JP2011077325A - Method of manufacturing group iii nitride semiconductor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a group III nitride substrate, capable of improving the efficiency of capturing indium of an epitaxial layer, and, at the same time, can suppress warpage. <P>SOLUTION: The method of manufacturing the group III nitride semiconductor substrate includes a slice process of obtaining the group III nitride semiconductor substrate by slicing an ingot 5 of a group III nitride semiconductor with a wire 7. In the slice process, the group III nitride semiconductor substrate is obtained so that a principal surface becomes a ä20-21} surface by slicing the ingot 5 in an axial direction which is tilted to a <1-100> direction from a ä0001} surface or the group III nitride semiconductor substrate is obtained so that the principal surface becomes a ä22-43} surface or a ä11-21} surface or by slicing the ingot 5 in an axial direction which is tilted to a <11-20> direction from a ä0001} surface. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a group III nitride semiconductor substrate.

  In recent years, semiconductors, including compound semiconductors, have expanded their application range by taking advantage of their various characteristics. For example, a compound semiconductor is useful as a base substrate for stacking epitaxial layers, and is used in semiconductor devices such as LEDs and LDs. As a method for manufacturing a compound semiconductor substrate, there is known a method of slicing a compound semiconductor ingot whose main surface has a specific plane orientation (for example, {0001} plane of GaN) parallel to the main surface or tilted several degrees. The semiconductor substrate cut out from the ingot is used as a semiconductor substrate of a semiconductor device after the main surface is ground or polished.

  Patent Document 1 discloses a method of forming a nonpolar or semipolar main surface by slicing or polishing a GaN bulk crystal grown in the c-axis direction. In Patent Document 1, (11-20) plane and (10-10) plane are obtained as nonpolar main surfaces, (10-1-1) plane, (10-1-3) plane as semipolar planes, The (10-11) plane, (10-13) plane, and (11-22) plane are obtained.

  Patent Document 2 discloses a method of slicing a GaN ingot whose main surface is a C-plane with a wire saw. Patent Document 2 discloses slicing by tilting the traveling direction of the wire by 3 degrees or more from the cleavage direction in order to suppress generation of cracks due to processing.

  Patent Document 3 discloses a method for producing a group III-V nitride semiconductor crystal having a nonpolar plane. Patent Document 3 discloses a method of slicing a crystal so that a nonpolar plane appears after forming a group III-V nitride semiconductor crystal having a C-plane as a main surface.

JP 2008-91598 A JP 2006-190909 A JP 2008-308401 A

Japanese Journal of Applied Physics vol.39 (2000) pp.413 Journal of Applied Physics vol.91 No.12 (2002) pp.9904

  Incidentally, in recent years, from the viewpoint of changing the emission wavelength of a semiconductor device using a group III nitride semiconductor substrate in a wide wavelength range, the epitaxial layer (active layer) formed on the main surface of the semiconductor substrate contains indium. A group III nitride semiconductor (for example, InGaN) is used. The emission wavelength can be changed by adjusting the indium composition in the epitaxial layer.

  However, when an epitaxial layer is grown on the main surface using a semiconductor substrate having a C-plane which is a polar surface, a large piezo electric field is generated and excellent indium uptake performance is not exhibited. There is. Further, if the A-plane or M-plane, which is a nonpolar plane, is used as the main surface of the GaN substrate, the lattice mismatch between the GaN substrate and the epitaxial layer increases and the dislocation density tends to increase. Therefore, a semiconductor substrate capable of stacking an epitaxial layer excellent in indium uptake performance is desired.

  Further, for example, in a GaN ingot having a C surface as a main surface, one main surface (front surface) tends to be a Ga surface and the other main surface (back surface) tends to be an N surface. In this case, since the hardness of the Ga surface is higher than the hardness of the N surface, there is a tendency that warpage occurs so that the Ga surface of the semiconductor substrate thus cut out has a convex shape. In addition, when a thin (thin) wire with low rigidity is used for slicing an ingot, the semiconductor substrate tends to be cut out so that the Ga surface becomes convex due to the difference in hardness between the Ga surface and the N surface. When an epitaxial layer is formed on a semiconductor substrate in which such warpage has occurred, the yield cannot be improved sufficiently, and therefore a semiconductor substrate capable of suppressing warpage is desired.

  The present invention has been made to solve the above-described problems, and can improve the indium uptake efficiency of the epitaxial layer and can also suppress the warpage of the group III nitride semiconductor substrate. The purpose is to provide.

  As a result of diligent research, the present inventors sliced an ingot of a group III nitride semiconductor in an axial direction inclined in a specific direction from the {0001} plane, and the main surface of the group III nitride semiconductor substrate has a specific plane orientation. It has been found that a group III nitride semiconductor substrate capable of improving the indium uptake efficiency of the epitaxial layer and suppressing the warpage can be obtained by using the semipolar plane having the structure.

  That is, the Group III nitride semiconductor substrate manufacturing method of the present invention is a Group III nitride semiconductor substrate manufacturing method including a slicing step of slicing a Group III nitride semiconductor ingot to obtain a Group III nitride semiconductor substrate. In the slicing step, the ingot is sliced in the axial direction inclined in the <1-100> direction from the {0001} plane, and the group III nitride semiconductor substrate is obtained so that the main surface becomes the {20-21} plane. Or a group III nitride semiconductor such that the ingot is sliced in the axial direction inclined in the <11-20> direction from the {0001} plane so that the main surface becomes the {22-43} plane or the {11-21} plane Get the substrate.

  In the method for producing a group III nitride semiconductor substrate of the present invention, a main surface has the specific plane orientation by slicing a group III nitride semiconductor ingot in an axial direction inclined in a specific direction from the {0001} plane. A group III nitride semiconductor substrate can be obtained easily and reliably. In addition, by obtaining a group III nitride semiconductor substrate so that the main surface is a semipolar surface having the specific plane orientation, it is possible to improve the indium uptake efficiency of the epitaxial layer and to suppress warping. Can do. The inventors of the present invention speculate that the cause of such warpage suppression is that the hardness difference between the front surface and the back surface of the semiconductor substrate is alleviated.

Further, prior to the slicing step, it is preferable to provide a surface processing step of the dislocation density of the {000-1} plane of the ingot and 1.0 × ^{10 10} / cm ² or less by a surface machining. In this case, since the plane orientation accuracy of the main surface of the semiconductor substrate can be improved, the indium uptake efficiency of the epitaxial layer can be further improved. Furthermore, since the generation of cracks during slicing of the ingot can be suppressed, the yield can also be improved.

  Moreover, it is preferable to provide the etching process of dry-etching the main surface of a group III nitride semiconductor substrate and wet-etching the main surface on the opposite side to the main surface after the slicing step. In this case, the work-affected layer generated on the main surface of the semiconductor substrate during slicing of the ingot can be efficiently removed at low cost according to the properties of the main surface.

  Moreover, it is preferable to provide the etching process of dry-etching the main surface of a group III nitride semiconductor substrate and the main surface on the opposite side to this main surface after a slicing process. In this case, the work-affected layer generated on the main surface of the semiconductor substrate when the ingot is sliced can be reliably removed in a short time.

  Further, in the slicing step, the ingot is sliced with a wire saw, the surface roughness Ra in the direction parallel to the wire running direction on the main surface of the group III nitride semiconductor substrate is set to 10 to 500 nm, and the surface in the direction perpendicular to the wire running direction Roughness Ra is preferably 60 to 800 nm. In this case, the main surface planarization step can be shortened or eliminated, and the processing time of the main surface of the semiconductor substrate can be shortened.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the group III nitride semiconductor substrate which can improve the indium taking-in efficiency of an epitaxial layer and can suppress curvature is provided. By improving the indium uptake efficiency of the epitaxial layer, the light emission characteristics of the semiconductor device can be improved. By suppressing the warpage of the group III nitride semiconductor substrate, the yield of semiconductor devices and the like can be improved.

It is a schematic sectional drawing which shows the epitaxial substrate using a group III nitride semiconductor substrate. It is a perspective view which shows the crystal structure of a hexagonal crystal. It is a figure which shows the process flow of the manufacturing method of a group III nitride semiconductor substrate. It is a figure which shows the ingot used for the manufacturing method of a group III nitride semiconductor substrate, and its slicing method. It is a figure which shows the ingot used for the manufacturing method of a group III nitride semiconductor substrate, and its slicing method. It is a figure which shows the measurement result of the surface roughness in the main surface of a group III nitride semiconductor substrate. It is a figure which shows the relationship between the off angle from the c-axis in the main surface of a GaN substrate, and the indium composition of an epitaxial layer. It is a figure which shows the calculation result regarding a piezoelectric field.

  Hereinafter, a preferred embodiment of a method for producing a group III nitride semiconductor substrate according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view showing an epitaxial substrate 10 using a group III nitride semiconductor substrate 1. Epitaxial substrate 10 includes a group III nitride semiconductor substrate 1 (hereinafter referred to as “nitride substrate 1”) as a base substrate and an epitaxial layer 3. The nitride substrate 1 has a front surface (main surface) 1a and a back surface (main surface) 1b opposite to the surface 1a.

  The nitride substrate 1 is formed of a group III nitride semiconductor having a hexagonal wurtzite crystal structure such as GaN, AlN, or InN. Here, a hexagonal crystal structure will be described with reference to FIG. FIG. 2 is a perspective view showing a hexagonal crystal structure. The hexagonal crystal has a hexagonal column with a regular hexagonal bottom. The axis in the height direction of the hexagonal column is the c-axis [0001], and the plane perpendicular to the c-axis is the C plane {0001}. The axis from the center of the hexagonal bottom surface toward the vertex is the a-axis [11-20], and the plane perpendicular to the a-axis is the A plane {11-20}. The axis perpendicular to the a axis is the m axis [1-100], and the plane perpendicular to the m axis is the M plane {1-100}. The a-axis and m-axis are perpendicular to the c-axis.

  The plane orientation of the surface 1a of the nitride substrate 1 is {20-21} plane, {22-43} plane or {11-21} plane, and among these, the {20-21} plane is preferable. The off angle between the normal line of the {20-21} plane and the c axis is 75 °, and the off angle between the normal line of the {22-43} plane and the c axis is 65 °, and {11-21 } The off-angle between the normal of the surface and the c-axis is 73 °.

The dislocation density of the surface 1a of the nitride substrate 1, 1 × 10 is preferably ⁴ / ^cm 2 ~1 × 10 ⁹ pieces / cm ^2, 1 × 10 ⁴ / ^cm 2 ~1 × 10 ⁷ cells / more preferably cm ^2. When the dislocation density is in the above range, reliability such as the lifetime of the light emitting device can be improved. The dislocation density can be calculated from the number of dislocations within a 10 μm square range of the surface observed with a TEM (transmission electron microscope).

  Epitaxial layer 3 is formed of a group III nitride semiconductor containing indium such as InGaN or InAlGaN. The epitaxial layer 3 can be formed by vapor phase growth methods such as HVPE, MOCVD, MOC, MBE, and sublimation.

  Epitaxial layer 3 is arranged on surface 1 a of nitride substrate 1. The epitaxial layer 3 is preferably provided so as to generate an emission wavelength of 500 to 550 nm. In order to obtain a sufficient emission intensity at such an emission wavelength, the epitaxial layer 3 needs to sufficiently take in indium. In the present embodiment, since the epitaxial layer 3 is formed on the surface 1a having the specific plane orientation and the indium uptake efficiency of the epitaxial layer 3 is excellent, sufficient emission intensity can be obtained even at an emission wavelength of 500 to 550 nm. Obtainable.

  Next, a method for manufacturing the nitride substrate 1 will be described with reference to FIGS. FIG. 3 is a diagram showing a process flow of a method for manufacturing a group III nitride semiconductor substrate. 4 and 5 are diagrams showing an ingot used in the method for manufacturing a group III nitride semiconductor substrate and a slicing method thereof.

  First, a base substrate such as a GaAs substrate is prepared (step S100). Next, a bulk crystal of a group III nitride semiconductor is grown on one surface of the base substrate, for example, in the c-axis direction (step S102). When the base substrate is a GaAs substrate, for example, a bulk crystal is formed on the (111) plane of the GaAs substrate. Bulk crystals such as GaN, AlN, and InN can be formed by the HVPE method or the like.

  The bulk crystal of the group III nitride semiconductor is preferably an n-type semiconductor doped with oxygen (O), silicon (Si), or the like. By using a semiconductor substrate obtained from a bulk crystal having an n-type semiconductor, restrictions during device manufacturing can be reduced.

  When a GaN bulk crystal is grown on the underlying substrate in the c-axis direction, the surface of the GaN bulk crystal tends to be a Ga plane and the back surface tends to be an N plane. The GaN bulk crystal is not limited to the configuration in which the Ga plane and the N plane are distinguished from each other on the front and back of the bulk crystal. The Ga plane and the N plane are random, striped, or dot on the same plane. The structure arranged in the shape may be sufficient. Thus, even in a configuration in which the Ga plane and the N plane are arranged on the same plane, warpage occurs depending on the constituent ratio of Ga atoms and N atoms on the front and back sides of the bulk crystal.

  After the bulk crystal is grown, the base substrate is removed from the bulk crystal (step S104) to obtain a group III nitride semiconductor ingot. The base substrate can be dissolved and removed by aqua regia, ground and removed by polishing, or separated and removed by peeling.

Next, external processing is performed on the ingot (steps S106 to S110). The lower part of the ingot in the thickness direction (lower part of the ingot) that has been in contact with the base substrate tends to be a crystal region having a high dislocation density, and since stress is concentrated, it tends to be a starting point of cracks when the ingot is sliced. Therefore, after removing the base substrate, it is preferable to perform a surface processing step in which the dislocation density in the lower portion of the ingot is set to a predetermined value or less by surface processing before the ingot slicing step (step S106). As surface processing, grinding removal of the lower part of an ingot is preferable. In grinding removal of the lower part of the ingot, the dislocation density on the back surface ({000-1} surface) of the ingot is preferably 1 × 10 ¹⁰ pieces / cm ² or less, and preferably 1 × 10 ⁷ pieces / cm ² or less. More preferred. In grinding removal of the lower part of the ingot, for example, a thickness of 100 to 1500 μm is removed from the bottom of the ingot.

  After surface processing of the lower part of the ingot, the lower part of the ingot is etched from the viewpoint of improving the flatness of the lower part of the ingot (step S108). Etching is performed in a temperature range of 50 to 100 ° C. using an aqueous potassium hydroxide (KOH) solution having a concentration of 1 to 8N.

  Next, the outer periphery processing of an ingot is performed (process S110). The outer periphery of the ingot is processed into, for example, a circle or a rectangle. 4A is a perspective view when the outer periphery of the ingot 5 is processed into a circular shape, and FIG. 4B is a plan view when the ingot 5 is viewed from above. When the outer periphery of the ingot 5 is processed into a circular shape, a first orientation flat (OF) surface indicating the cleavage direction of the ingot 5 is provided on the outer peripheral surface of the ingot 5 so that the surface orientations of the M surface and the A surface can be discriminated. 5a and a second OF (index flat: IF) surface 5b smaller than the first OF surface 5a are formed. In this embodiment, the main surface 5c of the ingot 5 is processed to be a C surface ({0001) surface, and the first OF surface 5a is the M surface and the second OF surface 5b is the A surface, or the first OF surface 5a is Processing is performed so that the A plane and the second OF plane 5b become the M plane. When the outer periphery of the ingot is processed into a rectangle, the ingot is processed so that the side surfaces thereof are the M plane and the A plane. After the outer periphery processing of the ingot, if necessary, the front and back main surfaces of the ingot may be further processed and etched.

  In the outer periphery processing, it is preferable that the surface orientation accuracy of the M and A surfaces is 5 ° or less. When the plane orientation accuracy is 5 ° or less, the indium uptake efficiency of the epitaxial layer can be further improved and the warpage can be further suppressed. In addition, surface orientations, such as M surface and A surface, can be measured using an X-ray diffractometer.

  Next, the ingot 5 is sliced to perform a slicing step for obtaining the nitride substrate 1. In the slicing step, the ingot 5 is sliced in an axial direction inclined in a predetermined direction from the {0001} plane so that the main surface becomes the {20-21} plane, {22-43} plane, or {11-21} plane. The nitride substrate 1 is obtained (step S112). A wire saw, an inner peripheral blade, an outer peripheral blade, wire electric discharge machining, and a laser can be used for slicing the ingot 5. Among these, it is preferable to use a wire saw from the viewpoint of excellent mass productivity, substrate quality, and cost.

  When producing the nitride substrate 1 whose main surface is the {20-21} plane, an ingot 5 is used in which the first OF surface 5a is the M surface and the second OF surface 5b is the A surface. As shown in FIG. 4B, the ingot 5 is tilted in the axial direction so that the tilt angle X from the C plane is 75 ° in the <1-100> direction (m-axis direction) from the {0001} plane. Slice. When slicing the ingot 5, the wire 7 is cut while reciprocating from the first OF surface (M surface) 5 a of the ingot 5.

  When the nitride substrate 1 whose main surface is the {22-43} plane or {11-21} plane is used, the ingot 5 in which the first OF surface 5a is the A plane and the second OF plane 5b is the M plane is used. When manufacturing the nitride substrate 1 whose main surface is the {22-43} plane, the inclination angle X from the C plane is 65 ° in the <11-20> direction (a-axis direction) from the {0001} plane. The ingot 5 is sliced in the axial direction inclined in the direction. When manufacturing the nitride substrate 1 whose main surface is the {11-21} plane, the axis is tilted from the {0001} plane in the <11-20> direction so that the tilt angle X from the C plane is 73 °. Slice ingot 5 in the direction. When slicing the ingot 5, the wire 7 is cut while reciprocating from the first OF surface (A surface) 5a of the ingot 5.

  As shown in FIG. 5, a plurality of ingots 5 may be sliced simultaneously in the ingot 5 using a multi-wire saw 20. The multi-wire saw 20 includes a work support 22, guide rollers 24 a to 24 c, a slurry nozzle 26, and a wire row 28. Note that these components included in the multi-wire saw 20 are respectively supported by a housing (not shown).

  The workpiece support 22 is a component for supporting a plurality of ingots 5 that are workpieces (workpieces). The work support 22 can be made of stainless steel, for example. The workpiece support 22 is disposed below the other components (guide rollers 24a to 24c, slurry nozzle 26, and wire row 28). A plurality of carbon support members 30 fixed to each of the plurality of ingots 5 are fixed on the work support table 22, and the plurality of ingots 5 are respectively positioned above the work support table 22 via the support materials 30. It is fixed to. The workpiece support 22 is placed on a moving table (not shown), and the ingot 5 is sent vertically upward (arrow A in the figure) when the moving table moves vertically upward.

  The guide rollers 24a to 24c are substantially columnar rotators, and are arranged so that the directions of the respective rotation axes are orthogonal to the vertical direction (arrow A) and parallel to each other. The guide rollers 24 a and 24 b are arranged apart from each other on the left and right of the vertical line passing through the work support base 22. The guide roller 24 c is disposed above the guide rollers 24 a and 24 b and on a vertical line passing through the work support base 22.

  The outer peripheral surfaces of the guide rollers 24a to 24c are made of, for example, resin. A plurality of grooves are formed at equal intervals on the outer peripheral surfaces of the guide rollers 24a to 24c. Then, a single wire 32 is spirally wound around the plurality of grooves of the guide rollers 24a to 24c, whereby the wire row 28 is configured. The wire 32 reciprocates in two directions as the guide rollers 24a to 24c alternately repeat forward rotation and reverse rotation. Of the wire 32 wound around the guide rollers 24 a to 24 c, the portion that travels on the lower end side of the guide rollers 24 a and 24 b travels at a position that intersects the ingot 5 that is sent upward by the movement of the work support 22. To do.

  The slurry nozzle 26 is an abrasive liquid supply means for injecting an abrasive liquid (slurry) in which loose abrasive grains are mixed into the wrapping oil toward the wire 32 and the ingot 5.

  The plurality of ingots 5 are sliced using the multi-wire saw 20 as follows. First, a plurality of ingots 5 are arranged side by side along the central axis direction so that their surfaces are opposed (or in contact with each other), and the central axis direction is perpendicular to the vertical direction (feeding direction A). And it attaches to the workpiece | work support stand 22 so that the extending | stretching direction B of the wire 32 and the main surface 5c of the ingot 5 may make the inclination | tilt angle X shown in FIG.4 (b). At this time, the plurality of ingots 5 are attached so that the first OF surface 5a faces the feed direction A (the first OF surface 5a and the feed direction A are substantially orthogonal).

  Subsequently, cutting of the ingot 5 is started. The guide rollers 24a to 24c are alternately rotated in the forward direction and the reverse direction, and the reciprocating travel of the wire 32 is started. Then, the work support 22 to which the ingot 5 is attached is moved upward, and the ingot 5 is sent to the wire 32 (wire row 28). At this time, spraying of the abrasive liquid from the slurry nozzle 26 is started.

  When the ingot 5 comes into contact with the wire 32, the ingot 5 starts to be cut by the action of the abrasive liquid that has entered between the ingot 5 and the wire 32. Then, the ingot 5 is fed in the feed direction A at a substantially constant speed while supplying the abrasive fluid. As described above, the ingot 5 is cut into a plate shape having a thickness corresponding to the wire interval of the wire row 28, and the nitride substrate 1 having the surface 1a having the predetermined plane orientation is cut out. Note that after the nitride substrate 1 is cut out, a grinding process (grinding) or a lapping process may be performed in order to planarize the front surface 1a and the back surface 1b of the nitride substrate 1.

  When slicing the ingot 5 with a wire saw as described above, the surface roughness Ra of the surface 1a of the nitride substrate 1 in the direction parallel to the wire traveling direction is 10 to 500 nm, and the direction perpendicular to the wire traveling direction (wire The surface roughness Ra in the cutting direction is preferably 60 to 800 nm. Similarly, it is preferable that the surface roughness of the back surface 1b of the nitride substrate 1 is in the above range. The surface roughness can be obtained by appropriately adjusting the particle diameter of the abrasive grains of the slurry, the wire diameter, the running condition of the wire, and the like when the ingot 5 is sliced. The surface roughness Ra is measured with a measurement length of, for example, 10 mm in each direction parallel to and perpendicular to the wire traveling direction using, for example, a stylus type surface roughness measuring machine (trade name: Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.). Can do.

  By adjusting the surface roughness to the above range, the flattening process of the front surface 1a and the back surface 1b can be shortened or made unnecessary, and the processing time of the nitride substrate 1 can be shortened. In addition, by setting the surface roughness of the back surface 1b of the nitride substrate 1 within the above range, the epitaxial layer 3 can be formed on the front surface 1a without requiring processing of the back surface 1b.

  When the ingot 5 is sliced with a wire saw as described above, the surface roughness of the front surface 1a and the back surface 1b of the nitride substrate 1 may have anisotropy. That is, the surface roughness of the front surface 1a and the back surface 1b is small in the roughness curved surface in the direction parallel to the wire traveling direction, and large in the roughness curved surface in the direction perpendicular to the wire traveling direction (wire cutting direction). There is a tendency to become things. When the surface roughness has such anisotropy, the crystal plane orientation can be identified, so that the orientation flat (OF) can be eliminated.

  On the front surface 1a and the back surface 1b of the nitride substrate 1 thus cut out, there is a work-affected layer in which the crystal lattice is disturbed. The work-affected layer is preferably removed since it causes cracks in the nitride substrate 1 and causes defects during growth of the epitaxial layer. The thickness of the work-affected layer is usually about 5 μm. Although the thickness of the work-affected layer depends on the processing conditions at the time of slicing, it correlates with the surface roughness of the substrate surface, and the work-affected layer tends to be thicker as the surface roughness of the substrate surface is rougher. The work-affected layer can be evaluated by observing a cross section using SEM, TEM, or CL (cathode luminescence).

After the nitride substrate 1 is cut out from the ingot 5, an etching process for etching the front surface 1a and the back surface 1b of the nitride substrate 1 is performed in order to remove the work-affected layer (step S114). Examples of the etching include etching in a liquid phase such as wet etching using a chemical solution, vapor etching using HCl or Cl ₂ , and etching in a gas phase such as dry etching. Examples of the chemical solution used in wet etching include strong alkalis such as KOH and NaOH, and phosphoric acid.

  In the case of a GaN substrate having a C plane as a main surface, the surface (C plane) tends to be a Ga plane. In this case, since the surface (Ga surface) is chemically very stable, it is difficult to perform etching in the liquid phase. Therefore, it is necessary to use gas phase etching for etching the surface (Ga surface). On the other hand, the {20-21} plane, {22-43} plane, and {11-21} plane tend to be main planes terminated by more Ga atoms than N atoms, but are etched in the liquid phase. The cost can be reduced. Further, from the viewpoint of shortening the required time, it is preferable to perform etching in a gas phase, and it is more preferable to perform dry etching.

  When the front surface 1a is a {20-21} plane, a {22-43} plane, and a {11-21} plane, the back surface 1b tends to be a main surface terminated with more N atoms than Ga atoms. Etching in the liquid phase is possible. In this case, from the viewpoint of shortening the required time and performing reliable etching, it is preferable to perform etching in a gas phase, and more preferable to perform dry etching.

  Through the above steps S100 to S114, the nitride substrate 1 whose surface 1a is the {20-21} plane, {22-43} plane, or {11-21} plane is obtained. By forming epitaxial layer 3 on surface 1a of nitride substrate 1 as described above, epitaxial substrate 10 is obtained.

  In the present embodiment, the group 1 nitride semiconductor ingot is sliced in the axial direction inclined in a specific direction from the {0001} plane, so that the surface 1a becomes the {20-21} plane, {22-43} plane, or {11 Nitride substrate 1 having a plane orientation of −21} plane can be obtained easily and reliably. Further, by obtaining the nitride substrate 1 so that the surface 1a becomes a semipolar plane having the specific plane orientation, the indium uptake efficiency of the epitaxial layer 3 can be improved, and the warp of the nitride substrate 1 can be improved. Can be suppressed.

  In the present embodiment, the light emission characteristics of the semiconductor device can be improved by improving the indium incorporation efficiency of the epitaxial layer 3. Regarding the cause of such an effect, if the surface 1a is a semipolar surface having the specific plane orientation, the generation of a piezo electric field is suppressed, and electrons and holes injected into the epitaxial layer 3 are separated. It is presumed that the light emission transition probability is improved because of suppression.

  In the present embodiment, by suppressing the warpage of the nitride substrate 1, the processing time of the nitride substrate 1 can be shortened, and the yield of the nitride substrate 1, the epitaxial substrate 10, and semiconductor devices using these is improved. be able to. The cause of such an effect is presumed to be due to the fact that the hardness difference between the front surface 1a and the back surface 1b of the nitride substrate 1 is relaxed.

  The present invention is not limited to the above embodiment. The plane orientations such as {20-21} plane, {22-43} plane, {11-21} plane, M plane, A plane described in the above description are not only specified by the description itself, Includes crystallographically equivalent planes and orientations. For example, {20-21} plane is crystallographically like (02-21) plane, (0-221) plane, (2-201) plane, (−2021) plane, (−2201) plane. Including equivalent surfaces.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not restrict | limited to these Examples.

[Production of ingot]
A GaAs substrate was prepared as a base substrate. A GaN single crystal (dopant: oxygen) was grown in the c-axis direction on the (111) plane of the GaAs substrate by HVPE. The base substrate was removed to obtain a GaN single crystal ingot.

[Removal effect at the bottom of the ingot]
The dislocation density at the bottom of the ingot was measured. The dislocation density was evaluated based on the dislocation density at a predetermined position along the c-axis direction from the bottom surface of the GaN ingot. The dislocation density was calculated from the number of dislocations within a 10 μm square range of the surface observed with a TEM (transmission electron microscope). Table 1 shows the measurement results of the dislocation density.

  The lower part of the ingot was removed from the bottom surface of the ingot to a predetermined position, and the crack generation rate when the ingot was sliced under the following cutting conditions was evaluated. Note that the GaN ingot was sliced so that the surface orientation of the surface of the substrate to be cut out was the {20-21} plane. Table 2 shows the evaluation results of the crack occurrence rate.

(ingot)
Ingot: GaN single crystal Ingot main surface: (0001) plane Ingot external shape: diameter 50.8 mm, thickness 10 mm
(Cutting conditions)
Abrasive material: Single crystal diamond Abrasive grain size: 5-20 μm
Concentration of abrasive grains in abrasive liquid: 50 g per liter
Lubricant: Mineral oil Equipment: Multi-wire saw Feeding speed (cutting speed): 1-5mm / h (variable speed depending on cutting position)
Wire travel speed: 300-600m / min (variable speed depending on cutting position)
Wire diameter: 0.16mm
Wire tension: 20N

As shown in Tables 1 and 2, since the dislocation density is 1 × 10 ¹⁰ pieces / cm ² or more from the bottom of the ingot to 100 μm, the crack generation rate may exceed 5% when the removal amount is less than 100 μm. confirmed. On the other hand, with the removal amount of 100 μm or more, the crack generation rate could be suppressed to 5% or less.

[Ingot slice]
After removing the lower part of the GaN ingot from the bottom surface of the ingot to a position of 100 μm, the ingot was sliced under the same cutting conditions as described above. The GaN ingot is adjusted by adjusting the angle of inclination between the cut surface and the C surface so that the surface is a {20-21} surface, {22-43} surface, {11-21} surface, C surface, A surface or M surface. Was sliced to obtain a GaN substrate.

[Evaluation of surface roughness]
Using a stylus type surface roughness measuring machine (Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.), the surface roughness of the GaN substrate whose surface was the {20-21} plane was measured. The measurement was performed at a measurement length of 10 mm in each of a direction parallel to the wire travel direction (<1-100> direction) and a direction perpendicular to the wire travel direction (<11-20> direction, wire cutting direction). The measurement results of the surface roughness are shown in Table 3 and FIG. 6A shows the measurement results of the surface roughness in the direction perpendicular to the wire travel direction (wire cutting direction), and FIG. 6B shows the surface roughness in the direction parallel to the wire travel direction. It is a measurement result.

[Etching evaluation]
When the thicknesses of the work-affected layers on the front and back surfaces of each GaN substrate were confirmed using a transmission electron microscope (TEM), the maximum thickness was 5 μm. Next, dry etching and wet etching were performed on the front surface (Ga surface) and back surface (N surface) of each GaN substrate, and the etching rate was measured. Etching was performed under the following conditions. Moreover, the following criteria evaluated the etching rate of dry etching and wet etching. The measurement results of the etching rate are shown in Tables 4 and 5. In the case of a GaN substrate having a C-plane surface, the surface was not etched by wet etching, and the etching rate could not be measured.

(Dry etching conditions)
Equipment: High-density plasma etching system (ICP)
Gas: Chlorine gas Gas flow rate: 100sccm
Pressure: 1Pa
Antenna output: 100W
Bias output: 50W
(Wet etching conditions)
Method: The front and back surfaces of the substrate were immersed in a chemical solution for a certain time.
Chemical solution: 8N potassium hydroxide aqueous solution Temperature: 60 ° C
(Evaluation criteria for etching rate)
A: The etching rate is particularly excellent.
B: The etching rate is excellent.
C: The etching rate is low or not etched.

  From Tables 4 and 5, it was confirmed that the etching can be performed regardless of the surface orientation in the case of dry etching. In addition, it is confirmed that wet etching can be applied to any of the front and back surfaces as long as the surface is a {20-21} plane, {22-43} plane, and {11-21} plane. It was.

[Evaluation of warpage]
After removing the work-affected layers on the front and back surfaces by dry etching, the warpage of each GaN substrate was evaluated. It was confirmed that the surface of each GaN substrate was warped in a convex shape. The amount of warpage is the distance (unit: μm) from the plane to the back of the GaN substrate when the GaN substrate is placed on the plane using a stylus type surface roughness measuring machine (Surfcom, manufactured by Tokyo Seimitsu Co., Ltd.) Was measured. The measurement length was 50 mm, and the measurement was performed along a direction perpendicular to the wire travel direction (wire cutting direction). Table 6 shows the measurement results of warpage.

  In a GaN substrate whose surface is a semipolar plane ((20-21) plane, (22-43) plane, (11-21) plane), the warpage is larger than that of a GaN substrate whose surface is a C plane or M plane. It was confirmed that it was reduced. Thereby, it is estimated that the GaN substrate whose surface is the semipolar surface has a small polarity, and the hardness difference between the front surface and the back surface is small.

[Evaluation of indium uptake efficiency]
The GaN ingot is sliced by changing the angle of inclination from the c-axis to the <1-100> direction (m-axis direction) or the <11-20> direction (a-axis direction), and the off-angle from the c-axis on the surface is different. A plurality of GaN substrates were produced. The GaN slice was performed under the same cutting conditions as above except that the tilt angle was changed. InGaN was epitaxially grown on the surfaces of these GaN substrates. The indium (In) composition of InGaN was measured using a two-crystal X-ray diffractometer.

  FIG. 7 is a diagram showing the relationship between the off-angle from the c-axis on the surface of the GaN substrate and the In composition of the epitaxial layer. In FIG. 7, the solid line indicates the ln composition with respect to the off angle from the c axis to the m axis direction, and the broken line indicates the ln composition with respect to the off angle from the c axis to the a axis direction.

  As shown in FIG. 7, the ln composition decreased as the off-angle increased in the range where the off-angle from the c-axis to the m-axis direction was 0 degree (C plane) to about 36 degrees. On the other hand, when the off angle from the c-axis to the m-axis direction further increased, the ln composition increased as the off-angle increased. In the range of about 58 to 80 degrees, excellent indium uptake was confirmed, and particularly excellent indium uptake was confirmed on the {20-21} plane (off angle from c-axis: 75 degrees).

  In addition, in the range where the off angle from the c-axis to the a-axis direction is from 0 degree (C plane) to about 36 degrees, the ln composition decreased as the off angle increased. On the other hand, when the off angle from the c-axis to the a-axis direction further increased, the ln composition increased as the off-angle increased. In the range of about 50 to 79 degrees, excellent indium uptake was confirmed. Excellent indium uptake was also confirmed in the {22-43} plane (off angle from the c-axis: 65 degrees) and the {11-21} plane (off angle from the c-axis: 73 degrees).

  When the surface of the GaN substrate was {20-21} plane, {22-43} plane, {11-21} plane, it was confirmed that the indium uptake efficiency was excellent. Thus, it is assumed that the influence of the piezoelectric field is small on these semipolar planes. FIG. 8 is a diagram showing the calculation results of the piezoelectric field shown in Non-Patent Documents 1 and 2. It is confirmed that the influence of the piezo electric field is reduced in the region where the inclination from the c-axis is 40 to 90 degrees. Accordingly, it is estimated that the influence of the piezoelectric field is small on the {20-21} plane, the {22-43} plane, and the {11-21} plane.

  DESCRIPTION OF SYMBOLS 1 ... Nitride substrate (III group nitride semiconductor substrate), 1a ... Front surface (main surface), 1b ... Back surface (opposite main surface), 5 ... Ingot, 7 ... Wire.

Claims (5)

A method of manufacturing a group III nitride semiconductor substrate comprising a slicing step of slicing a group III nitride semiconductor ingot to obtain a group III nitride semiconductor substrate,
In the slicing step, the group III nitride semiconductor substrate is obtained by slicing the ingot in the axial direction inclined in the <1-100> direction from the {0001} plane so that the main surface becomes the {20-21} plane. Alternatively, the group III nitriding is performed by slicing the ingot in the axial direction inclined in the <11-20> direction from the {0001} plane so that the main surface becomes the {22-43} plane or the {11-21} plane. A method for producing a group III nitride semiconductor substrate for obtaining a semiconductor substrate. Prior to said slicing step includes a surface processing step of the dislocation density of the {000-1} plane of the ingot by a surface machining 1.0 × ^{10 10} / cm ² or less, III group according to claim 1 A method for manufacturing a nitride semiconductor substrate.   3. The group III according to claim 1, further comprising an etching step of dry etching the main surface of the group III nitride semiconductor substrate and performing wet etching on the main surface opposite to the main surface after the slicing step. A method for manufacturing a nitride semiconductor substrate.   The group III nitride according to claim 1, further comprising an etching step of dry etching the main surface of the group III nitride semiconductor substrate and a main surface opposite to the main surface after the slicing step. A method for manufacturing a semiconductor substrate.   In the slicing step, the ingot is sliced with a wire saw, the surface roughness Ra of the group III nitride semiconductor substrate in the direction parallel to the wire traveling direction is 10 to 500 nm, and the direction perpendicular to the wire traveling direction The manufacturing method of the group III nitride semiconductor substrate as described in any one of Claims 1-4 which makes surface roughness Ra of 60-800 nm.

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