JP2009143802A - Gallium nitride substrate and nitride semiconductor epitaxial substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a GaN substrate which can provide a larger number of nitride semiconductor elements. <P>SOLUTION: An ingot 1 of a gallium nitride single crystal grown by a vapor-phase growth method is cut along specified planes S1, S2, and S3 to manufacture one or a plurality of single crystal gallium nitride substrates 7. The main surface of the single crystal gallium nitride substrate 7 is mirror-finished, and the main surface of the gallium nitride substrate 7 has a first region within 3 mm from the edge of the gallium nitride substrate 7, and a second region surrounded by the first region. The off angle formed by an axis crossing orthogonally with the main surface of the substrate and the C axis of the gallium nitride substrate takes the minimum value at a first point in the first region. The off angle formed by the axis crossing orthogonally with the main surface of the gallium nitride substrate 7 and the C axis of the gallium nitride substrate 7 is larger than zero over the second region of the main surface. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a gallium nitride substrate and a nitride semiconductor epitaxial substrate.

  Reference 1 (Japanese Patent Laid-Open No. 2001-196632) describes a nitride compound semiconductor light emitting device. A nitride-based compound semiconductor light-emitting device has an acceptor doping layer and an active layer made of a nitride-based compound semiconductor on a GaN substrate whose crystal orientation is inclined in the range of 0.05 ° to 2 ° with respect to the <0001> direction. is doing.

  Reference 2 (Japanese Patent Laid-Open No. 2000-223743) describes a nitride-based semiconductor light-emitting device. The nitride-based semiconductor light-emitting element is formed by forming a light-emitting layer made of a nitride-based semiconductor on the upper surface of a substrate made of GaN. The upper surface of the substrate of the nitride-based semiconductor light-emitting element is inclined at an angle of 0.03 to 10 degrees with respect to the C-plane.

  Reference 3 (Japanese Patent Laid-Open No. 2000-22212) describes a GaN wafer. A GaN wafer is produced by polishing. The off angle of the GaN wafer is within 3 degrees, the variation of the off angle is within 4 degrees in the plane, and the warpage of the GaN wafer is within 200 micrometers.

JP 2001-196632 A JP 2000-223743 A JP 2000-22212 A

  Documents 1 and 2 describe nitride semiconductor light emitting devices. These nitride semiconductor light emitting devices have a GaN substrate. The GaN wafer is produced by dividing it into pellets, and the size of the nitride semiconductor light emitting device is at most about 1 millimeter. Nitride semiconductor light emitting devices as described in Literature 1 and Literature 2 can be obtained only from a partial region of the GaN wafer. This is because a GaN wafer showing a desired angular distribution over the entire surface of the substrate has not been obtained.

  Accordingly, what is needed is that nitride semiconductor devices with suitable characteristics are fabricated in more areas of the wafer.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a GaN substrate capable of providing more nitride semiconductor elements, and a nitride semiconductor epitaxial substrate using the GaN substrate.

  One aspect of the present invention is a method of manufacturing a single crystal gallium nitride substrate. In this method, (a) a gallium nitride single crystal ingot grown in the direction of a predetermined axis by a vapor phase growth method is cut along a predetermined plane inclined with respect to the predetermined axis, A step of producing a plurality of single crystal gallium nitride substrates, wherein the main surface of the single crystal gallium nitride substrate is mirror-finished, and the main surface of the gallium nitride substrate is within 3 mm from the edge of the gallium nitride substrate The off-angle formed by the axis perpendicular to the main surface and the C-axis of the gallium nitride substrate is the first region and the second region surrounded by the first region. A minimum value is obtained at the first point in the first region on the main surface of the single crystal gallium nitride substrate.

  According to this method, a single crystal gallium nitride substrate is manufactured by cutting an ingot along a predetermined plane, and in this single crystal gallium nitride substrate, the off angle is a first point in the first region of the main surface. Take the minimum value.

  According to another aspect of the present invention, a method of manufacturing a single crystal gallium nitride substrate. This method includes (a) slicing a gallium nitride single crystal ingot grown by vapor deposition along a predetermined plane to produce one or a plurality of single crystal GaN slices, and (b) the single crystal GaN slice. Forming a single-crystal gallium nitride substrate having a main surface processed by polishing and / or grinding a sliced surface of a crystal GaN slice, wherein the main surface of the gallium nitride substrate is the gallium nitride A first region within 3 millimeters from the edge of the substrate and a second region surrounded by the first region; an axis orthogonal to the principal surface; and a C axis of the gallium nitride substrate; Is at a first point on the main surface of the single-crystal gallium nitride substrate, and the first point is in the first region.

  According to this method, since the ingot is sliced along a predetermined plane to produce a single crystal GaN slice, the single crystal nitridation in which the off-angle takes a minimum value at the first point in the first region of the main surface. A gallium substrate is produced.

  In the method of the present invention, an axis orthogonal to the main surface of the gallium nitride substrate may form an angle larger than zero with the C axis of the gallium nitride substrate in the first and second regions.

  According to this method, a single crystal gallium nitride substrate without a region having an off angle of zero is manufactured.

  In the method of the present invention, the off-angle takes a maximum value at a second point on the main surface of the gallium nitride substrate, and is an angle formed between an axis orthogonal to the main surface and the C axis of the gallium nitride substrate. May change substantially monotonously on a line segment connecting the first point and the second point.

  According to this method, the off-angle is zero in the second region of the main surface because it changes substantially monotonously on the line segment connecting the first point and the second point on the main surface. A single crystal gallium nitride substrate with no region is fabricated.

  In the method of the present invention, the off angle may be a value larger than zero on a non-closed curve on the main surface of the gallium nitride substrate, and the curve may be terminated at an edge of the main surface. Good.

  According to this method, a single crystal gallium nitride substrate in which a region having an off angle of zero is not present in the device manufacturing region is manufactured.

  Another aspect of the present invention is a gallium nitride substrate made of single-crystal gallium nitride and having a main surface. In this substrate, the off-angle formed by the axis orthogonal to the main surface and the C axis of the gallium nitride substrate is greater than zero over the main surface.

  According to this gallium nitride substrate, since the off-angle is larger than zero over the main surface, a semiconductor film having a good surface morphology can be formed on the gallium nitride substrate.

  Yet another aspect of the present invention is a gallium nitride substrate made of single-crystal gallium nitride and having a main surface. In the gallium nitride substrate, the main surface of the gallium nitride substrate has a first region within 3 millimeters from an edge of the gallium nitride substrate, and a second region different from the first region, The off-angle formed by the axis perpendicular to the main surface and the C axis of the gallium nitride substrate is greater than zero over the second region of the main surface.

  According to this gallium nitride substrate, since the off angle is larger than zero over the second region of the main surface, a semiconductor film having a good surface morphology in the second region can be formed on the gallium nitride substrate.

  In the gallium nitride substrate of the present invention, the off angle has a minimum value at a first point on the main surface of the single crystal gallium nitride substrate, and the first point is in the first region. May be.

  According to this method, since the ingot is sliced along a predetermined plane to produce a single crystal GaN slice, the single crystal nitridation in which the off-angle takes a minimum value at the first point in the first region of the main surface. A gallium substrate is produced. A semiconductor film having a good surface morphology at least in the second region can be formed on the gallium nitride substrate.

  In the gallium nitride substrate of the present invention, the off-angle is a value larger than zero on a non-closed curve on the main surface of the gallium nitride substrate, and the curve is terminated at an edge of the main surface. May be.

  According to this substrate, a single crystal gallium nitride substrate in which a region where the off angle is zero is not in the device manufacturing region is manufactured.

  In the gallium nitride substrate of the present invention, the maximum value of the distance between one point on the edge of the gallium nitride substrate and another point on the edge of the gallium nitride substrate is preferably 10 millimeters or more.

  According to this gallium nitride substrate, it is possible to provide a gallium nitride substrate in which the maximum value of the distance between one point on the edge and another point is 10 millimeters or more.

  In the gallium nitride substrate of the present invention, the area of the main surface of the gallium nitride substrate is preferably equal to or greater than the area of a circle having a diameter of 2 inches.

  According to this gallium nitride substrate, it is possible to provide a gallium nitride substrate having a main surface area larger than the area of a circle having a diameter of 2 inches.

  According to the gallium nitride substrate of the present invention, it is preferable that the off-angle is 0.15 degrees or more over the second region of the main surface. The surface morphology of the group III nitride semiconductor film formed on this gallium nitride substrate does not show a hexagonal pyramidal pattern.

  According to the gallium nitride substrate of the present invention, it is preferable that the off-angle is 0.3 degrees or more over the second region of the main surface. The group III nitride semiconductor film formed on the gallium nitride substrate does not exhibit a macrostep-like surface morphology.

  In the gallium nitride substrate of the present invention, the off angle is preferably less than 2 degrees over the second region of the main surface. The group III nitride semiconductor film formed on the gallium nitride substrate does not have a large scratch-like protrusion.

  In the gallium nitride substrate of the present invention, it is preferable that the off angle is 0.7 degrees or less over the second region of the main surface. In the group III nitride semiconductor film formed on this gallium nitride substrate, the surface morphology does not show scratch-like irregularities in the off-angle range of 0.7 degrees or less, and the surface roughness (Rms) is 0 at the maximum. Smaller to about 5 nanometers.

  According to still another aspect of the present invention, a nitride semiconductor epitaxial substrate includes the gallium nitride substrate described above and one or more group III nitride semiconductor films provided on the gallium nitride substrate. According to this nitride semiconductor epitaxial substrate, the group III nitride semiconductor film exhibits good surface morphology.

According to still another aspect of the present invention, a nitride semiconductor epitaxial substrate includes the above gallium nitride substrate and a first conductivity type Al _X1 Ga _Y1 In _1-X1-Y1 N provided on the gallium nitride substrate. (0 ≦ X1 ≦ 1,0 ≦ Y1 ≦ 1,0 ≦ X1 + Y1 ≦ 1) layer and, _Al is provided on the gallium nitride substrate _{X2 Ga Y2 in 1-X2-} Y2 N (0 ≦ X2 ≦ 1,0 ≦ Y2 ≦ 1, 0 ≦ X2 + Y2 ≦ 1) active layer and second conductivity type Al _X3 Ga _Y3 In _1-X3-Y3 N (0 ≦ X3 ≦ 1, 0) provided on the gallium nitride substrate ≦ Y3 ≦ 1, 0 ≦ X3 + Y3 ≦ 1).

According to the nitride semiconductor epitaxial substrate, the first conductivity type Al _X1 Ga _Y1 In _{1 -X1-Y1} N film, the Al _X2 Ga _Y2 In _{1 -X2-Y2} N film, and the second conductivity type Al _X3 Ga _Y3 In _1-X3-Y3 N film exhibits good surface morphology.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, it is possible to provide a GaN substrate that can provide more nitride semiconductor elements and a nitride semiconductor epitaxial substrate that uses this GaN substrate.

FIG. 1A illustrates a method for manufacturing a single crystal gallium nitride substrate. FIG. 1B is a drawing showing a III-V compound semiconductor substrate. FIG. 1C shows a cross-sectional view taken along the line I-I shown in FIG. FIG. 2A and FIG. 2B show a cross section of the ingot along the line II shown in FIG. FIG. 3A illustrates a single crystal gallium nitride substrate. FIG. 3B is a drawing showing a cross section taken along line II-II of a single crystal gallium nitride substrate produced by slicing an ingot along planes S1, S2, and S3. FIG. 3C is a drawing showing a cross section of one substrate of a single crystal gallium nitride substrate manufactured by slicing an ingot along planes T1, T2, and T3. FIG. 3D illustrates a single crystal gallium nitride substrate manufactured by a modification of the method for manufacturing a single crystal gallium nitride substrate. FIG. 4 is a drawing showing the relationship between the surface roughness of the gallium nitride film formed on the gallium nitride substrate and the off angle. FIG. 5 is a drawing showing the off-angle distribution on the main surface of the single crystal gallium nitride substrate shown in FIG. FIG. 6 is a drawing showing the off-angle distribution on the main surface of the single crystal gallium nitride substrate shown in FIG. FIG. 7 is a drawing showing the off-angle distribution on the main surface of another single crystal gallium nitride substrate. FIG. 8 is a diagram showing the relationship between the distance from the reference point and the off angle. 9A, 9B, and 9C are views showing a method of forming a nitride semiconductor epitaxial substrate and a method of manufacturing a gallium nitride based semiconductor device according to the present embodiment. FIGS. 10A and 10B are drawings showing a method of forming a nitride semiconductor epitaxial substrate and a method of manufacturing a gallium nitride based semiconductor device according to the present embodiment. FIG. 11A is a drawing showing a distribution of photoluminescence wavelengths of an epitaxial substrate using the substrate manufactured by the method shown in FIG. FIG. 11B shows a histogram of the distribution shown in FIG. The off angles on the main surface are distributed in the range of 0.15 degrees or more and 0.7 degrees or less. FIG. 12A is a drawing showing a distribution of photoluminescence intensity of an epitaxial substrate using the substrate manufactured by the method shown in FIG. FIG. 12B shows a histogram of the distribution shown in FIG.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Next, embodiments of the method for manufacturing a single crystal gallium nitride substrate, the gallium nitride substrate, and the nitride semiconductor epitaxial substrate of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

(First embodiment)
FIG. 1A illustrates a method for manufacturing a single crystal gallium nitride substrate. FIG. 1B is a drawing showing a III-V compound semiconductor substrate. FIG. 1C shows a cross-sectional view taken along the line I-I shown in FIG.

First, a gallium nitride single crystal ingot formed by vapor deposition is prepared. Referring to FIG. 1A, a gallium nitride single crystal ingot 1 is shown. The gallium nitride ingot 1 is manufactured as follows, for example. A mask is formed on a III-V compound semiconductor substrate 3 such as a GaAs (111) single crystal substrate as shown in FIG. This mask has windows arranged in an array in the [11-2] direction and the [−110] direction, respectively. A GaN buffer layer is grown on the mask window at a low temperature. Next, at a high temperature, another GaN layer is epitaxially grown on the GaN buffer layer and the mask by using a vapor deposition method such as a hydride vapor deposition (HVPE) method. Thereafter, the GaAs substrate is removed, and the GaN single crystal substrate 5 is manufactured. The GaAs substrate 3 can be removed by etching with aqua regia. A GaN epitaxial layer having a thickness of at least 10 millimeters is formed on the GaN single crystal substrate 5 to form a GaN ingot 1.

  The single crystal ingot 1 is grown in the direction of a predetermined axis Ax by a vapor phase growth method. On the other hand, as shown in FIG. 1B, the III-V compound semiconductor substrate 3 is not substantially warped. The single crystal ingot 1 shown in FIG. 1 (A) is warped in a convex or concave shape depending on the production conditions and / or the thickness of the ingot. In FIG. 1 (C), the gallium surface 1a is a curved surface curved in a concave shape, and C surfaces ((0001) surfaces) 3a, 3b, 3c in the single crystal ingot 1 are schematically shown.

  FIG. 2A and FIG. 2B show a cross section along the line I-I. FIG. 2A shows several C-axes C1, C2, and C3. The axis Ax extends along the C axis. For example, the distances D1, D2, and D3 between the axis C1 and the axis C2 in the X direction become narrower as the Z-axis coordinate becomes larger. These C surfaces extend along a convex surface or a concave surface.

  The gallium nitride substrate can be manufactured using, for example, the following method. The single crystal ingot 1 is cut along predetermined planes S1, S2, and S3 to produce one or a plurality of single crystal gallium nitride substrates. The predetermined axis is inclined with respect to an axis Ax extending in the longitudinal direction of the ingot 1.

  The predetermined planes S1, S2, and S3 are not orthogonal to any C-axis in the ingot 1. The planes S1, S2, and S3 are orthogonal to the axis Ox that does not intersect the ingot 1. For example, the angle formed between the plane S1 (similarly to the planes S2 and S3) and the C axis decreases substantially monotonically as the coordinate value on the X axis increases.

  FIG. 2B shows several C-axes C1, C2, and C3 as in FIG. 2A. The axes Ax and Ox extend along the C axis. The axis Ox extends in the longitudinal direction of the ingot 1.

  In the example shown in FIG. 2B, the single crystal ingot 1 is cut along predetermined planes T1, T2, and T3 to produce one or a plurality of single crystal gallium nitride substrates.

  The predetermined planes T1, T2, and T3 are also orthogonal to the C axis in the ingot 1. The planes T1, T2, and T3 are orthogonal to the axis Ox in the ingot 1. For example, the angle formed between the C axis passing through a certain plane and the plane T1 (the same applies to the planes T2 and T3) increases substantially monotonically as the one moves away from the axis Ox.

  FIG. 3A shows a single crystal gallium nitride substrate obtained by the method shown in FIG. The main surface 7a of the single crystal gallium nitride substrate 7 is mirror finished. The main surface 7a of the single crystal gallium nitride substrate 7 has a first region 7b within 3 millimeters from the edge, and a second region 7c surrounded by the first region 7b. A broken line 7d in FIG. 3A indicates a boundary between the first region 7a and the second region 7b.

  FIG. 3B is a drawing showing a cross section of one substrate of a single crystal gallium nitride substrate manufactured by slicing the ingot 1 along the planes S1, S2, and S3, and this cross section is along the line II-II. It has been taken. FIG. 3C is a drawing showing a cross section of one of the single crystal gallium nitride substrates manufactured by slicing the ingot 1 along the planes T1, T2, and T3. In the cross sections shown in FIGS. 3B and 3C, several C-axes are drawn with solid lines. In the single crystal gallium nitride substrate 9 shown in FIG. 3C, the off-angle is zero at a certain point near the center of the substrate, and the off-angle (Ang1, Ang2: Ang1 <Ang2) increases as the distance from this point increases. It has become. On the other hand, in the single crystal gallium nitride substrate 7 shown in FIG. 3B, there is no region where the off angle is zero in the main surface 7 a of the substrate 7. According to the method according to the embodiment, the single crystal gallium nitride substrate 7 is manufactured by cutting the ingot 1 along a predetermined plane. In the single crystal gallium nitride substrate 7, the off angle is the first of the main surface 7a. The minimum value is obtained at the first point (point 7e on the edge of the substrate in the substrate 7) in the region 7b. In the substrate 7, in the film formed on the region where the off angle is close to zero, the surface morphology shows a hexagonal pyramid appearance, which may hinder further improving the characteristics of the semiconductor device. The off angle is larger than zero over the entire second region 7c of the main surface 7a, and takes a minimum value at a point 7e in the first region 7b on the main surface 7a of the single crystal gallium nitride substrate 7. This minimum value is greater than zero.

  The axis orthogonal to the main surface 7a of the gallium nitride substrate 7 forms an angle larger than zero (Ang3, Ang4: Ang3 <Ang4) with the C axis of the gallium nitride substrate 7 in the first and second regions 7b and 7c. . According to this manufacturing method, a single crystal gallium nitride substrate without a region having an off angle of zero is manufactured. According to the gallium nitride substrate 7, since the off angle is larger than zero over the main surface, a semiconductor film having a good surface morphology can be formed on the gallium nitride substrate.

  FIG. 3D illustrates a single crystal gallium nitride substrate manufactured by a modification of the method for manufacturing a single crystal gallium nitride substrate. Also in this method, one or a plurality of single crystal GaN slices are obtained by slicing a gallium nitride single crystal ingot 1 grown in the direction of a predetermined axis Ax by vapor phase growth along predetermined planes S1, S2, and S3. Make it. For example, the single crystal gallium nitride substrate 11 having the main surface processed by polishing and / or grinding the slice surface of the single crystal GaN slice is formed.

  According to this manufacturing method, since the ingot is sliced along a predetermined plane to produce a single crystal GaN slice, the single crystal whose off-angle takes a minimum value at the first point in the first region of the main surface A gallium nitride substrate 11 is produced.

  The off-angle takes a minimum value at a point 11e in the first region 11b on the main surface 11a of the single crystal gallium nitride substrate 11. This minimum value is zero in this embodiment. In general, in the production of a semiconductor device, the outer peripheral region (for example, a region 3 millimeters from the edge of the substrate) 11b of the substrate 11 is not used for producing a semiconductor device. Therefore, a point or a region where the off angle is zero may be provided in the outer peripheral region 11b.

  According to this gallium nitride substrate 11, since the off angle is larger than zero over the second region 11c of the main surface, a semiconductor film having a good surface morphology is formed on the gallium nitride substrate 11 in the second region 11c. The

  In the substrate 7 (11) shown in FIG. 3B (and FIG. 3D), the off-angle is the first point 7e (on the main surface 7a (11a) of the gallium nitride substrate 7 (11). 11e) takes the minimum value and the second point 7f (11f) takes the maximum value. The off-angle changes substantially monotonously on a line segment connecting the point 7e (11e) indicating the minimum value and the point 7f (11f) indicating the maximum value. According to the substrates 7 and 11, the off-angle changes substantially monotonously on the line segment, and thus the single crystal gallium nitride substrates 7 and 11 to be manufactured have the second surface of the main surface 7a (11a). The region 7c (11c) does not have a region where the off angle is zero.

  In the gallium nitride substrates 7 and 11, the maximum value of the distance between the first point on the edge of the gallium nitride substrate 7 and 11 and the second point on the edge of the gallium nitride substrate 7 and 11 is 10 millimeters or more. You can Further, according to the gallium nitride substrates 7 and 11, it is possible to provide a gallium nitride substrate in which the areas of the main surfaces 7a and 11a are not less than the area of a circle having a diameter of 2 inches.

  FIG. 4 is a drawing showing the relationship between the surface roughness of the gallium nitride film formed on the gallium nitride substrate and the off angle. The horizontal axis indicates the off-angle of the gallium nitride substrate, and the vertical axis indicates the surface roughness (mean square root roughness: Rms) of the gallium nitride film. The thickness of the gallium nitride film formed on the gallium nitride substrate is 2 micrometers.

  In order to use a gallium nitride substrate with an accurately adjusted off angle in the experiment, a 10-inch square experimental substrate is specially cut by cutting a 2-inch gallium nitride substrate manufactured by the method described above. Make it. The variation in the off angle of the 2-inch diameter gallium nitride substrate available to the inventor is about 0.3 degrees, so the variation in the off angle in the experimental substrate is estimated to be within a range of about 0.06 degrees. The variation in thickness of each experimental substrate is in the range of about 1 micrometer or less.

A gallium nitride film is grown on these experimental substrates. In the hole measurement performed on the gallium nitride film, the carrier concentration is 200 cm ² / Vsec, and the carrier concentration is 5 × 10 ¹⁸ cm ⁻³ . The half width of the (0002) plane OMEGA scan using the X-ray diffraction method is 100 arcsec, and the gallium nitride film has good crystal quality. For this measurement, a thin film material crystallinity analysis X-ray diffractometer (in this embodiment, X'Pert MRD system, manufactured by Philips Japan) is used.

  The surface of the epitaxial film is measured with an atomic force microscope (AFM). As shown in FIG. 4, the surface roughness increases as the off-angle increases in a region having an angle of 0.5 degrees or more. When the surface of a gallium nitride film such as a gallium nitride film grown on a gallium nitride substrate is observed using a differential interference microscope, the surface morphology is classified as follows.

  In FIG. 4, hexagonal pyramidal protrusions / dents appear in an off-angle range OA1 of 0.15 degrees or less. In the off-angle range OA2 that is greater than 0.15 degrees and less than or equal to 0.3 degrees, stepped irregularities appear. In the off-angle range OA3 that is greater than 0.3 degree and less than or equal to 0.7 degree, a flat surface appears. In an off angle range OA4 that is greater than 0.7 degrees and less than 2 degrees, a scratch-like pattern appears. In the off angle range greater than 2 degrees, a large scratch-like pattern appears.

On the main surface of the single crystal gallium nitride substrate according to the above embodiment, the off angle is adjusted. By growing an Al _X1 Ga _{YIn 1- XYN} (0 ≦ X1 ≦ 1, 0 ≦ Y1 ≦ 1, 0 ≦ X1 + Y1 ≦ 1) film such as a gallium nitride film on this gallium nitride substrate, As shown, good surface morphology and surface roughness (Rms) are achieved.

  For example, in the off angle range of greater than zero and less than 2 degrees, the surface morphology shows a hexagonal pyramidal pattern, stepped unevenness, atomic step or scratch pattern, and the surface roughness (Rms) is 2 at the maximum. It becomes small to about nanometer. Light emitting diodes manufactured using this substrate emit light almost uniformly. A surface having a surface roughness (Rms) of less than 2 nanometers is suitable as a base for a quantum well structure active layer including a well layer having a thickness of about 1 to 5 nanometers.

  For example, in the off angle range of more than 0.15 degrees and less than 2.0 degrees, the surface morphology shows a step-like unevenness, atomic step or scratch-like pattern, and the surface roughness (Rms) is 2. It is about 0 nanometer. Light emitting diodes manufactured using this substrate emit light almost uniformly.

  For example, in an off angle range of greater than zero and less than or equal to 0.7 degrees, the surface morphology indicates a hexagonal pyramidal pattern, stepped unevenness, or atomic step pattern, and the surface roughness (Rms) is 0 at the maximum. Smaller to about 5 nanometers. Light emitting diodes manufactured using this substrate emit light substantially uniformly.

  For example, in an off angle range of greater than 0.15 degrees and less than or equal to 0.7 degrees, the surface morphology indicates stepped irregularities or atomic steps, and the surface roughness (Rms) is up to about 0.5 nanometers. Get smaller. Light emitting diodes manufactured using this substrate emit light uniformly.

  For example, in an off angle range of greater than 0.3 degrees and less than or equal to 0.7 degrees, the surface morphology shows flatness indicating atomic steps, and the surface roughness (Rms) is up to about 0.3 nanometers. Get smaller. The light emitting diode emits light uniformly over the entire surface. For example, since the variation in the off angle of a 2-inch gallium nitride substrate is about 0.3 degrees, a good surface morphology can be obtained on almost the entire surface of the gallium nitride substrate.

  FIG. 5 is a drawing showing the off-angle distribution on the main surface of the single crystal gallium nitride substrate shown in FIG. The minimum value and the maximum value of the off-angle are in a region from the edge of the substrate 13 to 3 millimeters. In this substrate 13, the off-angle is distributed in the range of 0.3 ° to 0.7 °. In the distribution shown in FIG. 5, the off angles are 0.3 to 0.4 degrees, 0.4 to 0.5 degrees, 0.5 to 0.6 degrees, 0.6 to Each band-like region of 0.7 degrees is lined up. When a group III nitride film is epitaxially grown on the substrate (2 inch size) 13, the surface morphology is improved over the entire epitaxial film.

  FIG. 6 is a drawing showing the off-angle distribution in the main surface of the single crystal gallium nitride substrate shown in FIG. In the distribution shown in FIG. 6, the off angle is 0.2 to 0.4 degree and the 0.4 to 0.6 degree in order from the bottom of the figure next to the area having the off angle of 0 to 0.2 degree. 0.6-0.8 degree, 0.8-1.0 degree, 1.0-1.2 degree, 1.2-1.4 degree, 1.4-1.6 degree, 1.6- The belt-shaped regions of 1.8 degrees and 1.8 to 2.0 degrees are arranged. In this substrate 15, the off angle is zero at one point close to the edge of the substrate. The off-angle increases with distance from this point. At the other end on the edge of the substrate, the off-angle is 2 degrees or less and close to 2 degrees.

FIG. 7 is a drawing showing the off-angle distribution on the main surface of another single crystal gallium nitride substrate. In the substrate 17, there is no point where the off angle is zero in the main surface of the substrate 17. In the distribution shown in FIG. 7, the off angles of 0.2 to 0.25 degrees, 0.25 to 0. 3 degrees, 0.3 to 0.35 degrees, 0.35 to 0.4 degrees, 0.4 to 0.45 degrees, 0.45 to 0.5 degrees, 0.5 to 0.55 degrees, 0. Band-shaped regions of 55 to 0.60 degrees, 0.65 to 0.70 degrees, and 0.70 to 0.75 degrees are arranged. The minimum and maximum off angles are in the region of 3 millimeters from the edge of the substrate. The minimum value of the off angle is 0.15 degrees, and the maximum value is 0.7 degrees. When a gallium nitride film is epitaxially grown on a substrate in the off-angle range, the substrate has a stepped or flat surface morphology. The radius of curvature of the C plane is 5.5 meters.

When the off-angle Angle is small using the distance L from the reference point where the off-angle is zero, the radius of curvature R, and the off-angle Angle,
Angle = L / R
It is expressed. FIG. 8 is a diagram showing the relationship between the distance from the reference point and the off angle. In FIG. 8, several lines L1, L2, L3, L4, L5, and L6 are drawn with respect to the radius of curvature, and these lines correspond to the radius of curvature of the C plane of the ingot. Lines L1, L2, L3, L4, L5, and L6 indicate a curvature radius of 1 meter, 1.5 meters, 2 meters, 2.5 meters, 3 meters, and 5 meters, respectively. In a 2-inch substrate, the radius of curvature is 1.5 meters or more in order to make the off-angle larger than zero and 2 degrees or less. Further, the substrate having the off-angle distribution shown in FIG. 5 is manufactured using an ingot having a curvature radius of 7.5 meters.

  As described above, the gallium nitride ingot warps in a concave or convex shape. When a flat substrate is produced by grinding at least one of this ingot and polishing, the off-angle exhibits a distribution on the main surface of the substrate. In the main surface of the substrate, lines showing equal off angles are represented by substantially concentric or concentric arcs.

  When the group III nitride single crystal film is epitaxially grown on the substrate, the surface morphology is not good in a region where the off angle is zero or close to zero. The characteristics of the semiconductor device formed on this region are not as good as those of the semiconductor device formed on the region exhibiting good surface morphology. If the element formation region of the substrate includes a region where the off angle is zero or close to zero, the yield in semiconductor production is lowered.

  If there is no region where the off angle is zero on the main surface of the substrate, the surface morphology of the epitaxial layer is improved, and as a result, the yield of semiconductor devices is improved.

  On the other hand, generally, the outer peripheral portion of the substrate deteriorates the characteristics of the semiconductor device due to, for example, nonuniform gas flow when performing vapor phase epitaxial growth. For this reason, the outer peripheral portion of the substrate is not utilized for manufacturing a semiconductor device. Therefore, it is preferable to slice the substrate so that the point where the off angle is zero is on the outer periphery of the substrate.

  Referring to FIGS. 5, 6, and 7, lines having equal off angles are shown in the main surface of the single crystal gallium nitride substrate. These lines are drawn for several off angles greater than zero. These curves terminate at the edge of the main surface (substrate edge) and are non-closed curves on the main surfaces 7a and 11a of the gallium nitride substrates 7 and 11. These are substantially convex curves.

  According to the gallium nitride substrates 7 and 11, the off angle is preferably 0.15 degrees or more over the second regions of the main surfaces 7a and 11a. The surface morphology of the group III nitride semiconductor film formed on the gallium nitride substrates 7 and 11 does not show a hexagonal pyramidal pattern. Preferably, the off-angle is 0.15 degrees or more over the first and second regions of the main surfaces 7a and 11a.

  According to the gallium nitride substrates 7 and 11, the off angle is preferably 0.3 degrees or more over the second regions of the main surfaces 7a and 11a. The group III nitride semiconductor film formed on the gallium nitride substrates 7 and 11 exhibits a substantially flat surface morphology. Preferably, the off angle is 0.3 degrees or more over the first and second regions of the main surfaces 7a and 11a.

  In the gallium nitride substrates 7 and 11, the off-angle is preferably less than 2 degrees over the second regions 7c and 11c of the main surfaces 7a and 11a. The group III nitride semiconductor film formed on the gallium nitride substrate does not show large scratch-like irregularities.

  In the gallium nitride substrates 7 and 11, the off angle is preferably 0.7 degrees or less over the second regions 7c and 11c of the main surfaces 7a and 11a. The group III nitride semiconductor film formed on the gallium nitride substrates 7 and 11 has a surface morphology of a hexagonal pyramid pattern, stepped unevenness, or atomic step in an off angle range of 0.7 degrees or less. A pattern is shown, and the surface roughness (Rms) decreases to a maximum of about 0.5 nanometer. Preferably, the off angle is 0.7 degrees or less over the first and second regions 7b, 7c, 11b, and 11c of the main surfaces 7a and 11a.

  As described above, according to the present embodiment, a GaN substrate that can provide more nitride semiconductor elements and a method of manufacturing the GaN substrate are provided.

(Second Embodiment)
9 (A) to 9 (C), FIG. 10 (A), and FIG. 10 (B) show a method of forming a nitride semiconductor epitaxial substrate and a method of manufacturing a gallium nitride based semiconductor device according to this embodiment. It is drawing which shows.

A single crystal gallium nitride substrate 21 is prepared. The single crystal gallium nitride substrate 21 can be manufactured by the method described in the first embodiment. Prior to the growth of the group III nitride film, pretreatment of the gallium nitride substrate 21 is performed in the OMVPE apparatus 23 as shown in FIG. The gallium nitride substrate 21 is placed on the susceptor 25 of the OMVPE apparatus 23. The gallium nitride substrate 21 is heat-treated while flowing the process gas, and the surface 21a of the gallium nitride substrate 21 is planarized. By this flattening, it is possible to reduce polishing scratches on the surface 21a of the gallium nitride substrate 21 caused by mechanical polishing. In a preferred embodiment, the process gas can include ammonia (NH ₃ ) and hydrogen (H ₂ ).

As shown in FIG. 9B, a gallium nitride-based film 29 is formed on the main surface 21a of the gallium nitride substrate 21 using a source gas. In the present embodiment, the GaN film is directly grown on the main surface 21 a of the gallium nitride substrate 21 using the OMVPE apparatus 23. The susceptor temperature is set higher than the pretreatment temperature. The source gas can include trimethyl gallium (TMG), ammonia (NH ₃ ), hydrogen (H ₂ ), and nitrogen (N 2). If required, silane (SiH ₄ ) can be used for the n-type dopant. After this step, the nitride semiconductor epitaxial substrate 32 including the group III nitride film formed on the gallium nitride substrate is obtained.

  As shown in FIG. 9C, a device region is formed. For the device region, one or more other group III nitride films 31 such as an active layer are formed on the main surface 21 a of the gallium nitride substrate 21. The active layer can have, for example, a single quantum well (SQW) structure or a multiple quantum well (MQW) structure. In this embodiment, an active layer having a multiple quantum well structure is formed. The susceptor temperature is set lower than the susceptor temperature in the growth of the GaN film. For example, an InGaN film is grown for a well layer having a multiple quantum well structure. Further, an InGaN film having a larger band gap than the InGaN semiconductor of the well layer is grown for the barrier layer. For example, to produce a light emitting diode, a multiple quantum well structure having five thin well layers is produced. After this step, a nitride semiconductor epitaxial substrate having a plurality of group III nitride films formed on the gallium nitride substrate is obtained.

Next, as shown in FIG. 9C, another group III nitride film 33 is formed on the main surface 21 a of the gallium nitride substrate 21. In this embodiment, an AlGaN film is grown on the active layer using the OMVPE apparatus 23. The susceptor temperature is higher than the temperature at the time of forming the active layer. The source gas can contain trimethylgallium (TMG), trimethylaluminum (TMA), ammonia (NH ₃ ), hydrogen (H ₂ ), and nitrogen (N ₂ ). If necessary, biscyclopentadienyl magnesium (CP ₂ Mg) can be used for the p-type dopant. For example, an Mg-doped AlGaN film is formed to obtain a p-type AlGaN film. After this step, a nitride semiconductor epitaxial substrate having a plurality of group III nitride films formed on the gallium nitride substrate is obtained.

  Subsequently, as shown in FIG. 9C, another gallium nitride film 35 is formed on the main surface 21 a of the gallium nitride substrate 21. In the present embodiment, an Mg-doped GaN film is grown on a p-type AlGaN film using the OMVPE apparatus 23 to obtain a p-type GaN film. By this step, a nitride semiconductor epitaxial substrate 37 having a plurality of group III nitride films formed on the gallium nitride substrate is obtained.

  Thereafter, as shown in FIG. 10A, an n-type ohmic electrode 39 is formed on the back surface 21 b of the gallium nitride substrate 21. The p-type ohmic electrode 41 and the pad electrode 43 are formed on the epitaxial film produced in the step shown in FIG.

  After the pad electrode is formed, the substrate is separated along broken lines CUT1 and CUT2 shown in FIG. 10B to obtain a semiconductor light emitting device 51 such as a light emitting diode. Using these manufacturing steps, a group III nitride semiconductor device can be manufactured.

  As described above, according to the present embodiment, a method for manufacturing a gallium nitride based semiconductor device is provided. According to the present embodiment, a nitride semiconductor epitaxial substrate is also produced. This nitride semiconductor epitaxial substrate includes a single crystal gallium nitride substrate having a predetermined distribution of off angles, and one or more group III nitride semiconductor layers provided on the gallium nitride substrate. According to this nitride semiconductor epitaxial substrate, the group III nitride semiconductor film exhibits good surface morphology.

The following nitride semiconductor epitaxial substrate can be manufactured using the method of manufacturing the nitride semiconductor epitaxial substrate according to the present embodiment. The nitride semiconductor epitaxial substrate includes a single-crystal gallium nitride substrate having a predetermined distribution of off angles, and a first conductivity type Al _X1 Ga _Y1 In _1-X1-Y1 N (0 ≦ 1) provided on the gallium nitride substrate. X1 ≦ 1, 0 ≦ Y1 ≦ 1, 0 ≦ X1 + Y1 ≦ 1) layer and Al _X2 Ga _Y2 In _1-X2-Y2 N (0 ≦ X2 ≦ 1, 0 ≦ Y2 ≦) provided on the gallium nitride substrate 1 and 0 ≦ X2 + Y2 ≦ 1) layer and a second conductivity type Al _X3 Ga _Y3 In _1-X3-Y3 N (0 ≦ X3 ≦ 1, 0 ≦ Y3 ≦) provided on the gallium nitride substrate. 1, 0 ≦ X3 + Y3 ≦ 1) layer. The active layer is provided between the first conductivity type Al _X1 Ga _Y1 In _1-X1-Y1 N layer and the second conductivity type Al _X3 Ga _Y3 In _1-X3-Y3 N layer. According to the nitride semiconductor epitaxial substrate, the first conductivity type Al _X1 Ga _Y1 In _{1 -X 1 -Y 1} N layer, the Al _{X 2} Ga _{Y 2} In _{1 -X} 2 _{-Y 2} N layer, and the second conductivity type Al _{X 3} Ga _{Y 3} In _{1 The -X3-Y3} N layer exhibits good surface morphology.

In one example epitaxial substrate,
n-type GaN substrate thickness: 400 micrometers,
n-type GaN film thickness: 1 micrometer,
Undoped In _0.15 Ga _0.85 N well layer: 2 nanometers
Undoped In _0.01 Ga _0.99 N barrier layer: 15 nanometers,
p-type AlGaN layer: 20 nanometers,
p-type GaN layer: 50 nanometers,
It is.

  FIG. 11A is a drawing showing a distribution of photoluminescence wavelengths of an epitaxial substrate using the substrate manufactured by the method shown in FIG. FIG. 11B shows a histogram of the distribution shown in FIG. The off angles on the main surface are distributed in the range of 0.15 degrees or more and 0.7 degrees or less. FIG. 12A is a drawing showing the distribution of photoluminescence intensity of the same epitaxial substrate. FIG. 12B shows a histogram of the distribution shown in FIG. FIGS. 11A and 12A show measurements made on an epitaxial substrate fabricated using a 2-inch gallium nitride substrate.

  According to the measurement results of FIGS. 11A and 11B, the average value is 441.5 nanometers, the standard deviation is 1.65 nanometers, and the distribution width is −2 nanometers to +2 nanometers.

  In the measurement results of FIGS. 12A and 12B, the value obtained by dividing the standard deviation SIG of the intensity by the average value AVE (SIG / AVE) is about 15%, and the light emission is almost uniform in the plane. I understand that. On the other hand, when using a substrate in which the off-angle of the substrate is also distributed in a range of zero degrees or more and less than 0.15 degrees and an angle range exceeding 2 degrees, the photoluminescence intensity decreases in these ranges, The photoluminescence wavelength is shifted to a long wavelength. These reduce the yield of semiconductor devices.

While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. In the present embodiment, for example, a semiconductor light emitting element such as a light emitting diode has been described. However, the present invention is not limited to the specific configuration disclosed in the present embodiment. In this embodiment, a gallium nitride film formed on a gallium nitride substrate is described as an example. However, a group III nitride semiconductor (Al _X In _Y Ga _1- XYN, 0 ≦ X <1, 0 ≦ Y <1, 0 ≦ X + Y <1) A film can also be formed. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

DESCRIPTION OF SYMBOLS 1 ... Gallium nitride single crystal ingot, 3 ... III-V compound semiconductor substrate, 5 ... GaN single crystal substrate, 3a, 3b, 3c ... C plane ((0001) plane), C1, C2, C3 of single crystal ingot Single-crystal ingot C-axis, D1, D2, D3... Spacing between axis C1 and axis C2, S1, S2, S3, T1, T2, T3... Plane indicating cutting position, 7... Single-crystal gallium nitride substrate, 7a. Main surface, 7b ... first region, 7c ... second region, 11 ... single crystal gallium nitride substrate, 11a ... main surface, 11b ... first region, 11c ... second region, 7e, 11e ... of substrate 1st point, 7f, 11f ... 2nd point on substrate, 21 ... single crystal gallium nitride substrate, 23 ... OMVPE device, 25 ... susceptor, 29 ... gallium nitride film, 31 ... group III nitride semiconductor film, 32 ... Chemical semiconductor epitaxial substrate, 33 ... I Group II nitride semiconductor film, 35 ... Group III nitride semiconductor film, 37 ... Semiconductor epitaxial substrate, 39 ... n-type ohmic electrode, 41 ... p-type ohmic electrode, 43 ... pad electrode, 51 ... semiconductor light emitting device

Claims (11)

A gallium nitride substrate made of single-crystal gallium nitride and having a main surface,
The main surface of the gallium nitride substrate has a first region within 3 millimeters from an edge of the gallium nitride substrate, and a second region different from the first region,
The gallium nitride substrate, wherein an off angle formed by an axis orthogonal to the main surface and a C axis of the gallium nitride substrate is greater than zero over the second region of the main surface.   The gallium nitride substrate according to claim 1, wherein the minimum value of the off-angle is in the first region on the main surface of the single crystal gallium nitride substrate. The off angle is a value greater than zero on a non-closed curve on the major surface of the gallium nitride substrate;
The gallium nitride substrate according to claim 1, wherein the curved line terminates at an edge of the main surface.   The maximum value of the distance between one point on the edge of the gallium nitride substrate and another point on the edge of the gallium nitride substrate is 10 millimeters or more. Gallium nitride substrate.   4. The gallium nitride substrate according to claim 1, wherein an area of the main surface of the gallium nitride substrate is equal to or larger than an area of a circle having a diameter of 2 inches. 5.   The gallium nitride substrate according to any one of claims 1 to 5, wherein the off angle is 0.15 degrees or more over the second region of the main surface.   The gallium nitride substrate according to any one of claims 1 to 6, wherein the off-angle is 0.3 degrees or more over the second region of the main surface.   The gallium nitride substrate according to any one of claims 1 to 7, wherein the off-angle is less than 2 degrees across the second region of the main surface.   The gallium nitride substrate according to any one of claims 1 to 8, wherein the off-angle is 0.7 degrees or less over the second region of the main surface. The gallium nitride substrate according to any one of claims 1 to 9,
A nitride semiconductor epitaxial substrate comprising one or a plurality of group III nitride semiconductor films provided on the gallium nitride substrate. The gallium nitride substrate according to any one of claims 1 to 9,
A first conductivity type Al _X1 Ga _Y1 In _1-X1-Y1 N (0 ≦ X1 ≦ 1, 0 ≦ Y1 ≦ 1, 0 ≦ X1 + Y1 ≦ 1) film provided on the gallium nitride substrate;
An active region including the _Al is provided on the gallium nitride substrate _{X2 Ga Y2 In 1-X2-} Y2 N (0 ≦ X2 ≦ 1,0 ≦ Y2 ≦ 1,0 ≦ X2 + Y2 ≦ 1) layer,
And a second conductivity type Al _X3 Ga _Y3 In _1-X3-Y3 N (0 ≦ X3 ≦ 1, 0 ≦ Y3 ≦ 1, 0 ≦ X3 + Y3 ≦ 1) film provided on the gallium nitride substrate. Semiconductor epitaxial substrate.

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