JP6334259B2 - Manufacturing method of free-standing substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a free-standing substrate made of a group III nitride semiconductor.

  As a first method for manufacturing a group III nitride semiconductor substrate such as a GaN substrate, a first group III nitride semiconductor layer is formed on a heterogeneous substrate such as a sapphire substrate, and then the heterogeneous substrate is removed to form a first method. By obtaining a base substrate composed of one group III nitride semiconductor layer and further forming a second group III nitride semiconductor layer on the base substrate, the base substrate and the group III nitride semiconductor layer (second group) There is a method for obtaining a group III nitride semiconductor substrate comprising a group III nitride semiconductor layer). In addition, the method of obtaining a base substrate is described in patent document 1, 2, etc., for example.

  Further, as a second method of manufacturing a group III nitride semiconductor substrate such as a GaN substrate, a different substrate such as a sapphire substrate is used as a base substrate, and a group III nitride semiconductor layer is formed on the base substrate, thereby forming a base layer. There is also a method for obtaining a group III nitride semiconductor substrate comprising a substrate and a group III nitride semiconductor layer.

JP 2003-55097 A JP 2008-120670 A

  According to the study of the present inventor, the group III nitride semiconductor layer formed on the base substrate often warps in a concave shape. The concave shape here means that in the group III nitride semiconductor layer formed on the base substrate, the surface opposite to the base substrate side is concave (the surface on the base substrate side is convex). To do. In particular, when a group III nitride semiconductor substrate is manufactured by the first method, the base substrate obtained by peeling from the dissimilar substrate is often warped in a concave shape, and thus formed on the base substrate. The group III nitride semiconductor layer (second group III nitride semiconductor layer) warps significantly in a concave shape.

  In addition, the inventor has confirmed that the group III nitride semiconductor layer warped in a concave shape is not only concave in shape but also has a c-axis inward in terms of physical properties. .

  Further, according to the study of the present inventors, even when a group III nitride semiconductor layer is formed on a flat base substrate, that is, a base substrate that does not warp in appearance, the group III nitride semiconductor layer The shape may be concave or the c-axis of the group III nitride semiconductor layer may be inward.

  This invention is made | formed in view of said subject, and provides the manufacturing method of the self-supporting board | substrate which suppressed concave curvature.

According to the present invention,
A preparation step of preparing a base substrate made of a nitride semiconductor and having a convex portion on the first surface;
A pretreatment step of etching the first surface with a chemical;
A growth step of epitaxially growing a nitride semiconductor layer on the first surface after the pretreatment step;
I have a,
The preparation step includes
Forming a carbon layer in which carbide MC (aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide) is dispersed as a first layer on a substrate;
A second step of forming a layer of carbide MC (aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide) as a second layer on the first layer;
A third step of nitriding the second layer;
A fourth step of forming a group III nitride semiconductor layer on the nitrided second layer;
After the fourth step, the group III nitride semiconductor layer is formed from a laminate including the base material, the first layer, the nitrided second layer, and the group III nitride semiconductor layer. Heating at a temperature higher than the heating at the time, a fifth step of separating the base material and the group III nitride semiconductor layer;
Have
A self-supporting substrate manufacturing method for obtaining the base substrate from the group III nitride semiconductor layer separated in the fifth step is provided.

  According to the present invention, it is possible to suppress the concave warpage of the self-standing substrate.

It is an example of the cross-sectional schematic diagram of the growth surface of a base substrate. It is a flowchart which shows an example of the flow of a process of the manufacturing method of the self-supporting substrate of this embodiment. It is a schematic diagram which shows an example of an HVPE apparatus. It is a figure for demonstrating the definition of the curvature of this embodiment. It is a figure for demonstrating the definition of the curvature of this embodiment. It is a figure for demonstrating the definition of the curvature of this embodiment. It is a figure for demonstrating the definition of the curvature of this embodiment. It is a figure for demonstrating the definition of the curvature of this embodiment. It is a figure for demonstrating the definition of the curvature of this embodiment. It is a flowchart which shows an example of the flow of a process of the manufacturing method of the self-supporting substrate of this embodiment. It is process drawing which shows an example of the manufacturing method of a base substrate. It is process drawing which shows an example of the manufacturing method of a base substrate. It is a figure for demonstrating an example of 1 process of the manufacturing method of a base substrate. It is a figure for demonstrating an example of 1 process of the manufacturing method of a base substrate. It is a figure for demonstrating an example of 1 process of the manufacturing method of a base substrate. It is a figure for demonstrating an example of 1 process of the manufacturing method of a base substrate. It is a figure for demonstrating an example of 1 process of the manufacturing method of a base substrate. 4 is a SEM image of a growth surface of a base substrate of Comparative Example 1. 2 is an SEM image of a growth surface of a base substrate in Example 1. 4 is a SEM image of a growth surface of a base substrate in Example 2. It is a figure for demonstrating the angle difference (alpha). It is a figure for demonstrating the effect of this embodiment. It is a figure for demonstrating the state which makes a substrate holder hold | maintain a base substrate.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

<< First Embodiment >>
First, an outline of the present embodiment will be described. In this embodiment, a self-supporting substrate is obtained by epitaxially growing a group III nitride semiconductor on a growth surface of a base substrate made of a group III nitride semiconductor.

  By the way, the present inventors have confirmed that a plurality of protrusions are formed on the growth surface 111 of the base substrate 10 as shown in FIG. Then, as shown in the following examples, when a group III nitride semiconductor is epitaxially grown on the growth surface 111 in a state where such a convex portion exists, the layer of the group III nitride semiconductor warps in a concave shape ( It was confirmed that the surface on the side opposite to the surface in contact with the base substrate 10 warps in a concave shape), and that the freestanding substrate is likely to warp.

  Therefore, in the present embodiment, a pretreatment (flattening treatment) for reducing the height of the convex portion is performed on the growth surface 111 of the base substrate 10, and then the group III nitride is formed on the growth surface 111 of the base substrate 10. The semiconductor is epitaxially grown. Thereby, the problem of the curvature of the free-standing substrate is reduced. In the second embodiment, an example of a manufacturing method of the base substrate 10 in which a plurality of convex portions may be formed on the growth surface 111 of the base substrate 10 will be described. FIG. 1 is a schematic diagram, and the ratio of the thickness of the base substrate 10 and the height of the mountain shown in the figure has no particular meaning in the present embodiment.

  First, with reference to FIG. 4 to FIG. 10, a detailed definition of “warpage” of a substrate (including a self-supporting substrate and a base substrate) in the present embodiment will be described. Each of FIGS. 4 to 9 is a schematic cross-sectional view, and the direction of the crystal axis is indicated by a dashed arrow. The inclination of the crystal axis can be measured by, for example, an X-ray diffraction method. Note that the warpage of the substrate is caused by the inclination of the crystal axis at the stage of crystal growth or the force by which the crystal axis is inclined.

  In the present embodiment, the “warp” of the substrate includes not only a warp manifested in the outer shape of the substrate but also a warp on the crystal structure (a state where the crystal axis is inclined and not parallel). The warp manifested in the outer shape of the substrate can be quantified by, for example, the radius of curvature of the growth surface of the substrate. Further, the warp on the crystal structure can be quantified by, for example, the curvature radius of a predetermined surface with the crystal axis as a normal line. In either case, the smaller the radius of curvature, the greater the warp. According to the method for manufacturing a self-supporting substrate of this embodiment, not only the warp manifested in the outer shape of the self-supporting substrate but also the warp on the crystal structure of the self-supporting substrate can be improved (the radius of curvature is increased).

  Hereinafter, a state in which the substrate is warped is specifically exemplified in the definition of the present embodiment. FIG. 4 shows a free-standing substrate 720 obtained by crystal growth of a group III nitride semiconductor layer 711 on a base substrate 710.

  In the case of the example shown in the figure, no warpage is apparent in the outer shape of the self-supporting substrate 720. However, the crystal axis of the group III nitride semiconductor layer 711 (the crystal axis extending in the thickness direction of the group III nitride semiconductor layer 711) is inclined. Specifically, the direction of the crystal axis at the peripheral portion of the exposed surface 771 of the group III nitride semiconductor layer 711 is inclined toward the center of the exposed surface 771 of the group III nitride semiconductor layer 711. As a result, the interval between the crystal axes becomes narrower from one surface 772 (surface in contact with the base substrate 710) of the group III nitride semiconductor layer 711 toward the exposed surface 771. In the present embodiment, such a state is also defined as a state in which the self-standing substrate 720 is warped in a concave shape.

  In the state of FIG. 4, warpage is further manifested in the outer shape of the free-standing substrate 720, and the group III nitride semiconductor layer 711 and the base substrate 710 are warped in a concave shape (the exposed surface 771 is warped in a concave shape in the figure). The state in which the surface 772 is warped in a convex shape is also defined as the state in which the self-supporting substrate 720 is warped in a concave shape.

  FIG. 5 shows a group III nitride semiconductor obtained by removing the base substrate 710 by polishing or the like from a laminate obtained by crystal growth of a group III nitride semiconductor layer 711 on the base substrate 710. A free-standing substrate 720 consisting of a plurality of layers 711 is shown.

  In the case of the example shown in the figure, warpage is obvious in the outer shape of the self-supporting substrate 720. That is, the exposed surface 771 warps in a concave shape, and the surface 772 warps in a convex shape. Further, the crystal axis of the group III nitride semiconductor layer 711 (the crystal axis extending in the thickness direction of the group III nitride semiconductor layer 11) is inclined. Specifically, the direction of the crystal axis at the peripheral portion of the exposed surface 771 of the group III nitride semiconductor layer 711 is inclined toward the center of the exposed surface 771 of the group III nitride semiconductor layer 711. As a result, the interval between the crystal axes becomes narrower from one surface 772 (the surface in contact with the base substrate 710) of the group III nitride semiconductor layer 711 toward the exposed surface 771. In the present embodiment, such a state is also defined as a state in which the self-standing substrate 720 is warped in a concave shape.

  FIG. 6 shows a thick film obtained by removing the base substrate 710 by polishing or the like from a laminate obtained by crystal growth of a thick group III nitride semiconductor layer 711 on the base substrate 710. 3A shows a layer 711 of the group III nitride semiconductor.

  In the state shown in the figure, no warpage is apparent in the outer shape of the layer 711 of the group III nitride semiconductor. However, the crystal axis of the group III nitride semiconductor layer 711 (the crystal axis extending in the thickness direction of the group III nitride semiconductor layer 711) is inclined. Specifically, the direction of the crystal axis at the peripheral portion of the exposed surface 771 of the group III nitride semiconductor layer 711 is inclined toward the center of the exposed surface 771 of the group III nitride semiconductor layer 711. As a result, the interval between the crystal axes becomes narrower from one surface 772 (the surface in contact with the base substrate 710) of the group III nitride semiconductor layer 711 toward the exposed surface 771.

  FIG. 7 shows a free-standing substrate 720 made of a group III nitride semiconductor layer cut out from the group III nitride semiconductor layer 711 shown in FIG. 6 by a broken line extending in the horizontal direction in FIG.

  In the case of the example shown in the figure, no warpage is apparent in the outer shape of the self-supporting substrate 720. However, the crystal axis (the crystal axis extending in the thickness direction of the free-standing substrate 720) is inclined. Specifically, the direction of the crystal axis at the peripheral edge of the exposed surface 721 of the free-standing substrate 720 is inclined toward the center of the exposed surface 721 of the free-standing substrate 720. As a result, the interval between the crystal axes becomes narrower from the one surface 722 of the freestanding substrate 720 toward the exposed surface 721. In the present embodiment, such a state is also defined as a state in which the self-standing substrate 720 is warped in a concave shape.

  FIG. 8 shows another example of a free-standing substrate 720 made of a group III nitride semiconductor layer cut out from a group III nitride semiconductor layer 711 shown in FIG. 6 by a broken line extending in the horizontal direction in FIG. Show.

  In the case of the example shown in the figure, warpage is obvious in the outer shape of the self-supporting substrate 720. That is, the exposed surface 721 is warped in a concave shape, and the surface 722 is warped in a convex shape. Further, the crystal axis (the crystal axis extending in the thickness direction of the freestanding substrate 720) is inclined. Specifically, the direction of the crystal axis at the peripheral edge of the exposed surface 721 of the free-standing substrate 720 is inclined toward the center of the exposed surface 721 of the free-standing substrate 720. As a result, the interval between the crystal axes becomes narrower from the one surface 722 of the freestanding substrate 720 toward the exposed surface 721. In the present embodiment, such a state is also defined as a state in which the self-standing substrate 720 is warped in a concave shape.

  FIG. 9 shows a self-supporting substrate 720 obtained by crystal growth of a group III nitride semiconductor layer 711 on a base substrate 710. In the case of the example shown in the figure, a warp is evident in the outer shape of the group III nitride semiconductor layer 711 in the free-standing substrate 720. That is, the exposed surface 771 is warped in a concave shape. Further, the crystal axis of the group III nitride semiconductor layer 711 (the crystal axis extending in the thickness direction of the group III nitride semiconductor layer 711) is inclined. Specifically, the direction of the crystal axis at the peripheral portion of the exposed surface 771 of the group III nitride semiconductor layer 711 is inclined toward the center of the exposed surface 771 of the group III nitride semiconductor layer 711. As a result, the interval between the crystal axes becomes narrower from one surface 772 (surface in contact with the base substrate 710) of the group III nitride semiconductor layer 711 toward the exposed surface 771. In the present embodiment, such a state is also defined as a state in which the self-standing substrate 720 is warped in a concave shape.

  Next, the configuration of the present embodiment will be described in detail. FIG. 2 is a flowchart showing a process flow of the method for manufacturing a self-supporting substrate according to the present embodiment. As shown in the figure, the method for manufacturing a self-supporting substrate of this embodiment includes a pretreatment step S10 and a growth step S20.

  In the pretreatment step S10, the growth surface (first surface) 111 (see FIG. 1) of the base substrate 10 made of a group III nitride semiconductor is etched with a chemical solution. As described above, there may be a plurality of convex portions on the growth surface 111 of the base substrate 10. By etching in this step, the height of the convex portion is reduced and the growth surface 111 of the base substrate 10 is planarized.

  In addition, how much the said process is performed is a design matter. If the process is sufficiently performed and the growth surface 111 is completely planarized, the problem of warpage of the free-standing substrate can be sufficiently reduced. However, if the above process is performed to some extent and the height of the convex portion is reduced as much as possible to flatten it, the problem of warpage can be alleviated to some extent. For example, it may be flattened to such an extent that a convex portion is gently present after the processing step.

  The chemical solution is, for example, phosphoric acid heated to 100 ° C. to 300 ° C., preferably 150 ° C. to 250 ° C., or 100 ° C. to 250 ° C., preferably 130 ° C. to 250 ° C., more preferably 180 ° C. A mixed solution of phosphoric acid and sulfuric acid heated to 250 ° C. or lower can be selected. The state in which the chemical solution is in contact with the growth surface 111 of the base substrate 10 can be continued for 45 minutes or longer and 2 hours or shorter, preferably 50 minutes or longer and 1 hour 30 minutes or shorter. The duration time can be adjusted according to the temperature of the chemical solution (within the above range, the higher the temperature of the chemical solution, the shorter the duration time).

  The inventor has confirmed that the growth surface 111 can be flattened as the temperature of the chemical solution increases and the treatment time increases. However, when the temperature of the chemical solution becomes too high, handling becomes difficult, and the time required to heat the chemical solution to that temperature increases. On the other hand, if the processing time is lengthened, the work efficiency becomes worse. By setting the temperature of the chemical solution within the above range and the processing time within the above range, these problems can be reduced and the conditions can be optimized. The height of the convex portion can be reduced (the growth surface 111 can be flattened) to such an extent that the problem of substrate warpage can be sufficiently improved. The processing method is not particularly limited, and for example, the base substrate 10 may be immersed in the chemical solution.

  In the growth step S20, a group III nitride semiconductor layer is formed by epitaxially growing a group III nitride semiconductor on the growth surface (first surface) 111 of the base substrate 10 after the pretreatment step S10. The means for epitaxial growth is not particularly limited, and known techniques such as HVPE (hydride vapor phase epitaxy) and MOVPE (organometallic vapor phase epitaxy) can be used.

  Here, an example of the process will be described by taking as an example a case where the group III nitride semiconductor layer is epitaxially grown by the HVPE method. For example, using a hydride vapor phase epitaxy (HVPE) apparatus 100 as shown in FIG. 3, a group III nitride semiconductor layer is epitaxially grown on the substrate 41 (underlying substrate 10).

  The illustrated HVPE apparatus 100 includes a reaction tube 121 and a substrate holder 123 provided in the reaction tube 121. The HVPE apparatus 100 includes a group III source gas supply unit 139 that supplies a group III source gas into the reaction tube 121 and a nitrogen source gas supply unit 137 that supplies a nitrogen source gas into the reaction tube 121. Further, the HVPE apparatus 100 includes a gas exhaust pipe 135 and heaters 129 and 130.

  The substrate holder 123 is rotatably provided on the downstream side of the reaction tube 121 by a rotation shaft 132. The gas discharge pipe 135 is provided on the downstream side of the substrate holder 123 in the reaction pipe 121.

  The group III source gas supply unit 139 includes a gas supply pipe 126, a source boat 128, a group III (Ga) source 127, and a layer below the shielding plate 136 among the reaction tubes 121. The nitrogen source gas supply unit 137 includes a gas supply pipe 124 and a layer on the shielding plate 136 in the reaction pipe 121. The group III source gas supply unit 139 generates a halide of group III atoms (for example, GaCl) and supplies it to the surface of the substrate 41 held by the substrate holder 123.

  The supply port of the gas supply pipe 126 is arranged on the upstream side in the group III source gas supply unit 139. For this reason, the supplied hydrogen halide gas (for example, HCl gas) comes into contact with the group III source material 127 in the source boat 128 in the group III source gas supply unit 139. Thereby, the halogen-containing gas supplied from the gas supply pipe 126 comes into contact with the surface of the group III raw material 127 in the source boat 128 or the volatilized group III molecule, and the group III molecule is halogenated to form a group III halide. A Group III source gas is produced. A heater 129 is disposed around the group III source gas supply unit 139, and the inside of the group III source gas supply unit 139 is maintained at a temperature of about 800 to 900 ° C., for example.

  The upstream side of the reaction tube 121 is divided into two layers by a shielding plate 136. Ammonia supplied from the gas supply pipe 124 passes through the nitrogen source gas supply unit 137 located on the upper side of the shielding plate 136 in the drawing, and decomposition is accelerated by heat. A heater 129 is disposed around the nitrogen source gas supply unit 137, and the nitrogen source gas supply unit 137 is maintained at a temperature of about 800 to 900 ° C., for example.

  A substrate holder 123 is disposed in the growth region 122 located on the downstream side of the reaction tube 121, and a group III nitride semiconductor such as GaN is grown in the growth region 122. A heater 130 is disposed around the growth region 122, and the inside of the growth region 122 is maintained at a temperature of about 1000 ° C. to 1050 ° C., for example.

  By the pretreatment step S10 and the growth step S20 described above, a stacked body in which the group 11 nitride semiconductor layer 11 is crystal-grown on the base substrate 10 is obtained. The thickness of the group III nitride semiconductor layer 11 may be, for example, 1 mm or more and 10 mm or less. In the present embodiment, this laminate may be a self-supporting substrate. Further, the group 11 nitride semiconductor layer 11 obtained by removing the base substrate 10 from the laminated body by polishing or the like may be used as a self-supporting substrate. Furthermore, a group III nitride semiconductor layer cut out by slicing the group III nitride semiconductor layer 11 may be used as a free-standing substrate.

  According to the method for manufacturing a self-supporting substrate of the present embodiment described above, the height of the protrusions is increased by the pretreatment step S10 even when there are a plurality of protrusions on the growth surface 111 of the prepared base substrate 10. After reducing the size and flattening the growth surface 111, a group III nitride semiconductor can be epitaxially grown on the growth surface 111. For this reason, the presence of the convex portion on the growth surface 111 of the base substrate 10 causes the group III nitride semiconductor layer epitaxially grown on the growth surface 111 to warp in a concave shape (on the side opposite to the surface in contact with the base substrate 10). The inconvenience can be reduced.

<< Second Embodiment >>
In the present embodiment, an example of a method for manufacturing the base substrate 10 in which a plurality of convex portions may be formed on the growth surface 111 of the base substrate 10 will be described. In addition, the manufacturing method of the base substrate 10 is not limited to a thing completely corresponding to this embodiment, What changed the one part process of the manufacturing method of this embodiment, and another manufacturing method may be sufficient. .

  FIG. 10 is a flowchart showing a process flow of the method for manufacturing a self-supporting substrate according to the present embodiment. As shown in the figure, the method for manufacturing a self-supporting substrate of the present embodiment includes a preparation step S1, a pretreatment step S10, and a growth step S20. The pretreatment step S10 and the growth step S20 are the same as those in the first embodiment.

  In the preparation step S1, the base substrate 10 having a convex portion on the growth surface 111 (first surface) is prepared before the pretreatment step S10. Note that the convex portion may be a resultant product that unintentionally appears on the growth surface 111 (first surface) as a result of manufacturing the base substrate 10 by a predetermined method.

The preparation step S1
(1) A first step of forming a carbon layer in which carbide MC (aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide) is dispersed on the substrate as a first layer;
(2) a second step of forming a layer of carbide MC (aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide) as a second layer on the first layer;
(3) a third step of nitriding the second layer;
(4) a fourth step of forming a group III nitride semiconductor layer on the nitrided second layer;
(5) After the fourth step, heating in forming the group III nitride semiconductor layer is performed on the stacked body including the base material, the first layer, the nitrided second layer, and the group III nitride semiconductor layer. A fifth step of heating at a higher temperature,
Have

  Hereinafter, each process will be described by taking as an example the case where the carbide MC is titanium carbide. Even when the carbide MC is other than titanium carbide, a self-supporting substrate can be manufactured in the same process.

<First step>
In the first step, a carbon layer in which titanium carbide is dispersed is formed on the substrate as the first layer. First, a base material is prepared. The substrate can be a different substrate from the group III nitride semiconductor formed thereon. The thickness of the substrate is 250 μm or more and 1500 μm or less, and preferably 400 μm or more and 600 μm or less. If the substrate is too thick, after the fourth step described below, cracks and cracks may occur due to the stress caused by the difference in thermal expansion coefficient between the substrate and the group III nitride semiconductor layer 36. . Such inconvenience can be reduced by setting the thickness of the base material to 400 μm or more and 600 μm or less. In this embodiment, for example, a sapphire (Al ₂ O ₃ ) substrate 30 having a thickness of 550 μm and a diameter of 3 inches is prepared as a base material. Next, a first layer 31 is formed on the sapphire substrate 30 (FIG. 11A).

  The first layer 31 is a carbon layer in which titanium carbide is dispersed. For example, the first layer 31 satisfies the atomic ratio C / Ti of Ti and C in the first layer 31 of 1.5 or more, preferably 3.0 or more, more preferably 3.5 or more. A carbon layer in which TiC is dispersed can be obtained. Such a first layer 31 functions as a bonding suppression film that suppresses bonding of the metal (titanium) in the titanium carbide layer (second layer) and the sapphire substrate 30.

  Such a first layer 31 can be formed by sputtering, for example. The film forming conditions of the first layer 31 can be as follows, for example.

Deposition method: Reactive sputtering Deposition temperature: 25-1000 ° C
Deposition time: 3-60 seconds Pressure: 0.2-0.5 Pa
Applied power: 100-300W
Sputtering gas: Ar gas Sputtering gas flow rate: 5-30 sccm
Reactive gas: Hydrocarbon (CH ₄ )
Reactive gas flow rate: 10.0sccm
Target: Ti
Film thickness: 0.1 nm to 0.4 nm

  When reactive sputtering is performed under a condition where the amount of introduced hydrocarbon is larger, more TiC can be dispersed in the first layer 31. In the case of the above film forming conditions, the amount of titanium carbide dispersed in the first layer 31 can be adjusted by appropriately adjusting the supply amount of methane gas. That is, by appropriately adjusting the supply amount of methane gas, the atomic ratio C / Ti of Ti and C in the first layer 31 can be adjusted to a desired value.

  Further, when reactive sputtering is performed under a condition in which the applied power is increased, more TiC can be dispersed in the first layer 31. That is, the amount of titanium carbide dispersed in the first layer 31 is adjusted by appropriately adjusting the applied power, and the atomic ratio C / Ti of Ti and C in the first layer 31 is set to a desired value. Can be adjusted.

  The first layer 31 is a film containing C as a main component, a carbon film as a base material, and a film containing TiC in the base material. For example, carbon is in a sea state (matrix), and TiC is dispersed in this matrix.

  The film formation temperature of the first layer 31 may be 25 ° C. or higher. In particular, the film formation temperature of the first layer 31 is preferably equal to or higher than the film formation temperature of the second layer 32. Specifically, it is preferable to form a film at 600 ° C. or higher, particularly 800 ° C. or higher.

  By doing so, the first layer 31 becomes a dense film, a uniform and highly crystalline layer is formed, and the high quality of the group III nitride semiconductor layer formed in the fourth step is realized. To do.

  In addition, when the film formation temperature of the first layer 31 is increased, a part of TiC dispersed in the first layer 31 also undergoes crystal orientation, thereby improving the crystal orientation of the second layer 32. It becomes.

  The thickness of the first layer 31 is preferably 0.1 nm or more and 0.4 nm or less. Especially, it is preferable that they are 0.2 nm or more and 0.3 nm. The thickness of the first layer 31 is a value calculated from film forming conditions (film forming time, etc.) by a sputtering apparatus.

  Further, the first layer 31 does not need to completely cover a region (in this embodiment, the entire surface of the sapphire substrate 30) in which the second layer 32 described later is formed in the sapphire substrate 30. The first layer 31 may completely cover the sapphire substrate 30 as a base material, or the island-like or dot-like film is distributed uniformly or mottled on the sapphire substrate 30 and locally. The aspect which the sapphire substrate 30 exposes may be sufficient.

  When the first layer 31 completely covers the sapphire substrate 30, the group III nitride semiconductor layer can be easily separated from the sapphire substrate 30. On the other hand, when the first layer 31 is an island-like or dot-like film, the crystal information of the sapphire substrate 30 is easily transmitted to the group III nitride semiconductor layer, and the group III nitride having high crystallinity. A semiconductor layer can be obtained.

<Second step>
In the second step, a titanium carbide layer is formed as the second layer 32 on the first layer 31 (FIG. 11B). The film forming conditions for the second layer 32 are, for example, as follows.

Film forming method: reactive sputtering film forming temperature: 500 to 1000 ° C.
Deposition time: 4.5 to 114 minutes Pressure: 0.2 to 0.5 Pa
Applied power: 100-300W
Sputtering gas: Ar gas Sputtering gas flow rate: 5-50 sccm
Reactive gas: CH ₄
Reactive gas flow rate: 10.0sccm
Target: Ti
Film thickness: 20 nm to 500 nm

  The titanium carbide layer which is the second layer 32 is a layer mainly composed of TiC, and C atoms are combined with Ti atoms to constitute TiC.

  The film formation temperature is preferably 500 ° C. or more and 1000 ° C. or less, preferably 600 ° C. or more, and preferably 900 ° C. or less. If the temperature is 600 ° C. or higher, a TiC layer having high crystallinity can be formed. If the temperature is higher than 900 ° C., uneven temperature distribution in the substrate surface is likely to occur, and thus the crystallinity of the TiC layer is likely to be distributed.

  In addition, the thickness of the titanium carbide layer is preferably 20 nm or more from the viewpoint of improving crystallinity and 500 nm or less from the viewpoint of production efficiency. In particular, from the viewpoint of improving crystallinity, 70 nm or more, and further 120 nm. The above is preferable. Moreover, it is preferable to set it as 150 nm or less from a viewpoint of obtaining a highly crystalline carbide layer, without spending much time for formation of a carbide layer.

<Cap layer forming step>
A cap layer 33 may be formed on the second layer 32 after the second step and before the third step (FIG. 11C). The cap layer 33 can be a carbon layer in which titanium carbide is dispersed. The film formation conditions of the carbon layer in which titanium carbide is dispersed are as follows, for example.

Deposition method: Reactive sputtering Deposition temperature: 25-1000 ° C
Deposition time: 2.5-25 minutes Pressure: 0.3-0.5 Pa
Applied power: 100-300W
Reactive gas: CH ₄
Reactive gas flow rate: 10.0sccm
Target: Ti
Film thickness: 5 nm to 50 nm

  When reactive sputtering is performed under a condition where the amount of introduced hydrocarbon is larger, more TiC can be dispersed in the cap layer 33. In the case of the above conditions, the amount of titanium carbide dispersed in the cap layer 33 can be adjusted by appropriately adjusting the supply amount of methane gas. That is, by appropriately adjusting the supply amount of methane gas, the atomic ratio C / Ti of Ti and C in the cap layer 33 can be adjusted to a desired value.

  Further, when reactive sputtering is performed under a condition where the applied power is increased, more TiC can be dispersed in the cap layer 33. That is, by appropriately adjusting the applied power, the amount of titanium carbide dispersed in the cap layer 33 can be adjusted, and the atomic ratio C / Ti of Ti and C in the cap layer 33 can be adjusted to a desired value.

  The cap layer 33 is a film containing C as a main component, a carbon film as a base material, and TiC in the base material. For example, carbon is in a sea state (matrix), and TiC is dispersed in this matrix.

  The TiC concentration in the cap layer 33 is lower than the concentration of C alone (C excluding C existing as TiC). The TiC concentration of the cap layer 33 is lower than the TiC concentration in the second layer 32. For example, the TiC concentration in the cap layer 33 is 33 to 49%.

  The film formation temperature of the cap layer 33 may be 25 ° C. or higher. In particular, the film formation temperature of the cap layer 33 is preferably equal to or higher than the film formation temperature of the second layer 32. Specifically, it is preferable to form a film at 600 ° C. or higher, particularly 800 ° C. or higher. By doing so, the cap layer 33 becomes a dense film, and the oxidation of the second layer 32 can be effectively prevented.

  Further, the film thickness of the cap layer 33 is preferably 5 nm or more and 50 nm or less, and more preferably 10 nm or more. By setting the cap layer 33 to 10 nm or more, it is possible to effectively prevent the second layer 32 from being oxidized. Further, the cap layer 33 completely covers the entire surface of the second layer 32.

<Third step>
In the third step, the second layer (titanium carbide layer) 32 is nitrided. For example, as shown in FIG. 2A, the second layer 32 is partially nitrided in an atmosphere of 300 ° C. or higher and 1000 ° C. or lower to form a nitrided titanium carbide layer 34. The nitrided titanium carbide layer 34 has a laminated structure of a titanium carbide layer 342 mainly containing titanium carbide and a titanium nitride layer 341 mainly containing titanium nitride. The nitriding conditions for the second layer 32 are, for example, as follows.

Nitriding temperature: 300 ° C to 950 ° C
Nitriding time: 5 to 30 minutes Nitriding gas: NH ₃ gas, H ₂ gas, N ₂ gas

When the cap layer 33 is formed on the second layer 32, the second layer 32 is covered with the cap layer 33. However, in the nitriding treatment of the second layer 32, the carbon in the cap layer 33 is vaporized as CH ₄ by the nitriding gas. For this reason, a gap reaching the second layer 32 is generated in the cap layer 33. Then, the nitriding gas reaches the second layer 32 through this gap, and the second layer 32 is partially nitrided to form a nitrided titanium carbide layer 34.

  The nitriding temperature is more preferably 500 ° C. or more and 700 ° C. or less, and particularly preferably 550 ° C. or less. By setting the nitriding temperature to 500 ° C. or higher, there is an effect of increasing the nitriding rate of the second layer 32. On the other hand, by setting the nitriding temperature to 700 ° C. or lower, the nitriding rate can be suppressed, and the inconvenience of nitriding to the first layer 31 can be suppressed. When the first layer 31 is nitrided, there is a disadvantage that the bond between the first layer 31 and the sapphire substrate 30 (base material) becomes stronger than before the nitridation.

When the nitriding temperature is higher than 550 ° C., CH ₄ is decomposed and C is precipitated as shown in the formula (1), and C is mixed with TiN, so that the crystallinity of the group III nitride semiconductor layer is lowered. There is a case. In order to suppress the precipitation of C, it is effective to increase the introduction of hydrogen and the partial pressure of ammonia.

CH ₄ → C + 2H ₂ ... (1) Formula

  The nitriding time is preferably 30 minutes or less. By setting the nitriding time to about 30 minutes, the second layer 32 can be appropriately nitrided.

  Note that ammonia is preferable as a reaction gas when nitriding the second layer 32. TiN can be formed even if nitrogen is used as a reaction gas in addition to ammonia, but as shown in the formula (2), TiN and C are formed, and when C is mixed in TiN, the crystal of the group III nitride semiconductor layer is formed. May affect quality.

2TiC + N ₂ → 2TiN + 2C (2) formula

  In the case where the cap layer 33 is formed on the second layer 32, titanium carbide contained in the cap layer 33 is partially nitrided and the nitrided cap layer 343 is formed by the third step. The In addition, titanium carbide contained in the first layer 31 may be partially nitrided to become TiN. These TiNs serve to take over the crystal information of the sapphire substrate 30 (base material) during the epitaxial growth of the subsequent group III nitride semiconductor, and form a group III nitride semiconductor with good crystallinity.

<4th process>
In the fourth step, the group III nitride semiconductor layer 36 is formed immediately above the nitrided titanium carbide layer 34 (the layer obtained by nitriding the second layer 32). When a cap layer is formed immediately above the second layer 32, a group III nitride semiconductor layer 36 is formed immediately above the nitrided cap layer 343 (FIG. 12B). Here, it is assumed that a GaN semiconductor layer is epitaxially grown as the group III nitride semiconductor layer 36. The group III nitride semiconductor layer 36 is not limited to GaN, and may be, for example, AlGaN. The growth conditions of the GaN semiconductor layer (group III nitride semiconductor layer 36) can be as follows, for example.

Film forming method: HVPE (hydride vapor phase epitaxy) film forming temperature: 1000 ° C. to 1050 ° C.
Deposition time: 30 minutes to 500 minutes Film thickness: 100 μm to 1500 μm

  In addition, after forming the low-temperature growth buffer layer of the group III nitride semiconductor at a temperature lower than the film formation temperature, the group III nitride semiconductor may be epitaxially grown under the above growth conditions.

  Further, after forming the group III nitride semiconductor facet, the group III nitride semiconductor may be epitaxially grown under the above growth conditions to obtain the group III nitride semiconductor layer 36 which is a flat film. The epitaxial growth of the group III nitride semiconductor may be realized by using, for example, a hydride vapor phase epitaxy (HVPE) apparatus shown in FIG.

  In the initial stage of the step of forming group III nitride semiconductor layer 36, the exposed surface of nitrided cap layer 343 or nitrided titanium carbide layer 34 may be further nitrided with a nitrogen source gas.

  In the initial stage of forming the group III nitride semiconductor layer 36, the titanium carbide and the group III nitride semiconductor on the exposed surface of the nitrided cap layer 343 or the nitrided titanium carbide layer 34 are as follows. It is thought that it reacts to. Here, a case where the group III nitride semiconductor is GaN will be described as an example.

Al ₄ C ₃ + 4GaN → 4AlN + 4Ga + 3C (3) formula

TiC + GaN → TiN + Ga + C (4) formula

  Further, depending on the crystallinity of the nitrided cap layer 343 and the nitrided titanium carbide layer 34, the following reaction may occur. The group III nitride semiconductor is thermally decomposed into nitrogen atoms and group III atoms. Nitrogen atoms generated by the thermal decomposition are formed on the surface of the titanium carbide layer 342 through gaps (for example, crystal grain boundaries or microcracks) in the nitrided cap layer 343 and the titanium nitride layer 341, and in some cases, the titanium carbide layer 342. May reach a gap (for example, a crystal grain boundary or a microcrack) in the surface layer, and a reaction may occur in which the surface of the titanium carbide layer 342 and the carbide of the surface layer become nitrides.

  As can be understood from the above description, in the initial stage of forming the group III nitride semiconductor layer 36, the thickness of the titanium nitride layer 341 in the nitrided titanium carbide layer 34 is increased, and the titanium carbide layer 342 The thickness is reduced.

  In addition, the group III atoms precipitated by the reactions (3) and (4) above and the thermal decomposition of the group III nitride semiconductor are disposed between the group III nitride semiconductor layer 36 and the nitrided cap layer 343. Therefore, a group III element precipitation layer is formed. When the nitrided cap layer 343 does not exist, a group III element precipitation layer is formed between the group III nitride semiconductor layer 36 and the nitrided titanium carbide layer 34.

  The thickness of group III nitride semiconductor layer 36 is, for example, 600 μm or less from the viewpoint of reducing the stress generated by the difference in linear expansion coefficient between sapphire substrate 30 (base material) and group III nitride semiconductor layer 36. In particular, it is preferably 450 μm or less, and more preferably 300 μm or less. Furthermore, the thickness of the group III nitride semiconductor layer 36 is preferably 50 μm or more from the viewpoint of handleability.

<Fifth step>
In the fifth step, after the fourth step, the sapphire substrate 30 (base material), the first layer 31, the nitrided titanium carbide layer 34 (the layer obtained by nitriding the second layer 32), and the group III The stacked body including the nitride semiconductor layer 36 (which may further include the nitrided cap layer 343) is heated at a temperature higher than the heating for forming the group III nitride semiconductor layer 36.

  When the laminated body returned to room temperature is observed after the heating in the fifth step, the sapphire substrate 30 (base material) and the group III nitride semiconductor layer 36 are separated. The separation position between the group III nitride semiconductor layer 36 and the sapphire substrate 30 (base material) is the first layer 31 located between the group III nitride semiconductor layer 36 and the sapphire substrate 30 (base material) and nitrided. It occurs inside the titanium carbide layer 34. That is, by performing the fifth step, the separation position between the group III nitride semiconductor layer 36 and the sapphire substrate 30 (base material) can be controlled. Further, the variation in separation shape can be reduced by controlling the separation position.

  By the way, from such a difference in separation position, in the case of the present embodiment, the present inventors do not perform separation using stress during cooling after heating, but perform heat treatment in the fifth step. I guess that separation occurred in the middle. The mechanism of separation during such heat treatment is not clear, but is assumed to be as follows.

  In the group III element precipitation layer formed between the group III nitride semiconductor layer 36 and the nitrided cap layer 343 (or the nitrided titanium carbide layer 34), group III atoms are present. ing. Furthermore, the group III nitride constituting the group III nitride semiconductor layer 36 is decomposed by the heat treatment, and group III atoms are formed.

  Since Group III atoms have a low melting point, they become liquid during the heat treatment process. The group III atoms pass through the nitrided cap layer 343 and the titanium nitride layer 341, and reach the titanium carbide layer 342 and the first layer 31 containing titanium carbide.

  Then, it is considered that the following reaction occurs in the titanium carbide layer 342 and the first layer 31. Here, an example in which the group III nitride semiconductor is Ga will be described.

Al ₄ C ₃ + 4Ga (l) → 4Al—Ga (l) + 3C (5) formula

TiC + Ga (l) → Ti-Ga (l) + C (6)

  From the viewpoint of advancing the reaction of the formulas (5) and (6), the group III atoms of the group III nitride semiconductor layer are different from the metal atoms constituting the first layer 31 and the second layer 32. It is preferable that

  By this reaction, the crystal structures of the titanium carbide layer 342 and the first layer 31 are destroyed, and the adhesion between the titanium carbide layer 342 and the first layer 31 and the sapphire substrate 30 (base material) is deteriorated. Then, separation occurs in the titanium carbide layer 342 and the first layer 31 (FIG. 12D).

  Since the group III nitride semiconductor layer 36 and the sapphire substrate 30 (base material) are separated by such a mechanism, even if the diameters of the group III nitride semiconductor layer 36 and the sapphire substrate 30 (base material) are large, the peeled shape Therefore, a desired substrate can be obtained with good productivity. For example, the diameters of the group III nitride semiconductor layer 36 and the sapphire substrate 30 (base material) can be 10 mm or more and 200 mm or less.

  In the fifth step, for example, the laminate is heated at a temperature higher than 1050 ° C. and lower than or equal to 1150 ° C., more preferably higher than 1050 ° C. and lower than or equal to 1100 ° C., more preferably higher than 1050 ° C. and lower than or equal to 1080 ° C. To do. When the heating temperature is increased, the reactions of formulas (5) and (6) can be advanced, but dislocations are likely to occur in the group III nitride semiconductor layer 36. In the case of the present embodiment, since the first layer 31 is provided immediately above the sapphire substrate 30 (base material), the sapphire substrate 30 (base) is heated at a lower temperature than in the case where the first layer 31 is not provided. Material) and the group III nitride semiconductor layer 36 can be sufficiently separated.

  In the fifth step, the laminate is heated at the above temperature for 5 hours to 30 hours. If the heating time is long, dislocations are likely to occur in the group III nitride semiconductor layer 36, and the manufacturing time is long, resulting in poor production efficiency. In the case of the present embodiment, since the first layer 31 is provided immediately above the sapphire substrate 30 (base material), the sapphire substrate 30 (by heating for a shorter time compared to the case where the first layer 31 is not provided). The base material) and the group III nitride semiconductor layer 36 can be separated.

  Here, an example of heat treatment will be described.

<First example>
In the fifth step, the laminated body in a heated state after the group III nitride semiconductor layer 36 is formed is continuously cooled at a temperature higher than the epitaxially grown temperature without cooling to a normal temperature (room temperature). You may heat. The heating can be performed using, for example, an HVPE apparatus in which the group III nitride semiconductor layer 36 is formed.

  For example, after forming the group III nitride semiconductor layer 36 with the HVPE apparatus, the supply of the source gas and the reaction gas is stopped while the stacked body is housed in the HVPE apparatus, and the heater temperature is raised to a desired value. The laminate may be heated.

<Second example>
For example, after forming the group III nitride semiconductor layer 36 by controlling the conditions of the third step or controlling the relationship between the thickness of the sapphire substrate 30 (base material) and the group III nitride semiconductor layer 36 (fourth step). And a laminated body including a sapphire substrate 30 (base material), a first layer 31, a nitrided titanium carbide layer 34 (a layer obtained by nitriding the second layer 32), and a group III nitride semiconductor layer 36. Even if the nitrided cap layer 343 is further cooled to room temperature, it is based on the stress caused by the difference in linear expansion coefficient between the sapphire substrate 30 (base material) and the group III nitride semiconductor layer 36. Thus, the sapphire substrate 30 (base material) and the group III nitride semiconductor layer 36 can be prevented from being separated. In such a case, after the group III nitride semiconductor layer 36 is formed in the fourth step, the stacked body is once cooled to room temperature, and then the fifth step can be performed. Control of the conditions of the third step is, for example, control of the flow rate (partial pressure) of NH ₃ gas (nitriding gas). When the flow rate of the NH ₃ gas is small, the sapphire substrate 30 (base material) and the group III nitride semiconductor layer 36 are easily separated by cooling after the fourth step. On the other hand, when the flow rate of NH ₃ gas is large, the sapphire substrate 30 (base material) and the group III nitride semiconductor layer 36 are difficult to separate by cooling after the fourth step.

  Also in this example, the HVPE apparatus 3 can be used for heating the laminate. For example, the laminated body may be arranged and heated in a region surrounded by the heaters 129 and 130 shown in FIG.

  For example, a jig 55 having a recess 511 formed on the surface as shown in FIG. 13 is prepared, and the laminate D is inserted into the recess 511. And the laminated body D with such a jig | tool 55 is accommodated in an HVPE apparatus. Then, the heaters 129 and 130 are driven to heat the plurality of stacked bodies D at the same time. In this heat treatment step, the growth of the group III nitride semiconductor layer 36 is stopped. Further, a heat treatment apparatus may be prepared separately from the HVPE apparatus 100 and the laminate D may be heat-treated.

<Third example>
Also in this example, the fifth step is performed after the laminate is cooled to room temperature. For example, the laminate D is heated in a state of being immersed in a liquid of a group III element. The group III element liquid is a liquid of the same element as the group III element contained in the group III nitride semiconductor layer 36. For example, when the group III nitride semiconductor layer 36 is GaN, the group III element liquid is a Ga liquid.

  The group III element liquid may be any liquid that is liquid at the heat treatment temperature of the laminate D. For example, even if it is solid at 25 ° C., it may be liquid at the heat treatment temperature of the laminate D. When it is solid at 25 ° C., for example, a powder of a group III element may be put in containers 5 and 6 described later.

  For example, a container 5 as shown in FIGS. 14 and 15 is prepared. FIG. 14 is a cross-sectional view orthogonal to the bottom surface of the container 5. FIG. 15 is a perspective view of the container 5 and is a view showing a laminate D disposed inside.

  The container 5 includes a container main body 50 whose upper surface is open, a lid 53 for closing the opening of the container main body 50, and a pin 52. The container main body 50 can accommodate a plurality of stacked bodies D therein. Yes.

  The container 5 is made of a heat-resistant material. For example, the container body 50, the lid 53, and the pins 52 are made of graphite.

  A plurality of pins 52 are inserted into the side wall 51 of the container body 50. Among the plurality of pins 52, some of the pins 52 have different attachment positions in the height direction with respect to the side wall 51 of the container 5, and are arranged in the order of the pins 52 </ b> A to 52 </ b> D from the bottom surface side of the container 5.

  First, the pins 52 </ b> A to 52 </ b> D inserted into the side wall 51 are pulled out from the side wall 51 of the container 5 to a certain extent. However, the pins 52A to 52D are not completely pulled out. Next, a predetermined amount of Group III element liquid is placed in the container 5, and then the laminate D is placed in the container 5. The laminate D is inserted into the container 5 so that the sapphire substrate 30 (base material) is on the upper side of the container 5. The laminate D is floated in the liquid by buoyancy. Then, the pin 52A is pushed into the inside of the container 5, and the outer peripheral edge of the sapphire substrate 30 (base material) of the laminate D is pressed with the pin 52.

  Thereafter, the liquid of the group III element is again filled in the container 5, and the second laminate D is inserted into the container 5. Then, the pin 52B located higher than the pin 52A is pushed into the container 5 and the outer peripheral edge of the sapphire substrate 30 (base material) of the second laminate D is pressed by the pin 52B. Such an operation is repeated, and the outer peripheral edge of the sapphire substrate 30 (base material) of each stacked body D is pressed by the pins 52A to 52D.

  If such a container 5 is used, the several laminated body D can be immersed in the liquid L of a III group element within the container 5. FIG. In the container 5, the whole laminated body D will be immersed in the liquid L of a III group element.

  Thereafter, the lid 53 is fitted into the opening of the container 5. Then, the container 5 filled with the group L element liquid L and having the plurality of laminated bodies D immersed in the group III element liquid L is disposed in the HVPE apparatus 100. Then, the heaters 129 and 130 are driven to simultaneously heat-treat the plurality of stacked bodies D immersed in the liquid of the group III element from the outside of the container 5. Moreover, a heat treatment apparatus may be prepared separately from the HVPE apparatus 100, and the laminated body D in the container 5 may be heat-treated.

  Moreover, the container for immersing the laminated body D in the liquid of a group III element is not restricted to what is shown in FIG.13 and FIG.14, You may use the container 6 shown in FIG.

  The container 6 includes a container main body 61 whose upper surface is open, a lid 62 that closes the opening of the container main body 61, and a jig 63 for placing the laminate D in the container main body 61.

  The container 6 is made of a heat resistant material. For example, the container body 61, the lid 62, and the jig 63 are made of graphite.

  The jig 63 includes a plurality of holding portions 631 formed by separating a plurality of grooves along the longitudinal direction, and a fixing portion 632 that integrally fixes the end portions of the holding portions 631 in the longitudinal direction. .

  For example, the laminated body D is held by the jig 63 by fitting the outer peripheral edge of the laminated body D into the grooves of the plurality of holding portions 631.

  With the jig 63, the plurality of stacked bodies D are installed at a predetermined interval. And the jig | tool 63 holding the some laminated body D is inserted in the container main body 61. FIG. Thereafter, the container main body 61 is filled with the group III element liquid, and the plurality of stacked bodies D are completely immersed in the group III element liquid.

  Thereafter, the opening of the container body 61 is closed with the lid 62. Next, the container 6 is placed in the HVPE apparatus 100. For example, the container 6 is disposed in an area surrounded by the heaters 129 and 130. Then, the heaters 129 and 130 are driven to simultaneously heat-treat the plurality of stacked bodies D immersed in the liquid of the group III element from the outside of the container 6. Further, a heat treatment apparatus may be prepared separately from the HVPE apparatus 3 and the laminate D in the container 6 may be heat-treated.

  In the heat treatment step, it is preferable to arrange the containers 5 and 6 in a non-oxidizing gas atmosphere such as nitrogen gas in order to suppress corrosion of the containers 5 and 6. Further, the containers 5 and 6 are filled with the liquid of the group III element, but the powder of the group III element that becomes liquid at the heat treatment temperature of the laminate D may be filled.

  The heat treatment in the fifth step is not limited to those exemplified above, and other forms can also be adopted.

  In addition, it is preferable to heat-process a laminated body in non-oxidizing gas. For example, nitrogen gas may be supplied from the nitrogen source gas supply unit, or non-oxidizing gas may be supplied from the pipe 40 to make the growth region 39 a non-oxidizing gas atmosphere.

As the non-oxidizing gas, at least one kind can be selected from any of rare gases such as Ar gas and N ₂ gas. By performing the heat treatment in a non-oxidizing gas atmosphere, oxidation of the group III nitride semiconductor layer 36 can be suppressed.

Among them, the non-oxidizing gas, it is preferable to use N ₂ gas. Since nitrogen has a lower nitriding power than ammonia, the use of N ₂ gas can suppress the desorption of N atoms on the surface of the group III nitride semiconductor layer 15 to a certain extent, while the group III nitride is moderately moderated. Can occur, and group III atoms can be generated. The generated group III atoms can cause the above-described reaction (5) or (6) to promote separation of the sapphire substrate 30 (base material) and the group III nitride semiconductor layer 36.

  After separation from the sapphire substrate 30 (base material), the structure on the side including the group III nitride semiconductor layer 36 is washed with an acid (for example, an aqueous hydrochloric acid solution or a mixed solution of phosphoric acid and sulfuric acid) to form III A group element droplet or a solidified droplet is removed. Further, when the first layer 31 and the nitrided titanium carbide layer 34 remain, these may be removed (etching, polishing, etc.). As a result, the base substrate 10 made of the group III nitride semiconductor layer 36 is obtained.

  As mentioned above, although this embodiment was described with reference to drawings, these are the illustration of this embodiment and various structures other than the above are also employable.

  For example, in each of the above embodiments, the sapphire substrate 30 is used as the base material, but a spinel substrate, a SiC substrate, a ZnO substrate, a silicon substrate, a GaAs substrate, a GaP substrate, or the like may be used.

  Furthermore, in the said embodiment, although the 1st layer 31, the 2nd layer 32, the cap layer 33, the GaN semiconductor layer 36, etc. were manufactured on specific manufacturing conditions, it is not the meaning to specifically limit. That is, the above-described film thickness and manufacturing conditions are merely examples, and can be appropriately changed according to the composition and structure of the semiconductor layer to be formed.

  In the said embodiment, although titanium carbide was used as the 2nd layer 32, it is not restricted to this. As the second layer 32, any carbide layer selected from aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, and tantalum carbide may be formed. Zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide is a non-stoichiometric compound and contains an excess of metal atoms compared to carbon atoms. Therefore, since excess metal atoms are relatively easily bonded to the substrate, it is particularly useful to form the first layer 31 as in the above embodiment.

  Furthermore, in the said embodiment, although the metal carbide contained in the 1st layer 31 and the metal carbide which comprises the 2nd layer 32 were made into the same kind, it is contained in the 1st layer 31 not only this but The metal carbide to be formed may be different from the metal carbide constituting the second layer 32. For example, the metal carbide contained in the first layer 31 may be zirconium carbide, and the carbide constituting the second layer 32 may be titanium carbide.

  Moreover, in the said embodiment, although the cap layer 33 was produced | generated, the cap layer 33 does not need to be. For example, when it can be handled in an atmosphere in which oxygen or water vapor in the glove box that serves to prevent the oxidation of the carbide layer is reduced, the oxidation of the carbide layer can be suppressed, and thus the cap layer 33 is unnecessary.

  Furthermore, in the said embodiment, although the 1st layer 31, the 2nd layer 32, and the cap layer 33 were formed into a film by sputtering, you may form into a film by not only this but another method. For example, the first layer 31 or the like may be generated by vacuum deposition. Furthermore, for example, the carbide layer may be formed by stacking a metal film and a carbon film while heating the substrate.

  According to the manufacturing method of the base substrate 10 described above, the sapphire substrate 30 (base material), the group III nitride semiconductor layer 36 and the separation position can be controlled, but a plurality of convex portions are formed on the growth surface 111 of the base substrate 10. May be formed. Further, the base substrate 10 may be warped when the growth surface 111 is concave. According to the method for manufacturing a self-supporting substrate described in the first embodiment, it is possible to manufacture a self-supporting substrate in which the problem of warpage is reduced by using such a base substrate 10.

<< Third Embodiment >>
In the present embodiment, when the growth surface 111 of the base substrate 10 is warped in a concave shape (when the outer shape is warped), the growth surface 111 is formed on the base substrate 10 after the pretreatment step S10 in the growth step S20. Is warped so as to be convex, and a group III nitride semiconductor is grown in this state. Other steps are the same as those in the first and second embodiments. Hereinafter, the growth step S20 will be described.

  First, an example of the structure of the substrate holder 450 that holds the base substrate 10 in the growth apparatus will be described in detail. As shown in FIG. 17, the substrate holder 450 is formed on a support surface 451a that supports a surface 112 on the opposite side of the growth surface 111 of the base substrate 10, and on a portion of the support surface 451a that faces the central portion of the base substrate 10. And a pressing portion 455 that presses the peripheral edge of the growth surface 111 of the base substrate 10 toward the support surface 451a. When the peripheral portion of the base substrate 10 is pressed against the support surface 451a by the pressing portion 455, the base substrate 10 is held by the substrate holder 450, and the protrusion 452 moves the central portion of the base substrate 10 from the support surface 451a. Press away. For this reason, as shown in FIG. 17, the base substrate 10 is warped so that the growth surface 111 thereof is convex.

  The substrate holder 450 has a disk-shaped main body 451, and the support surface 451 a is a portion including at least the central portion of one surface of the main body 451. The protrusion 452 protrudes from the support surface 451a. The substrate holder 450 further has a wall portion 453 that stands up from the peripheral edge portion of one surface of the main body portion 451. That is, the wall portion 453 is erected from one surface of the main body portion 451 in the same direction as the protruding direction of the protruding portion 452 from the support surface 451a. The wall portion 453 is formed in an annular shape, for example, and the base substrate 10 is held in a region surrounded by the wall portion 453.

  The pressing portion 455 includes, for example, an attaching / detaching member 456 that is detachably attached to the wall portion 453, and spacers 457, 458 interposed between the attaching / detaching member 456 and the base substrate 10.

  The detachable member 456 includes, for example, a positioning portion 456a for positioning the detachable member 456 with respect to the main body portion 451, and a plate-shaped pressing plate portion 456b that presses the base substrate 10 through the spacers 457 and 458. doing. With the positioning portion 456a applied to the side surface of the wall portion 453, by using a fastening member 460 such as a screw, the pressing plate portion 456b is attached to the end surface (top surface) in the standing direction of the wall portion 453, The detachable member 456 can be positioned and fixed with respect to the main body 451. The wall portion 453 is formed with a fastening hole 453a that opens on the top surface side. By fixing the fixing member 460 to the fixing hole 453a through the pressing plate portion 456b, the pressing plate portion 456b and eventually the entire detachable member 456 are fixed to the wall portion 453 (that is, to the main body portion 451). Is done.

  The pressing plate portion 456b is formed in an annular shape. In a state where the detachable member 456 is attached to the wall portion 453, the inner peripheral edge of the pressing plate portion 456 b is projected in an eaves-like shape inside the wall portion 453.

  Each of the spacers 457 and 458 is, for example, an annular plate member, and the outer diameter thereof is set to the same size as the outer diameter of the base substrate 10. The spacers 457 and 458 are for adjusting the amount of convex warp of the base substrate 10, and the number of the spacers 457 and 458 is appropriately selected according to the required amount of convex warp of the base substrate 10.

  The shapes of the spacers 457 and 458, the pressing plate portion 456b, the support surface 451a, and the like may be changed as appropriate according to the planar shape of the base substrate 10. As an example, when the planar shape of the base substrate 10 is circular, the spacers 457 and 458 are preferably annular, at least the inner peripheral shape of the pressing plate portion 456b is circular, and the support surface 451a is preferably circular.

  Next, an example of a procedure for holding the base substrate 10 by the substrate holder 450 will be described.

  First, the base substrate 10 is disposed in a region surrounded by the wall portion 453 in a posture facing the support surface 451a in a state where the pressing portion 455 (detachable member 456 and spacers 457 and 458) is removed from the main body portion 451. . At this time, the base substrate 10 is disposed so that the growth surface 111 of the base substrate 10 faces away from the support surface 451a.

  Next, a required number of spacers 457 and 458 are inserted into a region surrounded by the wall portion 453 so that the spacers 457 and 458 are opposed to the peripheral edge portion of the base substrate 10. Note that the spacers 457 and 458 overlap each other.

  Next, the detachable member 456 is positioned with respect to the wall portion 453, and the pressing plate portion 456b is attached to the wall portion 453. At this time, the bowl-shaped inner peripheral edge of the pressing plate portion 456b presses the peripheral edge portion of the growth surface 111 of the base substrate 10 toward the support surface 451a via the spacers 457 and 458. Thereby, the base substrate 10 is held by the substrate holder 450 in a state of being sandwiched between the main body 451 and the spacer 158. At this time, the central portion of the base substrate 10 is pressed in a direction away from the support surface 451a by the protrusion 452. For this reason, the base substrate 10 is warped so that the growth surface 111 side is convex (FIG. 17).

  Then, the base substrate 10 thus held by the substrate holder 450 is placed in, for example, an HVPE apparatus 100 as shown in FIG. 3, and a group III nitride is epitaxially grown on the growth surface 111. In addition, you may make it epitaxially grow by crystal growth methods, such as a MOVPE method, Na flux method, and an ammonothermal method.

  According to the embodiment described above, the group III nitride formed on the base substrate 10 by the pretreatment process described in the first embodiment and the mechanical restraint of the base substrate 10 described in the present embodiment. The problem of warpage in the semiconductor layer can be reduced more effectively. As a result, the problem of warping of the obtained free-standing substrate can be further reduced. In addition, since the degree to be improved by the pretreatment process described in the first embodiment can be reduced, the temperature of the chemical solution is lowered to facilitate handling, and the treatment time is shortened to improve efficiency. be able to.

<Comparative Example 1>
The base substrate obtained by the manufacturing method described in the second embodiment and not subjected to the pretreatment step S10 described in the first embodiment was used as the base substrate of Comparative Example 1. A specific method for obtaining the base substrate by the manufacturing method described in the second embodiment is as follows.

First, a 2-inch φ sapphire (Al ₂ O ₃ ) substrate having a thickness of 550 μm was prepared as a base material. A carbon layer (first layer) in which titanium carbide was dispersed was formed on the sapphire substrate under the following conditions. When the atomic ratio C / Ti of Ti and C in the first layer was measured by XPS (X-ray Photoelectron Spectroscopy), it was 4.

Deposition method: Reactive sputtering Deposition temperature: 800 ° C
Deposition time: 24 seconds Pressure: 0.4 Pa
Applied power: 150W
Sputtering gas: Ar gas Sputtering gas flow rate: 14.3 scc
Reactive gas: Hydrocarbon (CH ₄ )
Reactive gas flow rate: 10.0sccm
Target: Ti
Film thickness: 0.3nm

  Thereafter, a titanium carbide layer (second layer) was formed on the first layer under the following conditions.

Deposition method: Reactive sputtering Deposition temperature: 800 ° C
Deposition time: 30 minutes Pressure: 0.4 Pa
Applied power: 300W
Sputtering gas: Ar gas Sputtering gas flow rate: 27.0 sccm
Reactive gas: CH ₄
Reactive gas flow rate: 10.0sccm
Target: Ti
Film thickness: 100nm

  Thereafter, the second layer was nitrided under the following conditions.

Nitriding temperature: 925 ° C
Nitriding time: 30 minutes Nitriding gas: NH ₃ gas, H ₂ gas

  Thereafter, a GaN layer was formed on the nitrided second layer under the following conditions.

Film formation method: HVPE (hydride vapor phase epitaxy) film formation temperature: 1040 ° C.
Deposition time: 150 minutes Film thickness: 400 μm

  Thereafter, the stacked body after the GaN layer was formed was heated (fifth step) under the following conditions without being cooled to room temperature.

Heating temperature: 1100 ° C
Heating time: 12 hours Heating method: HVPE equipment

  After the fifth step, the laminate was cooled to room temperature and observed. The GaN layer and the sapphire substrate were separated. The isolation | separation location had arisen in the 1st layer and 2nd layer part located between a GaN layer and a sapphire substrate. The GaN layer thus obtained was used as a base substrate of Comparative Example 1.

<Example 1>
Example 1 is a base substrate obtained by the manufacturing method described in the second embodiment (the same manufacturing conditions as in Comparative Example 1) and in which the pretreatment step S10 described in the first embodiment is performed. Was used as the base substrate. Hereinafter, details of the pretreatment step S10 will be described.

  200 ml of phosphoric acid (85%) and 200 ml of sulfuric acid (96%) were mixed in a beaker and heated to 250 ° C. with a mantle heater. The temperature was maintained for 60 minutes, and the mantle heater was set to 150 ° C. and left to reach the set temperature. After confirming that the set temperature was reached, the base substrate (GaN layer) set on the jig was immersed in a heated phosphoric acid / sulfuric acid mixture and held for 60 minutes. After 60 minutes, the wafer was taken out, naturally cooled for about 10 minutes to prevent cracking due to rapid cooling, immersed in a beaker filled with ultrapure water, and held for 20 minutes while overflowing ultrapure water. The wafer was removed from the ultrapure water and dried with nitrogen blow. The base substrate thus obtained was used as the base substrate of Example 1.

<Example 2>
Example 2 is a base substrate obtained by the manufacturing method described in the second embodiment (the same manufacturing conditions as in Comparative Example 1) and in which the pretreatment step S10 described in the first embodiment is performed. Was used as the base substrate. Note that Example 2 is partially different from Example 1 in temperature conditions in the pretreatment step S10. Hereinafter, details of the pretreatment step S10 will be described.

  200 ml of phosphoric acid (85%) and 200 ml of sulfuric acid (96%) were mixed in a beaker and heated to 250 ° C. with a mantle heater. The temperature was maintained for 60 minutes, and the mantle heater was set to 200 ° C. and left to reach the set temperature. After confirming that the set temperature was reached, the base substrate (GaN layer) set on the jig was immersed in a heated phosphoric acid / sulfuric acid mixture and held for 60 minutes. After 60 minutes, the wafer was taken out, naturally cooled for about 10 minutes to prevent cracking due to rapid cooling, immersed in a beaker filled with ultrapure water, and held for 20 minutes while overflowing ultrapure water. The wafer was removed from the ultrapure water and dried with nitrogen blow. The base substrate thus obtained was used as the base substrate of Example 2.

<Example 3>
Example 3 is a base substrate obtained by the manufacturing method described in the second embodiment (the same manufacturing conditions as in Comparative Example 1) and in which the pretreatment step S10 described in the first embodiment is performed. Was used as the base substrate. Note that Example 3 is partially different from Example 1 and Example 2 in temperature conditions in the pretreatment step S10. Hereinafter, details of the pretreatment step S10 will be described.

  200 ml of phosphoric acid (85%) and 200 ml of sulfuric acid (96%) were mixed in a beaker and heated to 250 ° C. with a mantle heater. The temperature was maintained for 60 minutes, and the mantle heater was set to 230 ° C. and left to reach the set temperature. After confirming that the set temperature was reached, the base substrate (GaN layer) set on the jig was immersed in a heated phosphoric acid / sulfuric acid mixture and held for 60 minutes. After 60 minutes, the wafer was taken out, naturally cooled for about 10 minutes to prevent cracking due to rapid cooling, immersed in a beaker filled with ultrapure water, and held for 20 minutes while overflowing ultrapure water. The wafer was removed from the ultrapure water and dried with nitrogen blow. The base substrate thus obtained was used as the base substrate of Example 3.

<Observation of the growth surface of the underlying substrate>
FIGS. 18, 19, and 20 show the growth surfaces of the base substrates of Comparative Example 1, Example 1, and Example 2 observed with a scanning electron microscope (SEM), respectively. The upper side is an image obtained by observing the growth surface obliquely from above, and the lower side is an image obtained by observing a cross section of the growth surface.

  As can be seen from these figures, it can be seen that the base substrate obtained by the manufacturing method described in the second embodiment may have convex portions formed on the growth surface. Moreover, it turns out that the height of a convex part becomes low and is planarized by implementing pre-processing process S10. Furthermore, when the processing time is the same, it can be seen that the higher the temperature of the chemical solution is, the more flattened.

<Observation of warpage on the base substrate>
The back surface (peeling surface from the sapphire substrate) shape of the base substrate of Comparative Example 1 and Examples 1 to 3 was measured with a stylus type surface level meter. In each of the base substrates of Comparative Example 1 and Examples 1 to 3, the back side was warped in a convex shape. From this result, it was confirmed that the growth surface side of the base substrate of Comparative Example 1 and Examples 1 to 3 was warped in a concave shape.

<Observation of warpage on crystal structure of base substrate>
FIGS. 21A and 21B are schematic views of base substrates of examples and comparative examples, in which FIG. 21A is a front sectional view and FIG. 21B is a plan view. In FIG. 21A, the warpage on the outer shape of the base substrate is not shown, but there is actually a warp.

  Here, the definition of the c-axis angle difference α will be described. For each of the base substrates of Examples and Comparative Examples (2-inch φ, + c plane is the growth plane), the orientation of the c-axis at a total of four points P1, P2, P3, and P4 shown in FIG. Was measured with an X-ray diffractometer.

  Here, assuming that the center of the base substrate in plan view is the origin (0, 0), the plane coordinates of the point P1 are (−20, 0), the plane coordinates of the point P2 are (+20, 0), and the plane coordinates of the point P3. Is (0, -20), and the plane coordinates of the point P4 are (0, +20). Point P1 is a position shifted 20 mm in the −X direction from the origin, point P2 is a position shifted 20 mm in the + X direction from the origin, point P3 is a position shifted 20 mm in the −Y direction from the origin, and point P4 is 20 mm in the + Y direction from the origin. This is the shifted position.

  Also, the c-axis angle difference α is determined by the c-axis direction (direction A1) at the point A shown in FIG. 21A and the c-axis direction (direction B1 = direction B2) at the point B shown in FIG. ) And the angle difference.

  Point A and point B shown in FIG. 21A are two points arranged symmetrically with the origin in between, among points P1 to P4 shown in FIG. That is, the combination of the points A and B includes a first combination including the points P1 and P2 and a second combination including the points P3 and P4.

  The average value of the angle difference α obtained by each of the two combinations is defined as the angle difference of each base substrate.

  In any of Comparative Example 1 and Examples 1 to 3, the angle difference was included in the range of 0.8 ° to 1.2 °.

<Growth of III-nitride semiconductors on underlying substrate>
The base substrates of Comparative Example 1 and Examples 1 to 3 were held on the substrate holder 450 described in the third embodiment so that the growth surface (+ c surface) had a convex shape of 200 μm. Specifically, as shown in FIG. 23, the growth surface of the base substrate warped in a concave shape is warped in a convex shape, and the height difference between the central portion and the outer peripheral portion of the base substrate is 200 μm. And held by the substrate holder 450. Thereafter, the substrate holder 450 was set in the HVPE apparatus shown in FIG. 3, and a group III nitride semiconductor was grown. The laminated body of the base substrate thus obtained and the group III nitride semiconductor layer was used as a self-supporting substrate. The growth conditions for the group III nitride semiconductor are as follows.

Deposition temperature: 1050 ° C
Deposition time: 4 hours GaCl flow rate: 500 sccm
NH ₃ flow rate: 5000 sccm
Deposition thickness: 2mm

<Observation of crystal structure of free-standing substrate after group III nitride semiconductor growth>
On the exposed surface (growth surface) of the group III nitride semiconductor layer of the free-standing substrate released from the substrate holder 450 after the group III nitride semiconductor is grown on the base substrate, <observation of warpage on the crystal structure of the base substrate> Observation points were defined by the same method (see FIG. 21), and the angle difference was measured by the same method.

  Here, a value obtained by subtracting the angle difference observed in <Observation of warpage on the crystal structure of the self-supporting substrate> from the angle difference observed in <Observation of warpage on the crystal structure of the underlying substrate> Is defined.

  FIG. 22 shows a graph in which the improvement angles of Comparative Example 1 and Examples 1 to 3 are plotted. Data at a processing temperature of 150 ° C. is data of Example 1, data at a processing temperature of 200 ° C. is data of Example 2, and data at a processing temperature of 230 ° C. is data of Example 3. The data of Comparative Example 1 was plotted at a processing temperature of 0 ° C. for convenience.

  From FIG. 22, it can be seen that Examples 1 to 3 have a larger improvement angle than Comparative Example 1 and improved warpage on the crystal structure. It can also be seen that the higher the processing temperature, that is, the flatter the growth surface, the more the warp on the crystal structure is improved.

Hereinafter, examples of the reference form will be added.
1. A pretreatment step of etching the first surface of the base substrate made of a nitride semiconductor with a chemical solution;
A growth step of epitaxially growing a nitride semiconductor layer on the first surface after the pretreatment step;
A method for manufacturing a self-supporting substrate.
2. In the manufacturing method of the self-supporting substrate according to 1,
The said chemical | medical solution is a manufacturing method of the self-supporting board | substrate which is the liquid mixture of the phosphoric acid heated to 100 degreeC or more and 300 degrees C or less, or the phosphoric acid and sulfuric acid heated to 100 degreeC or more and 250 degrees C or less.
3. In the method for manufacturing a self-supporting substrate according to 1 or 2,
In the pretreatment step, a method of manufacturing a self-supporting substrate in which the state in which the chemical solution is in contact with the first surface is continued for 45 minutes or more and 2 hours or less.
4). In the method for manufacturing a self-supporting substrate according to any one of 1 to 3,
Before the pretreatment step, further comprising a preparation step of preparing the base substrate having a convex portion on the first surface,
A method for manufacturing a self-supporting substrate, wherein the height of the convex portion is reduced by the pretreatment step.
5. In the manufacturing method of the self-supporting substrate according to 4,
The preparation step includes
Forming a carbon layer in which carbide MC (aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide) is dispersed as a first layer on a substrate;
A second step of forming a layer of carbide MC (aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide) as a second layer on the first layer;
A third step of nitriding the second layer;
A fourth step of forming a group III nitride semiconductor layer on the nitrided second layer;
After the fourth step, the group III nitride semiconductor layer is formed from a stack including the base substrate, the first layer, the nitrided second layer, and the group III nitride semiconductor layer. A fifth step of heating at a temperature higher than the heating at the time,
A method for manufacturing a self-supporting substrate.

D Laminate 5 Container 6 Container 10 Base substrate 30 Sapphire substrate (base material)
31 First layer 32 Second layer 33 Cap layer 34 Nitride titanium carbide layer (second layer)
36 Group III nitride semiconductor layer 41 Substrate 50 Container body 51 Side wall 52 Pin 52A-52D Pin 53 Lid 55 Jig 61 Container main body 62 Lid 63 Jig 100 HVPE apparatus 111 Growth surface 112 Surface 121 Reaction tube 122 Growth region 123 Substrate holder 124 Gas supply pipe 125 Gas supply pipe 126 Gas supply pipe 127 Ga raw material 128 Source boat 129 Heater 130 Heater 132 Rotating shaft 135 Gas discharge pipe 136 Partition plate 137 Nitrogen raw material gas supply part 139 Group III raw material gas supply part 341 Titanium nitride layer 342 Titanium carbide layer 343 Nitrated cap layer 450 Substrate holder 451 Main body portion 451a Support surface 452 Protruding portion 453 Wall portion 453a Fastening hole 455 Holding portion 456 Removable member 456a Positioning portion 456b Holding plate portion 457 Spacer 458 Spacer 460 Fastening member 5 1 recess 631 holding part 632 fixed portion 710 underlying substrate 711 III group layers 720 self-supporting substrate 721 exposed surface 722 side of the nitride semiconductor 771 exposed surface 772 side

Claims (4)

A preparation step of preparing a base substrate made of a nitride semiconductor and having a convex portion on the first surface;
A pretreatment step of etching the first surface with a chemical;
A growth step of epitaxially growing a nitride semiconductor layer on the first surface after the pretreatment step;
I have a,
The preparation step includes
Forming a carbon layer in which carbide MC (aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide) is dispersed as a first layer on a substrate;
A second step of forming a layer of carbide MC (aluminum carbide, titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide or tantalum carbide) as a second layer on the first layer;
A third step of nitriding the second layer;
A fourth step of forming a group III nitride semiconductor layer on the nitrided second layer;
After the fourth step, the group III nitride semiconductor layer is formed from a laminate including the base material, the first layer, the nitrided second layer, and the group III nitride semiconductor layer. Heating at a temperature higher than the heating at the time, a fifth step of separating the base material and the group III nitride semiconductor layer;
Have
A self-supporting substrate manufacturing method for obtaining the base substrate from the group III nitride semiconductor layer separated in the fifth step . In the manufacturing method of the self-supporting substrate according to claim 1,
The said chemical | medical solution is a manufacturing method of the self-supporting board | substrate which is the liquid mixture of the phosphoric acid heated to 100 degreeC or more and 300 degrees C or less, or the phosphoric acid and sulfuric acid heated to 100 degreeC or more and 250 degrees C or less. In the manufacturing method of the self-supporting substrate according to claim 1 or 2,
In the pretreatment step, a method of manufacturing a self-supporting substrate in which the state in which the chemical solution is in contact with the first surface is continued for 45 minutes or more and 2 hours or less. In the manufacturing method of the self-supporting substrate according to any one of claims 1 to 3,
In the pretreatment step , a method for manufacturing a self-supporting substrate in which the height of the convex portion is reduced.