Indium phosphide single crystal substrate, method for producing indium phosphide single crystal substrate, and indium phosphide single crystal ingot

Abstract

In the present invention, when each of the first cleavage plane, the second cleavage plane, the third cleavage plane, and the fourth cleavage plane is observed using a Nomarski microscope, a first striped pattern is observed in at least one of the first cleavage plane, the second cleavage plane, the third cleavage plane, or the fourth cleavage plane. The direction from a first main surface toward a second main surface is defined as a first direction. Among intersections of the first striped pattern and the outer peripheral surface, an intersection closest to the first main surface in the first direction is defined as an origin. The direction perpendicular to the first direction and from the origin toward the central axis is defined as a second direction. When the value obtained by dividing the distance from the origin in the first direction by the width of the first striped pattern in the second direction is z, the value obtained by dividing the distance from the origin in the second direction by the width is x, and the first striped pattern is approximated to a cubic function, the cubic function is represented by mathematical expression 1.

Description

Indium phosphide single crystal substrate, method for manufacturing indium phosphide single crystal substrate, and indium phosphide single crystal ingot

[0001] The present disclosure relates to an indium phosphide single crystal substrate, a method for manufacturing an indium phosphide single crystal substrate, and an indium phosphide single crystal ingot.

[0002] Japanese Patent Laid-Open Publication No. 2019-043788 (Patent Document 1) describes a single crystal growth method including a melting step of melting a seed crystal and a single crystal raw material placed inside a crucible, and a disposing step of inserting a solid-liquid interface control unit into the melt in the crucible generated in the melting step and disposing the solid-liquid interface control unit directly above the solid-liquid interface inside the crucible. The solid-liquid interface control unit has at least one of a columnar control unit that heats a central portion of the solid-liquid interface and a cylindrical control unit that heats a peripheral portion of the solid-liquid interface.

[0003] Japanese Patent Application Laid-Open No. 2019-043788

[0004] The indium phosphide single crystal substrate according to the present disclosure is an indium phosphide single crystal substrate having a first main surface, a second main surface, and an outer peripheral surface. The second main surface is opposite the first main surface. The outer peripheral surface is continuous with each of the first and second main surfaces. The indium phosphide single crystal substrate contains an impurity of at least one of sulfur and tin. When the two planes that appear when the indium phosphide single crystal substrate is cleaved along a plane including the central axis of the outer peripheral surface are defined as the first cleavage plane and the second cleavage plane, respectively, and the two planes that appear when the indium phosphide single crystal substrate is cleaved along a plane perpendicular to the first cleavage plane and including the central axis are defined as the third cleavage plane and the fourth cleavage plane, respectively, the first cleavage plane is the (01-1) plane. The second cleavage plane is the (0-11) plane. The third cleavage plane is the (011) plane. The fourth cleavage plane is a (0-1-1) plane. When each of the first cleavage plane, the second cleavage plane, the third cleavage plane, and the fourth cleavage plane is observed using a Nomarski microscope, a first stripe pattern is observed on at least one of the first cleavage plane, the second cleavage plane, the third cleavage plane, or the fourth cleavage plane. The direction from the first main surface toward the second main surface is defined as the first direction, the intersection point between the first stripe pattern and the outer peripheral surface that is closest to the first main surface in the first direction is defined as the origin, the direction perpendicular to the first direction and from the origin toward the central axis is defined as the second direction, the value obtained by dividing the distance from the origin in the first direction by the width of the first stripe pattern in the second direction is defined as z, and the value obtained by dividing the distance from the origin in the second direction by the width is defined as x. When the first stripe pattern is approximated to a cubic function, the cubic function is expressed by Equation 1. a is 5.0×10 －６ Larger 6.0 x 10 －５ b is -7.0 x 10 －３ or more, which is 2.0 × 10 －３ c is smaller than 2.0 × 10 －２ Larger 7.0 x 10 －１ x at the inflection point of the cubic function is equal to or greater than 0.25 and equal to or less than 0.75.

[0005]

[0006] FIG. 1 is a plan view schematic diagram showing the configuration of an indium phosphide single crystal substrate according to the first embodiment. FIG. 2 is a side view schematic diagram showing the configuration of an indium phosphide single crystal substrate according to the first embodiment. FIG. 3 is a first plan view schematic diagram showing a state in which the indium phosphide single crystal substrate has been cleaved. FIG. 4 is a second plan view schematic diagram showing a state in which the indium phosphide single crystal substrate has been cleaved. FIG. 5 is a partial cross-sectional view schematic diagram showing an etching process of a cleaved surface of an indium phosphide single crystal substrate. FIG. 6 is a schematic diagram showing a first stripe pattern imaged using a Nomarski microscope. FIG. 7 is a schematic diagram showing a step of connecting a plurality of first lines. FIG. 8 is a schematic diagram showing a step of approximating a first virtual line to a cubic function. FIG. 9 is a schematic diagram showing a second stripe pattern imaged using a Nomarski microscope. FIG. 10 is a plan view schematic diagram showing the configuration of an indium phosphide single crystal ingot according to the first embodiment. FIG. 11 is a schematic side view showing the configuration of an indium phosphide single crystal ingot according to the first embodiment. FIG. 12 is a first schematic plan view showing the cleaved indium phosphide single crystal ingot. FIG. 13 is a second schematic plan view showing the cleaved indium phosphide single crystal ingot. FIG. 14 is a partial cross-sectional view showing an etching process for the cleaved surface of the indium phosphide single crystal ingot. FIG. 15 is a schematic view showing a third stripe pattern imaged using a Nomarski microscope. FIG. 16 is a schematic view showing a step of connecting a plurality of third lines. FIG. 17 is a schematic view showing a step of approximating the third virtual line to a cubic function. FIG. 18 is a schematic view showing a fourth stripe pattern imaged using a Nomarski microscope. FIG. 19 is a schematic cross-sectional view showing the configuration of an indium phosphide single crystal growth apparatus according to the first embodiment. FIG. 20 is a schematic plan view showing the configuration of an indium phosphide single crystal growth apparatus according to the first embodiment. Fig. 21 is a flow diagram schematically showing a method for manufacturing an indium phosphide single crystal substrate according to the first embodiment. Fig. 22 is a cross-sectional schematic diagram showing a crucible in which a seed crystal, an indium phosphide raw material, and a sealing material are placed. Fig. 23 is a cross-sectional schematic diagram showing a step of growing a crystal. Fig. 24 is a cross-sectional schematic diagram showing the configuration of an indium phosphide single crystal growth apparatus according to the second embodiment.FIG. 25 is a plan view schematically illustrating the configuration of an apparatus for growing an indium phosphide single crystal according to the second embodiment.

[0007] [Problem to be Solved by the Present Disclosure] An object of the present disclosure is to provide an indium phosphide single crystal substrate, a method for manufacturing an indium phosphide single crystal substrate, and an indium phosphide single crystal ingot that can improve the yield of epitaxial substrates.

[0008] Effect of the Present Disclosure According to the present disclosure, it is possible to provide an indium phosphide single crystal substrate, a method for manufacturing an indium phosphide single crystal substrate, and an indium phosphide single crystal ingot that can improve the yield of epitaxial substrates.

[0009] [Outline of the embodiment] First, an outline of the embodiment of the present disclosure will be described. In the crystallographic description in this specification, individual planes are indicated by (). Furthermore, for negative indices, in crystallography, a "-" (bar) is placed above the number, but in this specification, a negative sign is placed before the number.

[0010] (1) The indium phosphide single crystal substrate according to the present disclosure is an indium phosphide single crystal substrate having a first main surface, a second main surface, and an outer peripheral surface. The second main surface is opposite the first main surface. The outer peripheral surface is continuous with each of the first and second main surfaces. The indium phosphide single crystal substrate contains an impurity of at least one of sulfur and tin. When the two planes that appear when the indium phosphide single crystal substrate is cleaved along a plane including the central axis of the outer peripheral surface are defined as the first cleavage plane and the second cleavage plane, respectively, and the two planes that appear when the indium phosphide single crystal substrate is cleaved along a plane perpendicular to the first cleavage plane and including the central axis are defined as the third cleavage plane and the fourth cleavage plane, respectively, the first cleavage plane is the (01-1) plane. The second cleavage plane is the (0-11) plane. The third cleavage plane is the (011) plane. The fourth cleavage plane is a (0-1-1) plane. When each of the first cleavage plane, the second cleavage plane, the third cleavage plane, and the fourth cleavage plane is observed using a Nomarski microscope, a first stripe pattern is observed on at least one of the first cleavage plane, the second cleavage plane, the third cleavage plane, or the fourth cleavage plane. The direction from the first main surface toward the second main surface is defined as the first direction, the point closest to the first main surface in the first direction among the intersections between the first stripe pattern and the outer peripheral surface is defined as the origin, the direction perpendicular to the first direction and from the origin toward the central axis is defined as the second direction, the value obtained by dividing the distance from the origin in the first direction by the width of the first stripe pattern in the second direction is defined as z, and the value obtained by dividing the distance from the origin in the second direction by the width is defined as x. When the first stripe pattern is approximated to a cubic function, the cubic function is expressed by Equation 1. a is 5.0 x 10 －６ Larger 6.0 x 10 －５ b is -7.0 x 10 －３ or more, which is 2.0 × 10 －３ c is smaller than 2.0 × 10 －２ Larger 7.0 x 10 －１ x at the inflection point of the cubic function is equal to or greater than 0.25 and equal to or less than 0.75.

[0011]

[0012] As described above, the shape of the stripe pattern observed on the cleavage plane of the indium phosphide single crystal substrate according to the present disclosure is close to a cubic function. This reduces the variation in electrical properties within the surface of the epitaxial substrate. As a result, the yield of the epitaxial substrate can be improved.

[0013] (2) In the indium phosphide single crystal substrate according to (1) above, a first stripe pattern may be observed on at least one of the first cleavage plane or the second cleavage plane. A second stripe pattern may be observed on each of the third cleavage plane and the fourth cleavage plane. The shape of the second stripe pattern may be linear or convex in a direction parallel to the first direction. This can more effectively reduce variations in electrical characteristics within the surface of the epitaxial substrate.

[0014] (3) In the indium phosphide single crystal substrate according to (1) above, a first stripe pattern may be observed on at least one of the third cleavage plane or the fourth cleavage plane. A second stripe pattern may be observed on each of the first cleavage plane and the second cleavage plane. The shape of the second stripe pattern may be linear or convex in a direction parallel to the first direction. This can more effectively reduce variations in electrical characteristics within the surface of the epitaxial substrate.

[0015] (4) In the indium phosphide single crystal substrate according to any one of (1) to (3), when x is 0.2, z is 1.02 × 10 －２ Larger than 1.104 x 10 －１ If x is 0.4, z is 7.68×10 －３ Larger 1.89 x 10 －１ If x is 0.6, z is 3.12×10 －３ Larger 2.77 x 10 －１ If x is 0.8, z is 7.04×10 －３ Larger 3.90 x 10 －１ It may be smaller.

[0016] Thus, in the indium phosphide single crystal substrate according to the present disclosure, the unevenness of the first stripe pattern in the first direction may be reduced. This reduces internal stress in the indium phosphide single crystal substrate. Therefore, warping of the indium phosphide single crystal substrate can be suppressed when forming an epitaxial layer on the indium phosphide single crystal substrate. Therefore, variations in carrier concentration in the epitaxial layer can be reduced. As a result, variations in electrical characteristics within the surface of the epitaxial substrate can be more effectively reduced.

[0017] (5) In the indium phosphide single crystal substrate according to any one of (1) to (4), a is 7.0 × 10 －６ Larger than 5.0 x 10 －５ b may be smaller than -6.0 x 10 －３ Larger than 1x10 －３ c may be smaller than 5.0×10 －２ Larger 6.0 x 10 －１ When x is 0.2, z may be 1.80×10 －２ Larger 7.96 x 10 －２ When x is 0.4, z is 2.50×10 －２ Larger 1.33 x 10 －１ When x is 0.6, z is 2.70×10 －２ Larger 1.81 x 10 －１ When x is 0.8, z may be 3.00×10 －２ Larger 2.46 x 10 －１ It may be smaller.

[0018] (6) In the indium phosphide single crystal substrate according to (5) above, a is 1×10 －５ Larger 4.6 x 10 －５ b may be smaller than -5.8 x 10 －３ Greater than -1.0 x 10 －３ c may be less than 1.1×10 －１ Larger than 5.0 x 10 －１ When x is 0.2, z may be 2.50×10 －２Larger 7.12 x 10 －２ If x is 0.4, z is 4.39×10 －２ Larger 1.18 x 10 －１ If x is 0.6, z is 6.26×10 －２ Larger 1.58 x 10 －１ If x is 0.8, z is 8.70×10 －２ Larger 2.13 x 10 －１ It may be smaller.

[0019] (7) In the indium phosphide single crystal substrate according to any one of (1) to (6) above, the diameter of the second main surface may be 75 mm or more.

[0020] (8) A method for producing an indium phosphide single crystal substrate according to the present disclosure includes the following steps: a growth apparatus is prepared, the growth apparatus having a cylindrical crucible and a cylindrical heating element surrounding the crucible; a seed crystal is placed inside the crucible; an indium phosphide source material is placed on the seed crystal; a part of the seed crystal and the indium phosphide source are melted using the heating element to obtain an indium phosphide melt, and the indium phosphide melt is brought into contact with the remainder of the seed crystal; an indium phosphide single crystal is grown on the seed crystal by solidifying the indium phosphide melt; and the indium phosphide single crystal is cut. The growth apparatus includes a shielding plate, which is provided between the crucible and the heating element. When the positions located at 0°, 180°, 90°, and 270° from the central axis of the crucible and between the crucible and the heating element are designated as a first position, a second position, a third position, and a fourth position, respectively, a shielding plate is provided at the first position. No shielding plate is provided at the second, third, and fourth positions. The thickness of the shielding plate in the direction from the first position to the second position is 9 mm or less.

[0021] Therefore, in a cross section that includes the central axis of the crucible and is parallel to the direction from the first position to the second position, the shape of the solid-liquid interface approaches the shape of a cubic function. As a result, the shape of the stripe pattern observed on the cleavage plane of the indium phosphide single crystal substrate approaches the shape of a cubic function. As a result, the yield of epitaxial substrates manufactured using the indium phosphide single crystal substrate can be improved.

[0022] (9) According to the method for manufacturing an indium phosphide single crystal substrate according to (8) above, the shielding plate may have a flat plate shape.

[0023] (10) According to the method for manufacturing an indium phosphide single crystal substrate according to (8) or (9) above, the width of the shielding plate in the direction from the third position toward the fourth position may be 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal.

[0024] Therefore, the width of the first shielding plate in the direction from the third position to the fourth position can be prevented from becoming excessively small or large, thereby sufficiently lowering the temperature of the indium phosphide melt near the first shielding plate, and also preventing the irregularities of the first striped pattern from becoming excessively large.

[0025] (11) A method for producing an indium phosphide single crystal substrate according to the present disclosure includes the following steps: a growth apparatus is prepared, the growth apparatus having a cylindrical crucible and a cylindrical heating element surrounding the crucible; a seed crystal is placed inside the crucible; an indium phosphide source material is placed on the seed crystal; a portion of the seed crystal and the indium phosphide source are melted using the heating element to obtain an indium phosphide melt, and the indium phosphide melt is brought into contact with the remainder of the seed crystal; an indium phosphide single crystal is grown on the seed crystal by solidifying the indium phosphide melt; and the indium phosphide single crystal is cut. The growth apparatus includes a first shielding plate and a second shielding plate. The first shielding plate and the second shielding plate are each provided between the crucible and the heating element. If positions that are at 0°, 180°, 90°, and 270° angles as viewed from the central axis of the crucible and that are between the crucible and the heating element are designated as a first position, a second position, a third position, and a fourth position, respectively, a first shielding plate is provided at the first position. A second shielding plate is provided at the second position. Neither the first shielding plate nor the second shielding plate is provided at the third position or the fourth position. The value obtained by subtracting the thickness of the second shielding plate in the direction from the first position to the second position from the thickness of the first shielding plate in the direction from the first position to the second position is 2 mm or more and 9 mm or less.

[0026] Therefore, in a cross section that includes the central axis of the crucible and is parallel to the direction from the first position to the second position, the distance between both ends of the solid-liquid interface in the growth direction of the indium phosphide single crystal can be shortened, thereby reducing the unevenness of the first striped pattern.

[0027] (12) According to the method for manufacturing an indium phosphide single crystal substrate according to (11) above, the thickness of the first shielding plate in the direction from the first position to the second position may be 6 mm or more and 7 mm or less.

[0028] (13) According to the method for manufacturing an indium phosphide single crystal substrate according to (11) or (12) above, each of the first shielding plate and the second shielding plate may have a flat plate shape.

[0029] (14) In the method for manufacturing an indium phosphide single crystal substrate according to any one of (11) to (13) above, the width of the first shielding plate in the direction from the third position to the fourth position may be 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal, and the width of the second shielding plate in the direction from the third position to the fourth position may be 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal.

[0030] Therefore, it is possible to prevent the width of the second shielding plate from becoming excessively small in the direction from the third position to the fourth position, thereby making it possible to sufficiently lower the temperature of the portion of the indium phosphide melt close to the second shielding plate.

[0031] (15) An indium phosphide single crystal ingot according to the present disclosure includes a first end face, a second end face, and a cylindrical surface. The second end face is opposite the first end face. The cylindrical surface is continuous with each of the first end face and the second end face. The indium phosphide single crystal ingot contains at least one impurity, sulfur or tin. The impurity concentration in the second end face is higher than the impurity concentration in the first end face. When the indium phosphide single crystal ingot is cleaved along a plane including the central axis of the cylindrical surface, the two planes that appear are designated as the fifth cleavage plane and the sixth cleavage plane, respectively, and when the indium phosphide single crystal ingot is cleaved along a plane perpendicular to the fifth cleavage plane and including the central axis, the two planes that appear are designated as the seventh cleavage plane and the eighth cleavage plane, respectively, the fifth cleavage plane is the (01-1) plane. The sixth cleavage plane is the (0-11) plane. The seventh cleavage plane is the (011) plane. The eighth cleavage plane is the (0-1-1) plane. When each of the fifth cleavage plane, the sixth cleavage plane, the seventh cleavage plane, and the eighth cleavage plane is observed using a Nomarski microscope, a third stripe pattern is observed in at least one of the fifth cleavage plane, the sixth cleavage plane, the seventh cleavage plane, and the eighth cleavage plane. The direction from the first end face toward the second end face is defined as the growth direction, the point closest to the first end face in the growth direction among the intersections between the third striped pattern and the cylindrical surface is defined as the origin, the direction perpendicular to the growth direction and from the origin toward the central axis is defined as the third direction, the value obtained by dividing the distance from the origin in the growth direction by the width of the third striped pattern in the third direction is defined as z, and the value obtained by dividing the distance from the origin in the third direction by the width is defined as x. When the third striped pattern is approximated to a cubic function, the cubic function is expressed by Equation 2. a is 5.0×10 －６ Larger 6.0 x 10 －５ b is -7.0 x 10 －３ or more, which is 2.0 × 10 －３ c is smaller than 2.0 × 10 －２ Larger 7.0 x 10 －１ x at the inflection point of the cubic function is equal to or greater than 0.25 and equal to or less than 0.75.

[0032]

[0033] As described above, the shape of the stripe pattern observed on the cleavage plane of the indium phosphide single crystal ingot according to the present disclosure is close to a cubic function. Therefore, the shape of the stripe pattern observed on the cleavage plane of an indium phosphide single crystal substrate manufactured using the indium phosphide single crystal ingot is also close to a cubic function. This reduces the variation in electrical properties within the surface of the epitaxial substrate. As a result, the yield of the epitaxial substrate can be improved.

[0034] (16) In the indium phosphide single crystal ingot according to (15), a third stripe pattern may be observed on at least one of the fifth cleavage plane or the sixth cleavage plane. A fourth stripe pattern may be observed on each of the seventh cleavage plane and the eighth cleavage plane. The shape of the fourth stripe pattern may be linear or convex in the growth direction. This can more effectively reduce variations in electrical characteristics within the surface of the epitaxial substrate.

[0035] (17) In the indium phosphide single crystal ingot according to (15), a third stripe pattern may be observed on at least one of the seventh cleavage plane or the eighth cleavage plane. A fourth stripe pattern may be observed on each of the fifth cleavage plane and the sixth cleavage plane. The shape of the fourth stripe pattern may be linear or convex in the growth direction. This can more effectively reduce variations in electrical characteristics within the surface of the epitaxial substrate.

[0036] (18) In the indium phosphide single crystal ingot according to any one of (15) to (17) above, when x is 0.2, z is 1.02 × 10 －２ Larger than 1.104 x 10 －１ If x is 0.4, z is 7.68×10 －３ Larger 1.89 x 10 －１ If x is 0.6, z is 3.12×10 －３ Larger 2.77 x 10 －１ If x is 0.8, z is 7.04×10 －３ Larger 3.90 x 10 －１It may be smaller.

[0037] Thus, according to the indium phosphide single crystal ingot according to the present disclosure, the unevenness of the third striped pattern in the growth direction may be reduced. This reduces internal stress in the indium phosphide single crystal ingot. Therefore, when forming an epitaxial layer on an indium phosphide single crystal substrate produced using the indium phosphide single crystal ingot, warping of the indium phosphide single crystal substrate can be suppressed. Therefore, variation in carrier concentration in the epitaxial layer can be reduced. As a result, variation in electrical properties within the surface of the epitaxial substrate can be more effectively reduced.

[0038] (19) In the indium phosphide single crystal ingot according to any one of (15) to (18) above, a is 7.0 × 10 －６ Larger than 5.0 x 10 －５ b may be smaller than -6.0 x 10 －３ Larger than 1x10 －３ c may be smaller than 5.0×10 －２ Larger 6.0 x 10 －１ When x is 0.2, z may be 1.80×10 －２ Larger 7.96 x 10 －２ When x is 0.4, z is 2.50×10 －２ Larger 1.33 x 10 －１ When x is 0.6, z is 2.70×10 －２ Larger 1.81 x 10 －１ When x is 0.8, z may be 3.00×10 －２ Larger 2.46 x 10 －１ It may be smaller.

[0039] (20) According to the indium phosphide single crystal ingot according to (19) above, a is 1×10 －５ Larger 4.6 x 10 －５ b may be smaller than -5.8 x 10 －３ Greater than -1.0 x 10 －３ c may be less than 1.1×10－１ Larger than 5.0 x 10 －１ When x is 0.2, z may be 2.50×10 －２ Larger 7.12 x 10 －２ If x is 0.4, z is 4.39×10 －２ Larger 1.18 x 10 －１ If x is 0.6, z is 6.26×10 －２ Larger 1.58 x 10 －１ If x is 0.8, z is 8.70×10 －２ Larger 2.13 x 10 －１ It may be smaller.

[0040] (21) In the indium phosphide single crystal ingot according to any one of (15) to (20) above, the diameter of the second end face may be 75 mm or more.

[0041] [Details of the embodiment] Hereinafter, details of the embodiment of the present disclosure will be described with reference to the drawings. Note that in the following drawings, the same or corresponding parts are designated by the same reference numerals, and description thereof will not be repeated.

[0042] First Embodiment First, the configuration of an indium phosphide single crystal substrate according to the first embodiment will be described. Fig. 1 is a plan view schematic diagram showing the configuration of an indium phosphide single crystal substrate 100 according to the first embodiment. Fig. 2 is a side view schematic diagram showing the configuration of an indium phosphide single crystal substrate 100 according to the first embodiment. As shown in Figs. 1 and 2, the indium phosphide single crystal substrate 100 has a first main surface 1, a second main surface 2, and an outer peripheral surface 3.

[0043] The second main surface 2 is opposite the first main surface 1. The direction from the first main surface 1 to the second main surface 2 is defined as a first direction 101. The first direction 101 is the growth direction of the indium phosphide single crystal when the indium phosphide single crystal substrate 100 is manufactured. The second main surface 2 is, for example, the (100) plane of the indium phosphide single crystal. When viewed along a line perpendicular to the second main surface 2, the shape of the second main surface 2 is, for example, a circular shape. The outer peripheral surface 3 is continuous with each of the first main surface 1 and the second main surface 2. The central axis of the outer peripheral surface 3 is defined as a first central axis A1. The first central axis A1 extends along the first direction 101. The ridge line between the second main surface 2 and the outer peripheral surface 3 is defined as a first outer edge 8.

[0044] The diameter of the second main surface 2 is defined as a first diameter W1. The first diameter W1 is, for example, 100 mm (4 inches). The lower limit of the first diameter W1 is not particularly limited, but may be 75 mm (3 inches) or more, 100 mm (4 inches) or more, or 150 mm (6 inches) or more. The upper limit of the first diameter W1 is not particularly limited, but may be, for example, 400 mm (16 inches) or less. The first diameter W1 is the longest distance between two different points on the first outer edge 8.

[0045] As used herein, 3 inches refers to 75 mm or 76.2 mm (3 inches x 25.4 mm / inch). 4 inches refers to 100 mm or 101.6 mm (4 inches x 25.4 mm / inch). 6 inches refers to 150 mm or 152.4 mm (6 inches x 25.4 mm / inch). 16 inches refers to 400 mm or 406.4 mm (16 inches x 25.4 mm / inch).

[0046] At least one of a notch, an orientation flat, and an index flat may be provided on the outer peripheral surface 3. When at least one of a notch, an orientation flat, and an index flat is provided on the outer peripheral surface 3, the first center axis A1 is a line passing through the center of a circle that overlaps with the arc-shaped portion of the outer peripheral surface 3 when viewed along a line perpendicular to the second main surface 2.

[0047] The indium phosphide single crystal substrate 100 contains an impurity as a dopant. The impurity is at least one of sulfur (S) and tin (Sn). Specifically, the indium phosphide single crystal substrate 100 may contain only one of sulfur and tin as the impurity, or may contain both sulfur and tin as the impurities.

[0048] <Striped Pattern> Figure 3 is a first schematic plan view showing a state in which the indium phosphide single crystal substrate 100 has been cleaved. As shown in Figure 3, when the indium phosphide single crystal substrate 100 is cleaved along a plane that includes the first central axis A1 and is parallel to the (01-1) plane, a first cleavage plane 11 and a second cleavage plane 12 appear. The first cleavage plane 11 is the (01-1) plane. The second cleavage plane 12 is the (0-11) plane.

[0049] Fig. 4 is a second schematic plan view showing the state in which the indium phosphide single crystal substrate 100 has been cleaved. As shown in Fig. 4, when the indium phosphide single crystal substrate 100 is cleaved along a plane that includes the first central axis A1 and is parallel to the (011) plane, a third cleavage plane 13 and a fourth cleavage plane 14 appear. The third cleavage plane 13 is the (011) plane. The fourth cleavage plane 14 is the (0-1-1) plane.

[0050] When each of the first cleavage surface 11, the second cleavage surface 12, the third cleavage surface 13, and the fourth cleavage surface 14 is subjected to an etching treatment described below and then observed using a Nomarski microscope, a stripe pattern is observed on each of the first cleavage surface 11, the second cleavage surface 12, the third cleavage surface 13, and the fourth cleavage surface 14. The stripe patterns observed on the first cleavage surface 11, the second cleavage surface 12, the third cleavage surface 13, and the fourth cleavage surface 14 include a first stripe pattern 31 (see FIG. 6 ) and a second stripe pattern 32 (see FIG. 9 ). Details of the stripe patterns will be described later.

[0051] <Etching Treatment> The cleaved indium phosphide single crystal substrate 100 is subjected to the following etching treatment.

[0052] Etching treatment: A cleavage plane to be measured, among first cleavage plane 11, second cleavage plane 12, third cleavage plane 13, and fourth cleavage plane 14, was placed horizontally at a position 10 mm below the liquid surface 94 of a 25°C mixed liquid 91 consisting of 10 g of chromium (VI) oxide, 10 mL of a 50% by mass hydrofluoric acid solution, and 400 mL of pure water, and light from a 500 W reflector-type incandescent lamp 93 was irradiated toward the cleavage plane to be measured from a position 20 cm above the liquid surface 94 for 30 minutes to 60 minutes.

[0053] 5 is a partial cross-sectional schematic diagram showing the etching of a cleavage plane of an indium phosphide single crystal substrate 100. The above-mentioned etching method will be described in detail with reference to FIG. 5. The following description focuses on the etching of the first cleavage plane 11. The etching of the second cleavage plane 12, the third cleavage plane 13, and the fourth cleavage plane 14 can also be performed in a similar manner.

[0054] As shown in Fig. 5, first, a mixed solution 91 is prepared. The mixed solution 91 is composed of chromium (VI) oxide, a hydrofluoric acid solution, and pure water. The weight of the chromium (VI) oxide is 10 g. The concentration of the hydrofluoric acid solution is 50 mass %. The volume of the hydrofluoric acid solution is 10 mL. The volume of the pure water is 400 mL. The temperature of the mixed solution 91 is 25°C. The mixed solution 91 is placed in a tank 92.

[0055] The first cleavage plane 11 is polished. The arithmetic mean roughness Ra of the polished first cleavage plane 11 is set to be 0.1 nm or more and 0.5 nm or less. The arithmetic mean roughness (Ra) is a surface texture parameter defined in JIS (Japanese Industrial Standards) B0601:2013.

[0056] Next, the cleaved indium phosphide single crystal substrate 100 is placed in the mixed liquid 91. Specifically, the indium phosphide single crystal substrate 100 is placed so that the first cleavage plane 11 is positioned horizontally. From another perspective, the indium phosphide single crystal substrate 100 is placed so that the liquid surface 94 of the mixed liquid 91 and the first cleavage plane 11 are substantially parallel to each other.

[0057] The first cleavage plane 11 is disposed below the liquid surface 94. In the vertical direction V, the distance (first distance D1) between the liquid surface 94 and the first cleavage plane 11 is 10 mm. The direction from the liquid surface 94 toward the first cleavage plane 11 along the vertical direction V is also referred to as the depth direction. A reflector-type incandescent lamp 93 is disposed above the liquid surface 94. In the vertical direction V, the distance (second distance D2) between the liquid surface 94 and the reflector-type incandescent lamp 93 is 20 cm. As the reflector-type incandescent lamp 93, for example, an "Eye Lamp (registered trademark)" manufactured by Iwasaki Electric Co., Ltd. can be used. The power consumption of the reflector-type incandescent lamp 93 is, for example, 500 W.

[0058] Light is irradiated from a reflector-type incandescent lamp 93 toward the first cleavage surface 11. The light is irradiated along the arrow 90. The time (etching time) during which the light is irradiated onto the first cleavage surface 11 is set to be equal to or greater than 30 minutes and equal to or less than 60 minutes. In this manner, the first cleavage surface 11 is etched. As a result, a stripe pattern that can be observed using a Nomarski microscope is formed on the first cleavage surface 11.

[0059] The temperature of the mixed liquid 91 (25°C) mentioned above refers to the temperature at the start of the etching process using light. The temperature of the mixed liquid 91 may fluctuate during the etching process due to factors such as the light energy of the reflector-type incandescent lamp 93. In the etching process described above, the indium phosphide single crystal substrate 100 placed in the mixed liquid 91 may be oscillated at predetermined time intervals (for example, every minute). This allows the striped pattern formed on the first cleavage plane 11 to be more clearly defined. To make the striped pattern formed on the first cleavage plane 11 more clearly defined, the etching time is adjusted within a range of 30 minutes to 60 minutes.

[0060] <First Stripe Pattern> When each of the first cleavage plane 11, the second cleavage plane 12, the third cleavage plane 13, and the fourth cleavage plane 14 is observed using a Nomarski microscope, a first stripe pattern 31 is observed on at least one of the first cleavage plane 11, the second cleavage plane 12, the third cleavage plane 13, or the fourth cleavage plane 14. FIG. 6 is a schematic diagram showing the first stripe pattern 31 imaged using a Nomarski microscope. A case in which the first stripe pattern 31 is observed on the first cleavage plane 11 will be described using FIG. 6 . As shown in FIG. 6 , the first stripe pattern 31 is composed of a plurality of first lines 70. The first stripe pattern 31 is approximated to a cubic function by the following method.

[0061] First, a plurality of first lines 70 are joined together using an image captured using a Nomarski microscope. When joining the plurality of first lines 70 together, the plurality of first lines 70 to be joined together are first selected. The lines that reach the outer peripheral surface 3 are set as first selected lines 71. Note that, when there are a plurality of first lines 70 that reach the outer peripheral surface 3, the first line 70 that is closest to the first main surface 1 in the first direction 101 is set as the first selected line 71.

[0062] The intersection of the first selection line 71 and the outer peripheral surface 3 is defined as a first intersection 51. Of the intersections of the first stripe pattern 31 and the outer peripheral surface 3, the first intersection 51 is the closest to the first main surface 1 in the first direction 101. The direction perpendicular to the first direction 101 and extending from the first intersection 51 toward the first central axis A1 is defined as a second direction 102. The first selection line 71 reaches, for example, the second main surface 2. The intersection of the first selection line 71 and the second main surface 2 is defined as a second intersection 52.

[0063] 6 , a line that passes through the second intersection point 52 and is parallel to the first direction 101 is defined as a first virtual line 111. Of the multiple first lines 70, the first line 70 that intersects with the first virtual line 111 is defined as a second selected line 72. Note that, if there are multiple first lines 70 that intersect with the first virtual line 111, any one of the multiple first lines 70 that intersects with the first virtual line 111 is defined as the second selected line 72.

[0064] The intersection of the second selection line 72 and the first virtual straight line 111 is defined as a third intersection 53. In the second direction 102, the third intersection 53 is at the same position as the second intersection 52. The portion of the second selection line 72 that is in the second direction 102 with respect to the third intersection 53 reaches, for example, the second main surface 2. The intersection of the second selection line 72 and the second main surface 2 is defined as a fourth intersection 54.

[0065] 6 , a line that passes through the fourth intersection point 54 and is parallel to the first direction 101 is set as a second virtual line 112. Of the multiple first lines 70, a first line 70 that intersects with the second virtual line 112 is set as a third selected line 73. Note that, if there are multiple first lines 70 that intersect with the second virtual line 112, any one of the multiple first lines 70 that intersects with the second virtual line 112 is set as the third selected line 73.

[0066] The intersection of the third selection line 73 and the second virtual straight line 112 is defined as a fifth intersection 55. In the second direction 102, the fifth intersection 55 is at the same position as the fourth intersection 54. The portion of the third selection line 73 that is in the second direction 102 with respect to the fifth intersection 55 reaches, for example, the second main surface 2. The intersection of the third selection line 73 and the second main surface 2 is defined as a sixth intersection 56.

[0067] 6 , a line that passes through the sixth intersection point 56 and is parallel to the first direction 101 is set as a third virtual line 113. Of the multiple first lines 70, the first line 70 that intersects with the third virtual line 113 is set as a fourth selected line 74. Note that, if there are multiple first lines 70 that intersect with the third virtual line 113, any one of the multiple first lines 70 that intersects with the third virtual line 113 is set as the fourth selected line 74.

[0068] The intersection of the fourth selected line 74 and the third virtual straight line 113 is set to the seventh intersection 57. In the second direction 102, the seventh intersection 57 is at the same position as the sixth intersection 56. The portion of the fourth selected line 74 in the second direction 102 relative to the seventh intersection 57 reaches, for example, the outer peripheral surface 3. The intersection of the fourth selected line 74 and the outer peripheral surface 3 is set to the eighth intersection 58. As described above, the first selected line 71, the second selected line 72, the third selected line 73, and the fourth selected line 74 are selected as the first line 70 to be joined together.

[0069] Note that there is no particular limitation on the number of the first lines 70 to be joined. For example, when the portion of the fourth selected line 74 in the second direction 102 relative to the seventh intersection 57 reaches the second main surface 2, five or more first lines 70 are selected as the first lines 70 to be joined.

[0070] Next, the first selection line 71, the second selection line 72, the third selection line 73, and the fourth selection line 74 are joined together. Fig. 7 is a schematic diagram showing the process of joining a plurality of first lines 70. As shown in Fig. 7, the first selection line 71 and the second selection line 72 are joined together so that the second intersection 52 and the third intersection 53 coincide. Specifically, the first selection line 71 and the second selection line 72 are joined together by, for example, moving the second selection line 72 along the first direction 101. The portion of the second selection line 72 between the first intersection 51 and the second intersection 52 is, for example, removed.

[0071] Similarly, the second selected line 72 and the third selected line 73 are connected together so that the fourth intersection 54 and the fifth intersection 55 coincide with each other. The third selected line 73 and the fourth selected line 74 are connected together so that the sixth intersection 56 and the seventh intersection 57 coincide with each other. In this way, the multiple first lines 70 are connected together. As a result, the first virtual line 68 is created.

[0072] 7, the first imaginary line 68 has a first intersection point 51 and an eighth intersection point 58. The first intersection point 51 and the eighth intersection point 58 are each an end point of the first imaginary line 68. The eighth intersection point 58 is opposite the first intersection point 51.

[0073] The shape of each of the multiple first lines 70 (see FIG. 6 ) is substantially the same as the shape of a portion of the first virtual line 68 cut out. From another perspective, the shape of the first stripe pattern 31 (see FIG. 6 ) is substantially the same as the shape of a portion of the shape created by arranging the multiple first virtual lines 68 along the first direction 101 cut out.

[0074] 6, the width of the first stripe pattern 31 in the second direction 102 is defined as a first width H1. The first width H1 is substantially the same as the width of the first cleavage plane 11 in the second direction 102. As shown in FIG. 7, the length of the first virtual line 68 in the second direction 102 is substantially the same as the first width H1.

[0075] Next, the first virtual line 68 is approximated by a cubic function. FIG. 8 is a schematic diagram illustrating the process of approximating the first virtual line 68 to a cubic function. Specifically, as shown in FIG. 8 , the first virtual line 68 is first arranged on a two-dimensional plane with the horizontal axis representing the second direction 102 and the vertical axis representing the first direction 101. A plurality of first measurement points 59 overlapping the first virtual line 68 are arranged. The number of the plurality of first measurement points 59 is, for example, 19. In the second direction 102, each of the plurality of first measurement points 59 is arranged between the first intersection 51 and the eighth intersection 58. The plurality of first measurement points 59 are arranged at equal intervals in the second direction 102. In the second direction 102, the interval between the plurality of first measurement points 59 is, for example, 5% of the first width H1. In the second direction 102 , the distance between the first intersection 51 and the first measurement point 59 closest to the first intersection 51 is the same as the spacing between the multiple first measurement points 59 .

[0076] Using the first intersection 51 as the origin, the coordinates of each of the multiple first measurement points 59 and the eighth intersection 58 are measured. Specifically, the distance in the first direction 101 between each of the multiple first measurement points 59 and the eighth intersection 58 and the first intersection 51 is measured. Hereinafter, the distance in the first direction 101 between an arbitrary point and the first intersection 51 will also be referred to as the first direction distance. The distance in the second direction 102 between the arbitrary point and the first intersection 51 will also be referred to as the second direction distance. The first intersection 51 will also be referred to as the first origin 51.

[0077] The value obtained by dividing the first direction distance by the first width H1 is defined as z. The value obtained by dividing the second direction distance by the first width H1 is defined as x. The first virtual line 68 is approximated to a cubic function using the measured first direction distance and second direction distance. The least squares method is used to approximate the first virtual line 68 to a cubic function. The first virtual line 68 approximated to a cubic function is expressed by Equation 1.

[0078] z = ax ３+bx ２ +cx (Formula 1) In Formula 1, a, b, and c are each a constant. The cubic function expressed by Formula 1 is a cubic function that approximates first stripe pattern 31 (see FIG. 6).

[0079] In the cubic function that approximates the first stripe pattern 31, a is 5.0×10 －６ Larger 6.0 x 10 －５ a is not particularly limited, but is preferably 7.0 × 10 －６ Larger than 5.0 x 10 －５ It may be smaller than 1×10 －５ Larger 4.6 x 10 －５ It may be smaller, 2 x 10 －５ Larger 4.55 x 10 －５ It may be smaller.

[0080] In the cubic function that approximates the first stripe pattern 31, b is −7.0×10 －３ or more, which is 2.0 × 10 －３ b is not particularly limited, but is preferably −6.0×10 －３ Larger than 1x10 －３ It may be smaller than -5.8 x 10 －３ Greater than -1.0 x 10 －３ It may be smaller than -5.8 x 10 －３ Greater than -2.0 x 10 －３ It may be smaller.

[0081] In the cubic function that approximates the first stripe pattern 31, c is 2.0×10 －２ Larger 7.0 x 10 －１ c is not particularly limited, but is preferably 5.0 × 10 －２ Larger 6.0 x 10 －１ It may be smaller than 1.1 × 10 －１ Larger than 5.0 x 10 －１ It may be smaller, 2.5 x 10 －１ Larger 4.5 x 10 －１ It may be smaller.

[0082] In the cubic function that approximates the first stripe pattern 31, when x is 0.2, z is 1.02×10 －２ Larger than 1.104 x 10 －１ When x is 0.2, z is, but is not particularly limited to, 1.80 × 10 －２ Larger 7.96 x 10 －２ It may be smaller, 2.50 x 10 －２ Larger 7.12 x 10 －２ It may be smaller than 4.00 x 10 －２ Larger 7.00 x 10 －２ It may be smaller.

[0083] In the cubic function that approximates the first stripe pattern 31, when x is 0.4, z is 7.68×10 －３ Larger 1.89 x 10 －１ When x is 0.4, z is, but is not limited to, 2.50×10 －２ Larger 1.33 x 10 －１ It may be smaller, 4.39 x 10 －２ Larger 1.18 x 10 －１ It may be smaller than 6.00 x 10 －２ Larger 1.10 x 10 －１ It may be smaller.

[0084] In the cubic function that approximates the first stripe pattern 31, when x is 0.6, z is 3.12×10 －３ Larger 2.77 x 10 －１ When x is 0.6, z is, but is not particularly limited to, 2.70 × 10 －２ Larger 1.81 x 10 －１ It may be smaller, or 6.26 x 10 －２ Larger 1.58 x 10 －１ It may be smaller, 7.50 x 10 －２ Larger 1.45 x 10 －１ It may be smaller.

[0085] In the cubic function that approximates the first stripe pattern 31, when x is 0.8, z is 7.04×10 －３ Larger 3.90 x 10－１ When x is 0.8, z is, but is not particularly limited to, 3.00 × 10 －２ Larger 2.46 x 10 －１ It may be smaller, 8.70 x 10 －２ Larger 2.13 x 10 －１ It may be smaller than 1.00 x 10 －１ Larger than 2.00 x 10 －１ It may be smaller.

[0086] The value of x at the inflection point of the cubic function approximating first stripe pattern 31 is 0.25 or more and 0.75 or less. The value of x at the inflection point of the cubic function approximating first stripe pattern 31 is not particularly limited, and may be, for example, 0.27 or more and 0.7 or less, or 0.35 or more and 0.6 or less.

[0087] The coefficient of determination when first stripe pattern 31 is approximated to a cubic function is, for example, 0.8 or more. The coefficient of determination indicates the degree of fit of the cubic function that approximates first stripe pattern 31 to first stripe pattern 31. The coefficient of determination when first stripe pattern 31 is approximated to a cubic function may be, for example, 0.9 or more, 0.95 or more, or 0.99 or more.

[0088] The shape of the stripe pattern observed on the second cleavage plane 12 may be substantially identical to the shape of the stripe pattern observed on the first cleavage plane 11 rotated 180° about the first central axis A1. The shape of the stripe pattern observed on the fourth cleavage plane 14 may be substantially identical to the shape of the stripe pattern observed on the third cleavage plane 13 rotated 180° about the first central axis A1.

[0089] <Second Stripe Pattern> When first stripe pattern 31 is observed on at least one of first cleavage plane 11 and second cleavage plane 12, for example, second stripe pattern 32 is observed on each of third cleavage plane 13 and fourth cleavage plane 14.

[0090] 9 is a schematic diagram showing the second stripe pattern imaged using a Nomarski microscope, in which the second stripe pattern 32 is observed on the third cleavage plane 13.

[0091] 9 , the second stripe pattern 32 is composed of a plurality of second lines 80. Some of the plurality of second lines 80 may be spaced apart from each of the first main surface 1 and the second main surface 2. From another perspective, both ends of each of the plurality of second lines 80 may reach the outer circumferential surface 3. At least some of the plurality of second lines 80 reach at least one of the first main surface 1 or the second main surface 2.

[0092] The second stripe pattern 32 has a convex shape in a direction parallel to the first direction 101, for example. Specifically, the shape of each of the multiple second lines 80 is convex in the first direction 101, for example. From another perspective, the shape of each of the multiple second lines 80 is convex in the growth direction of the indium phosphide single crystal, for example. When all of the multiple second lines 80 reach at least one of the first main surface 1 or the second main surface 2, second virtual lines (not shown) are created by connecting the multiple second lines 80 using a method similar to the method for connecting the multiple first lines 70 (see FIG. 6 ) described above. In this case, the shape of the second stripe pattern 32 can be confirmed by checking the shape of the second virtual lines.

[0093] The shape of the second stripe pattern 32 may be linear. The shape of the second stripe pattern 32 is linear or convex in a direction parallel to the first direction 101. When the shape of the second stripe pattern 32 is linear, the second stripe pattern 32 extends in a direction parallel to the second main surface 2. The second stripe pattern 32 may be inclined at an angle of, for example, 5° or less with respect to the second main surface 2. When the shape of the second stripe pattern 32 is linear, each of the multiple second lines 80 is linear.

[0094] When the first stripe pattern 31 is observed on at least one of the third cleavage plane 13 and the fourth cleavage plane 14, the second stripe pattern 32 may be observed on each of the first cleavage plane 11 and the second cleavage plane 12. The first stripe pattern 31 may be observed on each of the first cleavage plane 11, the second cleavage plane 12, the third cleavage plane 13, and the fourth cleavage plane 14.

[0095] The shape of the striped pattern is thought to resemble the shape of growth stripes in the indium phosphide single crystal substrate 100. From another perspective, the shape of the striped pattern is thought to correspond to the distribution of impurity concentration in the indium phosphide single crystal substrate 100. Specifically, when the above-mentioned etching process is performed, the amount of etching on the cleavage plane changes depending on the magnitude of the impurity concentration in the indium phosphide single crystal substrate 100. For this reason, it is thought that when the above-mentioned etching process is performed on the cleavage plane, irregularities are formed on the cleavage plane depending on the magnitude of the impurity concentration.

[0096] <Indium phosphide single crystal ingot> Next, the configuration of the indium phosphide single crystal ingot according to the first embodiment will be described. Fig. 10 is a schematic plan view showing the configuration of the indium phosphide single crystal ingot 200 according to the first embodiment. Fig. 11 is a schematic side view showing the configuration of the indium phosphide single crystal ingot 200 according to the first embodiment. As shown in Figs. 10 and 11 , the indium phosphide single crystal ingot 200 has a first end face 21, a second end face 22, and a cylindrical surface 23.

[0097] The second end face 22 is opposite the first end face 21. The direction from the first end face 21 to the second end face 22 is defined as the growth direction 109. The second end face 22 is a (100) plane of the indium phosphide single crystal. When viewed along a line perpendicular to the second end face 22, the shape of the second end face 22 is, for example, circular. The cylindrical surface 23 is continuous with each of the first end face 21 and the second end face 22. The central axis of the cylindrical surface 23 is defined as a second central axis A2. The second central axis A2 extends along the growth direction 109. The ridge between the second end face 22 and the cylindrical surface 23 is defined as a second outer edge 28.

[0098] The diameter of the second end surface 22 is defined as a second diameter W2. The second diameter W2 is, for example, 100 mm (4 inches). The lower limit of the second diameter W2 is not particularly limited, but may be 75 mm (3 inches) or more, 100 mm (4 inches) or more, or 150 mm (6 inches) or more. The upper limit of the second diameter W2 is not particularly limited, but may be, for example, 400 mm (16 inches) or less. The second diameter W2 is the longest distance between any two different points on the second outer edge 28.

[0099] At least one of a notch, an orientation flat, and an index flat may be provided on the cylindrical surface 23. When at least one of a notch, an orientation flat, and an index flat is provided on the cylindrical surface 23, the second center axis A2 is a line passing through the center of a circle that overlaps with the arc-shaped portion of the cylindrical surface 23 when viewed along a line perpendicular to the second end face 22.

[0100] The indium phosphide single crystal ingot 200 contains an impurity as a dopant. The impurity is at least one of sulfur (S) and tin (Sn). Specifically, the indium phosphide single crystal ingot 200 may contain only one of sulfur and tin as the impurity, or may contain both sulfur and tin as the impurity. The impurity concentration at the second end face 22 is higher than the impurity concentration at the first end face 21.

[0101] <Striped Pattern> Figure 12 is a first schematic plan view showing a state in which an indium phosphide single crystal ingot 200 has been cleaved. As shown in Figure 12, when the indium phosphide single crystal ingot 200 is cleaved along a plane that includes the second central axis A2 and is parallel to the (01-1) plane, a fifth cleavage plane 15 and a sixth cleavage plane 16 appear. The fifth cleavage plane 15 is the (01-1) plane. The sixth cleavage plane 16 is the (0-11) plane.

[0102] Figure 13 is a second schematic plan view showing the state in which the indium phosphide single crystal ingot 200 has been cleaved. As shown in Figure 13, when the indium phosphide single crystal ingot 200 is cleaved along a plane that includes the second central axis A2 and is parallel to the (011) plane, a seventh cleavage plane 17 and an eighth cleavage plane 18 appear. The seventh cleavage plane 17 is the (011) plane. The eighth cleavage plane 18 is the (0-1-1) plane.

[0103] When fifth cleavage plane 15, sixth cleavage plane 16, seventh cleavage plane 17, and eighth cleavage plane 18 are each subjected to an etching treatment described below and then observed using a Nomarski microscope, stripe patterns are observed on fifth cleavage plane 15, sixth cleavage plane 16, seventh cleavage plane 17, and eighth cleavage plane 18. The stripe patterns observed on fifth cleavage plane 15, sixth cleavage plane 16, seventh cleavage plane 17, and eighth cleavage plane 18 include third stripe pattern 33 (see FIG. 15 ) and fourth stripe pattern 34 (see FIG. 18 ). Details of the stripe patterns will be described later.

[0104] <Etching Treatment> The cleaved indium phosphide single crystal ingot 200 is subjected to the following etching treatment.

[0105] Etching treatment: A cleavage plane to be measured, among fifth cleavage plane 15, sixth cleavage plane 16, seventh cleavage plane 17, and eighth cleavage plane 18, was placed horizontally at a position 10 mm below the liquid surface 94 of mixed liquid 91 at 25°C, which was made up of 10 g of chromium (VI) oxide, 10 mL of a 50% by mass hydrofluoric acid solution, and 400 mL of pure water, and light from a 500 W reflector-type incandescent lamp 93 was irradiated toward the cleavage plane to be measured from a position 20 cm above liquid surface 94 for 30 minutes to 60 minutes.

[0106] Fig. 14 is a partial cross-sectional schematic diagram showing the etching of the cleavage planes of an indium phosphide single crystal ingot 200. A detailed method of the above-mentioned etching process will be described using Fig. 14. The following describes the etching of the fifth cleavage plane 15. The etching of the sixth cleavage plane 16, the seventh cleavage plane 17, and the eighth cleavage plane 18 can also be performed in a similar manner.

[0107] As shown in FIG. 14 , first, a mixed solution 91 is prepared. The mixed solution 91 is composed of chromium (VI) oxide, a hydrofluoric acid solution, and pure water. In the mixed solution 91, the chromium (VI) oxide, the hydrofluoric acid solution, and the pure water are blended in a ratio of 10 g by weight of chromium (VI), 10 mL by volume of the hydrofluoric acid solution, and 400 mL by volume of the pure water. The volume of the mixed solution 91 is set to a volume that allows the indium phosphide single crystal ingot 200 to be submerged in the mixed solution 91 inside the tank 92. The concentration of the hydrofluoric acid solution is set to 50% by mass. The temperature of the mixed solution 91 is set to 25° C. The mixed solution 91 is then poured into the tank 92.

[0108] The fifth cleavage plane 15 is polished. The arithmetic mean roughness Ra of the polished fifth cleavage plane 15 is set to be 0.1 nm or more and 0.5 nm or less.

[0109] Next, the cleaved indium phosphide single crystal ingot 200 is placed in the mixed liquid 91. Specifically, the indium phosphide single crystal ingot 200 is placed so that the fifth cleavage plane 15 is positioned horizontally. From another perspective, the indium phosphide single crystal ingot 200 is placed so that the liquid surface 94 of the mixed liquid 91 and the fifth cleavage plane 15 are substantially parallel to each other.

[0110] The fifth cleavage plane 15 is disposed below the liquid surface 94. In the vertical direction V, the distance between the liquid surface 94 and the fifth cleavage plane 15 (third distance D3) is 10 mm. The direction from the liquid surface 94 toward the fifth cleavage plane 15 along the vertical direction V is also referred to as the depth direction. A reflector-type incandescent lamp 93 is disposed above the liquid surface 94. In the vertical direction V, the distance between the liquid surface 94 and the reflector-type incandescent lamp 93 (fourth distance D4) is 20 cm. As the reflector-type incandescent lamp 93, for example, an "Eye Lamp (registered trademark)" manufactured by Iwasaki Electric Co., Ltd. can be used. The power consumption of the reflector-type incandescent lamp 93 is, for example, 500 W.

[0111] Light is irradiated from a reflector-type incandescent lamp 93 toward fifth cleavage plane 15. The light is irradiated along arrow 90. The time (etching time) during which fifth cleavage plane 15 is irradiated with light is set to 30 minutes or more and 60 minutes or less. In this manner, fifth cleavage plane 15 is etched. As a result, a striped pattern that can be observed using a Nomarski microscope is formed on fifth cleavage plane 15.

[0112] The temperature of the mixed liquid 91 (25°C) mentioned above refers to the temperature at the start of the etching process using light. The temperature of the mixed liquid 91 may fluctuate during the etching process due to factors such as the light energy of the reflector-type incandescent lamp 93. In the etching process described above, the indium phosphide single crystal ingot 200 placed in the mixed liquid 91 may be oscillated at predetermined time intervals (e.g., every minute). This allows the striped pattern formed on the fifth cleavage plane 15 to be more clearly defined. To make the striped pattern formed on the fifth cleavage plane 15 more clearly defined, the etching time is adjusted within a range of 30 minutes to 60 minutes.

[0113] <Third Stripe Pattern> When each of the fifth cleavage plane 15, the sixth cleavage plane 16, the seventh cleavage plane 17, and the eighth cleavage plane 18 is observed using a Nomarski microscope, a third stripe pattern 33 is observed on at least one of the fifth cleavage plane 15, the sixth cleavage plane 16, the seventh cleavage plane 17, or the eighth cleavage plane 18. FIG. 15 is a schematic diagram showing the third stripe pattern 33 imaged using a Nomarski microscope. A case in which the third stripe pattern 33 is observed on the fifth cleavage plane 15 will be described using FIG. 15 . As shown in FIG. 15 , the third stripe pattern 33 is composed of a plurality of third lines 79. The third stripe pattern 33 is approximated to a cubic function by the following method.

[0114] First, a plurality of third lines 79 are connected together using an image captured using a Nomarski microscope. When the plurality of third lines 79 are connected together, the plurality of third lines 79 to be connected are first selected. The line that reaches the cylindrical surface 23 is set as the fifth selected line 75. Note that, when there are a plurality of third lines 79 that reach the cylindrical surface 23, the third line 79 that is closest to the first end face 21 in the growth direction 109 is set as the fifth selected line 75.

[0115] The intersection of the fifth selection line 75 and the cylindrical surface 23 is defined as a ninth intersection 61. Of the intersections of the third stripe pattern 33 and the cylindrical surface 23, the ninth intersection 61 is the closest to the first end face 21 in the growth direction 109. The direction perpendicular to the growth direction 109 and extending from the ninth intersection 61 toward the second central axis A2 is defined as a third direction 103. The fifth selection line 75 reaches, for example, the second end face 22. The intersection of the fifth selection line 75 and the second end face 22 is defined as a tenth intersection 62.

[0116] 15 , a line that passes through the tenth intersection point 62 and is parallel to the growth direction 109 is set as a fourth virtual line 114. Of the multiple third lines 79, the third line 79 that intersects with the fourth virtual line 114 is set as a sixth selected line 76. Note that, if there are multiple third lines 79 that intersect with the fourth virtual line 114, any one of the multiple third lines 79 that intersects with the fourth virtual line 114 is set as the sixth selected line 76.

[0117] The intersection of the sixth selection line 76 and the fourth virtual straight line 114 is set to the eleventh intersection 63. In the third direction 103, the eleventh intersection 63 is at the same position as the tenth intersection 62. The portion of the sixth selection line 76 in the third direction 103 relative to the eleventh intersection 63 reaches, for example, the cylindrical surface 23. The intersection of the sixth selection line 76 and the cylindrical surface 23 is set to the twelfth intersection 64. As described above, the fifth selection line 75 and the sixth selection line 76 are selected as the third line 79 to be joined together.

[0118] Note that there is no particular limitation on the number of third lines 79 to be joined. For example, when the portion of the sixth selected line 76 in the third direction 103 relative to the eleventh intersection 63 reaches the second end face 22, two or more third lines 79 are selected as the third lines 79 to be joined.

[0119] Next, the fifth selection line 75 and the sixth selection line 76 are joined together. FIG. 16 is a schematic diagram showing the process of joining a plurality of third lines 79. As shown in FIG. 16, the fifth selection line 75 and the sixth selection line 76 are joined together so that the tenth intersection 62 and the eleventh intersection 63 coincide with each other. Specifically, the fifth selection line 75 and the sixth selection line 76 are joined together by, for example, moving the sixth selection line 76 along the growth direction 109. The portion of the sixth selection line 76 between the ninth intersection 61 and the tenth intersection 62 is, for example, removed. In this way, the third virtual line 69 is created.

[0120] 16 , the third imaginary line 69 has a ninth intersection 61 and a twelfth intersection 64. The ninth intersection 61 and the twelfth intersection 64 are each an end point of the third imaginary line 69. The twelfth intersection 64 is opposite the ninth intersection 61.

[0121] The shape of each of the multiple third lines 79 (see FIG. 15 ) is substantially the same as the shape of a portion of the third virtual line 69 cut out. From another perspective, the shape of the third stripe pattern 33 (see FIG. 15 ) is substantially the same as the shape of a portion of the shape created by arranging the multiple third virtual lines 69 along the growth direction 109 cut out.

[0122] 15 , the width of the third stripe pattern 33 in the third direction 103 is set to a second width H2. The second width H2 is substantially the same as the width of the fifth cleavage plane 15 in the third direction 103. As shown in FIG. 16 , the length of the third virtual line 69 in the third direction 103 is substantially the same as the second width H2.

[0123] Next, the third virtual line 69 is approximated by a cubic function. FIG. 17 is a schematic diagram showing the process of approximating the third virtual line 69 to a cubic function. Specifically, as shown in FIG. 17 , the third virtual line 69 is first arranged on a two-dimensional plane with the horizontal axis representing the third direction 103 and the vertical axis representing the growth direction 109. A plurality of second measurement points 65 are arranged so as to overlap with the third virtual line 69. The number of the second measurement points 65 is, for example, 19. In the third direction 103, each of the second measurement points 65 is arranged between the ninth intersection 61 and the twelfth intersection 64. The second measurement points 65 are arranged at equal intervals in the third direction 103. In the third direction 103, the interval between the second measurement points 65 is, for example, 5% of the second width H2. In the third direction 103 , the distance between the ninth intersection 61 and the second measurement point 65 closest to the ninth intersection 61 is the same as the spacing between the multiple second measurement points 65 .

[0124] Using the ninth intersection 61 as the origin, the coordinates of each of the multiple second measurement points 65 and the twelfth intersection 64 are measured. Specifically, the distance in the growth direction 109 between each of the multiple second measurement points 65 and the twelfth intersection 64 and the ninth intersection 61 is measured. The distance in the third direction 103 between each of the multiple second measurement points 65 and the twelfth intersection 64 and the ninth intersection 61 is measured. Hereinafter, the distance in the growth direction 109 between an arbitrary point and the ninth intersection 61 is also referred to as the growth direction distance. The distance in the third direction 103 between an arbitrary point and the ninth intersection 61 is also referred to as the third direction distance. The ninth intersection 61 is also referred to as the second origin 61.

[0125] The value obtained by dividing the growth direction distance by the second width H2 is defined as z, and the value obtained by dividing the third direction distance by the second width H2 is defined as x. Using the measured growth direction distance and third direction distance, the third virtual line 69 is approximated to a cubic function. The least squares method is used to approximate the third virtual line 69 to a cubic function. The third virtual line 69 approximated to a cubic function is expressed by Equation 2.

[0126] z = ax ３ +bx ２ +cx (Equation 2) In Equation 2, a, b, and c are each a constant. The cubic function expressed by Equation 2 is a cubic function that approximates third stripe pattern 33 (see FIG. 15 ).

[0127] In the cubic function that approximates the third stripe pattern 33, a is 5.0×10 －６ Larger 6.0 x 10 －５ a is not particularly limited, but is preferably 7.0 × 10 －６ Larger than 5.0 x 10 －５ It may be smaller than 1×10 －５ Larger 4.6 x 10 －５ It may be smaller, 2 x 10 －５ Larger 4.55 x 10 －５ It may be smaller.

[0128] In the cubic function that approximates the third stripe pattern 33, b is −7.0×10 －３ or more, which is 2.0 × 10 －３ b is not particularly limited, but is preferably −6.0×10 －３ Larger than 1x10 －３ It may be smaller than -5.8 x 10 －３ Greater than -1.0 x 10 －３ It may be smaller than -5.8 x 10 －３ Greater than -2.0 x 10 －３ It may be smaller.

[0129] In the cubic function that approximates the third stripe pattern 33, c is 2.0×10 －２ Larger 7.0 x 10 －１ c is not particularly limited, but is preferably 5.0 × 10 －２Larger 6.0 x 10 －１ It may be smaller than 1.1 × 10 －１ Larger than 5.0 x 10 －１ It may be smaller, 2.5 x 10 －１ Larger 4.5 x 10 －１ It may be smaller.

[0130] In the cubic function approximating the third stripe pattern 33, when x is 0.2, z is 1.02×10 －２ Larger than 1.104 x 10 －１ When x is 0.2, z is, but is not particularly limited to, 1.80×10 －２ Larger 7.96 x 10 －２ It may be smaller, 2.50 x 10 －２ Larger 7.12 x 10 －２ It may be smaller than 4.00 x 10 －２ Larger 7.00 x 10 －２ It may be smaller.

[0131] In the cubic function approximating the third stripe pattern 33, when x is 0.4, z is 7.68×10 －３ Larger 1.89 x 10 －１ When x is 0.4, z is, but is not particularly limited to, 2.50 × 10 －２ Larger 1.33 x 10 －１ It may be smaller, 4.39 x 10 －２ Larger 1.18 x 10 －１ It may be smaller than 6.00 x 10 －２ Larger 1.10 x 10 －１ It may be smaller.

[0132] In the cubic function approximating the third stripe pattern 33, when x is 0.6, z is 3.12×10 －３ Larger 2.77 x 10 －１ When x is 0.6, z is, but is not particularly limited to, 2.70 × 10 －２ Larger 1.81 x 10 －１ It may be smaller, or 6.26 x 10 －２ Larger 1.58 x 10 －１It may be smaller, 7.50 x 10 －２ Larger 1.45 x 10 －１ It may be smaller.

[0133] In the cubic function approximating the third stripe pattern 33, when x is 0.8, z is 7.04×10 －３ Larger 3.90 x 10 －１ When x is 0.8, z is, but is not particularly limited to, 3.00 × 10 －２ Larger 2.46 x 10 －１ It may be smaller, 8.70 x 10 －２ Larger 2.13 x 10 －１ It may be smaller than 1.00 x 10 －１ Larger than 2.00 x 10 －１ It may be smaller.

[0134] The value of x at the inflection point of the cubic function approximating third stripe pattern 33 is 0.25 or more and 0.75 or less. The value of x at the inflection point of the cubic function approximating third stripe pattern 33 is not particularly limited, and may be, for example, 0.27 or more and 0.7 or less, or 0.35 or more and 0.6 or less.

[0135] The coefficient of determination when the third stripe pattern 33 is approximated to a cubic function is, for example, 0.8 or more. The coefficient of determination indicates the degree of fit of the cubic function that approximates the third stripe pattern 33 to the third stripe pattern 33. The coefficient of determination when the third stripe pattern 33 is approximated to a cubic function may be, for example, 0.9 or more, 0.95 or more, or 0.99 or more.

[0136] The shape of the stripe pattern observed on sixth cleavage plane 16 may be substantially identical to the shape of the stripe pattern observed on fifth cleavage plane 15 rotated 180° about second central axis A2. The shape of the stripe pattern observed on eighth cleavage plane 18 may be substantially identical to the shape of the stripe pattern observed on seventh cleavage plane 17 rotated 180° about second central axis A2.

[0137] <Fourth stripe pattern> When the third stripe pattern 33 is observed on at least one of the fifth cleavage plane 15 or the sixth cleavage plane 16, for example, the fourth stripe pattern 34 is observed on each of the seventh cleavage plane 17 and the eighth cleavage plane 18.

[0138] 18 is a schematic diagram showing the fourth stripe pattern 34 captured using a Nomarski microscope, showing an image of the fourth stripe pattern 34 observed on the seventh cleavage plane 17.

[0139] 18 , the fourth stripe pattern 34 is formed by a plurality of fourth lines 89. Some of the plurality of fourth lines 89 may be spaced apart from each of the first end face 21 and the second end face 22. From another perspective, both ends of each of the plurality of fourth lines 89 may reach the cylindrical surface 23. At least some of the plurality of fourth lines 89 reach at least one of the first end face 21 or the second end face 22.

[0140] The fourth stripe pattern 34 has, for example, a convex shape in the growth direction 109. Specifically, the shape of each of the multiple fourth lines 89 has, for example, a convex shape in the growth direction 109. Note that when all of the multiple fourth lines 89 reach at least one of the first end face 21 or the second end face 22, the multiple fourth lines 89 are connected together to create a fourth virtual line (not shown) using a method similar to the method for connecting the multiple third lines 79 (see FIG. 15 ) described above. In this case, the shape of the fourth stripe pattern 34 can be confirmed by checking the shape of the fourth virtual line.

[0141] The shape of the fourth stripe pattern 34 may be linear. The shape of the fourth stripe pattern 34 is linear or convex in the growth direction 109. When the shape of the fourth stripe pattern 34 is linear, the fourth stripe pattern 34 extends in a direction parallel to the second end face 22. The fourth stripe pattern 34 may be inclined at an angle of, for example, 5° or less with respect to the second end face 22. When the shape of the fourth stripe pattern 34 is linear, each of the multiple fourth lines 89 is linear.

[0142] When the third stripe pattern 33 is observed on at least one of the seventh cleavage plane 17 and the eighth cleavage plane 18, the fourth stripe pattern 34 may be observed on each of the fifth cleavage plane 15 and the sixth cleavage plane 16. The third stripe pattern 33 may be observed on each of the fifth cleavage plane 15, the sixth cleavage plane 16, the seventh cleavage plane 17, and the eighth cleavage plane 18.

[0143] The above describes a method for observing a stripe pattern by cleaving an indium phosphide single crystal ingot 200. However, the stripe pattern may also be observed by cleaving the indium phosphide single crystal substrate 100 described above after cutting the indium phosphide single crystal ingot 200 to produce the indium phosphide single crystal substrate 100.

[0144] <Indium phosphide single crystal substrate manufacturing apparatus> Next, the configuration of the indium phosphide single crystal growth apparatus 300 according to the first embodiment will be described. Fig. 19 is a cross-sectional schematic diagram showing the configuration of the indium phosphide single crystal growth apparatus 300 according to the first embodiment.

[0145] As shown in FIG. 19, the indium phosphide single crystal growth apparatus 300 mainly comprises a crucible 40 , a crucible holder 49 , a heating element 48 , a first shielding plate 81 , and a high-pressure vessel 47 .

[0146] The crucible 40 is made of a material that can withstand the heat generated when melting the raw material. Specifically, the crucible 40 is made of, for example, pyrolytic boron nitride (PBN). The crucible 40 has a seed crystal holding portion 41 and a single crystal growing portion 42. The crucible 40 has a cylindrical shape. The central axis of the crucible 40 is defined as a third central axis A3.

[0147] The seed crystal holder 41 has a cylindrical shape. The seed crystal holder 41 holds a seed crystal. The seed crystal holder 41 defines a first space 97. The seed crystal holder 41 is open toward a fourth direction 104. The seed crystal holder 41 has a bottom 41 a and an outer periphery 41 b.

[0148] The bottom 41a constitutes the bottom of the crucible 40. The third central axis A3 passes through the bottom 41a. The outer peripheral portion 41b is continuous with the bottom 41a. The outer peripheral portion 41b is annular in shape. The outer peripheral portion 41b surrounds the third central axis A3. The outer peripheral portion 41b is provided in a fourth direction 104 relative to the bottom 41a. The fourth direction 104 is the growth direction of the indium phosphide single crystal. The direction opposite to the fourth direction 104 is a fifth direction 105. When viewed in the fourth direction 104, the outer shape of the outer peripheral portion 41b is circular. The third central axis A3 extends along the fourth direction 104.

[0149] The single crystal growth portion 42 holds an indium phosphide source material. The single crystal growth portion 42 is continuous with the seed crystal holder 41. The single crystal growth portion 42 is provided on the seed crystal holder 41. In other words, the single crystal growth portion 42 is provided in a fourth direction 104 relative to the seed crystal holder 41. The single crystal growth portion 42 has a first portion 42 a and a second portion 42 b.

[0150] The first portion 42a is continuous with the outer peripheral portion 41b. The first portion 42a is annular in shape. The first portion 42a surrounds the third central axis A3. The outer diameter of the first portion 42a increases with increasing distance from the seed crystal holder 41 along the fourth direction 104. Similarly, the inner diameter of the first portion 42a increases with increasing distance from the seed crystal holder 41 along the fourth direction 104. The first portion 42a forms a second space 98. The second space 98 is continuous with the first space 97. The second space 98 is located in the fourth direction 104 relative to the first space 97.

[0151] The second portion 42b is continuous with the first portion 42a. The second portion 42b is provided in the fourth direction 104 relative to the first portion 42a. The second portion 42b has a hollow cylindrical shape. From another perspective, the second portion 42b has an annular shape. When viewed in the fourth direction 104, the second portion 42b has a circular shape. The second portion 42b surrounds the third central axis A3. The second portion 42b forms a third space 99. The third space 99 is continuous with the second space 98. The third space 99 is located in the fourth direction 104 relative to the second space 98. The second space 98 is located between the first space 97 and the third space 99. The inner diameter W3 of the second portion 42b is, for example, 75 mm or more.

[0152] The heating element 48 heats the crucible 40. Specifically, for example, when power is supplied to the heating element 48, the heating element 48 heats the crucible 40. The heating element 48 has a cylindrical shape. The heating element 48 surrounds the crucible 40. The heating element 48 is spaced apart from the crucible 40. The heating element 48 has a first heating element portion 48a and a second heating element portion 48b.

[0153] The first heating element 48a surrounds the single crystal growth portion 42. When viewed in the fifth direction 105, the first heating element 48a has an annular shape. The second heating element 48b is provided in the fifth direction 105 relative to the first heating element 48a. The second heating element 48b surrounds the seed crystal holder 41. When viewed in the fifth direction 105, the second heating element 48b has an annular shape.

[0154] The first shielding plate 81 is provided between the crucible 40 and the heating element 48. Specifically, the first shielding plate 81 is provided, for example, between the single crystal growth portion 42 and the first heating element portion 48a. In the direction in which the third central axis A3 extends, the first shielding plate 81 is provided in the fourth direction 104 relative to the seed crystal holder 41. The first shielding plate 81 blocks a portion of the thermal energy supplied from the heating element 48 to the crucible 40. The first shielding plate 81 has a flat plate shape. The first shielding plate 81 is made of PBN. The length of the first shielding plate 81 in the fourth direction 104 is defined as a first length L1. The first length L1 is, for example, 200 mm. The first length L1 is, for example, longer than the length of the second portion 42b in the fourth direction 104.

[0155] The crucible holder 49 holds the crucible 40. The crucible holder 49 surrounds the seed crystal holder 41. The crucible holder 49 surrounds the first portion 42a. The high-pressure vessel 47 surrounds the crucible 40, the heating element 48, and the first shielding plate 81.

[0156] Fig. 20 is a schematic plan view showing the configuration of an indium phosphide single crystal growth apparatus 300 according to the first embodiment. The high-pressure vessel 47 is not shown in Fig. 20 . As shown in Fig. 20 , the positions that are at 0°, 180°, 90°, and 270° angles from the third central axis A3 and that are between the crucible 40 and the heating element 48 are designated as a first position P1, a second position P2, a third position P3, and a fourth position P4, respectively. The direction that passes through the first position P1, the third position P3, and the second position P2 in this order around the third central axis A3 is designated as a circumferential direction R.

[0157] The first shielding plate 81 is provided at the first position P1. The first shielding plate 81 is not provided at each of the second position P2, the third position P3, and the fourth position P4. From another perspective, the thermal energy supplied from the heating element 48 to the crucible 40 is not blocked by the first shielding plate 81 at each of the second position P2, the third position P3, and the fourth position P4. Note that in FIG. 20 , for convenience of explanation, the first position P1, the second position P2, the third position P3, and the fourth position P4 are each indicated by a dot, but the first shielding plate 81 does not have to overlap with the dots shown in FIG. 20 . When viewed in the fifth direction 105, the first shielding plate 81 only needs to intersect with a line passing through the third central axis A3 and the first position P1.

[0158] In the circumferential direction R, for example, the first shielding plate 81 is not provided between the third position P3 and the second position P2 and between the second position P2 and the fourth position P4. In other words, for example, the first shielding plate 81 is not provided in the directions from 90° to 270° as viewed from the third center axis A3.

[0159] The direction from the first position P1 to the second position P2 is defined as a sixth direction 106. The sixth direction 106 is perpendicular to the third central axis A3. The direction from the third position P3 to the fourth position P4 is defined as a seventh direction 107. The seventh direction 107 is perpendicular to both the sixth direction 106 and the third central axis A3.

[0160] The thickness of the first shielding plate 81 in the sixth direction 106 is defined as a first thickness T1. The first thickness T1 is 9 mm or less. The first thickness T1 is, for example, 6 mm. The lower limit of the first thickness T1 is not particularly limited, but may be, for example, 4 mm or more, or 5 mm or more. The upper limit of the first thickness T1 is not particularly limited, but may be, for example, 8 mm or less, or 7 mm or less.

[0161] The width of the first shielding plate 81 in the seventh direction 107 is defined as a third width H3. The third width H3 is, for example, 70 mm. The third width H3 is, for example, 50 mm or more and 120 mm or less. The third width H3 is, for example, 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal produced using the growth apparatus 300. From another perspective, the third width H3 is 0.5 to 1.2 times the inner diameter W3 of the second portion 42b. The third width H3 may be 0.55 to 1.0 times, or 0.6 to 0.8 times, the maximum diameter of the indium phosphide single crystal. The cross section shown in FIG. 19 is a cross section taken along line XIX-XIX in FIG. 20. The cross section shown in FIG. 19 is a cross section that includes the third central axis A3 and is parallel to the sixth direction 106.

[0162] <Method for Manufacturing Indium Phosphide Single Crystal Substrate> Next, a method for manufacturing the indium phosphide single crystal substrate 100 according to the first embodiment will be described. The indium phosphide single crystal substrate 100 is manufactured using a vertical boat method. The vertical boat method includes, for example, a vertical Bridgman (VB) method, a vertical gradient freeze (VGF) method, and a hybrid method that combines the VB method and the VGF method.

[0163] Fig. 21 is a flow chart schematically showing the method for manufacturing an indium phosphide single crystal substrate according to the first embodiment. As shown in Fig. 21, the method for manufacturing an indium phosphide single crystal substrate 100 according to the first embodiment mainly includes a step of preparing a growth apparatus (S10), a step of arranging a seed crystal (S20), a step of arranging a raw material (S30), a step of arranging a sealant (S40), a step of melting the raw material (S50), a step of growing a crystal (S60), and a step of cutting the crystal (S70).

[0164] First, a step (S10) of preparing a growth apparatus is carried out. Specifically, a growth apparatus 300 (see FIGS. 19 and 20) for growing an indium phosphide single crystal according to the first embodiment is prepared. In the step (S10) of preparing a growth apparatus, the crucible 40 is heated in an oxygen atmosphere, thereby forming boron oxide (B ２O ３ A boron oxide film (not shown) may be formed on the surface of the silicon substrate. The boron oxide film functions as a sealant.

[0165] Next, the step of placing a seed crystal (S20) is performed. FIG. 22 is a cross-sectional schematic diagram showing a crucible in which a seed crystal 84, an indium phosphide source material 85, and a sealing material 86 are placed. As shown in FIG. 22 , in the step of placing a seed crystal (S20), the seed crystal 84 is placed inside the seed crystal holder 41. In other words, the seed crystal 84 is placed in the first space 97 (see FIG. 19 ). The seed crystal 84 is made of an indium phosphide single crystal. The seed crystal 84 may contain at least one of sulfur and tin as impurity atoms. Specifically, the seed crystal 84 may contain only one of sulfur and tin as impurity atoms, or may contain both sulfur and tin as impurity atoms.

[0166] Next, a raw material disposing step (S30) is performed. As shown in FIG. 22 , a plurality of indium phosphide raw materials 85 are disposed on a seed crystal 84. Each of the plurality of indium phosphide raw materials 85 is made of, for example, polycrystalline indium phosphide. Each of the plurality of indium phosphide raw materials 85 has, for example, a cylindrical shape. The plurality of indium phosphide raw materials 85 are stacked on the seed crystal 84. At least one of sulfur and tin is disposed inside the crucible 40 as an impurity. Specifically, only one of sulfur and tin may be disposed inside the crucible 40 as an impurity, or both sulfur and tin may be disposed inside the crucible 40 as impurities.

[0167] Next, a step (S40) of disposing a sealant is performed. As shown in Fig. 22, a sealant 86 is disposed on the plurality of indium phosphide raw materials 85. The sealant 86 is made of, for example, boron oxide. The sealant 86 has a cylindrical shape.

[0168] Next, the step (S50) of melting the raw material is performed. The crucible 40 is heated by supplying current to the heating element 48. The first shielding plate 81 blocks a portion of the thermal energy supplied from the heating element 48 to the crucible 40. The current supplied to the first heating element portion 48a is greater than the current supplied to the second heating element portion 48b. Therefore, the temperature of the crucible 40 decreases in the fifth direction 105 toward the bottom 41a of the crucible 40. This causes a portion of the seed crystal 84 and the indium phosphide raw material 85 to melt. The molten portion of the seed crystal 84 and the indium phosphide raw material 85 become an indium phosphide melt 87. This results in the indium phosphide melt 87 being obtained. The indium phosphide melt 87 comes into contact with the remaining portion of the seed crystal 84. The sealant 86 melts, turning into a liquid sealant 88. A liquid encapsulant 88 covers the indium phosphide melt 87 .

[0169] Next, the step of growing a crystal (S60) is carried out. FIG. 23 is a cross-sectional schematic diagram showing the step of growing a crystal (S60). As shown in FIG. 23 , crucible 40 is pulled down along fifth direction 105. The temperature of a portion of indium phosphide melt 87 close to the remainder of seed crystal 84 drops. The rate at which crucible 40 is pulled down is, for example, 2.0 mm / h or more and 5.0 mm / h or less. As a result, the raw material melt in contact with the remainder of seed crystal 84 solidifies, thereby growing indium phosphide single crystal 400.

[0170] In the crystal growing step (S60), an interface (solid-liquid interface I) is formed between the indium phosphide single crystal 400 and the indium phosphide melt 87. The shape of the solid-liquid interface I changes due to the temperature distribution of the indium phosphide melt 87. The solid-liquid interface I near the lower temperature portion of the indium phosphide melt 87 is formed closer to the fourth direction 104 than the solid-liquid interface I near the higher temperature portion of the indium phosphide melt 87. The temperature of the portion of the indium phosphide melt 87 closer to the first shielding plate 81 is lower than the temperature of the portion of the indium phosphide melt 87 farther from the first shielding plate 81. Therefore, the portion of the solid-liquid interface I closer to the first shielding plate 81 is formed closer to the fourth direction 104 than the portion of the solid-liquid interface I farther from the first shielding plate 81. As a result, the shape of the solid-liquid interface I in a cross section including the third central axis A3 and parallel to the sixth direction 106 approaches the shape of a cubic function.

[0171] As the crucible 40 continues to be pulled down, the indium phosphide melt 87 in the crucible 40 solidifies. In this way, the indium phosphide single crystal 400 is produced. The maximum diameter of the indium phosphide single crystal 400 is substantially the same as the inner diameter W3 of the second portion 42b.

[0172] Next, a step (S70) of cutting the crystal is carried out. For example, the indium phosphide single crystal 400 is cut using a wire saw, thereby producing the indium phosphide single crystal substrate 100 (see FIGS. 1 and 2). In this manner, the indium phosphide single crystal substrate 100 is manufactured.

[0173] In the step (S70) of cutting the crystal, the indium phosphide single crystal 400 may be cut to produce the indium phosphide single crystal ingot 200. In this way, the indium phosphide single crystal ingot 200 is manufactured.

[0174] Second Embodiment Next, the configuration of a method for manufacturing an indium phosphide single crystal substrate 100 according to a second embodiment will be described. The method for manufacturing an indium phosphide single crystal substrate 100 according to the second embodiment differs from the method for manufacturing an indium phosphide single crystal substrate according to the first embodiment mainly in that the indium phosphide single crystal growth apparatus 300 further includes a second shielding plate 82, but in other respects is substantially the same as the method for manufacturing an indium phosphide single crystal substrate according to the first embodiment. Below, the differences from the method for manufacturing an indium phosphide single crystal substrate according to the first embodiment will be mainly described.

[0175] Figure 24 is a cross-sectional view schematically illustrating the configuration of an indium phosphide single crystal growth apparatus 300 according to the second embodiment. Figure 25 is a plan view schematically illustrating the configuration of an indium phosphide single crystal growth apparatus 300 according to the second embodiment. The cross section shown in Figure 24 is taken along line XXIV-XXIV in Figure 25. The cross section shown in Figure 24 is a cross section that includes the third central axis A3 and is parallel to the sixth direction 106.

[0176] 24 and 25 , the indium phosphide single crystal growth apparatus 300 has a second shielding plate 82. The second shielding plate 82 is provided between the crucible 40 and the heating element 48. Specifically, the second shielding plate 82 is provided, for example, between the single crystal growth section 42 and the first heating element section 48a. The second shielding plate 82 blocks a portion of the thermal energy supplied from the heating element 48 to the crucible 40.

[0177] The second shielding plate 82 has a flat plate shape. The second shielding plate 82 is made of PBN. In the fourth direction 104, the second shielding plate 82 is provided at substantially the same position as the first shielding plate 81. The length of the second shielding plate 82 in the fourth direction 104 is set to a second length L2. The second length L2 is, for example, 200 mm. The second length L2 may be substantially the same as the first length L1.

[0178] The second shielding plate 82 is provided at the second position P2. From another perspective, the crucible 40 is provided between the first shielding plate 81 and the second shielding plate 82. In the indium phosphide single crystal growth apparatus 300 according to the second embodiment, the first shielding plate 81 and the second shielding plate 82 are not provided at the third position P3 and the fourth position P4. From another perspective, at the third position P3 and the fourth position P4, the thermal energy supplied from the heating element 48 to the crucible 40 is not blocked by the first shielding plate 81 and the second shielding plate 82. In the circumferential direction R, no object is provided between the first shielding plate 81 and the second shielding plate 82.

[0179] The thickness of the second shielding plate 82 in the sixth direction 106 is defined as a second thickness T2. The second thickness T2 is, for example, 2 mm. The second thickness T2 is thinner than the first thickness T1. The value obtained by subtracting the second thickness T2 from the first thickness T1 is 2 mm or more and 9 mm or less. The value obtained by subtracting the second thickness T2 from the first thickness T1 is not particularly limited, but may be, for example, 3 mm or more and 8 mm or less, or 5 mm or more and 7 mm or less.

[0180] The width of the second shielding plate 82 in the seventh direction 107 is set to a fourth width H4. The fourth width H4 is, for example, 70 mm. The fourth width H4 is, for example, 50 mm or more and 120 mm or less. The fourth width H4 is, for example, 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal produced using the growth apparatus 300. From another perspective, the fourth width H4 is 0.5 to 1.2 times the inner diameter W3 of the second portion 42b. The fourth width H4 may be 0.55 to 1.0 times, or 0.6 to 0.8 times, the maximum diameter of the indium phosphide single crystal.

[0181] Next, the effects of the indium phosphide single crystal substrate 100, the indium phosphide single crystal ingot 200, and the method for manufacturing an indium phosphide single crystal substrate according to the present disclosure will be described.

[0182] An epitaxial substrate may be manufactured by forming an epitaxial layer on an indium phosphide single crystal substrate 100. A high yield is required for the epitaxial substrate. However, the electrical characteristics of the epitaxial substrate may vary greatly within the surface of the epitaxial substrate. This may result in a decrease in the yield of the epitaxial substrate.

[0183] The inventors have investigated measures for improving the yield of epitaxial substrates and have found the following. Specifically, the inventors have found that the yield of epitaxial substrates is improved when epitaxial substrates are manufactured using an indium phosphide single crystal substrate 100 in which a specific stripe pattern is observed when the cleaved surface of the indium phosphide single crystal substrate 100 is observed using a Nomarski microscope. The stripe pattern observed when the cleaved surface of the indium phosphide single crystal substrate 100 is observed using a Nomarski microscope is thought to be caused by growth stripes in the indium phosphide single crystal substrate 100. The shape of the growth stripes in the indium phosphide single crystal substrate 100 is similar to the shape of the solid-liquid interface I when the indium phosphide single crystal substrate 100 is manufactured.

[0184] If the unevenness of the growth striations of the indium phosphide single crystal substrate 100 is excessively large, the internal stress of the indium phosphide single crystal substrate 100 increases. In this case, when an epitaxial layer is formed on the indium phosphide single crystal substrate 100, the indium phosphide single crystal substrate 100 is heated, causing the indium phosphide single crystal substrate 100 to warp excessively. This is thought to increase the variation in temperature distribution on the main surface (e.g., second main surface 2) of the indium phosphide single crystal substrate 100 on which the epitaxial layer is formed. This increases the variation in carrier concentration in the epitaxial layer. As a result, it is thought to increase the variation in electrical characteristics within the surface of the epitaxial substrate.

[0185] After careful consideration, the inventors discovered that the variation in the electrical properties of the epitaxial substrate is smaller when the shape of the stripe pattern is close to a cubic function, compared to when the shape of the stripe pattern is convex in the first direction 101 or convex in the direction opposite to the first direction 101.

[0186] In the indium phosphide single crystal substrate 100 according to the present disclosure, when each of the first cleavage plane 11, the second cleavage plane 12, the third cleavage plane 13, and the fourth cleavage plane 14 is observed using a Nomarski microscope, a first stripe pattern 31 is observed on at least one of the first cleavage plane 11, the second cleavage plane 12, the third cleavage plane 13, and the fourth cleavage plane 14. When the first stripe pattern 31 is approximated to a cubic function, it is expressed by the above formula 1. a is 5.0×10 －６ Larger 6.0 x 10 －５ b is -7.0 x 10 －３ or more, which is 2.0 × 10 －３ c is smaller than 2.0 × 10 －２ Larger 7.0 x 10 －１ is smaller. The value of x at the inflection point of the cubic function is 0.25 or more and 0.75 or less. As such, the shape of the stripe pattern observed on the cleavage plane of the indium phosphide single crystal substrate 100 according to the present disclosure is close to a shape of a cubic function. This makes it possible to reduce variations in the electrical characteristics within the surface of the epitaxial substrate. As a result, it is possible to improve the yield of epitaxial substrates.

[0187] In the indium phosphide single crystal substrate 100 according to the present disclosure, a first stripe pattern 31 may be observed on at least one of the first cleavage plane 11 and the second cleavage plane 12, and a second stripe pattern 32 may be observed on each of the third cleavage plane 13 and the fourth cleavage plane 14. The first stripe pattern 31 may be observed on at least one of the third cleavage plane 13 and the fourth cleavage plane 14, and a second stripe pattern 32 may be observed on each of the first cleavage plane 11 and the second cleavage plane 12. The shape of the second stripe pattern 32 is linear or convex in a direction parallel to the first direction 101. This makes it possible to more effectively reduce variations in electrical characteristics within the surface of the epitaxial substrate.

[0188] According to the indium phosphide single crystal substrate 100 of the present disclosure, when x is 0.2, z is 1.02×10 －２ Larger than 1.104 x 10 －１ If x is 0.4, z is 7.68×10 －３ Larger 1.89 x 10 －１ If x is 0.6, z is 3.12×10 －３ Larger 2.77 x 10 －１ If x is 0.8, z is 7.04×10 －３ Larger 3.90 x 10 －１ The thickness of the first stripe pattern 31 may be smaller than the thickness of the first stripe pattern 31. As described above, according to the indium phosphide single crystal substrate 100 according to the present disclosure, the unevenness of the first stripe pattern 31 in the first direction 101 is reduced. This makes it possible to more effectively reduce the internal stress of the indium phosphide single crystal substrate 100. Therefore, when forming an epitaxial layer on the indium phosphide single crystal substrate 100, warping of the indium phosphide single crystal substrate 100 can be suppressed. This makes it possible to reduce variations in carrier concentration in the epitaxial layer. As a result, it is possible to more effectively reduce variations in electrical characteristics within the surface of the epitaxial substrate.

[0189] According to the method for manufacturing the indium phosphide single crystal substrate 100 according to the first embodiment, the growth apparatus 300 includes a first shielding plate 81. The first shielding plate 81 is provided at the first position P1. The first shielding plate 81 is not provided at each of the second position P2, the third position P3, and the fourth position P4. The thickness of the first shielding plate 81 in the sixth direction 106 is 9 mm or less. Therefore, in a cross section including the third central axis A3 and parallel to the sixth direction 106, the shape of the solid-liquid interface I approaches the shape of a cubic function. This causes the shape of the stripe pattern observed on the cleavage plane of the indium phosphide single crystal substrate 100 to approach the shape of a cubic function. As a result, the yield of epitaxial substrates manufactured using the indium phosphide single crystal substrate 100 can be improved.

[0190] If the width of the first shielding plate 81 in the seventh direction 107 is excessively small, the temperature of the portion of the indium phosphide melt 87 close to the first shielding plate 81 cannot be sufficiently reduced. Therefore, the shape of the solid-liquid interface I cannot be made to resemble a cubic function. Furthermore, if the width of the first shielding plate 81 in the seventh direction 107 is excessively large, the width of the solid-liquid interface I in the fourth direction 104 becomes excessively large. Therefore, the unevenness of the first striped pattern 31 becomes excessively large. According to the manufacturing method for the indium phosphide single crystal substrate 100 according to the first embodiment, the width of the first shielding plate 81 in the seventh direction 107 is 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal 400. Therefore, the width of the first shielding plate 81 in the seventh direction 107 can be prevented from becoming excessively small or large. This allows the temperature of the portion of the indium phosphide melt 87 close to the first shielding plate 81 to be sufficiently reduced. Moreover, the unevenness of the first stripe pattern 31 can be prevented from becoming excessively large.

[0191] According to the method for manufacturing an indium phosphide single crystal substrate 100 according to the second embodiment, the growth apparatus 300 includes a first shielding plate 81 and a second shielding plate 82. The first shielding plate 81 is provided at the first position P1. The second shielding plate 82 is provided at the second position P2. The first shielding plate 81 and the second shielding plate 82 are not provided at the third position P3 and the fourth position P4. The value obtained by subtracting the thickness of the second shielding plate 82 in the sixth direction 106 from the thickness of the first shielding plate 81 in the sixth direction 106 is 2 mm or more and 9 mm or less. Therefore, in a cross section including the third central axis A3 and parallel to the sixth direction 106, the distance between both ends of the solid-liquid interface I in the fourth direction 104 can be shortened. This reduces the unevenness of the first striped pattern 31.

[0192] If the width of the second shielding plate 82 in the seventh direction 107 is excessively small, the temperature of the portion of the indium phosphide melt 87 close to the second shielding plate 82 cannot be sufficiently lowered. Therefore, the distance between both ends of the solid-liquid interface I in the fourth direction 104 cannot be sufficiently shortened. According to the method for manufacturing the indium phosphide single crystal substrate 100 according to the first embodiment, the width of the first shielding plate 81 in the seventh direction 107 is 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal 400. Therefore, it is possible to prevent the width of the second shielding plate 82 in the seventh direction 107 from becoming excessively small. This makes it possible to sufficiently lower the temperature of the portion of the indium phosphide melt 87 close to the second shielding plate 82.

[0193] In the indium phosphide single crystal ingot 200 according to the present disclosure, when the fifth cleavage plane 15, the sixth cleavage plane 16, the seventh cleavage plane 17, and the eighth cleavage plane 18 are each observed using a Nomarski microscope, a third stripe pattern 33 is observed on at least one of the fifth cleavage plane 15, the sixth cleavage plane 16, the seventh cleavage plane 17, and the eighth cleavage plane 18. When the third stripe pattern 33 is approximated to a cubic function, it is expressed by the above formula 2. a is 5.0×10 －６ Larger 6.0 x 10 －５ b is -7.0 x 10 －３ or more, which is 2.0 × 10 －３ c is smaller than 2.0 × 10 －２ Larger 7.0 x 10 －１ is smaller. x at the inflection point of the cubic function is 0.25 or more and 0.75 or less. As such, the shape of the stripe pattern observed on the cleavage plane of the indium phosphide single crystal ingot 200 according to the present disclosure is close to a cubic function. Therefore, the shape of the stripe pattern observed on the cleavage plane of the indium phosphide single crystal substrate 100 produced using the indium phosphide single crystal ingot 200 is also close to a cubic function. This makes it possible to reduce variations in the electrical properties within the surface of the epitaxial substrate. As a result, it is possible to improve the yield of epitaxial substrates.

[0194] In the indium phosphide single crystal ingot 200 according to the present disclosure, when the third stripe pattern 33 is observed on at least one of the fifth cleavage plane 15 and the sixth cleavage plane 16, the fourth stripe pattern 34 may be observed on each of the seventh cleavage plane 17 and the eighth cleavage plane 18. When the third stripe pattern 33 is observed on at least one of the seventh cleavage plane 17 and the eighth cleavage plane 18, the fourth stripe pattern 34 may be observed on each of the fifth cleavage plane 15 and the sixth cleavage plane 16. The shape of the fourth stripe pattern 34 is linear or convex in the growth direction 109. This makes it possible to more effectively reduce variations in electrical properties within the surface of the epitaxial substrate.

[0195] According to the indium phosphide single crystal ingot 200 of the present disclosure, when x is 0.2, z is 1.02×10 －２ Larger than 1.104 x 10 －１ If x is 0.4, z is 7.68×10 －３ Larger 1.89 x 10 －１ If x is 0.6, z is 3.12×10 －３ Larger 2.77 x 10 －１ If x is 0.8, z is 7.04×10 －３ Larger 3.90 x 10 －１ The thickness of the third stripe pattern 33 may be smaller than the thickness of the indium phosphide single crystal ingot 200. As described above, according to the indium phosphide single crystal ingot 200 of the present disclosure, the unevenness of the third stripe pattern 33 in the growth direction 109 is reduced. This reduces the internal stress of the indium phosphide single crystal ingot 200. Therefore, when an epitaxial layer is formed on the indium phosphide single crystal substrate 100 produced using the indium phosphide single crystal ingot 200, warping of the indium phosphide single crystal substrate 100 can be suppressed. This reduces variations in carrier concentration in the epitaxial layer. As a result, variations in electrical properties within the surface of the epitaxial substrate can be more effectively reduced.

[0196] <Sample Preparation> First, indium phosphide single crystal substrates 100 according to Samples 1 to 11 were prepared. The indium phosphide single crystal substrates 100 according to Samples 1 to 4 were used as comparative examples. The indium phosphide single crystal substrates 100 according to Samples 5 to 11 were used as working examples. The indium phosphide single crystal substrates 100 according to Samples 1 to 11 were manufactured according to the manufacturing method for the indium phosphide single crystal substrate 100 described above.

[0197]

[0198] Table 1 shows the manufacturing conditions for the indium phosphide single crystal substrates 100 according to Samples 1 to 4. As shown in Table 1, the diameter (first diameter W1) of the indium phosphide single crystal substrates 100 according to Samples 1 to 4 was set to 100 mm.

[0199] In producing the indium phosphide single crystal substrate 100 according to Samples 1 and 4, the growth apparatus 300 did not have the second shielding plate 82. In producing the indium phosphide single crystal substrate 100 according to Samples 2 and 3, the growth apparatus 300 had the second shielding plate 82.

[0200] In sample 1, the thickness (first thickness T1) of the first shielding plate 81 was set to 12 mm. The width (third width H3) of the first shielding plate 81 was set to 70 mm. In sample 2, the first thickness T1 was set to 6 mm. The third width H3 was set to 70 mm. The thickness (second thickness T2) of the second shielding plate 82 was set to 6 mm. The width (fourth width H4) of the second shielding plate 82 was set to 70 mm.

[0201] In sample 3, the first thickness T1 was 6 mm. The third width H3 was 70 mm. The second thickness T2 was 5 mm. The fourth width H4 was 70 mm. In sample 4, the first thickness T1 was 10 mm. The third width H3 was 70 mm.

[0202]

[0203] Table 2 shows the manufacturing conditions for the indium phosphide single crystal substrates 100 according to Samples 5 to 11. As shown in Table 2, in manufacturing the indium phosphide single crystal substrates 100 according to Samples 5 to 9, the growth apparatus 300 did not have the second shielding plate 82. In manufacturing the indium phosphide single crystal substrates 100 according to Samples 10 and 11, the growth apparatus 300 had the second shielding plate 82.

[0204] In sample 5, the first diameter W1 was set to 100 mm, the first thickness T1 was set to 6 mm, and the third width H3 was set to 70 mm. In sample 6, the first diameter W1 was set to 75 mm, the first thickness T1 was set to 6 mm, and the third width H3 was set to 56 mm.

[0205] In Sample 7, the first diameter W1 was set to 100 mm, the first thickness T1 was set to 6 mm, and the third width H3 was set to 70 mm. In Sample 8, the first diameter W1 was set to 150 mm, the first thickness T1 was set to 8 mm, and the third width H3 was set to 105 mm.

[0206] In sample 9, the first diameter W1 was set to 100 mm. The first thickness T1 was set to 7 mm. The third width H3 was set to 70 mm. In sample 10, the first diameter W1 was set to 150 mm. The first thickness T1 was set to 7 mm. The third width H3 was set to 105 mm. The second thickness T2 was set to 2 mm. The fourth width H4 was set to 105 mm.

[0207] In Sample 11, the first diameter W1 was 100 mm, the first thickness T1 was 6 mm, the third width H3 was 70 mm, the second thickness T2 was 2 mm, and the fourth width H4 was 70 mm.

[0208] <Evaluation Method> Epitaxial substrates were fabricated by forming an epitaxial layer on the second main surface 2 using the indium phosphide single crystal substrates 100 according to Samples 1 to 11. The electrical property yield of the epitaxial substrates was evaluated. Specifically, carrier density was mapped within the surface of the epitaxial substrate using a carrier density measurement device. Carrier density is one type of electrical property. The percentage of the entire measurement surface of the epitaxial substrate that had a carrier density within a predetermined specification was calculated as the yield.

[0209] A stripe pattern shape was confirmed in the indium phosphide single crystal substrate 100 according to Samples 1 to 11. Specifically, the indium phosphide single crystal substrate 100 was cleaved along a plane that included the first central axis A1 and was parallel to the sixth direction 106 (FIGS. 20 and 25). The above-described etching treatment was performed on the cleaved surface. The stripe pattern was observed by observing the etched cleaved surface using a Normarski microscope.

[0210] Using the above-described method, z was measured when x was 0.2, when x was 0.4, when x was 0.6, and when x was 0.8. Using the above-described method, the stripe pattern was approximated to a cubic function. The number of first measurement points 59 was set to 19. a, b, c, and x at the inflection point were calculated.

[0211] <Evaluation results>

[0212]

[0213] Table 3 shows the evaluation results of the indium phosphide single crystal substrate 100 for Samples 1 to 4. As shown in Table 3, the striped pattern observed in Samples 1 to 4 was not the first striped pattern 31. Specifically, in Sample 1, c was 7.0 × 10 －１ At the inflection point, x was greater than 0.75. In sample 2, a was 5.0 × 10 －６ b was 2.0 × 10 －３ c was 2.0 × 10 －２At the inflection point, x was less than 0.25.

[0214] In sample 3, a is 5.0 × 10 －６ c was 2.0 × 10 －２ At the inflection point, x was less than 0.25. In sample 4, c was 7.0 × 10 －１ At the inflection point, x was greater than 0.75.

[0215] In samples 1 and 4, when x is 0.2, z is 1.104 × 10 －１ When x is 0.4, z is 1.89 × 10 －１ When x is 0.6, z is 2.77 × 10 －１ When x is 0.8, z is 3.90 × 10 －１ That was all.

[0216] In samples 2 and 3, when x is 0.2, z is 1.02 × 10 －２ When x is 0.4, z is 7.68 × 10 －３ When x is 0.6, z is 3.12 × 10 －３ In sample 3, when x was 0.8, z was 7.04 × 10 －３ It was as follows.

[0217]

[0218] Table 4 shows the evaluation results of the indium phosphide single crystal substrates 100 according to Samples 5 to 11. As shown in Table 4, in Samples 5 to 11, the first striped patterns 31 were observed.

[0219] In samples 5 to 11, a was 5.0 × 10 －６ Larger 6.0 x 10 －５ b was −7.0×10 －３ or more, which is 2.0 × 10 －３ was smaller than 2.0 × 10 －２ Larger 7.0 x 10 －１It was smaller.

[0220] In samples 5 to 11, when x is 0.2, z is 1.02 × 10 －２ Larger than 1.104 x 10 －１ When x is 0.4, z is 7.68 × 10 －３ Larger 1.89 x 10 －１ When x was 0.6, z was 3.12 × 10 －３ Larger 2.77 x 10 －１ When x was 0.8, z was 7.04 × 10 －３ Larger 3.90 x 10 －１ It was smaller.

[0221] In samples 5 to 7, a was 7.0 × 10 －６ Larger than 5.0 x 10 －５ b was smaller than -6.0 × 10 －３ Larger than 1x10 －３ was smaller than 5.0 × 10 －２ Larger 6.0 x 10 －１ It was smaller.

[0222] In samples 5 to 7, when x is 0.2, z is 1.80 × 10 －２ Larger 7.96 x 10 －２ When x was 0.4, z was 2.50 × 10 －２ Larger 1.33 x 10 －１ When x is 0.6, z is 2.70 × 10 －２ Larger 1.81 x 10 －１ When x was 0.8, z was 3.00 × 10 －２ Larger 2.46 x 10 －１ It was smaller.

[0223] In sample 5, a is 1×10 －５ Larger 4.6 x 10 －５ b was smaller than -5.8 × 10 －３ Greater than -1.0 x 10 －３was smaller than 1.1 × 10 －１ Larger than 5.0 x 10 －１ It was smaller.

[0224] In sample 5, when x is 0.2, z is 2.50 × 10 －２ Larger 7.12 x 10 －２ When x was 0.4, z was 4.39 × 10 －２ Larger 1.18 x 10 －１ When x is 0.6, z is 6.26 × 10 －２ Larger 1.58 x 10 －１ When x is 0.8, z is 8.70 × 10 －２ Larger 2.13 x 10 －１ It was smaller.

[0225] As shown in Table 3, the electrical property yields of the epitaxial substrates fabricated using the indium phosphide single crystal substrates 100 according to Samples 1 to 4 were 58% or less. On the other hand, as shown in Table 4, the electrical property yields of the epitaxial substrates fabricated using the indium phosphide single crystal substrates 100 according to Samples 5 to 11 were 80% or more. The electrical property yields of the epitaxial substrates fabricated using the indium phosphide single crystal substrates 100 according to Samples 5 to 7 were 90% or more.

[0226] From the above results, it was confirmed that the indium phosphide single crystal substrate 100 according to the example can improve the yield of epitaxial substrates compared to the indium phosphide single crystal substrate 100 according to the comparative example. It was confirmed that the method for manufacturing the indium phosphide single crystal substrate 100 according to the example can improve the yield of epitaxial substrates compared to the method for manufacturing the indium phosphide single crystal substrate 100 according to the comparative example.

[0227] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above description, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0228] 1 First main surface, 2 Second main surface, 3 Outer peripheral surface, 8 First outer edge, 11 First cleavage plane, 12 Second cleavage plane, 13 Third cleavage plane, 14 Fourth cleavage plane, 15 Fifth cleavage plane, 16 Sixth cleavage plane, 17 Seventh cleavage plane, 18 Eighth cleavage plane, 21 First end face, 22 Second end face, 23 Cylindrical surface, 28 Second outer edge, 31 First striped pattern, 32 Second striped pattern, 33 Third striped pattern, 34 Fourth striped pattern, 40 Crucible, 41 Seed crystal holding portion, 41a Bottom, 41b Outer peripheral portion, 42 Single crystal growth portion, 42a First portion, 42b Second portion, 47 High pressure vessel, 48 Heating element, 48a First heating element portion, 48b Second heating element portion, 49 Crucible holder, 51, first intersection (first origin), 52, second intersection, 53, third intersection, 54, fourth intersection, 55, fifth intersection, 56, sixth intersection, 57, seventh intersection, 58, eighth intersection, 59, first measurement point, 61, ninth intersection (second origin), 62, tenth intersection, 63, eleventh intersection, 64, twelfth intersection, 65, second measurement point, 68, first virtual line, 69, third virtual line, 70, first line, 71, first selected line, 72, second selected line, 73, third selected line, 74, fourth selected line, 75, fifth selected line, 76, sixth selected line, 79, third line, 80, second line, 81, first shielding plate, 82, second shielding plate, 84, seed crystal, 85, indium phosphide raw material, 86, sealing material, 87, indium phosphide melt, 88 Liquid encapsulant, 89 Fourth line, 90 Arrow, 91 Mixed liquid, 92 Tank, 93 Reflector incandescent lamp, 94 Liquid level, 97 First space, 98 Second space, 99 Third space, 100 Indium phosphide single crystal substrate, 101 First direction, 102 Second direction, 103 Third direction, 104 Fourth direction, 105 Fifth direction, 106 Sixth direction, 107 Seventh direction, 109 Growth direction, 111 First virtual line, 112 Second virtual line, 113 Third virtual line, 114 Fourth virtual line, 200 Indium phosphide single crystal ingot, 300 Growth apparatus, 400 Indium phosphide single crystal, A1 First central axis, A2 Second central axis, A3 Third central axis, D1 First distance, D2 Second distance, D3 Third distance, D4 ​​Fourth distance, H1 First width, H2 Second width, H3 third width, H4 fourth width, I solid-liquid interface, L1 first length, L2 second length, P1 first position, P2 second position, P3 third position, P4 fourth position, R circumferential direction, T1 first thickness, T2 second thickness, V vertical direction,W1: first diameter, W2: second diameter, W3: inner diameter.

Claims

1. A first major surface; a second major surface opposite the first major surface; and an indium phosphide single crystal substrate having an outer peripheral surface continuous with each of the first main surface and the second main surface, containing impurities of at least one of sulfur and tin, two surfaces that appear when the indium phosphide single crystal substrate is cleaved along a plane that includes the central axis of the outer peripheral surface are defined as a first cleavage plane and a second cleavage plane, respectively; When the indium phosphide single crystal substrate is cleaved along a plane perpendicular to the first cleavage plane and including the central axis, two planes that appear are defined as a third cleavage plane and a fourth cleavage plane, respectively. the first cleavage plane is a (01-1) plane, the second cleavage plane is a (0-11) plane, the third cleavage plane is a (011) plane, the fourth cleavage plane is a (0-1-1) plane, when each of the first cleavage surface, the second cleavage surface, the third cleavage surface, and the fourth cleavage surface is observed using a Nomarski microscope, a first stripe pattern is observed on at least one of the first cleavage surface, the second cleavage surface, the third cleavage surface, and the fourth cleavage surface; a direction from the first main surface toward the second main surface is defined as a first direction; an intersection point between the first stripe pattern and the outer peripheral surface that is closest to the first main surface in the first direction is set as an origin; a direction perpendicular to the first direction and directed from the origin toward the central axis is defined as a second direction; a value obtained by dividing the distance from the origin in the first direction by the width of the first striped pattern in the second direction is defined as z; a value obtained by dividing the distance from the origin in the second direction by the width is defined as x; When the first stripe pattern is approximated by a cubic function, The cubic function is expressed by Equation 1: a is 5.0 × 10 －６ Larger 6.0 x 10 －５ is as follows: b is -7.0 × 10 －３ or more, which is 2.0 × 10 －３ Smaller, c is 2.0 × 10 －２ Larger 7.0 x 10 －１ Smaller, The indium phosphide single crystal substrate, wherein the x at the inflection point of the cubic function is 0.25 or more and 0.75 or less. [Equation 1]

2. the first stripe pattern is observed on at least one of the first cleavage plane or the second cleavage plane; a second stripe pattern is observed on each of the third cleavage plane and the fourth cleavage plane; 2. The indium phosphide single crystal substrate according to claim 1, wherein the second striped pattern has a linear shape or a convex shape in a direction parallel to the first direction.

3. the first stripe pattern is observed on at least one of the third cleavage plane and the fourth cleavage plane; a second stripe pattern is observed on each of the first cleavage plane and the second cleavage plane; 2. The indium phosphide single crystal substrate according to claim 1, wherein the second striped pattern has a linear shape or a convex shape in a direction parallel to the first direction.

4. When the x is 0.2, the z is 1.02 × 10 －２ Larger than 1.104 x 10 －１ Smaller, When the x is 0.4, the z is 7.68×10 －３ Larger 1.89 x 10 －１ Smaller, When the x is 0.6, the z is 3.12 × 10 －３ Larger 2.77 x 10 －１ Smaller, When the x is 0.8, the z is 7.04 × 10 －３ Larger 3.90 x 10 －１ The indium phosphide single crystal substrate according to any one of claims 1 to 3, wherein the indium phosphide single crystal substrate is smaller than 1000 nm.

5. The a is 7.0 × 10 －６ Larger than 5.0 x 10 －５ Smaller, The b is −6.0×10 －３ Larger than 1x10 －３ Smaller, The c is 5.0 × 10 －２ Larger 6.0 x 10 －１ Smaller, When the x is 0.2, the z is 1.80 × 10 －２ Larger 7.96 x 10 －２ Smaller, When the x is 0.4, the z is 2.50×10 －２ Larger 1.33 x 10 －１ Smaller, When the x is 0.6, the z is 2.70 × 10 －２ Larger 1.81 x 10 －１ Smaller, When the x is 0.8, the z is 3.00 × 10 －２ Larger 2.46 x 10 －１ 5. The indium phosphide single crystal substrate of claim 4, wherein the indium phosphide single crystal substrate is smaller than the indium phosphide single crystal substrate of claim 4.

6. The a is 1×10 －５ Larger 4.6 x 10 －５ Smaller, The b is −5.8×10 －３ Greater than -1.0 x 10 －３ Smaller, The c is 1.1 × 10 －１ Larger than 5.0 x 10 －１ Smaller, When the x is 0.2, the z is 2.50 × 10 －２ Larger 7.12 x 10 －２ Smaller, When the x is 0.4, the z is 4.39×10 －２ Larger 1.18 x 10 －１ Smaller, When the x is 0.6, the z is 6.26×10 －２ Larger 1.58 x 10 －１ Smaller, When the x is 0.8, the z is 8.70×10 －２ Larger 2.13 x 10 －１ 6. The indium phosphide single crystal substrate of claim 5, wherein the indium phosphide single crystal substrate is smaller than 1000 nm.

7. 4. The indium phosphide single crystal substrate according to claim 1, wherein the second main surface has a diameter of 75 mm or more.

8. providing a growth apparatus including a cylindrical crucible and a cylindrical heating element surrounding the crucible; placing a seed crystal within the crucible; placing an indium phosphide source on the seed crystal; a step of melting a portion of the seed crystal and the indium phosphide raw material using the heating element to obtain an indium phosphide melt, and bringing the indium phosphide melt into contact with the remainder of the seed crystal; growing an indium phosphide single crystal on the seed crystal by solidifying the indium phosphide melt; and cutting the indium phosphide single crystal. the growth apparatus includes a shielding plate provided between the crucible and the heating element, When positions that are in the directions of 0°, 180°, 90°, and 270° as viewed from the central axis of the crucible and that are between the crucible and the heating element are defined as a first position, a second position, a third position, and a fourth position, respectively, The shielding plate is provided at the first position, the shielding plate is not provided at each of the second position, the third position, and the fourth position; a thickness of the shielding plate in the direction from the first position to the second position of 9 mm or less.

9. 9. The method for producing an indium phosphide single crystal substrate according to claim 8, wherein the shielding plate has a flat plate shape.

10. 10. The method for manufacturing an indium phosphide single crystal substrate according to claim 8 or 9, wherein the width of the shielding plate in the direction from the third position toward the fourth position is 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal.

11. providing a growth apparatus including a cylindrical crucible and a cylindrical heating element surrounding the crucible; placing a seed crystal within the crucible; placing an indium phosphide source on the seed crystal; a step of melting a portion of the seed crystal and the indium phosphide raw material using the heating element to obtain an indium phosphide melt, and bringing the indium phosphide melt into contact with the remainder of the seed crystal; growing an indium phosphide single crystal on the seed crystal by solidifying the indium phosphide melt; and cutting the indium phosphide single crystal. the growth apparatus includes a first shielding plate and a second shielding plate different from the first shielding plate, each of the first shielding plate and the second shielding plate is provided between the crucible and the heating element; When positions that are in the directions of 0°, 180°, 90°, and 270° as viewed from the central axis of the crucible and that are between the crucible and the heating element are defined as a first position, a second position, a third position, and a fourth position, respectively, The first shielding plate is provided at the first position, the second shielding plate is provided at the second position, the first shielding plate and the second shielding plate are not provided at the third position and the fourth position, respectively; a value obtained by subtracting the thickness of the second shielding plate in the direction from the first position to the second position from the thickness of the first shielding plate in the direction from the first position to the second position is 2 mm or more and 9 mm or less.

12. The method for producing an indium phosphide single crystal substrate according to claim 11 , wherein the thickness of the first shielding plate in the direction from the first position to the second position is 6 mm or more and 7 mm or less.

13. 13. The method for manufacturing an indium phosphide single crystal substrate according to claim 11 or 12, wherein each of the first shielding plate and the second shielding plate has a flat plate shape.

14. a width of the first shielding plate in a direction from the third position toward the fourth position is 0.5 to 1.2 times the maximum diameter of the indium phosphide single crystal, 13. The method for manufacturing an indium phosphide single crystal substrate according to claim 11 or 12, wherein a width of the second shielding plate in a direction from the third position toward the fourth position is 0.5 to 1.2 times the maximum diameter.

15. A first end surface; a second end surface opposite the first end surface; an indium phosphide single crystal ingot having a cylindrical surface connected to each of the first end surface and the second end surface, containing impurities of at least one of sulfur and tin, a concentration of the impurity at the second end facet is higher than a concentration of the impurity at the first end facet; two surfaces that appear when the indium phosphide single crystal ingot is cleaved along a plane including a central axis of the cylindrical surface are designated as a fifth cleavage plane and a sixth cleavage plane, respectively; When the indium phosphide single crystal ingot is cleaved along a plane perpendicular to the fifth cleavage plane and including the central axis, the two planes that appear are defined as a seventh cleavage plane and an eighth cleavage plane, respectively. the fifth cleavage plane is a (01-1) plane, the sixth cleavage plane is a (0-11) plane, the seventh cleavage plane is a (011) plane, the eighth cleavage plane is a (0-1-1) plane, when each of the fifth cleavage plane, the sixth cleavage plane, the seventh cleavage plane, and the eighth cleavage plane is observed using a Nomarski microscope, a third stripe pattern is observed on at least one of the fifth cleavage plane, the sixth cleavage plane, the seventh cleavage plane, and the eighth cleavage plane; a direction from the first end face toward the second end face is a growth direction, an intersection point between the third striped pattern and the cylindrical surface that is closest to the first end surface in the growth direction is set as an origin; a direction perpendicular to the growth direction and from the origin toward the central axis is defined as a third direction; a value obtained by dividing the distance from the origin in the growth direction by the width of the third striped pattern in the third direction is defined as z; a value obtained by dividing the distance from the origin in the third direction by the width is defined as x; When the third stripe pattern is approximated by a cubic function, The cubic function is expressed by Equation 2: a is 5.0 × 10 －６ Larger 6.0 x 10 －５ is as follows: b is -7.0 × 10 －３ or more, which is 2.0 × 10 －３ Smaller, c is 2.0 × 10 －２ Larger 7.0 x 10 －１ Smaller, An indium phosphide single crystal ingot, wherein the x at the inflection point of the cubic function is 0.25 or more and 0.75 or less. [Equation 2]

16. the third stripe pattern is observed on at least one of the fifth cleavage plane and the sixth cleavage plane; a fourth stripe pattern is observed on each of the seventh cleavage plane and the eighth cleavage plane; 16. The indium phosphide single crystal ingot according to claim 15, wherein the fourth striped pattern has a linear shape or a convex shape in the growth direction.

17. the third stripe pattern is observed on at least one of the seventh cleavage plane and the eighth cleavage plane; a fourth stripe pattern is observed on each of the fifth cleavage plane and the sixth cleavage plane; 16. The indium phosphide single crystal ingot according to claim 15, wherein the fourth striped pattern has a linear shape or a convex shape in the growth direction.

18. When the x is 0.2, the z is 1.02 × 10 －２ Larger than 1.104 x 10 －１ Smaller, When the x is 0.4, the z is 7.68×10 －３ Larger 1.89 x 10 －１ Smaller, When the x is 0.6, the z is 3.12 × 10 －３ Larger 2.77 x 10 －１ Smaller, When the x is 0.8, the z is 7.04 × 10 －３ Larger 3.90 x 10 －１ 18. The indium phosphide single crystal ingot of any one of claims 15 to 17, wherein the indium phosphide single crystal ingot is smaller than 1000 nm.

19. The a is 7.0 × 10 －６ Larger than 5.0 x 10 －５ Smaller, The b is −6.0×10 －３ Larger than 1x10 －３ Smaller, The c is 5.0 × 10 －２ Larger 6.0 x 10 －１ Smaller, When the x is 0.2, the z is 1.80 × 10 －２ Larger 7.96 x 10 －２ Smaller, When the x is 0.4, the z is 2.50×10 －２ Larger 1.33 x 10 －１ Smaller, When the x is 0.6, the z is 2.70 × 10 －２ Larger 1.81 x 10 －１ Smaller, When the x is 0.8, the z is 3.00 × 10 －２ Larger 2.46 x 10 －１ 20. The indium phosphide single crystal ingot of claim 18, wherein the indium phosphide single crystal ingot is smaller than 1000 nm.

20. The a is 1×10 －５ Larger 4.6 x 10 －５ Smaller, The b is −5.8×10 －３ Greater than -1.0 x 10 －３ Smaller, The c is 1.1 × 10 －１ Larger than 5.0 x 10 －１ Smaller, When the x is 0.2, the z is 2.50 × 10 －２ Larger 7.12 x 10 －２ Smaller, When the x is 0.4, the z is 4.39×10 －２ Larger 1.18 x 10 －１ Smaller, When the x is 0.6, the z is 6.26×10 －２ Larger 1.58 x 10 －１ Smaller, When the x is 0.8, the z is 8.70×10 －２ Larger 2.13 x 10 －１ 20. The indium phosphide single crystal ingot of claim 19, wherein the indium phosphide single crystal ingot is smaller than 100.

21. 18. The indium phosphide single crystal ingot according to claim 15, wherein the diameter of the second end face is 75 mm or more.

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