JPWO2015193955A1 - Manufacturing method of nitride semiconductor single crystal substrate - Google Patents

Abstract

Disclosed is a method for manufacturing a nitride semiconductor single crystal substrate capable of efficiently producing a high-quality nitride semiconductor single crystal substrate by alleviating strain in the nitride semiconductor single crystal to be grown and suppressing generation of cracks. I will provide a. In one embodiment of the present invention, a template 10 in which a first nitride semiconductor single crystal layer 2 is grown on a heterogeneous substrate 1 is prepared, and a first nitride semiconductor single layer by laser light irradiation is prepared. A groove 3 composed of a plurality of linear grooves is formed in the template 10 by groove processing of the crystal layer 2 and the different substrate 1, and the laser beam is formed on the inner surface of the groove 3 simultaneously with the groove processing of the different substrate 1. A step of forming HAZ4, which is a region formed by heat generated by irradiation, a step of growing the second nitride semiconductor single crystal layer 5 on the template 10 in which the groove 3 is formed, and a second nitride And a step of cutting a nitride semiconductor single crystal substrate 6 from the semiconductor single crystal layer 5.

Description

  The present invention relates to a method for manufacturing a nitride semiconductor single crystal substrate.

  Conventionally, a technique for growing a nitride semiconductor crystal on a heterogeneous substrate such as sapphire is known (see, for example, Patent Documents 1 to 4).

  According to Patent Document 1, after forming a base layer made of a nitride semiconductor on a heterogeneous substrate, the base layer is etched to the heterogeneous substrate to form irregularities, and then the nitride semiconductor is formed on the base layer having irregularities. Grow. A gap is formed between the different substrate and the nitride semiconductor in the recess, and when the different substrate is irradiated with electromagnetic waves in this state, the different substrate and the nitride semiconductor can be separated at their interface.

  According to Patent Documents 2 and 3, a base layer made of a nitride semiconductor is formed on a different substrate, and then irregularities are formed only on the base layer, and then a nitride semiconductor is grown on the base layer having the irregularities. In the recess, a gap is formed between the heterogeneous substrate and the nitride semiconductor, and the nitride semiconductor grows in the vertical direction and the horizontal direction. Thereby, the stress in the growing nitride semiconductor is relieved.

  According to Patent Document 4, after forming a base layer made of a nitride semiconductor on a heterogeneous substrate, a groove is formed on the surface of the heterogeneous substrate exposed in the groove provided in the base layer, and then on the base layer Nitride semiconductor is grown. In the recess, a gap is formed between the dissimilar substrate and the nitride semiconductor. Since the groove is formed on the surface of the heterogeneous substrate, when the stress is generated due to the difference in coefficient of thermal expansion between the heterogeneous substrate and the grown nitride semiconductor, the heterogeneous substrate breaks and relieves the stress in the nitride semiconductor. be able to.

Japanese Patent Laid-Open No. 2001-176813 JP 2003-124576 A Special table 2013-504865 gazette JP 2011-057479 A

  One of the objects of the present invention is to provide a nitride semiconductor capable of efficiently obtaining a high-quality nitride semiconductor single crystal substrate by relieving strain in the grown nitride semiconductor single crystal and suppressing the generation of cracks. The object is to provide a method for manufacturing a single crystal substrate.

  In order to achieve the above object, one embodiment of the present invention provides a method for manufacturing a nitride semiconductor single crystal substrate of [1] to [16].

[1] A step of preparing a template in which a first nitride semiconductor single crystal layer is grown on a different substrate, and groove processing of the first nitride semiconductor single crystal layer and the different substrate by laser light irradiation. A plurality of linear grooves formed in the template, and at the same time as the groove processing of the heterogeneous substrate, HAZ is a region formed on the inner surface of the plurality of linear grooves by the heat of the laser light irradiation Forming a second nitride semiconductor single crystal layer on the template in which the plurality of linear grooves are formed, and nitride from the second nitride semiconductor single crystal layer A method of manufacturing a nitride semiconductor single crystal substrate, comprising: cutting a semiconductor single crystal substrate.

[2] The method for producing a nitride semiconductor single crystal substrate according to [1], wherein the laser beam has a wavelength of 300 nm or more.

[3] The method for producing a nitride semiconductor single crystal substrate according to [1] or [2], wherein the laser beam is a CW laser beam or a pulsed laser beam having a pulse width of 1 nanosecond or more.

[4] The groove processing of the first nitride semiconductor single crystal layer, the groove processing of the heterogeneous substrate, and the formation of the HAZ are continuously performed by one irradiation of the laser beam, or a plurality of times The method for producing a nitride semiconductor single crystal substrate according to any one of [1] to [3], which is performed stepwise by irradiation.

[5] The above [1] to [4], wherein the first nitride semiconductor single crystal layer is an Al _x Ga _(1-x) N (0 ≦ X ≦ 1) crystal grown by MOCVD or HVPE. ] The manufacturing method of the nitride semiconductor single crystal substrate of any one of.

[6] The second nitride semiconductor single crystal layer is an Al _Y Ga _(1-Y) N (0 ≦ Y ≦ 1) crystal grown by an HVPE method, according to the above [1] to [5] The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1.

[7] Any one of [1] to [6], wherein the plurality of linear grooves have the same width on the lower surface of the first nitride semiconductor single crystal layer and a width on the upper surface of the different substrate. A method for producing a nitride semiconductor single crystal substrate according to Item.

[8] The heterogeneous substrate is a sapphire substrate,
The method for producing a nitride semiconductor single crystal substrate according to any one of [1] to [7], wherein a depth of the plurality of linear grooves in the heterogeneous substrate is 200 μm or less.

[9] The width of the plurality of linear grooves on the upper surface of the first nitride semiconductor single crystal layer is 10 μm or more and 100 μm or less, according to any one of [1] to [8]. A method of manufacturing a nitride semiconductor single crystal substrate.

[10] The top surface of the first nitride semiconductor single crystal layer is a c-plane of the nitride semiconductor single crystal constituting the first nitride semiconductor single crystal layer or a plane inclined within 5 ° from the c-plane. The plurality of linear grooves are linear grooves parallel to the a-plane or m-plane of the nitride semiconductor single crystal, and the pattern of the plurality of linear grooves is a central axis of the template. The method for producing a nitride semiconductor single crystal substrate according to any one of the above [1] to [9], which has a rotational symmetry of 3 times or 6 times with respect to.

[11] The plurality of linear grooves include linear grooves arranged at equal intervals parallel to each other, and the pitch of the linear grooves arranged at equal intervals parallel to each other is 100 μm or more and 10 mm or less. The method for producing a nitride semiconductor single crystal substrate according to any one of [1] to [10].

[12] The first nitride semiconductor single crystal layer according to any one of [1] to [11], wherein the first nitride semiconductor single crystal layer is partitioned into a plurality of regions having the same area by the plurality of linear grooves. Manufacturing method of nitride semiconductor single crystal substrate.

[13] The method according to any one of [1] to [12], wherein the second nitride semiconductor single crystal layer is grown so as to be a continuous film covering the upper portions of the plurality of linear grooves. A method of manufacturing a nitride semiconductor single crystal substrate.

[14] The second nitride semiconductor single crystal in a state where unevenness corresponding to the shape of the region of the first nitride semiconductor single crystal layer partitioned by the plurality of linear grooves is left at the growth interface. The method for producing a nitride semiconductor single crystal substrate according to any one of [1] to [13], wherein a layer is grown.

[15] The above-mentioned [1] to [14], wherein the first nitride semiconductor single crystal layer is grown substantially undoped, and the second nitride semiconductor single crystal layer is grown by doping impurities. The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1.

[16] The method for producing a nitride semiconductor single crystal substrate according to [15], wherein the impurity having a concentration of 5 × 10 ¹⁷ cm ⁻³ or more is doped and grown.

  According to the present invention, a nitride semiconductor single crystal substrate capable of efficiently obtaining a high-quality nitride semiconductor single crystal substrate by relieving strain in the nitride semiconductor single crystal to be grown and suppressing generation of cracks. The manufacturing method of can be provided.

FIG. 1A is a vertical cross-sectional view schematically showing a manufacturing process of the nitride semiconductor single crystal substrate according to the first embodiment. FIG. 1B is a vertical cross-sectional view schematically showing a manufacturing process of the nitride semiconductor single crystal substrate according to the first embodiment. FIG. 1C is a vertical cross-sectional view schematically showing the manufacturing process of the nitride semiconductor single crystal substrate according to the first embodiment. FIG. 1D is a vertical cross-sectional view schematically showing the manufacturing process of the nitride semiconductor single crystal substrate according to the first embodiment. FIG. 1E is a vertical cross-sectional view schematically showing the manufacturing process of the nitride semiconductor single crystal substrate according to the first embodiment. FIG. 2A is a top view illustrating an example of a groove pattern formed on a template. FIG. 2B is a top view illustrating an example of a groove pattern formed on the template. FIG. 3A is a top view illustrating an example of a groove pattern formed on a template. FIG. 3B is a top view illustrating an example of a pattern of grooves formed on the template. FIG. 4A is a top view illustrating an example of a pattern of grooves formed on a template. FIG. 4B is a top view illustrating an example of a groove pattern formed on the template. FIG. 5A is a vertical cross-sectional view schematically showing a manufacturing process of the nitride semiconductor single crystal substrate according to the second embodiment. FIG. 5B is a vertical cross-sectional view schematically showing the manufacturing process of the nitride semiconductor single crystal substrate according to the second embodiment. FIG. 5C is a vertical cross-sectional view schematically showing the manufacturing process of the nitride semiconductor single crystal substrate according to the second embodiment. FIG. 6A is a vertical cross-sectional view schematically showing a manufacturing process of the nitride semiconductor single crystal substrate according to the second embodiment. FIG. 6B is a vertical cross-sectional view schematically showing the manufacturing process of the nitride semiconductor single crystal substrate according to the second embodiment. FIG. 6C is a vertical cross-sectional view schematically showing a manufacturing process of the nitride semiconductor single crystal substrate according to the second embodiment.

[First Embodiment]
1A to 1E are vertical sectional views schematically showing a manufacturing process of a nitride semiconductor single crystal substrate according to the first embodiment.

  First, as shown in FIG. 1A, a heterogeneous substrate 1 made of a material different from a nitride semiconductor is prepared. Next, as shown in FIG. 1B, the first nitride semiconductor single crystal layer 2 is heteroepitaxially grown on the heterogeneous substrate 1 to obtain the template 10. Next, as shown in FIG. 1C, the groove 3 is formed in the template 10. At this time, a HAZ (Heat Affected Zone, heat affected zone) 4 is formed on the inner surface of the groove 3. Next, as shown in FIG. 1D, the second nitride semiconductor single crystal layer 5 is epitaxially grown on the template 10 subjected to the groove processing. Next, as shown in FIG. 1E, the nitride semiconductor single crystal substrate 6 is cut out from the second nitride semiconductor single crystal layer 5. Hereinafter, details of each of these steps will be described.

  First, as shown in FIG. 1A, a heterogeneous substrate 1 made of a material different from a nitride semiconductor is prepared. The diameter of the heterogeneous substrate 1 is based on the target diameter of the second nitride semiconductor substrate 5 finally obtained, and the outer peripheral portion of the second nitride semiconductor single crystal layer 5 removed by processing after crystal growth. It is determined in consideration of the thickness of the material. The step of removing the outer peripheral portion of the second nitride semiconductor single crystal layer 5 will be described later.

  As the heterogeneous substrate 1, a sapphire substrate is preferably used. Specifically, for example, a c-plane sapphire substrate having a diameter of 65 mm and a thickness of 400 μm that is commercially available for GaN epitaxial crystal growth can be used.

Compared to a sapphire substrate, there are many restrictions on use in terms of the formation of HAZ4, stability during crystal growth (reactivity), availability, etc., but Si substrate, GaAs substrate, ZnO substrate, Ga ₂ An O ₃ substrate or the like can also be used.

  Next, as shown in FIG. 1B, the first nitride semiconductor single crystal layer 2 is heteroepitaxially grown on the heterogeneous substrate 1. As a result, a template 10 composed of the heterogeneous substrate 1 and the first nitride semiconductor single crystal layer 2 is obtained.

The first nitride semiconductor single crystal layer 2 is made of a nitride semiconductor single crystal represented by a composition formula Al _x Ga _(1-x) N (0 ≦ x ≦ 1). The first nitride semiconductor single crystal layer 2 is, for example, an undoped GaN thin film having a thickness of 2 μm.

  The first nitride semiconductor single crystal layer 2 is preferably formed by MOCVD (Metal Organic Chemical Vapor Deposition) method or HVPE (Hydride Vapor Phase Epitaxy) method. This is because a technique for growing a nitride semiconductor single crystal layer on a dissimilar substrate such as sapphire has already been established by these methods, and a template having a nitride semiconductor single crystal with good crystallinity on the surface can be easily obtained. It is.

  Further, in order to improve the crystallinity of the first nitride semiconductor single crystal layer 2 and to ensure the flatness of the surface, it is desirable to apply a low-temperature buffer layer insertion technique widely used for heteroepitaxial growth of GaN. . A technique for heteroepitaxially growing a GaN crystal on a sapphire substrate using a low-temperature buffer layer is disclosed in, for example, Japanese Patent No. 3026087.

  When the nitride semiconductor single crystal is directly grown on the heterogeneous substrate 1, three-dimensional island-like growth of the nitride semiconductor single crystal occurs at the initial stage of growth, and stress is generated in the nitride semiconductor single crystal due to this. To do. In the present embodiment, the first nitride semiconductor single crystal layer 2 is formed on the heterogeneous substrate 1 and the second nitride semiconductor single crystal layer 5 is grown on the first nitride semiconductor single crystal layer 5. Crystal growth proceeds from the beginning in step flow mode without occurring. For this reason, the stress generated in the second nitride semiconductor single crystal layer 5 can be reduced and the distortion can be suppressed.

  The thickness of the first nitride semiconductor single crystal layer 2 is preferably 1 μm or more and 10 μm or less. Since the first nitride semiconductor single crystal layer 2 is formed by heteroepitaxial growth on the heterogeneous substrate 1, the initial stage of growth is three-dimensional island growth, and in order for the surface to be a flat continuous film, It is necessary to grow to a certain thickness. When the thickness of the first nitride semiconductor single crystal layer 2 is less than 1 μm, pits are generated on the surface, and the second nitride semiconductor single crystal layer 5 is grown on the surface in the step flow mode. Becomes difficult. If the thickness of the first nitride semiconductor single crystal layer 2 is greater than 10 μm, the template 10 becomes large due to the difference in linear expansion coefficient between the heterogeneous substrate 1 and the first nitride semiconductor single crystal layer 2. In addition to being warped, it becomes difficult to form a groove in the next process, and in a severe case, a crack is generated in the first nitride semiconductor single crystal layer 2.

  Further, the upper surface of the first nitride semiconductor single crystal layer 2 grown on the heterogeneous substrate 1 is, for example, from the c-plane or c-plane of the nitride semiconductor single crystal constituting the first nitride semiconductor single crystal layer 2 The surface is inclined within 5 °. When the upper surface of the first nitride semiconductor single crystal layer 2 is a surface inclined from the c-plane, the offset angle (inclination angle) from the c-plane is preferably within 5 °. If the offset angle exceeds 5 °, the interface shape when the second nitride semiconductor single crystal layer 5 is laterally grown and associated on the groove 3 is disturbed, and abnormal growth and ungrown regions are likely to occur. It is. Lateral growth of the second nitride semiconductor single crystal layer 5 will be described later.

  Next, as shown in FIG. 1C, a groove 3 reaching the inside of the heterogeneous substrate 1 is formed in the template 10 by performing groove processing on the first nitride semiconductor single crystal layer 2 and the heterogeneous substrate 1. The groove 3 is composed of a plurality of linear grooves. For example, the linear groove constituting the groove 3 is a linear groove, the width of the linear groove is 40 μm, the depth is 60 μm, and the groove pitch (distance between the centers of adjacent grooves) is 1 mm. is there.

  Here, the HAZ 4 is formed on the inner surface of the groove 3 in the heterogeneous substrate 1 by forming the groove 3 by laser processing under a specific condition. HAZ is generally a welding term that means a heat-affected zone, but in the present invention, when a heterogeneous substrate 1 is irradiated with laser light under specific conditions, Define. A region in which local strain is accumulated is observed around the HAZ 4 of the heterogeneous substrate 1 by strain observation using polarized light.

  When the second nitride semiconductor single crystal layer 5 is grown on the raw template 10, the second nitride semiconductor single crystal 5 resists the strain accumulated in the first nitride semiconductor single crystal layer 2. Stress is generated in the layer 5. Therefore, as in the present embodiment, the second nitride semiconductor single crystal layer 5 is grown on the template 10 in which the grooves 3 are formed, thereby causing the second nitride semiconductor single crystal layer 5 to generate cracks. Vapor phase epitaxial growth can be performed while suppressing. The groove 3 can release the stress in the second nitride semiconductor single crystal layer 5 caused by the strain of the first nitride semiconductor single crystal layer 2 and reduce the strain.

  However, when the groove 3 is formed, the surface of the template 10 that becomes the crystal growth start region is partitioned by the groove 3, so that the growth is started from each section immediately after the start of the growth of the second nitride semiconductor single crystal layer 5. The started crystals meet on the groove 3 to cover the groove 3. There is a possibility that the second nitride semiconductor single crystal layer 5 is distorted due to the deviation of the crystal lattice during the association.

  As a result of intensive studies to solve this problem, the present inventors have found that when HAZ4 is formed on the inner surface of the groove 3, the crystal lattice at the time of crystal association on the groove 3 is as described above. It has been found that HAZ4 absorbs and relaxes the strain of second nitride semiconductor single crystal layer 5 resulting from the shift of the thickness, and second nitride semiconductor single crystal layer 5 having excellent crystallinity grows.

  Further, since HAZ 4 also has an effect of locally reducing the strength of the heterogeneous substrate 1, a large difference due to the difference in linear expansion coefficient between the heterogeneous substrate 1 and the second nitride semiconductor single crystal layer 5 during crystal cooling. When strain is generated in the second nitride semiconductor single crystal layer 5, the strain in the second nitride semiconductor single crystal layer 5 can be released by preferentially generating cracks in the heterogeneous substrate 1. .

  For the laser processing of the groove 3, for example, a CW (continuous wave oscillation) laser processing machine having a wavelength of 532 nm or a wavelength of 355 nm using a harmonic of a commercially available Nd: YAG laser or a pulsed laser can be used.

  The laser processing conditions for forming the HAZ 4 when forming the groove 3 are such that the region from the inner surface of the groove 3 to a certain depth is heated by laser light irradiation. Specifically, the wavelength of the laser beam is preferably 300 nm or more, and a CW laser or a pulse laser having a pulse width of 1 nanosecond or more is preferable.

  When the wavelength of the laser beam is shorter than 300 nm, the absorption efficiency of the laser beam of the heterogeneous substrate 1 such as a sapphire substrate is increased, so that the heated region is limited to the immediate vicinity of the inner surface of the groove 3. Also, when the laser pulse width is shorter than 1 nanosecond, the peak intensity of the laser becomes high, so the molecular bond of the heterogeneous substrate 1 is cut by the light energy, and the molecule is removed without thermal diffusion to the peripheral portion. Since the processing proceeds due to a phenomenon called “ablation”, heat generation at the processing interface is hardly generated. Under these processing conditions, heat is not transmitted to the inside of the heterogeneous substrate 1, and the HAZ 4 having a sufficient depth is not formed.

  On the other hand, since it is necessary to avoid that HAZ 4 is formed so deep that cracks are generated in heterogeneous substrate 1 at the time of formation of groove 3, the strain of second nitride semiconductor single crystal layer 5 is sufficiently relieved, and The wavelength and pulse width of the laser light are required to be set so that the HAZ 4 is formed to a depth that does not cause cracks in the heterogeneous substrate 1 when the grooves 3 are formed.

  The HAZ 4 may be formed only in the vicinity of the surface of the heterogeneous substrate 1, but as shown in FIG. 1C, it is preferably formed on the inner surface of the groove 3 when the groove 3 is laser processed. When the groove 3 is formed by laser processing, not only can the HAZ 4 be formed by heat generation, but there is an advantage that the groove 3 having a complicated pattern can be formed as compared with other processing methods such as dicing. For example, although it is difficult to form a complicated pattern as shown in FIGS. 3A and 3B described later by dicing, a laser processing machine capable of controlling the laser irradiation position in conjunction with CAD (Computer Aided Design) Therefore, it can be formed easily.

  Further, according to laser processing, the groove processing of the first nitride semiconductor single crystal layer 2 and the groove processing of the heterogeneous substrate 1 may be continuously performed by one-time laser light irradiation, but the same position of the template 10 is used. Since it is also possible to irradiate with a laser, the groove 3 can be formed stepwise by irradiating a plurality of times of laser light. That is, after irradiating the template 10 once with a laser and grooving the first nitride semiconductor single crystal layer 2, irradiating the same portion with the laser again to grooving the dissimilar substrate 1, and simultaneously forming the HAZ 4 Can be formed. In this case, it is possible to more reliably irradiate the different type substrate 1 with the laser. Further, by irradiating the heterogeneous substrate 1 with the laser a plurality of times, it is possible to form the HAZ 4 having a sufficient depth that can effectively relieve the distortion of the second nitride semiconductor single crystal layer 5.

  When grooving is performed by a laser processing machine, the first nitride semiconductor single crystal layer 2 and the processing waste of the different substrate 1 (for example, processing waste of GaN or sapphire) adhere to the inside or the periphery of the groove 3. In order to remove this, the grooved template 10 is subjected to ultrasonic cleaning using pure water or an organic solvent, or bubbling cleaning using an acid (for example, cleaning with a mixed solution of hydrochloric acid and hydrogen peroxide solution). After that, it is preferable to wash well with pure water. By performing sufficient cleaning, it is possible to remove the processing waste of the first nitride semiconductor single crystal layer 2 that is likely to be the starting point of abnormal growth of the second nitride semiconductor single crystal layer 5 grown on the template 10. . It is possible to etch away the processing waste of the first nitride semiconductor single crystal layer 2 using an etchant such as a heated phosphoric acid and sulfuric acid mixed acid, but it is possible to dissolve a nitride semiconductor such as GaN. Since the etchant often dissolves and removes the HAZ 4 formed on the sapphire substrate, care must be taken when the heterogeneous substrate 1 is a sapphire substrate.

  The width of the linear grooves constituting the grooves 3 on the upper surface of the first nitride semiconductor single crystal layer 2 is preferably 10 μm or more and 100 μm or less. If the width of the upper surface of the first nitride semiconductor single crystal layer 2 in the groove 3 is narrower than 10 μm, the depth of the HAZ 4 may be insufficient. In this case, the second nitride semiconductor single crystal When the layer 5 is grown, it becomes difficult to sufficiently relax the strain generated at the crystal association part. On the other hand, if the width of the upper surface of the first nitride semiconductor single crystal layer 2 in the groove 3 is larger than 100 μm, the laterally grown second nitride semiconductor single crystal layer 5 may not be able to cover the upper portion of the groove 3. In that case, crystals that nucleate and grow in the grooves 3 are mixed in the second nitride semiconductor single crystal layer 5, and the crystallinity of the second nitride semiconductor single crystal layer 5 is deteriorated. End up.

  The linear groove constituting the groove 3 has a width on the lower surface of the first nitride semiconductor single crystal layer 2 substantially equal to a width on the upper surface of the heterogeneous substrate 1, and a surface other than the inner surface of the groove of the heterogeneous substrate 1 is a template. It is preferable that it is not exposed to the surface side of 10. Although the width in the first nitride semiconductor single crystal layer 2 may be narrower than the width in the heterogeneous substrate 1, it is technically difficult to perform groove processing of such a shape. Conversely, if the width in the first nitride semiconductor single crystal layer 2 is wider than the width in the heterogeneous substrate 1, the first nitride semiconductor single crystal layer 5 is grown when the first nitride semiconductor single crystal layer 5 is grown. Causes of the appearance of a crystal growth mode different from the crystal growth mode on the semiconductor single crystal layer 2 due to the exposure of the surface of the heterogeneous substrate 1, disturbing the crystallinity of the growing second nitride semiconductor single crystal layer 5 It becomes.

  In order to make the width of the linear groove constituting the groove 3 in the first nitride semiconductor single crystal layer 2 substantially equal to the width in the heterogeneous substrate 1, the first nitride semiconductor single crystal layer 2 It is preferable that the grooving and the grooving of the heterogeneous substrate 1 are continuously performed in the same process, that is, by one-time laser beam irradiation.

  When the heterogeneous substrate 1 is a sapphire substrate, the depth of the groove 3 in the heterogeneous substrate 1 is preferably not less than the opening width of the groove 3 and not more than 200 μm, and more preferably not less than the opening width and not more than 100 μm. Unlike sapphire, sapphire is unlikely to melt when heated, so it is relatively difficult to form deep grooves 3 by laser processing under conditions where HAZ 4 is formed. If the groove 3 deeper than 200 μm is to be formed, it becomes difficult to discharge the sapphire dissolved in the groove 3 to the outside of the groove 3, which prevents the laser irradiation to the sapphire substrate and forms the HAZ 4 at the bottom of the groove 3. Make it difficult. In addition, since the melted sapphire re-solidifies, a large strain is generated. Therefore, before the second nitride semiconductor single crystal layer 5 is grown, fine cracks are formed in the sapphire substrate or the first nitride semiconductor single crystal layer 2. Increased risk. If the depth of the groove 3 in the heterogeneous substrate 1 is smaller than the opening width, polycrystals nucleated in the groove 3 come out, and the crystallinity of the second nitride semiconductor single crystal layer 5 is deteriorated. There is a fear.

  Moreover, it is preferable that the pattern of the groove | channel 3 has periodicity. Thereby, the time at which the second nitride semiconductor single crystal layer 5 grows over the groove 3 is made substantially uniform in the plane of the template 10, and the quality uniformity of the second nitride semiconductor single crystal layer 5 is achieved. Can be increased.

  Further, when the grooves 3 are formed from a plurality of parallel straight grooves or a combination thereof, the grooves parallel to each other are arranged at equal intervals, and the center interval (pitch) of each groove is 100 μm or more. And it is preferable that it is 10 mm or less, and it is more preferable that it is 5 mm or less. When the interval between the grooves is smaller than 100 μm, the association interface density when the second nitride semiconductor single crystal layer 5 is laterally grown at the upper portion of the groove 3 to be associated may increase. In this case, the crystal growth This step flow mode collapses and it becomes easy to shift to the three-dimensional island growth mode. When the crystal growth mode becomes the three-dimensional island growth mode, a new large strain is generated in the second nitride semiconductor single crystal layer 5. On the other hand, if the groove interval is wider than 10 mm, the density of the HAZ 4 in the heterogeneous substrate 1 may decrease, and in this case, the strain remaining in the second nitride semiconductor single crystal layer 5 increases. End up.

  2A, 2B, 3A, 3B, 4A, and 4B are top views showing examples of patterns of grooves 3 formed on the template 10, respectively. The top surface of the first nitride semiconductor single crystal layer 2 shown in FIGS. 2A, 2B, 3A, 3B, 4A, and 4B is a c-plane of the single crystal that constitutes the first nitride semiconductor single crystal layer 2. The c-axis of the single crystal constituting the first nitride semiconductor single crystal layer 2 is oriented perpendicular to the paper surface. Grooves 3 shown in FIGS. 2A, 2B, 3A, 3B, 4A, and 4B have a lattice pattern in which a plurality of lines are combined, and all the grooves are connected.

  The grooves 3 shown in FIGS. 2A and 2B have a lattice pattern in which equilateral triangles are arranged. When the groove 3 is formed so that the center of one equilateral triangle included in the lattice pattern is located on the central axis of the template 10, the pattern of the groove 3 shown in FIGS. The template 10 has three-fold rotational symmetry with respect to the central axis. When the groove 3 is formed so that the vertex of the equilateral triangle is located on the central axis of the template 10, the pattern of the groove 3 shown in FIGS. 2A and 2B is six times with respect to the central axis of the template 10. Have rotational symmetry.

  The grooves 3 shown in FIGS. 3A and 3B have a lattice pattern in which regular hexagons are arranged. When the groove 3 is formed so that the center of one regular hexagon included in the lattice pattern is located on the central axis of the template 10, the pattern of the groove 3 shown in FIGS. The template 10 has 6-fold rotational symmetry with respect to the central axis. When the groove 3 is formed so that the regular hexagonal apex is positioned on the central axis of the template 10, the pattern of the groove 3 shown in FIGS. 3A and 3B is three times with respect to the central axis of the template 10. Have rotational symmetry.

  The grooves 3 shown in FIGS. 4A and 4B have a lattice pattern in which regular hexagons and regular triangles are arranged. When the groove 3 is formed so that the center of one regular hexagon included in the lattice pattern is located on the central axis of the template 10, the pattern of the groove 3 shown in FIGS. The template 10 has 6-fold rotational symmetry with respect to the central axis. When the groove 3 is formed so that the center of the equilateral triangle is located on the central axis of the template 10, the pattern of the groove 3 shown in FIGS. 4A and 4B is three times with respect to the central axis of the template 10. Have rotational symmetry.

  The pattern of the groove 3 shown in FIGS. 2A and 3A is composed of a combination of lines parallel to the a-axis (perpendicular to the m-axis) of the single crystal constituting the first nitride semiconductor single crystal layer 2, The pattern of the groove 3 shown in 3B is constituted by a combination of lines parallel to the m-axis (perpendicular to the a-axis) of the single crystal constituting the first nitride semiconductor single crystal layer 2.

  When the upper surface of the first nitride semiconductor single crystal layer 2 is a c-plane or a plane inclined within 5 ° from the c-plane, the pattern of the groove 3 is the first nitride semiconductor single crystal layer 2. (The groove 3 is parallel to the a-plane or the m-plane of the nitride semiconductor single crystal of the first nitride semiconductor single crystal layer 2). It is preferable that the pattern has a 3-fold symmetry or a 6-fold symmetry with respect to the central axis of the template 10. In this case, when the second nitride semiconductor single crystal layer 5 covers the upper part of the groove 3 by lateral growth, adjacent crystals are easily bonded to each other, and an ungrown region is less likely to remain. The crystal growth interface of the second nitride semiconductor single crystal layer 5 can be a flat continuous film without disturbing the growth mode.

  In particular, when the heterogeneous substrate 1 is a sapphire substrate and the groove 3 is constituted by a combination of grooves parallel to the a-plane of the nitride semiconductor single crystal, the linear groove constituting the groove 3 is an easy cleavage surface of sapphire. Becomes parallel. For this reason, the strength of the region immediately below the groove 3 of the heterogeneous substrate 1 is reduced, and when the second nitride semiconductor single crystal layer 5 is distorted, the heterogeneous substrate 1 is likely to crack, and the second nitride The distortion of the semiconductor single crystal layer 5 can be effectively released.

  Grooves 3 shown in FIGS. 2A, 2B, 3A, and 3B partition the first nitride semiconductor single crystal layer 2 into a plurality of regions (regular triangular regions) having substantially the same area. By dividing the first nitride semiconductor single crystal layer 2 into a plurality of substantially equal areas, it is possible to reduce the unevenness of the surface of the second nitride semiconductor single crystal layer 5 grown thereon, The growth of the second nitride semiconductor single crystal layer 5 can proceed smoothly, and the in-plane uniformity of the characteristics of the nitride semiconductor single crystal substrate cut out from the second nitride semiconductor single crystal layer 5 can be enhanced. .

  Depending on the growth conditions of the HVPE, the second nitride semiconductor single crystal layer 5 is left with the irregularities corresponding to the shape of the region of the first nitride semiconductor single crystal layer 2 partitioned by the grooves 3 left at the growth interface. It is also possible to grow. As long as the second nitride semiconductor single crystal layer 5 can be grown thick while maintaining the form of a continuous film, the growth interface may be flat or may have irregularities. In some cases, it is effective to intentionally form irregularities on the surface of the second nitride semiconductor single crystal layer 5 for the purpose of controlling the dislocation density distribution inside the crystal. When it is desired to perform crystal growth by forming large irregularities, a groove 3 having a pattern for partitioning the first nitride semiconductor single crystal layer 2 into regions having different areas as shown in FIGS. 4A and 4B is formed. do it.

  The grooves 3 shown in FIGS. 4A and 4B partition the first nitride semiconductor single crystal layer 2 into two types of regions (regular hexagonal region and equilateral triangular region) having different areas. When the second nitride semiconductor single crystal layer 5 is grown on the template 10 shown in FIGS. 4A and 4B, the growth interface on a region having a large area (a regular hexagonal region in the example shown in FIGS. 4A and 4B). However, the growth interface on the small area (regular triangular area in the example shown in FIGS. 4A and 4B) is lowered, and irregularities are formed on the surface of the second nitride semiconductor single crystal layer 5. Thus, the unevenness of the surface of the second nitride semiconductor single crystal layer 5 can be controlled by the pattern of the groove 3.

  The pattern of the groove 3 shown in FIG. 4A is constituted by a combination of lines parallel to the a-axis (perpendicular to the m-axis) of the nitride semiconductor single crystal of the first nitride semiconductor single crystal layer 2 and shown in FIG. 4B. The pattern of the groove 3 is constituted by a combination of lines parallel to the m-axis (perpendicular to the a-axis) of the nitride semiconductor single crystal of the first nitride semiconductor single crystal layer 2.

  The pattern of the groove 3 may be another pattern such as a rhombus pattern or a concentric circle pattern. Moreover, the groove | channel 3 may be comprised from many discontinuous grooves. Further, the width and depth of the groove 3 may vary within the plane of the template 10. Further, a part of the groove 3 may penetrate to the back side of the template 10. Further, groove processing may also be performed on the back side of the different substrate 1.

Next, as shown in FIG. 1D, the second nitride semiconductor single crystal layer 5 is epitaxially grown on the template 10 subjected to the groove processing. The second nitride semiconductor single crystal layer 5 is made of a nitride semiconductor single crystal represented by a composition formula Al _Y Ga _(1-Y) N (0 ≦ Y ≦ 1), and in particular, made of a GaN crystal. preferable. The second nitride semiconductor single crystal layer 5 is, for example, a Si-doped GaN crystal layer having a thickness of 5 mm.

  Since the second nitride semiconductor single crystal layer 5 needs to have a sufficient thickness for cutting out the nitride semiconductor single crystal substrate, it is desirable that the second nitride semiconductor single crystal layer 5 be grown by the HVPE method having a high crystal growth rate. In addition, since the HVPE method performs crystal growth in a reactor having a hot wall structure, compared with the MOCVD method in which crystal growth is performed in a reactor having a cold wall structure, the crystal growth is performed on the template 10 subjected to groove processing. However, there is an advantage that it is difficult to achieve temperature distribution in the growth region in the substrate surface, and it is easy to achieve uniform crystal growth. Details of the growth technique of GaN by the HVPE method are disclosed in, for example, Japanese Patent No. 3535583. Details of a technique for doping Si when growing GaN by the HVPE method are disclosed in, for example, Japanese Patent No. 3279528. The second nitride semiconductor single crystal layer 5 may be grown by a liquid phase growth method such as a flux method or an ammonothermal method.

  It is preferable that first nitride semiconductor single crystal layer 2 and second nitride semiconductor single crystal layer 5 have the same composition. This is due to the occurrence of strain and defects in the second nitride semiconductor single crystal layer 5 due to lattice mismatch between the first nitride semiconductor single crystal layer 2 and the second nitride semiconductor single crystal layer 5. This is to suppress.

  The first nitride semiconductor single crystal layer 2 can be grown substantially undoped, and the second nitride semiconductor single crystal layer 5 can be grown by intentionally doping impurities. Here, “substantially undoped” means that impurities are not intentionally doped. In the case of HVPE growth, even if impurities are not intentionally doped, Si or O due to the quartz jig in the furnace is mixed in the crystal, and usually an n-type crystal grows. A crystal that is not doped with impurities and is grown so as to have an impurity concentration as low as possible is defined herein as an undoped crystal. The second nitride semiconductor single crystal layer 5 may be grown substantially undoped.

When the thin first nitride semiconductor single crystal layer 2 is grown flat on the heterogeneous substrate 1, the impurity concentration is desirably as low as possible. This is because when the crystal is doped with impurities, the impurity atoms adsorbed on the growth interface hinder the formation of initial growth nuclei of the nitride semiconductor and promote three-dimensional island growth, which makes it difficult to flatten the crystal surface. On the other hand, the second nitride semiconductor single crystal layer 5 from which the nitride semiconductor single crystal substrate 6 for producing various devices is cut is intentionally doped in order to control the conductivity of the nitride semiconductor single crystal substrate. To be doped. Si, S, Se, Ge, O, Fe, Mg, Zn, or the like is often used as the impurity element doped into the nitride semiconductor single crystal substrate 6. Further, the impurity concentration in the crystal required for the nitride semiconductor single crystal substrate 6 is usually 5 × 10 ¹⁷ cm ⁻³ or more, and in the case of being large, it is 1 × 10 ¹⁸ cm ⁻³ or more. In this case, the second nitride semiconductor single crystal layer 5 has impurities such as Si, S, Se, Ge, O, Fe, Mg, and Zn at a concentration of 5 × 10 ¹⁷ cm ⁻³ or higher, or 1 × Doping is performed at a concentration of 10 ¹⁸ cm ⁻³ or more.

  However, when a crystal doped with an impurity at a high concentration is grown on an undoped crystal, strain due to the difference between the lattice constants of the both occurs, resulting in crystal defects and cracks in the crystal. Therefore, normally, when growing a crystal to be doped with impurities, the amount of impurity doping is gradually increased, and the impurity concentration in the crystal is gradually increased from the undoped state, so that the local strain is increased. Measures such as mitigation of the accumulation are taken, but the substrate cut out from the crystal thus grown has a low impurity concentration at the site formed at the initial stage of crystal growth, so there is a variation in electrical characteristics between the substrates. There are problems such as an increase in size and a low yield because an area that does not meet the product specifications is created.

  On the other hand, according to the present embodiment, distortion caused by the lattice constant difference between the undoped first nitride semiconductor single crystal layer 2 and the second nitride semiconductor single crystal layer 5 doped with impurities at a high concentration is reduced. It can be released by the HAZ 4 formed on the inner surface of the groove 3 provided in the template 10, and strain is not easily accumulated in the second nitride semiconductor single crystal layer 5. Therefore, the second nitride semiconductor single crystal layer 5 doped with impurities at a high concentration can be directly grown on the undoped first nitride semiconductor single crystal layer 2.

  The second nitride semiconductor single crystal layer 5 is required to have a certain thickness in order to cut out the nitride semiconductor single crystal substrate in the next step. In order for the self-supporting nitride semiconductor single crystal substrate to have sufficient strength, for example, when the diameter is 50 mm, a thickness of at least 350 μm is required immediately after slicing, and considering the cutting allowance of the slice, The thickness of the second nitride semiconductor single crystal layer 5 is required to be 500 μm or more. Furthermore, since the improvement effect of the variation in crystal orientation and dislocation density in the crystal increases as the crystal becomes thicker, it is advantageous to grow the second nitride semiconductor single crystal layer 5 thicker. For this reason, the thickness of the second nitride semiconductor single crystal layer 5 is preferably 500 μm or more, and more preferably 1 mm or more.

  The second nitride semiconductor single crystal layer 5 is a continuous film that laterally grows on the first nitride semiconductor single crystal layer 2 of the template 10 and covers the opening of the groove 3. Here, in order to prevent generation of voids and ungrown regions in the second nitride semiconductor single crystal layer 5, lateral growth starts as soon as possible after the second nitride semiconductor single crystal layer 5 starts growing. It is preferable that the opening of groove 3 is immediately covered with second nitride semiconductor single crystal layer 5. If voids or ungrown regions are formed in the second nitride semiconductor single crystal layer 5, distortion is likely to occur in the second nitride semiconductor single crystal layer 5, causing cracks during processing. In addition, a through-hole or a large pit is generated in the nitride semiconductor single crystal substrate cut out from the second nitride semiconductor single crystal layer 5 and becomes a factor that hinders acquisition of a high-quality nitride semiconductor single crystal substrate. .

  In order to quickly cover the opening of the groove 3 with the second nitride semiconductor single crystal layer 5, the crystal growth conditions of the second nitride semiconductor single crystal layer 5 may be optimized. For example, when a GaN single crystal is grown as the second nitride semiconductor single crystal layer 5 by the HVPE method, the lateral growth becomes easier as the substrate temperature during the growth is increased. Although it depends on the structure of the furnace and other crystal growth conditions, for example, the surface temperature of the template 10 is 1000 ° C. or higher, and preferably 1050 ° C. or higher, which facilitates lateral growth. Further, the lower the V / III ratio of the raw material (the molar ratio of the V group raw material and the III group raw material supplied to the substrate), the easier it is to grow laterally. Although this also depends on the structure of the furnace and other crystal growth conditions, for example, if the V / III ratio is 10 or less, preferably 5 or less, lateral growth is easy. The composition of the atmosphere gas during growth is such that the lower the hydrogen gas concentration, the easier the lateral growth is possible, and it is preferable that the raw material carrier gas does not contain hydrogen gas if possible. These are desirable growth conditions when the second nitride semiconductor single crystal layer 5 is laterally grown on the trench 3, and once the crystal covers the upper portion of the trench 3, these growth conditions are changed. It doesn't matter.

  Next, as shown in FIG. 1E, the nitride semiconductor single crystal substrate 6 is cut out from the second nitride semiconductor single crystal layer 5. Here, a substrate having irregularities on the upper surface, which is cut out from the outermost surface side of the second nitride semiconductor single crystal layer 5, is referred to as a nitride semiconductor single crystal substrate 7. For cutting the second nitride semiconductor single crystal layer 5, a multi-wire saw generally used for cutting Si or GaAs crystals can be used. A GaN crystal cutting technique using a multi-wire saw is disclosed in, for example, Japanese Patent Application Laid-Open No. 2013-032278. Moreover, you may use the existing technique using an inner peripheral blade slicer, an outer peripheral blade slicer, a (multi) wire saw, a wire electric discharge machine, etc. In general, saw marks and processing strain often remain on the surface of the cut-out nitride semiconductor single crystal substrate 6, so that these are removed on the front and back surfaces of the cut nitride semiconductor single crystal substrate 6. It is preferable to perform the polishing process.

  Here, in order to suppress the cracking of the crystal when the nitride semiconductor single crystal substrate 6 is cut out, the thickness of the outer peripheral portion of the crystal including the non-c-plane growth region is 5 mm or more before cutting the crystal as described above. It is preferable to remove the region (not shown). When the second nitride semiconductor single crystal layer 5 is grown on the template 10 whose surface is c-plane, the surface of most regions of the second nitride semiconductor single crystal layer 5 is also c-plane, A region where the crystal growth interface is not the c-plane (non-c-plane growth region) is formed in the portion. This non-c-plane growth region is known to have a difference in impurity atom incorporation efficiency compared to a region where the growth interface grows on the c-plane, and the interface between the non-c-plane growth region and the c-plane growth region In the vicinity, distortion due to the difference in impurity concentration in each region occurs. For this reason, prior to the step of cutting the nitride semiconductor single crystal substrate from the second nitride semiconductor single crystal layer 5, it is possible to remove the regions having different impurity concentrations and the strain accumulated regions on the outer periphery of the crystal. This is effective for obtaining a nitride semiconductor single crystal substrate 6 with high uniformity of characteristics, and is effective for preventing the occurrence of cracks when slicing the second nitride semiconductor single crystal layer 5. By removing the region having a thickness of 5 mm or more on the outer peripheral portion of the second nitride semiconductor single crystal layer 5, the region where the strain is accumulated can be effectively removed. As a method for removing the outer peripheral portion of the second nitride semiconductor single crystal layer 5, a method such as grinding or electric discharge machining can be used. When removing a region having a thickness of 5 mm or more on the outer peripheral portion of second nitride semiconductor single crystal layer 5, heterogeneous substrate 1 having a diameter 10 mm or more larger than the diameter of target nitride semiconductor single crystal substrate 6 is used. Is required.

  For example, the technique disclosed in International Application No. PCT / JP2014 / 051806 is preferably used for removing the crystal outer peripheral portion. Specifically, for example, the outer peripheral portion of the second nitride semiconductor single crystal layer 5 is ground and removed using a cup-type diamond electrodeposition grindstone having an inner diameter of 52 mm, and subsequently, nitrided with a thickness of 500 μm using a multi-wire saw. Six semiconductor semiconductor single crystal substrates 6 are cut out. However, since the crystal does not always break when such removal of the crystal periphery is not performed, the removal of the crystal periphery is not essential. As will be described later, when a part of the nitride semiconductor single crystal substrate 6 is used as a seed crystal of another nitride semiconductor single crystal, the lower side from which the nitride semiconductor single crystal substrate 6 used as the seed crystal is cut out In this region, the outer peripheral portion may not be removed so as not to reduce the diameter, and only the outer peripheral portion of the other upper region may be removed.

  A plurality of nitride semiconductor single crystal substrates 6 can be cut out from the second nitride semiconductor single crystal layer 5. In addition, the nitride semiconductor single crystal substrate 6 with an off angle can be easily obtained by intentionally inclining and cutting the cut surface from a plane perpendicular to the crystal growth orientation. In order to obtain a nitride semiconductor single crystal substrate 6 with an off angle, it is possible to use a heterogeneous substrate 1 with an off angle as a base, but the second nitride semiconductor single crystal layer increases as the off angle increases. Therefore, it is preferable to grow the second nitride semiconductor single crystal layer 5 on the c-plane without using the heterogeneous substrate 1 with an off angle. Further, the second nitride semiconductor single crystal layer 5 grown on the c-plane can be cut at the c-plane and then obliquely processed in the polishing step to form an off-angle. Since a large machining cost is required for the crystal layer 5, the efficiency is poor. If the second nitride semiconductor single crystal layer 5 grown on the c-plane is cut obliquely, a plurality of off-angle nitride semiconductor single crystal substrates 6 are in demand from one second nitride semiconductor single crystal layer 5 It can be cut out accordingly, and there is no waste of crystals. In this case, cutting the plurality of nitride semiconductor single crystal substrates 6 in parallel from one second nitride semiconductor single crystal layer 5 is the least wasteful method, but the angle cut for each substrate as necessary. It is also possible to change. For example, after a nitride semiconductor single crystal substrate 6 used as a seed crystal from the second nitride semiconductor single crystal layer 5 is cut out at the c-plane, the remaining portion is sliced with an off angle. It is also possible.

  For example, the cut out nitride semiconductor single crystal substrate 6 is chamfered on the outer peripheral portion and mirror-polished on the front and back surfaces, and finally finished into a GaN substrate having a diameter of 50.8 mm and a thickness of 400 μm.

  Before the nitride semiconductor single crystal substrate 6 is cut out from the second nitride semiconductor single crystal layer 5, an orientation flat (OF) or an index flat (IF) is formed on the outer periphery of the second nitride semiconductor single crystal layer 5. A flat surface portion may be formed. Further, when the nitride semiconductor single crystal substrate 6 is cut out from the second nitride semiconductor single crystal layer 5, the surface to be cut may be a surface other than the c plane such as an m plane, a plane, or r plane.

[Second Embodiment]
In the second embodiment, a third nitride semiconductor single crystal layer is homoepitaxially grown on the nitride semiconductor single crystal substrate 6 or the nitride semiconductor single crystal substrate 7 obtained in the first embodiment. A nitride semiconductor single crystal substrate is cut out from the three nitride semiconductor single crystal layers.

  5A to 5C are vertical sectional views schematically showing a manufacturing process of the nitride semiconductor single crystal substrate according to the second embodiment. In the example shown in FIGS. 5A to 5C, a nitride semiconductor single crystal substrate 6 having a flat upper surface is used as a seed crystal for epitaxial growth.

  First, as shown in FIG. 5A, the nitride semiconductor single crystal substrate 6 obtained in the first embodiment is prepared. Next, as shown in FIG. 5B, the third nitride semiconductor single crystal layer 11 is thickly epitaxially grown on the nitride semiconductor single crystal substrate 6. Next, as shown in FIG. 5C, the nitride semiconductor single crystal substrate 12 is cut out from the third nitride semiconductor single crystal layer 11. Hereinafter, details of each of these steps will be described.

  First, as shown in FIG. 5A, the nitride semiconductor single crystal substrate 6 obtained in the first embodiment is prepared as a seed crystal. The nitride semiconductor single crystal substrate 6 has a feature that variation in crystal orientation distribution in the substrate surface is very small compared to a nitride semiconductor single crystal substrate obtained by conventional heteroepitaxial growth. For this reason, when the nitride semiconductor single crystal substrate 6 is used as a seed crystal and the nitride semiconductor single crystal layer is homoepitaxially grown thereon, the strain due to the crystal orientation distribution of the seed crystal as in the conventional case becomes a grown crystal layer. Therefore, a good quality nitride semiconductor single crystal can be obtained.

  The nitride semiconductor single crystal substrate 6 may be a substrate cut out from any position of the second nitride semiconductor single crystal layer 5, but from a position closer to the upper surface of the second nitride semiconductor single crystal layer 5. A cut-out substrate is preferable because it has a small variation in crystal orientation and a low dislocation density.

  The surface of the nitride semiconductor single crystal substrate 6 is preferably subjected to mirror polishing and etching for removing processing strain in advance.

  Next, as shown in FIG. 5B, the third nitride semiconductor single crystal layer 11 is thickly epitaxially grown on the nitride semiconductor single crystal substrate 6. For the growth of the third nitride semiconductor single crystal layer 11, the technique used for the growth of the second nitride semiconductor single crystal layer 5 in the first embodiment can be applied.

  The third nitride semiconductor single crystal layer 11 grows on the flat nitride semiconductor single crystal substrate 6 without unevenness, and therefore covers the groove on the seed crystal surface like the second nitride semiconductor single crystal layer 5. Therefore, there is no need for lateral growth conditions, and the degree of freedom in setting crystal growth conditions is high. However, since there is no mechanism for releasing the strain to the base side when strain is generated in the third nitride semiconductor single crystal layer 11, the nitride semiconductor single crystal substrate 6 and the third crystal substrate 6 are connected to suppress the generation of strain. The impurity concentrations of the nitride semiconductor single crystal layer 11 are preferably matched.

  Next, as shown in FIG. 5C, the nitride semiconductor single crystal substrate 12 is cut out from the third nitride semiconductor single crystal layer 11. For the cutting of the nitride semiconductor single crystal substrate 12 and the subsequent processing, the technique used for the cutting of the nitride semiconductor single crystal substrate 6 and the subsequent processing in the first embodiment can be applied.

  The nitride semiconductor single crystal substrate 6 as a seed crystal remaining after cutting the nitride semiconductor single crystal substrate 11 is subjected to mirror polishing on the surface, and then subjected to etching to remove processing strain, thereby It can be used repeatedly as a crystal, and can also be used as a nitride semiconductor single crystal substrate.

  Further, the nitride semiconductor single crystal substrate 12 cut out from the third nitride semiconductor single crystal layer 11 can be newly used as a seed crystal for nitride semiconductor single crystal growth. In this way, a high-quality nitride semiconductor single crystal substrate with few crystal defects can be obtained by repeating the generational change of the seed crystal.

  However, as described in the first embodiment, if the processing for removing the outer peripheral portion of the nitride semiconductor single crystal layer is performed before the substrate is cut out, the diameter of the seed crystal becomes smaller each time the generation is repeated. The problem arises. Therefore, by removing the outer peripheral portion from the side opposite to the growth surface of the nitride semiconductor single crystal layer, the outer peripheral portion is not removed only in the portion where the seed crystal substrate is cut out, so that the as-grown growth interface where the crystal diameter does not change. Can be cut out each time as a seed crystal.

  A plurality of nitride semiconductor single crystal substrates 12 can be cut out from the third nitride semiconductor single crystal layer 11 by the same method as the cutting of the nitride semiconductor single crystal substrate 6 in the first embodiment. Further, when the nitride semiconductor single crystal substrate 12 is cut out from the third nitride semiconductor single crystal layer 11, the cut surface can be intentionally inclined from the plane perpendicular to the crystal growth orientation.

  Before the nitride semiconductor single crystal substrate 12 is cut out from the third nitride semiconductor single crystal layer 11, an orientation flat (OF) or an index flat (IF) is formed on the outer periphery of the third nitride semiconductor single crystal layer 11. A flat surface portion may be formed. Further, when the nitride semiconductor single crystal substrate 12 is cut out from the third nitride semiconductor single crystal layer 11, the surface to be cut may be a surface other than the c plane such as an m plane, a plane, or r plane.

  6A to 6C are vertical sectional views schematically showing the manufacturing process of the nitride semiconductor single crystal substrate according to the second embodiment. In the example shown in FIGS. 6A to 6C, a nitride semiconductor single crystal substrate 7 having an uneven surface is used as a seed crystal for epitaxial growth.

  When the nitride semiconductor single crystal substrate 7 cut out from the outermost surface of the second nitride semiconductor single crystal layer 5 according to the first embodiment is used, the surface is polished as shown in FIGS. Can be used in an as-grown state.

  The growth surface of as-grown often exhibits a form reflecting the temperature distribution of the crystal growth apparatus and the characteristics of the raw material gas flow, and the processing strain accompanying polishing or the like is not accumulated. For this reason, when the third nitride semiconductor single crystal layer 11 is grown in the same furnace as that used for the growth of the second nitride semiconductor single crystal layer 5, the second nitride semiconductor single crystal layer 11 is grown. By using the nitride semiconductor single crystal substrate 7 having the as-grown growth surface of the crystal layer 5 as a seed crystal, the growth of the third nitride semiconductor single crystal layer 11 can be started in a more natural form. In addition, since the growth surface of as-grown is a part that usually has to be removed during substrate processing, if this can be reused, the utilization efficiency of the raw material is improved.

  First, as shown in FIG. 6A, the nitride semiconductor single crystal substrate 7 obtained in the first embodiment is prepared. Next, as shown in FIG. 6B, the third nitride semiconductor single crystal layer 13 is thickly epitaxially grown on the nitride semiconductor single crystal substrate 7. Next, as illustrated in FIG. 6C, the nitride semiconductor single crystal substrate 14 is cut out from the third nitride semiconductor single crystal layer 13.

  When the nitride semiconductor single crystal substrate 7 is used in an as-grown state having irregularities, the nitride semiconductor single crystal substrate 15 cut out from the outermost surface of the second nitride semiconductor single crystal layer 13 has irregularities. It is also possible to use this nitride semiconductor single crystal substrate 15 as a seed crystal for epitaxial growth.

(Effect of embodiment)
According to the first embodiment, the strain generated in the second nitride semiconductor single crystal layer 5 grown on the heterogeneous substrate 1 is effectively released, and the growing second nitride semiconductor is obtained. Deformation (warpage generation) of the single crystal layer 5 can be suppressed. As a result, the nitride semiconductor single crystal substrate 6 with little variation in crystal orientation can be manufactured. Since a device formed on the nitride semiconductor single crystal substrate 6 with little variation in crystal orientation has little variation in characteristics, the use of the nitride semiconductor single crystal substrate 6 can improve the manufacturing yield of the device.

  Further, by reducing the residual stress in the second nitride semiconductor single crystal layer 5 grown on the heterogeneous substrate 1, cracks in processing steps such as cutting and polishing of the second nitride semiconductor single crystal layer 5 are reduced. Generation and cracking can be prevented. Further, if the residual stress in the second nitride semiconductor single crystal layer 5 is reduced, the planarization process of the surface in the polishing process is facilitated, the processing process can be simplified, and the processing yield can be improved. . Furthermore, even in the device manufacturing process using the nitride semiconductor single crystal substrate 6 cut out from the second nitride semiconductor single crystal layer 5, the occurrence of cracks due to the state of the substrate can be significantly suppressed.

  The above effect becomes larger when manufacturing a large-diameter substrate which is likely to cause variations in crystal orientation and cracks, and the yield can be greatly improved. For example, the first embodiment is more effective when the diameter of the nitride semiconductor single crystal substrates 6 and 7 is 75 mm or more, and more effective when the diameter is 150 mm or more.

  In addition, according to the second embodiment, using the nitride semiconductor single crystal substrates 6 and 7 obtained in the first embodiment as seed crystals, a higher quality nitride semiconductor single crystal substrate 12, 14 can be formed. Higher quality devices can be formed on the nitride semiconductor single crystal substrates 12 and 14.

  In addition, the nitride semiconductor single crystal substrates 6 and 7 have defects such as dislocations in the substrate surface as compared with a substrate formed by a growth method using a mask, which is represented by a conventional ELO (Epitaxial Lateral Overgrowth) method. It also has the feature that there is little variation in density and electrical characteristics. The average value of the dislocation density tends to be higher than that of the low dislocation density region of the conventional substrate. This is also a new nitride semiconductor using the obtained nitride semiconductor single crystal substrates 6 and 7 as seed crystals. It can be reduced by forming a single crystal substrate and repeating generational changes.

  In addition, according to the first embodiment, the second nitride semiconductor single crystal layer 5 doped with impurities at a high concentration can be directly grown on the undoped template 10, so that the second nitride can be grown. The material yield for forming the semiconductor single crystal layer 5 can be improved. In addition, variation in impurity concentration between the second nitride semiconductor single crystal layers 5 formed on different templates 10 can be suppressed to a low level.

  In addition, since the first and second embodiments can be implemented using an apparatus used for conventional substrate manufacturing, the cost burden for the obtained effect is very small. In particular, by using the nitride semiconductor single crystal substrate 7 having an as-grown growth surface as a seed crystal for the next crystal growth, waste of material can be suppressed, and at the same time, a third nitride semiconductor single crystal layer having high crystallinity 13 can be homoepitaxially grown.

  The results of manufacturing and evaluating a nitride semiconductor single crystal substrate based on the above embodiment will be described below.

Example 1
A single crystal sapphire c-plane substrate having a diameter of 65 mm and a thickness of 400 μm is used as the heterogeneous substrate 1, and an undoped GaN layer is grown as a first nitride semiconductor single crystal layer 2 on the template by MOCVD. 10 was obtained. TMG (trimethylgallium) and NH ₃ were used as raw materials for the undoped GaN layer.

  The growth pressure is normal pressure. First, the surface of the heterogeneous substrate 1 is thermally cleaned at 1200 ° C. for 10 minutes in a hydrogen gas atmosphere to clean the surface, and then the substrate temperature is lowered to 600 ° C. to form an undoped GaN layer. A low temperature buffer layer was grown to 20 nm, and then the substrate temperature was raised to 1050 ° C. to grow 2 μm of the first nitride semiconductor single crystal layer 2 made of an undoped GaN layer. As the carrier gas, a mixed gas of hydrogen and nitrogen was used. The crystal growth rate was about 4 μm / h. When the template 10 is taken out of the furnace after crystal growth and the surface of the undoped GaN layer as the first nitride semiconductor single crystal layer 2 is observed with an optical microscope, a flat continuous film without pits is obtained. It could be confirmed.

  Next, grooves 3 were formed on the surface of the obtained template 10 using a commercially available Nd: YLF laser processing machine having a wavelength of 532 nm, a rated output of 12 W, and a pulse width of 200 nanoseconds. The pattern of the grooves 3 was as shown in FIG. 2A. The plurality of linear grooves constituting the groove 3 had a width of 40 μm, a depth of 60 μm, and a parallel groove pitch (distance between the centers of adjacent grooves) of 1 mm.

  Next, one-to-one hydrochloric acid and hydrogen peroxide solution are applied to the template 10 for the purpose of removing GaN and sapphire powdery processing waste adhering to the inside or the periphery of the groove 3 during the groove processing by the laser processing machine. Bubbling washing was performed in the liquid mixed in the above. Then, it was washed well with running pure water, ultrasonically washed in methyl alcohol, and then dried.

Next, a Si-doped GaN crystal having a thickness of 5 mm to be the second nitride semiconductor single crystal layer 5 was homoepitaxially grown on the template 10 in which the grooves 3 were formed by the HVPE method. In the HVPE growth, the metal Ga heated to 800 ° C. was heated to 1060 ° C. using GaCl and NH ₃ produced by contacting HCl gas as raw materials and SiH ₂ Cl ₂ gas diluted with hydrogen as a dopant gas. This was supplied onto the template 10 to grow a Si-doped GaN crystal. The furnace pressure during growth was normal pressure, the carrier gas composition was 50% nitrogen and 50% hydrogen, and the V / III ratio of the source gas was 4. The growing crystal was rotated at 5 rpm, and the growth rate of the GaN crystal was 250 to 300 μm / h. The target carrier concentration of the grown crystal is 1 × 10 ¹⁸ cm ⁻³ .

  When the GaN crystal was grown in this way and taken out from the furnace after cooling, a GaN crystal having a central thickness of 5.0 mm was obtained. A periodic concavo-convex structure corresponding to the pattern of the groove 3 formed in the template 10 was observed on the upper surface of the GaN crystal, and the height difference of the concavo-convex was about 100 μm. The morphology of the crystal surface has a shape reflecting the crystal orientation of the GaN single crystal grown in the c-axis direction, which confirms that the single crystal film has been grown. Further, the appearance of the crystal did not show any cracks or abnormal growth, and no ungrown regions or pits were observed. Further, when the sapphire substrate was observed from the back surface side, fine cracks having substantially the same pitch as the grooves 3 formed on the front surface were observed, but these cracks did not progress to the GaN crystal side. These cracks in the sapphire substrate are presumed to have occurred due to the difference in coefficient of linear expansion between the sapphire substrate and the GaN crystal during crystal cooling.

  Next, the GaN substrate as the nitride semiconductor single crystal substrate 6 was cut out from the 5.0 mm-thick GaN crystal as the second nitride semiconductor single crystal layer 5 thus grown on the template 10. First, prior to cutting the GaN crystal, the outer peripheral portion of the GaN crystal was ground and removed using a cup-type diamond electrodeposition grindstone having an inner diameter of 52 mm. Next, the GaN crystal having an outer diameter of 52 mm is attached to a pedestal for slicing, and is cut perpendicularly to the crystal growth direction using a multi-wire saw, and GaN as a nitride semiconductor single crystal substrate 6 having a thickness of 500 μm is obtained. Acquired the substrate. In the step of removing the outer peripheral portion of the GaN crystal and the cutting step, no crack was generated in the GaN crystal, and six GaN substrates were obtained.

  When the sapphire substrate remaining after obtaining the GaN substrate was divided and the cross section was observed with a microscope, it was observed that the groove 3 was filled with GaN polycrystalline grains, but the upper part of the groove 3 was the second nitride semiconductor. The GaN single crystal, which is the single crystal layer 5, protrudes from both sides of the groove 3 and is closed and bonded, and no deterioration of the GaN single crystal due to the polycrystalline grains in the groove 3 was observed.

  The obtained GaN substrate was subjected to OF and IF processing on the outer periphery using a beveling apparatus, and chamfered to a diameter of 50.8 mm. Further, lapping and polishing were performed on the front and back surfaces of the GaN substrate, and finally, a mirror surface substrate having a thickness of 400 μm was finished. In this polishing process, there were no defects such as cracks in the GaN substrate during processing.

  When the angle formed by the c-axis and the substrate surface at the center of the mirror-finished GaN substrate was examined using an X-ray diffraction method, it was 0.00 °. Furthermore, when the same measurement was performed at a total of 8 points in ± 5 mm increments from the center on the diameter of the GaN substrate, and the variation of the measurement results at the total of 9 points was examined, the variation was very small, the maximum value and the minimum value. The difference in values was 0.05 °.

Moreover, when the dislocation density of the GaN substrate cut out from the outermost surface side of the GaN crystal was evaluated by the dark spot density observed by cathodoluminescence, the measurement was performed at 9 points in the plane, which was 6 × 10 ^{7 to} 9 × 10 ⁷ cm ^−. It was confirmed that it was in the range of ² .

(Comparative Example 1)
When a Si-doped GaN crystal was grown by HVPE without forming the groove 3 on the template 10 created under the same conditions as in Example 1, a crack was generated when the thickness of the GaN crystal reached 20 μm or more. A thick GaN crystal capable of cutting the substrate could not be obtained.

(Comparative Example 2)
Grooves 3 having the same shape as in Example 1 were formed on template 10 created under the same conditions as in Example 1 using a commercially available laser processing machine having a wavelength of 532 nm, a rated output of 10 W, and a pulse width of 15 picoseconds. Next, the template 10 was washed and dried under the same conditions as in Example 1, and then a 5 mm thick Si-doped GaN crystal was homoepitaxially grown on the template 10 by the HVPE method. This GaN crystal could be grown without generating cracks.

  The obtained GaN crystal was subjected to outer periphery removal, cutting, and polishing under the same conditions as in Example 1. In these steps, cracks were not generated in the GaN crystal, and six GaN substrates could be obtained.

  When the angle formed by the c-axis and the substrate surface at the center of the obtained GaN substrate was examined using an X-ray diffraction method, it was 0.00 °. Further, on the diameter of the GaN substrate, the same measurement was performed at a total of 8 points in increments of ± 5 mm from the center, and when the variation of the measurement results at the total of 9 points was examined, the variation was larger than that of Example 1, The difference between the maximum value and the minimum value was 0.18 °.

  This variation in crystal orientation in the plane of the GaN substrate is caused by the fact that the groove 3 is formed by using a laser having a short pulse width, so that the HAZ 4 having a sufficient depth is not formed on the inner surface of the groove 3, and the distortion in the GaN crystal Is thought to be due to not being fully released.

(Comparative Example 3)
A commercially available single crystal sapphire c-plane substrate having a diameter of 65 mm and a thickness of 400 μm is used as the heterogeneous substrate 1, and an undoped GaN layer as the first nitride semiconductor single crystal layer 2 is grown on the groove 3. Formed. The processing conditions and shape of the groove 3 were the same as in Example 1.

Next, an undoped GaN layer was grown as the first nitride semiconductor single crystal layer 2 on the sapphire substrate in which the groove 3 was formed by MOCVD to obtain a template. TMG (trimethylgallium) and NH ₃ were used as raw materials for the undoped GaN layer.

  The growth pressure is normal pressure. First, the surface of the heterogeneous substrate 1 is thermally cleaned at 1200 ° C. for 10 minutes in a hydrogen gas atmosphere to clean the surface, and then the substrate temperature is lowered to 600 ° C. to form an undoped GaN layer. A low temperature buffer layer was grown to 20 nm, and then the substrate temperature was raised to 1050 ° C. to grow 2 μm of the first nitride semiconductor single crystal layer 2 made of an undoped GaN layer. As the carrier gas, a mixed gas of hydrogen and nitrogen was used.

  Next, a Si-doped GaN crystal having a thickness of 5 mm as the second nitride semiconductor single crystal layer 5 was homoepitaxially grown on the template by HVPE. The growth conditions of the HVPE method were the same as in Example 1.

  When the GaN crystal is grown in this way and taken out from the furnace after cooling, a polycrystalline region that seems to have a starting point in the pattern of the groove 3 formed in the template 10 is observed over a wide range on the surface of the crystal. It was confirmed that no film was obtained. This is because, since the undoped GaN layer as the first nitride semiconductor single crystal layer 2 is formed after the formation of the groove 3, the growth selectivity is low on the inner wall of the groove 3 when the undoped GaN layer is formed (sapphire substrate). GaN polycrystal is deposited via a low temperature buffer layer (which is easy to grow on), and the polycrystal is grown from the groove 3 when the GaN crystal as the second nitride semiconductor single crystal layer 5 is grown. Conceivable. In Example 1, since the groove 3 was formed after the formation of the undoped GaN layer as the nitride semiconductor single crystal layer 2, the groove 3 was grown when the GaN crystal as the second nitride semiconductor single crystal layer 5 was grown. It is considered that a single crystal film was obtained because there was no polycrystal inside and it was selectively grown from the undoped GaN layer.

(Comparative Example 4)
A GaN single crystal substrate was fabricated using a crystal growth method (VAS method) described in Japanese Patent No. 3631724, which is a conventional technique. First, a commercially available single crystal sapphire c-plane substrate having a diameter of 65 mm and a thickness of 400 μm was used, and an undoped GaN layer having a thickness of 500 nm was grown thereon by MOCVD to obtain a template. TMG and NH ₃ were used as raw materials for the undoped GaN layer.

Next, a metal Ti film having a thickness of 30 nm is vacuum-deposited on the template, and this is put in a MOCVD furnace, and in a mixed gas stream of 80% hydrogen and 20% NH ₃ at 1050 ° C. for 30 minutes. Heat treatment was performed for a minute. As a result, the metal Ti film was deformed into a mesh shape and simultaneously nitrided to form a mesh-like TiN film. Innumerable voids were formed in the GaN layer under the TiN film.

  The base substrate thus prepared was put in an HVPE furnace, and a Si-doped GaN crystal was grown on the same under the same conditions as in Example 1 to a thickness of 2 mm. Although the growth experiment was performed several times, cracks occurred when the thickness of the GaN crystal exceeded 3 mm. Therefore, the growth was stopped when the thickness of the GaN crystal reached 2 mm with a margin. After the growth, the GaN crystal cooled and taken out from the HVPE furnace was naturally peeled from the template according to the characteristics of the VAS method. The obtained self-standing substrate-like GaN crystal was confirmed to be warped downward in the convex direction by visual observation.

  The GaN crystal thus obtained was penetrated to a diameter of 52 mm in the same manner as in Example 1 and cut with a wire saw to obtain two 500 μm GaN substrates. Of the two GaN substrates, the substrate obtained from the upper surface side of the GaN crystal was cracked at the time of cutting. The GaN substrate obtained from the lower surface side of the GaN crystal remaining without breaking was subjected to the same external shape processing and polishing processing as in Example 1, and finally a GaN mirror substrate having a diameter of 50.8 mm and a thickness of 400 μm was obtained.

When the variation in angle between the c-axis of the obtained GaN mirror substrate and the substrate surface was examined by the same method as in Example 1, the difference between the maximum value and the minimum value was 0.23 °. Moreover, when the dislocation density of the substrate cut out from the outermost surface side of the GaN crystal was evaluated by the dark spot density observed by cathodoluminescence, it was 1 × 10 ^{6 to} 6 × 10 ⁶ cm ^{−2 by} measuring 9 points in the plane. It was confirmed that it was in the range of.

(Example 2)
As the heterogeneous substrate 1, a commercially available single crystal sapphire c-plane substrate having a diameter of 120 mm and a thickness of 700 μm is used, and an undoped AlGaN layer is grown thereon as the first nitride semiconductor single crystal layer 2 by the HVPE method. 10 was obtained. GaCl, AlCl ₃ , and NH ₃ were used as raw materials for the undoped AlGaN layer. GaCl and AlCl ₃ were produced in the furnace by bringing metal Ga and metal Al placed in the HVPE furnace into contact with HCl at high temperature.

  The growth pressure is normal pressure. First, an AlN buffer layer is grown to 20 nm on a sapphire substrate at 1050 ° C., then an undoped GaN layer is grown to 2 μm at the same substrate temperature, and the first nitride semiconductor single crystal layer 2 is further grown. An AlGaN layer of 3 μm was grown. As the carrier gas, a mixed gas of hydrogen and nitrogen was used. At this time, the supply amount ratio of HCl to be brought into contact with metal Ga and HCl to be brought into contact with metal Al was set to 2: 1. The crystal growth rate was about 40 μm / h. After the crystal growth, the template 10 is taken out from the furnace, and the surface of the undoped AlGaN layer as the first nitride semiconductor single crystal layer 2 is observed with an optical microscope. As a result, a flat continuous film without pits is obtained. It could be confirmed. Further, as a result of evaluation by X-ray diffraction measurement, it was confirmed that the Al composition of the undoped AlGaN layer was 20%.

  Next, grooves 3 were formed on the surface of the obtained template 10 using the same laser processing machine as used in Example 1. The pattern of the grooves 3 was as shown in FIG. 2B. A plurality of linear grooves constituting the groove 3 had a width of 50 μm, a depth of 120 μm, and a parallel groove pitch (distance between the centers of adjacent grooves) of 2 mm.

  Next, in order to remove AlGaN and sapphire powdery processing waste adhering to the inside and the periphery of the groove 3 during the groove processing by the laser processing machine, a liquid in which hydrochloric acid and hydrogen peroxide solution are mixed with the template 10 Bubbling washing was performed inside. Then, it was washed well with running pure water, ultrasonically washed in methyl alcohol, and then dried.

  Next, an undoped AlGaN crystal having a thickness of 5 mm to be the second nitride semiconductor single crystal layer 5 was homoepitaxially grown on the template 10 by the HVPE method. In HVPE growth, a SiC-coated graphite plate having a hole with an inner diameter of 115 mm was set on the surface of the template 10 as a mask, and a region where no AlGaN crystal grew on the outermost periphery of the template 10 was intentionally provided. Further, the composition of the carrier gas during crystal growth is 90% nitrogen and 10% hydrogen, the supply amount ratio of HCl in contact with metal Ga and HCl in contact with metal Al is 2: 1, and the V / III ratio of the source gas Was 4. The growing crystal was rotated at 5 rpm, and the growth rate of the AlGaN crystal was 250 to 300 μm / h.

  In this way, an undoped AlGaN crystal as the second nitride semiconductor single crystal layer 5 was grown and taken out of the furnace after cooling. No adhesion of the AlGaN crystal was found in the region under the mask of the template 10, An AlGaN crystal having an outer diameter of 115 mm and a central thickness of 5.2 mm could be grown on a 120 mm diameter region. There was no appearance of cracks or abnormal growth in the appearance of the AlGaN crystal. Further, no deep pits were observed on the upper surface of the AlGaN crystal, and fine irregularities corresponding to the pattern of the grooves 3 formed in the template 10 were observed, but the surface was almost flat. When the sapphire substrate was observed from the back side, fine cracks were observed as in the case of the sapphire substrate of Example 1, but these cracks did not progress to the AlGaN crystal side.

  Next, an AlGaN substrate as the nitride semiconductor single crystal substrate 6 was cut out from the AlGaN crystal as the second nitride semiconductor single crystal layer 5 obtained. First, prior to cutting the AlGaN crystal, the outer peripheral portion of the AlGaN crystal was ground and removed using a cup-type diamond electrodeposition grindstone having an inner diameter of 105 mm. Next, an AlGaN crystal having an outer diameter of 105 mm is pasted on a pedestal for slicing, and using a multi-wire saw, the surface is inclined by 0.5 ° from the direction perpendicular to the crystal growth direction to the m-axis side of the crystal. By cutting, an AlGaN substrate having a thickness of 900 μm was obtained. In the outer peripheral removal step and the cutting step of the AlGaN crystal, no crack was generated in the AlGaN crystal, and thus four AlGaN substrates were obtained.

  The obtained AlGaN substrate was subjected to OF and IF processing on the outer periphery using a beveling apparatus, and chamfered to a diameter of 100 mm. Further, lapping and polishing were performed on the front and back surfaces of the AlGaN substrate, and finally, a mirror substrate having a thickness of 800 μm was finished. In this polishing process, there were no defects such as cracks in the AlGaN substrate during processing.

  When the angle formed by the c-axis and the substrate surface at the center of the mirror-finished AlGaN substrate was examined using an X-ray diffraction method, it was 0.50 °. Furthermore, on the diameter of the AlGaN substrate, the same measurement was performed for a total of 8 points in increments of ± 10 mm from the center along the direction in which the c-axis is tilted. The difference between the value and the minimum value was 0.08 °.

(Example 3)
As the heterogeneous substrate 1, a commercially available single crystal sapphire c-plane substrate having a diameter of 165 mm and a thickness of 900 μm is used, and an undoped GaN layer is grown thereon as the first nitride semiconductor single crystal layer 2 by MOCVD. 10 was obtained. TMG and NH ₃ were used as raw materials for the undoped GaN layer.

  The growth pressure is normal pressure. First, the surface of the heterogeneous substrate 1 is cleaned in a hydrogen gas atmosphere at 1200 ° C. for 10 minutes to clean the surface, and then the substrate temperature is lowered to 600 ° C. to form an undoped GaN layer. The low temperature buffer layer was grown to 20 nm, and then the substrate temperature was raised to 1050 ° C. to grow the undoped GaN layer as the first nitride semiconductor single crystal layer 2 by 1.5 μm. As the carrier gas, a mixed gas of hydrogen and nitrogen was used. The crystal growth rate was about 3 μm / h. When the template 10 is taken out of the furnace after crystal growth and the surface of the undoped GaN layer as the first nitride semiconductor single crystal layer 2 is observed with an optical microscope, a flat continuous film without pits is obtained. It could be confirmed.

  Next, grooves 3 were formed on the surface of the obtained template 10 using the same laser processing machine as used in Example 1. The pattern of the grooves 3 was as shown in FIG. 4A. The width of the plurality of linear grooves constituting the groove 3 was 60 μm, the depth was 100 μm, and the pitch of parallel grooves (distance between the centers of adjacent grooves) was 2.4 mm.

  Next, one-to-one hydrochloric acid and hydrogen peroxide solution are applied to the template 10 for the purpose of removing GaN and sapphire powdery processing waste adhering to the inside or the periphery of the groove 3 during the groove processing by the laser processing machine. Bubbling washing was performed in the liquid mixed in the above. Then, it was washed well with running pure water, ultrasonically washed in methyl alcohol, and then dried.

Next, a Ge-doped GaN crystal having a thickness of 3 mm, which becomes the second nitride semiconductor single crystal layer 5, was homoepitaxially grown on the template 10 in which the groove 3 was formed by the HVPE method. In the HVPE growth, GaCl and NH ₃ produced by bringing HCl gas into contact with metal Ga heated to 800 ° C. are used as raw materials, and GeCl ₄ is used as a dopant raw material, which is supplied onto the template 10 heated to 1050 ° C. A Ge-doped GaN crystal was grown. The furnace pressure during growth was normal pressure, the carrier gas composition was 95% nitrogen and 5% hydrogen, and the V / III ratio of the source gas was 2. The growing crystal was rotated at 5 rpm, and the growth rate of the GaN crystal was 200 to 250 μm / h. The target carrier concentration of the grown crystal is 5 × 10 ¹⁸ cm ⁻³ .

  When the GaN crystal was grown in this way and taken out from the furnace after cooling, a GaN crystal having a central thickness of 3.0 mm was obtained. On the upper surface of the GaN crystal, a morphology corresponding to the pattern of the groove 3 formed in the template 10 was observed. That is, a hexagonal plane appears in the region grown on the hexagonal region defined by the grooves 3 of the template 10, and a triangular plane appears in the region grown on the triangular region. Then, faceted grown slopes appeared around these planes, and grooves existed at the boundaries between the regions. In addition, since the area of the hexagonal region partitioned by the groove 3 of the template 10 is larger than the area of the triangular region partitioned by the groove 3, the above hexagonal plane grown on the hexagonal region. The region grew to a higher level than the region of the triangular plane grown on the triangular region, and the height difference was about 300 μm. Such irregularities existed only in the vicinity of the surface of the GaN crystal having a thickness of 3.0 mm, and a single-crystal continuous film was grown under the irregularities, and the appearance of the crystals was cracked or There was no appearance of abnormal growth. No pits were observed on the upper surface of the GaN crystal.

  Next, a GaN substrate as the nitride semiconductor single crystal substrate 6 was cut out from the GaN crystal as the second nitride semiconductor single crystal layer 5 grown on the template 10. First, prior to cutting the GaN crystal, the outer peripheral portion of the second nitride semiconductor single crystal layer 5 was ground and removed using a cup-type diamond electrodeposition grindstone having an inner diameter of 155 mm. Next, the surface side of the GaN crystal having an outer diameter of 155 mm was affixed to a slicing pedestal and cut perpendicularly to the crystal growth direction using an electric discharge machine to obtain a GaN crystal having a thickness of 1200 μm. In the outer periphery removing step and the cutting step of the GaN crystal, no crack was generated in the GaN crystal, and two GaN substrates were obtained.

  The obtained GaN substrate was notched on the outer periphery and chamfered and shaped using a beveling device to a diameter of 150 mm. Further, lapping and polishing were performed on the front and back surfaces of the GaN substrate, and finally, a mirror substrate having a thickness of 500 μm was finished. In this polishing process, there were no defects such as cracks in the GaN substrate during processing.

  When the angle formed by the c-axis and the substrate surface at the center of the mirror-finished GaN substrate was examined using an X-ray diffraction method, it was 0.02 °. Furthermore, the same measurement was performed for a total of 6 points in increments of ± 20 mm from the center along the direction of inclination of the c-axis on the diameter of the substrate. The difference between the value and the minimum value was 0.11 °.

Example 4
One obtained from the outermost surface side of the second nitride semiconductor single crystal layer 5 is selected from the GaN substrates as the nitride semiconductor single crystal substrate 6 obtained in Example 1, and this is used as a seed crystal. Made growth. The GaN substrate used as the seed crystal was subjected to mirror polishing on the front and back surfaces, and then subjected to etching by RIE (Reactive Ion Etching) on the surface side (Ga surface side) for the purpose of removing processing damage. Thereafter, the GaN substrate is put into an HVPE furnace, and the Si film having a thickness of 5 mm as the third nitride semiconductor single crystal layer 11 is grown under the same conditions as the growth conditions of the second nitride semiconductor single crystal layer 5 of Example 1. Doped GaN crystals were homoepitaxially grown. There was no appearance of cracks or abnormal growth in the appearance of the obtained GaN crystal, and no pits were found on the upper surface.

  Next, a GaN substrate as the nitride semiconductor single crystal substrate 12 was cut out from the GaN crystal. When cutting the GaN crystal, the outer peripheral portion of the GaN crystal was not removed, and a multi-wire saw was used to cut perpendicularly to the crystal growth direction to obtain a GaN substrate having a thickness of 500 μm. In the GaN crystal cutting step, no crack was generated in the GaN crystal, and six GaN substrates were obtained.

  The obtained GaN substrate was subjected to OF and IF processing on the outer periphery using a beveling apparatus, and chamfered to a diameter of 49 mm. In addition, lapping and polishing were performed on the front and back surfaces of the GaN substrate to finally finish a mirror substrate having a thickness of 400 μm. In this polishing process, there were no defects such as cracks in the GaN substrate during processing.

  When the angle formed by the c-axis and the substrate surface at the center of the mirror-finished GaN substrate was examined using an X-ray diffraction method, it was 0.01 °. Further, on the diameter of the GaN substrate, the same measurement was performed for a total of 8 points in increments of ± 5 mm from the center, and when the variation of the measurement results of the 9 points was examined, the variation was even smaller than in Example 1. The difference between the maximum value and the minimum value was 0.03 °.

Moreover, when the dislocation density of the GaN substrate cut out from the outermost surface side of the GaN crystal was evaluated by the dark spot density observed by cathodoluminescence, it was 4 × 10 ^{6 to} 7 × 10 ⁶ cm ^{− by} measuring 9 points in the plane. It was confirmed that it was in the range of ² . Accordingly, it was confirmed that the dislocation density can be gradually lowered by reusing the nitride semiconductor single crystal substrate obtained in the above embodiment as a seed crystal.

(Comparative Example 5)
One of the GaN substrates obtained in Comparative Example 4 was selected without cracks, and this was used as a seed crystal in an HVPE furnace to grow the second nitride semiconductor single crystal layer 5 of Example 1. A Si-doped GaN crystal having a thickness of 3 mm was homoepitaxially grown under the same conditions. The growth experiment was carried out several times. However, if the thickness of the GaN crystal exceeds 4 mm, cracks will occur in the GaN crystal with good reproducibility when slicing the grown GaN crystal. The thickness was set to 3 mm with a margin. There was no appearance of cracks or abnormal growth in the appearance of the GaN crystal thus obtained, and no pits were found on the upper surface.

  Next, a GaN substrate was cut out from the GaN crystal. When cutting the GaN crystal, the outer peripheral portion of the GaN crystal was not removed, and a multi-wire saw was used to cut perpendicularly to the crystal growth direction to obtain a GaN substrate having a thickness of 500 μm. Since the thickness of the grown crystal was kept thin, no crack was generated in the crystal in the cutting process, and three GaN substrates were obtained.

  The obtained GaN substrate was subjected to OF and IF processing on the outer periphery using a beveling apparatus, and chamfered to a diameter of 49 mm. Further, lapping and polishing were performed on the front and back surfaces of the GaN substrate, and finally, a mirror surface substrate having a thickness of 400 μm was finished. In this polishing process, there were no defects such as cracks in the GaN substrate during processing.

  When the angle formed by the c-axis and the substrate surface at the center of the mirror-finished GaN substrate was examined using an X-ray diffraction method, it was 0.04 °. Furthermore, the same measurement was performed on a total of 8 points in ± 5mm increments along the direction in which the c-axis is tilted on the diameter of the substrate. The difference between the maximum value and the minimum value was 0.15 °.

  From this result, when a GaN substrate with large crystal orientation variation is used as a seed crystal, distortion occurs in the grown crystal and cracks easily occur, and even in a substrate obtained without cracking, in-plane crystal It was confirmed that the orientation variation remained large as usual.

(Example 5)
Under the same conditions as in Example 1, a template was prepared by growing a Si-doped GaN crystal having a thickness of 5 mm as the second nitride semiconductor single crystal layer 5 on the template 10.

  Next, a conductive wax is applied to the GaN crystal side and attached to a fixing jig, and a crystal is engraved from the sapphire substrate side as the heterogeneous substrate 1 by using a cup-type diamond electrodeposition grindstone having an inner diameter of 52 mm. Removal work was performed. Here, the outer peripheral portion removal operation was completed while leaving a 1 mm thick region on the surface side of the GaN crystal.

  The GaN crystal whose outer peripheral portion was ground and removed was cut perpendicularly to the crystal growth direction using a wire electric discharge machine with the GaN crystal side attached to a fixing jig. When cutting the GaN crystal, a GaN substrate as a nitride semiconductor single crystal substrate 6 having a thickness of 500 μm is obtained from the region from which the outer peripheral portion has been removed, and the region on the outermost surface side from which the outer peripheral portion has not been removed has a thickness. It was left as a substrate of about 1 mm. No cracks are generated in the GaN crystal in the outer peripheral portion removing step and the cutting step, and five GaN substrates having a thickness of 500 μm and a single 1 mm thick nitride semiconductor single crystal substrate having an as-grown surface. A GaN substrate as 7 was obtained.

  The GaN substrate cut out to 500 μm was subjected to OF and IF processing on the outer periphery using a beveling device, and chamfered to a diameter of 50.8 mm. In addition, lapping and polishing were performed on the front and back surfaces of the GaN substrate to finally finish a mirror substrate having a thickness of 400 μm. In this polishing process, there were no defects such as cracks in the GaN substrate during processing.

(Example 6)
The back surface (cut surface) side of the GaN substrate as the nitride semiconductor single crystal substrate 7 having an as-grown surface obtained in Example 5 is flattened by grinding so that the thickness of the central portion of the substrate becomes 800 μm. did. This GaN substrate is cleaned, put in an HVPE furnace as a seed crystal substrate, and the third nitride semiconductor single crystal layer 13 is grown under the same conditions as the growth conditions of the second nitride semiconductor single crystal layer 5 of Example 1. A 5 mm thick Si-doped GaN crystal was homoepitaxially grown.

  There was no appearance of cracks or abnormal growth in the appearance of the obtained GaN crystal, and no pits were found on the upper surface. Further, there is no problem in the subsequent cutting process, and the characteristics of the obtained GaN substrate as the nitride semiconductor single crystal substrate 14 are the GaN substrate as the nitride semiconductor single crystal substrate 12 fabricated in Example 5. Was equal to or better than. This confirmed that a GaN substrate having an as-grown surface can be used as a seed crystal.

  Although the embodiments and examples of the present invention have been described above, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the invention.

  For example, instead of the second nitride semiconductor single crystal layer 5 or the third nitride semiconductor single crystal layer 11 of the above embodiment, a multilayer structure of a nitride semiconductor single crystal for forming a device is epitaxially grown. May be.

  The embodiments and examples described above do not limit the invention according to the claims. It should be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

  Provided is a method for manufacturing a nitride semiconductor single crystal substrate that can alleviate strain in a nitride semiconductor single crystal to be grown and suppress the generation of cracks, thereby efficiently obtaining a high-quality nitride semiconductor single crystal substrate. .

1 heterogeneous substrate 2 first nitride semiconductor single crystal layer 3 groove 4 HAZ (heat affected zone)
5 Second nitride semiconductor single crystal layer 6, 7 Nitride semiconductor single crystal substrate 10 Template 11, 13 Third nitride semiconductor single crystal layer 12, 14, 15 Nitride semiconductor single crystal substrate

Claims (16)

Preparing a template in which a first nitride semiconductor single crystal layer is grown on a heterogeneous substrate;
A plurality of linear grooves are formed in the template by grooving the first nitride semiconductor single crystal layer and the dissimilar substrate by laser light irradiation, and the plurality of lines are formed simultaneously with the grooving of the dissimilar substrate. Forming HAZ, which is a region formed by heat by irradiation of the laser beam, on the inner surface of the groove,
Growing a second nitride semiconductor single crystal layer on the template in which the plurality of linear grooves are formed;
Cutting a nitride semiconductor single crystal substrate from the second nitride semiconductor single crystal layer;
A method for manufacturing a nitride semiconductor single crystal substrate including: The wavelength of the laser light is 300 nm or more,
The method for manufacturing a nitride semiconductor single crystal substrate according to claim 1. The laser beam is a CW laser beam or a pulse laser beam having a pulse width of 1 nanosecond or more.
A method for producing a nitride semiconductor single crystal substrate according to claim 1 or 2. The groove processing of the first nitride semiconductor single crystal layer, the groove processing of the dissimilar substrate, and the formation of the HAZ are continuously performed by one irradiation of the laser light, or are performed by a plurality of irradiations. Done
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-3. The first nitride semiconductor single crystal layer is an Al _x Ga _(1-x) N (0 ≦ X ≦ 1) crystal grown by MOCVD or HVPE.
The manufacturing method of the nitride semiconductor single-crystal substrate of any one of Claims 1-4. The second nitride semiconductor single crystal layer is an Al _Y Ga _(1-Y) N (0 ≦ Y ≦ 1) crystal grown by an HVPE method.
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-5. The plurality of linear grooves have the same width on the lower surface of the first nitride semiconductor single crystal layer and the width on the upper surface of the heterogeneous substrate,
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-6. The heterogeneous substrate is a sapphire substrate;
A depth of the plurality of linear grooves in the heterogeneous substrate is 200 μm or less;
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-7. The width of the plurality of linear grooves on the upper surface of the first nitride semiconductor single crystal layer is 10 μm or more and 100 μm or less.
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-8. The upper surface of the first nitride semiconductor single crystal layer is a c-plane of the nitride semiconductor single crystal constituting the first nitride semiconductor single crystal layer or a plane inclined within 5 ° from the c-plane,
The plurality of linear grooves are linear grooves parallel to the a-plane or m-plane of the nitride semiconductor single crystal;
The plurality of linear groove patterns have a rotational symmetry of 3 or 6 times with respect to the central axis of the template.
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-9. The plurality of linear grooves include linear grooves arranged at equal intervals parallel to each other, and the pitch of the linear grooves arranged at equal intervals parallel to each other is 100 μm or more and 10 mm or less.
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-10. The first nitride semiconductor single crystal layer is partitioned into a plurality of equal areas by the plurality of linear grooves.
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-11. Growing the second nitride semiconductor single crystal layer so as to be a continuous film covering the upper portions of the plurality of linear grooves;
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-12. The second nitride semiconductor single crystal layer is grown in a state where irregularities corresponding to the shape of the region of the first nitride semiconductor single crystal layer partitioned by the plurality of linear grooves are left at the growth interface. Let
The method for manufacturing a nitride semiconductor single crystal substrate according to claim 1. Growing the first nitride semiconductor single crystal layer substantially undoped and growing the second nitride semiconductor single crystal layer by doping impurities;
The manufacturing method of the nitride semiconductor single crystal substrate of any one of Claims 1-14. Doping and growing the impurity having a concentration of 5 × 10 ¹⁷ cm ⁻³ or more,
The method for manufacturing a nitride semiconductor single crystal substrate according to claim 15.

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