 mm. .
On the other hand, from the viewpoint of improving manufacturing efficiency, it is preferable that the pattern mask includes linear openings arranged at a pitch of 10 mm or less, and further, linear patterns arranged at a pitch of 4 mm or less, 3 mm or less, or 2 mm or less. An opening may be included.
Considering both of the above viewpoints, the pattern mask is provided with linear openings arranged with a pitch of 1 mm or more and 4 mm or less and linear openings arranged with a pitch of over 4 mm, or with a pitch of 1 mm or more and 3 mm or less. Or a linear opening arranged with a pitch exceeding 3 mm, or a linear opening arranged with a pitch of 1 mm or more and 2 mm or less and a pitch exceeding 2 mm. A linear opening may be provided. In any of these cases, the pattern mask may be provided with linear openings arranged at a pitch exceeding 4 mm.
Of the examples shown in FIGS. 8 to 10, the non-openings included in the unit pattern of the pattern mask are all quadrangular in FIGS. 8 (c) and (d), FIGS. 9 (e) and (f), and FIG. 10. (J) and (k). In the example of FIG. 9H where the periodic opening pattern is a flat honeycomb pattern, all the non-openings included in the unit pattern of the pattern mask are hexagonal.

(3) Step S3
In Step S3, a GaN crystal is grown ammonothermally through the pattern mask arranged in Step S2 on the nitrogen polar surface on the GaN seed prepared in Step S1.
The growth process of the GaN crystal in step S3 will be described with reference to FIG.
FIG. 13A is a cross-sectional view showing a state before crystal growth starts. A pattern mask 30 having a linear opening 31 is provided on the nitrogen polar surface 22 of the GaN seed 20.
FIG. 13B shows that the GaN crystal 40 starts to grow on the nitrogen polar surface 22 exposed inside the linear opening 31 provided in the pattern mask 30.
After passing through the pattern mask 30, the GaN crystal 40 grows not only in the [000-1] direction but also in the lateral direction (direction parallel to the nitrogen polar surface 22) as shown in FIG. A gap G is formed between the crystal 40 and the pattern mask 30. As a result, orientation disorder of the GaN crystal 40 that may occur due to contact with the pattern mask 30 is suppressed.

In the growth stage shown in FIG. 13C, the GaN crystal 40 has a through hole T above the non-opening portion of the pattern mask 30.
As the GaN crystal 40 further grows, the gap G is gradually filled, but is not completely filled, and the through hole T is closed with the void V remaining as shown in FIG.
After the through hole T is closed, the GaN crystal 40 is further grown in the [000-1] direction as shown in FIG. It is considered that the stress generated between the GaN seed 20 and the GaN crystal 40 is relaxed by the void V, and consequently the strain of the GaN crystal 40 is reduced.
The growth amount of the GaN crystal 40 in the [000-1] direction after the through hole T is closed is preferably 1 mm or more, more preferably 2 mm or more, more preferably 3 mm or more, and there is no particular upper limit.
Note that in step S3, the GaN crystal grows also on the gallium polar surface 21 of the GaN seed 20, but is not shown in FIG.

When the through hole T is closed at the stage of FIG. 13D, either or both of dislocations are generated on the coreless surface, or the dislocations are simultaneously bent in the [000-1] direction on the coreless surface. For this reason, a dislocation array appears on the main surface of the C-plane GaN substrate cut out from the GaN crystal formed in the stage of FIG. The shape of the dislocation array is a shape of an intersection formed by an extended surface obtained by extending the coreless surface in the [000-1] direction and a main surface of the C-plane substrate.
Since the coreless surface is formed on the non-opening portion of the pattern mask, when the pattern mask has a plurality of closed non-opening portions, a plurality of dislocation arrays are discretely formed on the main surface of the C-plane GaN substrate. Appear in When the arrangement of the plurality of closed non-openings in the pattern mask is periodic, the arrangement of the plurality of dislocation arrays on the main surface of the C-plane GaN substrate is also periodic. When the arrangement of the plurality of closed non-openings in the pattern mask is two-dimensional, the arrangement of the plurality of dislocation arrays on the main surface of the C-plane GaN substrate is also two-dimensional.
The closed non-opening portion is a non-opening portion surrounded by a linear opening, and among the various examples shown in FIGS. c) and (d), FIGS. 9 (e) to (h), and FIGS. 10 (i) to (k). In these examples, the arrangement of closed non-openings in the pattern mask is periodic and two-dimensional.

The influence of the orientation of the linear opening provided in the pattern mask on the growth of the GaN crystal 40 will be described as follows.
As the inventors have learned through experiments, when the opening pattern provided in the pattern mask is a stripe type, the growth of the GaN crystal 40 is most reliably performed from the stage of FIG. 13C to the stage of FIG. 13D. The reason is that the through hole T generated in the GaN crystal 40 is most easily closed when the longitudinal direction of the linear opening is inclined about 12 ° with respect to the direction of the line of intersection between the nitrogen polar surface and the M plane. It is. The through-hole T is difficult to block when the inclination is close to 0 ° and when it is close to 30 °.
On the other hand, when an intersection is introduced into the pattern formed by the linear openings 31, the through holes T generated in the GaN crystal 40 are easily blocked even if the linear openings 31 are parallel to the M plane.
For the reason, the present inventors consider that the concave angle effect described below is related.

FIG. 14A is a plan view showing a part of the GaN seed on the nitrogen polar surface side where a pattern mask in which linear openings form intersections is arranged. The pattern mask 30 is provided with a first linear opening 311 and a second linear opening 312 having different longitudinal directions, and a continuous intersection is formed therebetween.
FIG. 14B shows a state in which the growth stage GaN crystal 40 shown in FIG. 13C is formed on the GaN seed shown in FIG. The GaN crystal 40 grows along the linear opening. What is indicated by a broken line is the outline of the linear openings 311 and 312 hidden under the GaN crystal 40.
Each of the four arrows in FIG. 14B indicates a recessed portion formed on a side portion of the GaN crystal 40 that grows on the intersection formed by the linear openings 311 and 312. The direction of the arrow represents the recessed direction of the recessed portion.
The formation of such a recessed portion causes a re-entrant angle effect, and Ga
The N crystal 40 is prompted to grow in the direction opposite to the arrow. That is, the driving force for growing the GaN crystal so as to close the through-hole generated above the non-opening portion of the pattern mask is generated by the recess angle effect.
In other words, when the opening pattern is a stripe type, the reason why the orientation of the linear opening has a dominant influence on the ease of closing of the through hole is presumed to be because the concave angle effect does not occur. .

A similar mechanism can occur when the linear openings form discontinuous intersections rather than continuous intersections. This will be described with reference to FIG.
FIG. 15A is a plan view showing a part of the GaN seed on the nitrogen polar surface side where a pattern mask in which linear openings form discontinuous intersections is arranged. A discontinuous intersection is formed by the first linear opening 311 and the second linear opening 312 divided into two.
When a GaN crystal is grown on the GaN seed, the distance between the first linear opening 311 and the second linear opening 312 is small, so that the shape of the GaN crystal in the growth stage of FIG. This is the same as when growing on a specific intersection. That is, as shown in FIG. 15 (b), recessed portions indicated by arrows are formed on the side portions of the GaN crystal 40 grown on the discontinuous intersections. The resulting indentation angle effect encourages the GaN crystal 40 to grow in the direction opposite the arrow.
One skilled in the art will appreciate that the above described depression angle effect can occur when GaN crystals are grown on the various intersections illustrated in FIGS.

Below, the crystal growth apparatus and crystal growth conditions which can be preferably used in step S3 will be described.
For the growth of the GaN crystal by the ammonothermal method in step S3, a crystal growth apparatus of the type shown in FIG. 16 can be preferably used.
Referring to FIG. 16, the crystal growth apparatus 100 includes an autoclave 101 and a Pt capsule 102 installed therein.
The capsule 102 has a raw material dissolution zone 102a and a crystal growth zone 102b that are partitioned by a baffle 103 made of Pt. Feed stock F is placed in the raw material melting zone 102a. A seed S suspended by a Pt wire 104 is installed in the crystal growth zone 102b.
A gas line to which the vacuum pump 105, the ammonia cylinder 106 and the nitrogen cylinder 107 are connected is connected to the autoclave 101 and the capsule 102 via the valve 108. When NH ₃ (ammonia) is introduced into the capsule 102, the amount of NH ₃ supplied from the ammonia cylinder 106 can be confirmed with the mass flow meter 109.

For feedstock, polycrystalline GaN produced by a method of reacting gaseous GaCl obtained by bringing HCl (hydrogen chloride) gas into contact with simple substance Ga (metal gallium) under heating and NH ₃ gas is preferably used. Can do.
Mineralizers for promoting the dissolution of the feedstock include one or more ammonium halides selected from NH ₄ Cl (ammonium chloride), NH ₄ Br (ammonium bromide) and NH ₄ I (ammonium iodide). , NH ₄ F is preferably used in combination.
Particularly preferably, NH ₄ F and NH ₄ I are used in combination.
When using a growth temperature of 650 ° C. or lower, it is not recommended to use only an ammonium halide other than NH ₄ F as a mineralizer. This is because the growth direction of the GaN crystal is substantially only the [000-1] direction and no lateral growth occurs.
On the other hand, when NH ₄ F is used alone as a mineralizer, lateral growth is strongly promoted.
It becomes difficult to grow the GaN crystal in the mode shown in FIG. 13, that is, to grow the GaN crystal so that a gap is formed between the GaN crystal and the pattern mask.

When growing a GaN crystal on the seed S, NH ₃ is also introduced into the space between the autoclave 101 and the capsule 102 and then heated by a heater (not shown) from the outside of the autoclave 101, The inside is set to a supercritical state or a subcritical state.
Etching also occurs on the surface of the seed S until the feedstock F is sufficiently dissolved and the solvent reaches saturation. If necessary, for the purpose of promoting the etch-back of the seed S before the start of growth, a temperature inversion period in which the temperature gradient between the raw material dissolution zone 102a and the crystal growth zone 102b is reversed from that during crystal growth. Can also be provided.
The growth temperature is preferably 550 ° C. or higher. Although it is not impeded to use a growth temperature of 1000 ° C. or higher, a sufficiently high quality GaN crystal can be grown even at 700 ° C. or lower.
The growth pressure can be set, for example, within a range of 100 to 250 MPa, but is not limited thereto.

As an example, NH ₄ F and NH ₄ I are used as mineralizers so that the molar ratios to NH ₃ are 0.5% and 4.0%, respectively, the pressure is about 220 MPa, the temperature Ts of the raw material dissolution zone GaN can be grown under the condition that the average value of the temperature Tg of the crystal growth zone is about 600 ° C. and the temperature difference Ts−Tg between these two zones is about 5 ° C. (Ts> Tg).
It is possible to increase the growth rate of the GaN crystal by increasing the temperature difference between the raw material melting zone and the crystal growth zone. However, if the growth rate is too high, the growth of the GaN crystal is shown in FIG. There is a problem that it is difficult to proceed from the stage of FIG. 13D to the stage of FIG. 13D, that is, it is difficult to close the through hole of the GaN crystal.
In step S3, every time the feedstock is used up, the capsule can be replaced and the GaN crystal regrowth can be repeated.
In order to impart n-type conductivity to the grown GaN crystal, it may be doped with O (oxygen), Si (silicon), Ge (germanium), S (sulfur), or the like.
In order to make the GaN crystal to be grown semi-insulating, it may be doped with iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), magnesium (magnesium) or the like.

(4) Step S4
By processing the GaN crystal grown in step S3, GaN substrates having various plane orientations can be manufactured. The processing may include slicing the GaN crystal using a slicer such as a single wire saw or a multi-wire saw. The slice thickness can be appropriately determined according to the purpose, but is usually 100 μm or more and 20 mm or less.
The planarization of the cut surface of the GaN crystal can be performed by either or both of grinding and lapping. Removal of the damaged layer from the cut surface can be performed by one or both of CMP and etching.
When slicing the GaN crystal 40 grown in step S3 in parallel or substantially parallel to the C-plane to produce a C-plane GaN substrate, if slicing is performed at the position indicated by the broken line in FIG. A C-plane GaN substrate is obtained. Such a substrate can be suitably used for manufacturing a semiconductor device or a GaN layer bonded substrate, and can be suitably used as a seed when growing a bulk GaN crystal by various crystal growth techniques. Such a substrate is also a preferred example of a GaN seed to be prepared in step S1 described above.

On the other hand, when the GaN crystal 40 is sliced at a position indicated by a broken line in FIG. 17B, the obtained C-plane GaN substrate has a through hole in the main surface, but is not suitable for use as a substrate for a semiconductor device. It can be used as a seed when bulk GaN crystals are grown ammonothermally using an acidic mineralizer containing F. This is because if the acidic mineralizer contains F, a GaN crystal grows so as to block even if there is a through hole in the seed.
In one example, in step S3, the growth of the GaN crystal 40 does not completely proceed to the stage of FIG. 13D, that is, in a state where all or part of the through hole T remains unclosed. However, in such a case, in step S4, only the C-plane GaN substrate having a through hole can be obtained regardless of the position where the grown GaN crystal 40 is sliced. This C-plane GaN substrate with through-holes can be used as a seed when growing a bulk GaN crystal in an ammonothermal manner using an acidic mineralizer containing F.

The case where a GaN crystal is grown by the acidic ammonothermal method without using a pattern mask on the nitrogen-polar surface of the C-plane GaN substrate manufactured by the method of the embodiment is as follows.
A growth apparatus of the type shown in FIG. 16 can be preferably used.
As the feedstock, polycrystalline GaN produced by a method of reacting gaseous GaCl obtained by bringing HCl gas into contact with simple substance Ga under heating and NH ₃ gas can be preferably used.
NH ₄ F can be preferably used as the mineralizer. NH ₄ Cl, may be one or more ammonium halide is selected from _NH 4 Br and NH ₄ I in combination with NH ₄ F, for example, may be a combination of NH ₄ F and NH ₄ I.
The concentration of NH ₄ F can be 0.1 to 1% in terms of a molar ratio to NH ₃ . The concentration of ammonium halide other than NH ₄ F can be set to 1 to 5% in terms of a molar ratio to NH ₃ .
The pressure and temperature can be set, for example, within a range of 100 to 250 MPa and within a range of 550 to 650 ° C., but are not limited thereto.

3. Experimental results 3.1. Experiment 1
<Production of C-plane GaN substrate>
As a GaN seed, a C-plane GaN substrate cut out from a GaN crystal grown by the HVPE method was prepared. This C-plane GaN substrate had a CMP-finished nitrogen polar surface and a gallium polar surface, respectively. The orientation of the nitrogen polar surface was within 1 ° from the [000-1] direction.
On the nitrogen polar surface of the GaN seed, a pattern mask having a stripe type opening pattern made of a laminated film having a 100 nm thick Pt layer on a 100 nm thick TiW layer was formed. A lift-off method was used for patterning the mask. The line width of the linear openings constituting the opening pattern was 50 μm, and the pitch between the linear openings was 4 mm. The stripe direction was tilted by 12 ° from the line of intersection between the nitrogen polar surface of the GaN seed and the M plane.

After forming the pattern mask, a GaN crystal was grown on the GaN seed by an ammonothermal method using a crystal growth apparatus of the type shown in FIG.
As the feedstock, polycrystalline GaN synthesized by a method of reacting gaseous GaCl obtained by bringing HCl gas into contact with simple substance Ga under heating and NH ₃ gas was used.
NH ₄ F and NH ₄ I were used in combination as mineralizers. The amount of NH ₄ F and NH ₄ I is NH
_The molar ratio to _{3 was} 0.5% and 4.0%, respectively. NH ₄ I was synthesized by introducing HI (hydrogen iodide) into a Pt capsule after NH ₃ was added.

The growth conditions were such that the average value of the temperature Tg of the crystal growth zone and the temperature Ts of the raw material dissolution zone was 598 ° C., the temperature difference between the crystal growth zone and the raw material dissolution zone was 5 ° C. (Ts> Tg), and the pressure was 220 MPa.
After 35 days from the start of growth, the capsule was opened, the GaN seed was taken out, and when the GaN crystal grown on the [000-1] side was observed, the growth front reached above the pattern mask. The growth rate was not uniform in the plane, and the through holes formed above the non-opening portions of the pattern mask started to close in part, but were not closed in most parts.
After observation, the GaN seed was transferred to a newly prepared capsule, and regrowth was performed again under the same ammonothermal growth conditions. The growth was terminated when 35 days had passed since the start of regrowth.

During the regrowth, the through hole of the GaN crystal was completely closed and the growth front was flattened.
When the grown GaN crystal was separated from the GaN seed and the surface on the [0001] side (side bonded to the GaN seed) was observed, a plurality of V grooves parallel to each other were formed at equal intervals.
The longitudinal direction of the V-groove was the same as the longitudinal direction of the linear openings provided in the pattern mask, and the pitch between the V-grooves was the same as the pitch between the linear openings. This indicates that the GaN crystal has grown in the manner shown in FIG. 13 and that the residual void formed as a result is the V-groove.
The depth of the V groove measured with a laser microscope was 1.9 mm at the deepest portion. When combined with the observation results before regrowth, it was considered that the above-described through-hole generated in the growing GaN crystal started to close when the GaN crystal grew 1 to 2 mm in the [000-1] direction.
The GaN single crystal grown by the ammonothermal method was sliced in parallel to the C plane to obtain a plurality of blank substrates. One of them was processed to prepare a C-plane GaN substrate having a thickness of 350 μm and having both main surfaces subjected to CMP.

<X-ray rocking curve measurement>
XRC of (004) reflection on the gallium polar surface of the produced C-plane GaN substrate was measured using an X-ray diffractometer (Spectris Co., Ltd., Panalytic X'Pert Pro MRD) using CuKα as an X-ray source. . The incident side optical system includes a 1/2 slit, an X-ray mirror, Ge (
440) A 4-crystal monochromator and a cross slit of w0.2 mm × h1 mm were used, and the 0D mode of the PIXcel ^3D (registered trademark) detector was used as the light receiving optical system. The resolution of the optical system was 5-6 arcsec. The X-ray beam size on the sample surface was set to be 0.2 mm × 5 mm when the X-ray incident angle was 90 ° (the X-ray incident direction was orthogonal to the sample surface). At the time of measurement, the direction in which the beam size was 5 mm and the X-ray incident surface were orthogonal to each other.

First, ω scans were performed at 1 mm intervals on a 70 mm long line segment passing through the approximate center of the gallium polar surface and parallel to the m-axis. In each ω scan, the X-ray incident surface was parallel to the m-axis. That is, X-rays were incident on the gallium polar surface of the sample from a direction orthogonal to the a-axis.
The XRC peak angle and FWHM of (004) reflection at all measurement points were as shown in Table 1 below.

The maximum value, average value, and standard deviation of FWHM among all measurement points were 26.3 arcsec, 11.7 arcsec, and 3.8 arcsec, respectively.
The difference between the maximum value and the minimum value of the peak angle between all measurement points was 0.17 °.
Measurement point No. 16 to the measurement point no. Looking at the section of 40 mm length including 40 measurement points up to 55, the maximum value, average value and standard deviation of FWHM are 17.0 arcsec, 10.4 arcsec and 2.8 arcsec, respectively, and the peak angle of The difference between the maximum value and the minimum value was 0.10 °.

Next, ω scans were performed at 1 mm intervals on a line segment having a length of 59 mm parallel to the a axis passing through the approximate center of the gallium polar surface. In each ω scan, the X-ray incident surface was parallel to the a-axis. That is, X-rays were incident on the gallium polar surface of the sample from a direction perpendicular to the m-axis.
The XRC peak angle and FWHM of (004) reflection at all measurement points were as shown in Table 2 below.

The maximum value, average value, and standard deviation of FWHM between all measurement points were 24.3 arcsec, 13.0 arcsec, and 4.2 arcsec, respectively. The difference between the maximum value and the minimum value of the peak angle between all measurement points was 0.16 °.
Measurement point No. 11 to measuring point No. Looking at a section of 40 mm length including 40 measurement points up to 50, the maximum value, average value and standard deviation of FWHM are 23.2 arcsec, 12.7 arcsec and 3.7 arcsec, respectively, and the peak angle of The difference between the maximum value and the minimum value was 0.11 °.

<Infrared absorption spectrum measurement>
When the infrared absorption spectrum of the produced C-plane GaN substrate was measured, a plurality of absorption peaks attributed to a gallium vacancy-hydrogen complex were observed at 3100-3500 cm ⁻¹ . Some of the plurality of absorption peaks, the peak wavelength was contained four peaks in each 3150cm around ^-1, 3164 cm around ^-1, around 3176Cm ^-1 and around 3188cm ^-1.

3.2. Experiment 2 <Production of C-plane GaN substrate>
A C-plane GaN substrate having a thickness of 330 μm cut out from the GaN crystal grown in an ammonothermal manner in the experiment 1 is used as a GaN seed, and a crystal growth apparatus of the type shown in FIG. A GaN crystal was grown. The GaN seed was CMP-finished on both main surfaces in order to remove the damage layer formed during planarization by grinding.
As the feedstock, polycrystalline GaN synthesized by a method of reacting gaseous GaCl obtained by bringing HCl gas into contact with simple substance Ga under heating and NH ₃ gas was used.
NH ₄ F and NH ₄ I were used as mineralizers. The amounts of NH ₄ F and NH ₄ I were each 1% in terms of a molar ratio to NH ₃ . NH ₄ I was synthesized by introducing HI into a Pt capsule after NH ₃ was added.

The growth conditions are as follows: the average value of the temperature Tg of the crystal growth zone and the temperature Ts of the raw material dissolution zone is 605 to 610 ° C., the temperature difference between the crystal growth zone and the raw material dissolution zone is 5 to 10 ° C. (Ts> Tg), and the pressure is 220 MPa. It was.
By growing for 28 days, a GaN crystal grew in the [000-1] direction by 1.8 mm on the nitrogen polar surface of the GaN seed.
Next, the grown GaN crystal was processed to produce a C-plane GaN substrate having a diameter of 50 mm. The main surface of the GaN substrate was ground and flattened on both sides, and further subjected to CMP to remove the damaged layer. The final substrate thickness was 350 μm.

<X-ray rocking curve measurement>
XRC of (004) reflection on the gallium polar surface of the produced C-plane GaN substrate was measured in the same manner as in Experiment 1.
First, ω scans were performed at 1 mm intervals on a line segment having a length of 48 mm parallel to the m-axis passing through the approximate center of the gallium polar surface. In each ω scan, the X-ray incident surface was parallel to the m-axis. That is, X-rays were incident on the gallium polar surface of the sample from a direction orthogonal to the a-axis.
The XRC peak angle and FWHM of (004) reflection at all measurement points were as shown in Table 3 below.

The maximum value, average value, and standard deviation of FWHM between all measurement points were 17.5 arcsec, 10.2 arcsec, and 2.3 arcsec, respectively.
The difference between the maximum value and the minimum value of the peak angle between all measurement points was 0.08 °.
Measurement point No. 5 to the measurement point No. Looking at a section of 40 mm in length including 40 measurement points up to 44, the maximum value, average value, and standard deviation of FWHM are 12.6 arcsec, 9.6 arcsec, and 1.4 arcsec, respectively. The difference between the maximum value and the minimum value was 0.07 °.

Next, ω scans were performed at 1 mm intervals on a line segment having a length of 49 mm parallel to the a-axis passing through the approximate center of the gallium polar surface. In each ω scan, the X-ray incident surface was parallel to the a-axis. That is, X-rays were incident on the gallium polar surface of the sample from a direction perpendicular to the m-axis.
The XRC peak angle and FWHM of (004) reflection at all measurement points were as shown in Table 4 below.

The maximum value, average value, and standard deviation of FWHM between all measurement points were 18.2 arcsec, 9.5 arcsec, and 2.5 arcsec, respectively.
The difference between the maximum value and the minimum value of the peak angle between all measurement points was 0.07 °.
Measurement point No. 5 to the measurement point No. Looking at a section of 40 mm length including 40 measurement points up to 44, the maximum value, average value and standard deviation of FWHM are 18.2 arcsec, 9.5 arcsec and 2.7 arcsec, respectively, and the peak angle of The difference between the maximum value and the minimum value was 0.06 °.
<Infrared absorption spectrum measurement>
When the infrared absorption spectrum of the produced C-plane GaN substrate was measured, a plurality of absorption peaks attributed to the gallium vacancy-hydrogen complex were observed at 3140 to 3200 cm ⁻¹ .

3.3. Experiment 3
<Production of C-plane GaN substrate>
As a primary GaN seed, a C-plane GaN substrate cut out from a GaN crystal grown by the HVPE method was prepared. This C-plane GaN substrate had a CMP-finished nitrogen polar surface and a gallium polar surface, respectively. The orientation of the nitrogen polar surface was within 1 ° from [000-1].
On the nitrogen polar surface of the primary GaN seed, a pattern mask having a square lattice type periodic opening pattern made of a laminated film having a 100 nm thick Pt layer on a 100 nm thick TiW layer was formed. A lift-off method was used for patterning the mask.
The square lattice type periodic opening pattern was composed of a first linear opening and a second linear opening that formed an angle of 60 ° with each other. The line width of each linear opening was 50 μm. The pitch between the first linear openings was 4 mm, and the pitch between the second linear openings was 2 mm.
The longitudinal directions of the first linear opening and the second linear opening were respectively inclined by 12 ° from one of the intersecting lines between the nitrogen polar surface of the primary GaN seed and the M plane.

After forming the pattern mask, a GaN crystal was grown on the primary GaN seed by an acidic ammonothermal method using a crystal growth apparatus of the type shown in FIG.
As the feedstock, polycrystalline GaN synthesized by a method of reacting gaseous GaCl obtained by bringing HCl gas into contact with simple substance Ga under heating and NH ₃ gas was used.
NH ₄ F and NH ₄ I were used in combination as mineralizers. The amount of NH ₄ F and NH ₄ I is NH
_The molar ratio to _{3 was} 0.5% and 4.0%, respectively. NH ₄ I was synthesized by introducing HI (hydrogen iodide) into a Pt capsule after NH ₃ was added. The growth conditions are: the average value of the temperature Tg of the crystal growth zone and the temperature Ts of the raw material dissolution zone is 605 to 610 ° C., the temperature difference between the crystal growth zone and the raw material dissolution zone is 3 to 8 ° C. (Ts> Tg), and the pressure is 220 MPa. It was.
By growing for 22 days, a GaN crystal grew 3.2 mm in the [000-1] direction on the nitrogen polar surface of the primary GaN seed.

The GaN crystal grown in an ammonothermal manner was processed to produce a C-plane GaN substrate having a thickness of 430 μm. Specifically, a multi-wire saw was used to slice a GaN crystal parallel to the C plane, and after grinding and planarizing both main surfaces of the resulting blank substrate, the damaged layer was removed by further CMP finishing. .
Next, the same pattern mask as the pattern mask provided in the primary GaN seed was formed on the nitrogen-polar surface of the C-plane GaN substrate using a lift method. The orientation of the inclined square lattice pattern provided on the pattern mask was also the same as that of the primary GaN seed.

After forming the pattern mask, the C-plane GaN substrate was used as a secondary GaN seed, and a GaN crystal was grown by an acidic ammonothermal method.
A crystal growth apparatus of the type shown in FIG. 16 was used.
As the feedstock, polycrystalline GaN synthesized by a method of reacting gaseous GaCl obtained by bringing HCl gas into contact with simple substance Ga under heating and NH ₃ gas was used.
NH ₄ F and NH ₄ I were used in combination as mineralizers. The amount of NH ₄ F and NH ₄ I is NH
_The molar ratio with respect to ₃ was 1.0%. NH ₄ I was synthesized by introducing HI (hydrogen iodide) into a Pt capsule after NH ₃ was added.
The growth conditions are as follows: the average value of the temperature Tg of the crystal growth zone and the temperature Ts of the raw material dissolution zone is 605 to 610 ° C., the temperature difference between the crystal growth zone and the raw material dissolution zone is 5 to 10 ° C. (Ts> Tg), and the pressure is 220 MPa. It was.
With the growth for 28 days, a GaN crystal grew in the [000-1] direction by 2.0 mm on the nitrogen polar surface of the secondary GaN seed.
Next, the grown GaN crystal was processed to produce a conductive C-plane GaN substrate having a diameter of 50 mm. The main surface of the GaN substrate was ground and flattened on both sides, and further subjected to CMP to remove the damaged layer. The final substrate thickness was 309 μm.

<X-ray rocking curve measurement>
XRC of (004) reflection on the gallium polar surface of the produced C-plane GaN substrate was measured in the same manner as in Experiment 1.
First, ω scans were performed at intervals of 1 mm on a 47 mm long line segment passing through the approximate center of the gallium polar surface and parallel to the m-axis. In each ω scan, the X-ray incident surface was parallel to the m-axis. That is, X-rays were incident on the gallium polar surface of the sample from a direction orthogonal to the a-axis.
The XRC peak angle and FWHM of (004) reflection at all measurement points were as shown in Table 5 below.

The maximum value, average value, and standard deviation of FWHM between all measurement points were 19.7 arcsec, 11.2 arcsec, and 2.7 arcsec, respectively.
The difference between the maximum value and the minimum value of the peak angle between all measurement points was 0.10 °.
Measurement point No. 4 to the measurement point No. Looking at the section of 40 mm length including 40 measurement points up to 43, the maximum value, average value and standard deviation of FWHM are 19.7 arcsec, 11.2 arcsec and 3.1 arcsec, respectively, and the peak angle The difference between the maximum value and the minimum value was 0.10 °.

Next, ω scans were performed at 1 mm intervals on a line segment having a length of 46 mm parallel to the a-axis passing through the approximate center of the gallium polar surface. In each ω scan, the X-ray incident surface was parallel to the a-axis. That is, X-rays were incident on the gallium polar surface of the sample from a direction perpendicular to the m-axis.
The XRC peak angle and FWHM of (004) reflection at all measurement points were as shown in Table 6 below.

The maximum value, average value, and standard deviation of FWHM between all measurement points were 18.8 arcsec, 10.6 arcsec, and 2.1 arcsec, respectively.
The difference between the maximum value and the minimum value of the peak angle between all measurement points was 0.11 °.
Measurement point No. 4 to the measurement point No. Looking at a section of 40 mm in length including 40 measurement points up to 43, the maximum value, average value, and standard deviation of FWHM are 18.8 arcsec, 10.6 arcsec, and 2.1 arcsec, respectively. The difference between the maximum value and the minimum value was 0.10 °.

  As mentioned above, although this invention was demonstrated according to specific embodiment, each embodiment was shown as an example and does not limit the scope of the present invention. Each embodiment described in the present specification can be variously modified without departing from the gist of the invention, and is combined with the features described by the other embodiments within the scope that can be implemented. be able to.

10 C-plane GaN substrate 11 Gallium polar surface 12 Nitrogen polar surface 13 Side surface 20 Seed substrate 21 Gallium polar surface 22 Nitrogen polar surface 23 Side surface 30 Pattern mask 31 Linear opening 40 GaN crystal G Gap T Through hole V Void K Intersection 100 Crystal Growth apparatus 101 Autoclave 102 Capsule 102a Raw material dissolution zone 102b Crystal growth zone 103 Baffle 104 Pt wire 105 Vacuum pump 106 Ammonia cylinder 107 Nitrogen cylinder 108 Valve 109 Mass flow meter

Claims (24)

A C-plane GaN substrate capable of drawing at least one first line segment, which is a virtual line segment having a length of 40 mm, satisfying at least one of the following conditions (A1) and (B1) on the main surface:
(A1) On the first line segment, when the X-ray incident surface at the time of each ω scan is parallel to the first line segment and (004) XRC of reflection is measured at intervals of 1 mm, between all measurement points The XRC FWHM maximum is less than 30 arcsec;
(B1) On the first line segment, when the X-ray incident surface at the time of each ω scan is parallel to the first line segment and (004) XRC of reflection is measured at intervals of 1 mm, between all measurement points The difference between the maximum value and the minimum value of the XRC peak angle is less than 0.2 °.   The C-plane GaN substrate according to claim 1, wherein the first line segment satisfies the condition (A1). The C-plane GaN substrate according to claim 2, wherein the first line segment satisfies the following condition (A2) in addition to the condition (A1):
(A2) The XRC FWHM average among all measurement points on the first line segment obtained from the XRC measurement is less than 20 arcsec. The C-plane GaN substrate according to claim 2, wherein the first line segment satisfies the following condition (A3) in addition to the condition (A1):
(A3) The average and standard deviation of XRC FWHM between all measurement points on the first line segment obtained from the XRC measurement are less than 12 arcsec and less than 5 arcsec, respectively. At least one second line segment that is a virtual line segment having a length of 40 mm that satisfies at least one of the following conditions (C1) and (D1) can be drawn on the main surface on which the first line segment can be drawn. The C-plane GaN substrate according to any one of 1 to 4:
(C1) The second line segment is orthogonal to at least one of the first line segments, and on the second line segment, the X-ray incident surface at the time of each ω scan is made parallel to the second line segment. (004) When the XRC of reflection is measured at 1 mm intervals, the maximum value of FWHM of XRC between all measurement points is less than 30 arcsec;
(D1) The second line segment is orthogonal to at least one of the first line segments, and the X-ray incident surface at the time of each ω scan is parallel to the second line segment on the second line segment. When the XRC of (004) reflection is measured at 1 mm intervals, the difference between the maximum value and the minimum value of the peak angle of XRC between all measurement points is less than 0.2 °.   The C-plane GaN substrate according to claim 5, wherein the second line segment satisfies the condition (C1). The C-plane GaN substrate according to claim 6, wherein the second line segment satisfies the following condition (C2) in addition to the condition (C1):
(C2) The average FWHM of XRC between all measurement points on the second line segment obtained from the XRC measurement is less than 20 arcsec. The C-plane GaN substrate according to claim 6, wherein the second line segment satisfies the following condition (C3) in addition to the condition (C1):
(C3) The average and standard deviation of XRC FWHM between all measurement points on the second line segment obtained from the XRC measurement are less than 12 arcsec and less than 5 arcsec, respectively. The C-plane GaN substrate according to any one of claims 1 to 8, comprising a plurality of dislocation arrays arranged periodically on the main surface.   The C-plane GaN substrate according to claim 9, wherein the dislocation array is two-dimensionally arranged on the main surface.   The C-plane GaN substrate according to claim 10, wherein the dislocation array on the main surface has periodicity in two or more directions. The C-plane GaN substrate according to claim 1, wherein the concentration of Li, Na, K, Mg, and Ca is less than 1 × 10 ¹⁶ atoms / cm ³ .   The C-plane GaN substrate according to claim 12 containing F.   The C-plane GaN substrate according to claim 13, which contains one or more halogens selected from Cl, Br, and I in addition to F.   The C-plane GaN substrate according to claim 14 containing F and I. The C-plane GaN substrate according to claim 1, wherein the H concentration is 5 × 10 ¹⁷ atoms / cm ³ or more and 1 × 10 ²⁰ atoms / cm ³ or less. The C-plane GaN substrate according to claim ¹ , comprising a GaN crystal having an infrared absorption peak at 3140 to 3200 cm ⁻¹ belonging to a gallium vacancy-hydrogen complex.   The C-plane GaN substrate according to any one of claims 1 to 17, wherein each of the sizes in the [1-100] direction, the [10-10] direction, and the [01-10] direction is 45 mm or more.   The C-plane GaN substrate according to any one of claims 1 to 18, which has a disk shape and a diameter of 45 mm or more.   The C-plane GaN substrate according to any one of claims 1 to 19, which has a gallium polar surface whose orientation is within 5 ° from [0001].   A nitride semiconductor device comprising: preparing the C-plane GaN substrate according to any one of claims 1 to 20; and epitaxially growing one or more nitride semiconductors on the prepared C-plane GaN substrate. Manufacturing method.   21. A process for producing an epitaxial substrate, comprising: preparing the C-plane GaN substrate according to any one of claims 1 to 20; and epitaxially growing one or more nitride semiconductors on the prepared C-plane GaN substrate. Method.   A step of preparing a C-plane GaN substrate according to any one of claims 1 to 20, and a step of epitaxially growing a nitride semiconductor crystal on the prepared C-plane GaN substrate. Production method.   A method for producing a GaN layer bonded substrate, comprising: preparing the C-plane GaN substrate according to any one of claims 1 to 20; and bonding the prepared C-plane GaN substrate to a different composition substrate.