JP6753703B2 - Method for manufacturing compound semiconductor substrate, pellicle film, and compound semiconductor substrate - Google Patents

Description

The present invention relates to a method for producing a compound semiconductor substrate, a pellicle film, and a compound semiconductor substrate, and more specifically, to a method for producing a compound semiconductor substrate, a pellicle film, and a compound semiconductor substrate having a SiC (silicon carbide) film. ..

Compared to Si (silicon), SiC has excellent heat resistance and withstand voltage resistance, and has a small power loss when used as an electronic device. For this reason, SiC is being increasingly used as a next-generation semiconductor material, for example, in high-performance and power-saving inverter devices, power modules for home appliances, and power semiconductor devices for electric vehicles.

In addition, since SiC has a higher Young's modulus, higher yield strength at high temperature, and higher chemical stability than Si, it has been considered to use SiC as a MEMS (Micro Electro Mechanical Systems). There is. Further, since SiC has a high light transmittance, other applications utilizing these properties are also being studied.

The SiC film is usually formed by forming a SiC film on a Si substrate and then etching a part or all of the Si substrate. When etching the Si substrate, the Si substrate on which the SiC film is formed is immersed in the chemical solution. Techniques for forming a SiC film are disclosed in, for example, Patent Documents 1 to 3 below.

In Patent Document 1 below, a SiC film having a thickness of about 1 μm is formed on the surface of a Si substrate, and a substrate opening is formed by removing one surface of the SiC film at an arbitrary area to form a SiC film. A technique for etching a Si substrate through a substrate opening using a film as a mask is disclosed. When etching the Si substrate, a mixed solution of hydrofluoric acid and nitric acid is used.

Patent Document 2 below discloses a technique for producing an X-ray mask containing a SiC film. In this technique, a 2 μm-thick SiC film is formed on a Si wafer, a protective film and an X-ray absorbing film are formed on the SiC film, an etching-resistant substance is applied to the lower surface of the Si wafer in a ring shape, and water is applied. The central part of the Si wafer is removed using an aqueous sodium oxide solution.

Patent Document 3 below discloses a technique of forming a 3C-SiC layer on one surface of a Si substrate including a reinforcing portion and dissolving the Si substrate with an etching solution mixed with hydrofluoric acid, nitric acid, or the like. ..

Japanese Unexamined Patent Publication No. 09-310170 Japanese Unexamined Patent Publication No. 07-118854 Japanese Unexamined Patent Publication No. 2015-202990

The SiC film is required to be thin. For example, in the case of MEMS using SiC, thinning of SiC is required from the viewpoint of increasing sensitivity. Further, in the case of a pellicle using SiC, a thin film of SiC is required from the viewpoint of further improving light transmission.

However, the SiC film could not be thinned by the conventional technique. When the SiC film is thinned (for example, when the thickness is 10 μm or less), the mechanical strength is lower than when the SiC film is thick, so that the SiC film is cracked during etching of the Si substrate. Or, the phenomenon that the SiC film is peeled off from the Si substrate has occurred.

The present invention is for solving the above problems, and an object of the present invention is to provide a compound semiconductor substrate, a pellicle film, and a method for manufacturing a compound semiconductor substrate capable of thinning a SiC film.

A compound semiconductor substrate according to one aspect of the present invention includes a Si substrate having an annular planar shape and a SiC film formed on one main surface of the Si substrate and having a thickness of 20 nm or more and 10 μm or less. Is not formed on the other main surface of the Si substrate.

In the compound semiconductor substrate, the width of the Si substrate decreases as the distance from the SiC film increases, preferably when viewed in a cross section cut in a plane perpendicular to the surface of the SiC film.

The compound semiconductor substrate preferably further includes a film different from SiC formed on one main surface of the SiC film.

In the compound semiconductor substrate, the film different from SiC is preferably made of graphene, graphite, or GaN (gallium nitride).

The pellicle film according to another aspect of the present invention uses the above-mentioned compound semiconductor substrate.

The method for producing a compound semiconductor substrate according to still another aspect of the present invention includes a step of forming a SiC film on one main surface of the Si substrate and a step of removing at least a part of the other main surface of the Si substrate by wet etching. In the step of removing at least a part of the other main surface of the Si substrate, the Si substrate and the SiC film are moved relative to the chemical solution used for wet etching.

In the above manufacturing method, preferably, in the step of removing at least a part of the other main surface of the Si substrate, the Si substrate and the SiC film are moved in a direction in a plane parallel to one main surface of the SiC film.

In the above manufacturing method, preferably, in the step of removing at least a part of the other main surface of the Si substrate, the chemical solution used for wet etching is applied to the other main surface of the Si substrate in a state where the Si substrate and the SiC film are rotated. inject.

In the above manufacturing method, preferably, a step of forming a recess having Si as a bottom surface in the center of the other main surface of the Si substrate is further provided, and in a step of removing at least a part of the other main surface of the Si substrate, the recess is provided. The SiC film is exposed on the bottom surface of the.

In the above manufacturing method, preferably, after the step of forming the recess in the central portion of the other main surface of the Si substrate, the step of forming the SiC film on one main surface of the Si substrate is performed.

In the above manufacturing method, preferably, after the step of forming the SiC film on one main surface of the Si substrate, a step of forming a recess in the central portion of the other main surface of the Si substrate is performed.

In the above manufacturing method, preferably, in the step of forming a recess in the central portion of the other main surface of the Si substrate, Si is used as a mask using a mask layer made of an oxide film or a nitride film formed on the other main surface of the Si substrate as a mask. The central portion of the other main surface of the substrate is removed by wet etching.

In the above manufacturing method, preferably, in the step of forming the SiC film, the SiC film is formed on one main surface and side surface of the Si substrate and the outer peripheral portion of the other main surface of the Si substrate, and the other main surface of the Si substrate is formed. In the step of removing at least a part of the above, the other main surface of the Si substrate is removed by using the SiC film formed on the outer peripheral portion of the other main surface of the Si substrate as a mask.

In the above manufacturing method, preferably, a mixed acid containing hydrofluoric acid and nitric acid is used as the chemical solution used for wet etching in the step of removing at least a part of the other main surface of the Si substrate.

In the above manufacturing method, preferably, after the step of removing at least a part of the other main surface of the Si substrate, a step of forming a GaN film on one main surface of the SiC film is further provided.

The above manufacturing method preferably further includes a step of changing a part of the SiC film into a graphene film or a graphite film.

The production method preferably further includes a step of forming a graphene film or a graphite film on one main surface of the SiC film.

According to the present invention, it is possible to provide a compound semiconductor substrate, a pellicle film, and a method for manufacturing a compound semiconductor substrate, which can reduce the thickness of a SiC film.

It is sectional drawing which shows the structure of the compound semiconductor substrate 1 in 1st Embodiment of this invention. It is a top view which shows the structure of the compound semiconductor substrate 1 when viewed from the direction perpendicular to the surface 12a of the SiC film 12 in the 1st Embodiment of this invention. It is sectional drawing which shows the 1st step of the manufacturing method of the compound semiconductor substrate 1 in 1st Embodiment of this invention. It is sectional drawing which shows the 2nd step of the manufacturing method of the compound semiconductor substrate 1 in 1st Embodiment of this invention. It is sectional drawing which shows the 1st process of the modification of the process shown in FIG. It is sectional drawing which shows the 2nd process of the modification of the process shown in FIG. It is sectional drawing which shows the 3rd step of the manufacturing method of the compound semiconductor substrate 1 in 1st Embodiment of this invention. It is sectional drawing which shows the 4th step of the manufacturing method of the compound semiconductor substrate 1 in 1st Embodiment of this invention. It is sectional drawing which shows the 5th step of the manufacturing method of the compound semiconductor substrate 1 in 1st Embodiment of this invention. It is a figure which shows typically the 1st method of the wet etching of Si in 1st Embodiment of this invention. It is a figure which shows typically the 2nd method of wet etching of Si in 1st Embodiment of this invention. It is a figure which shows typically the 3rd method of the wet etching of Si in 1st Embodiment of this invention. It is an enlarged view of the part A in the compound semiconductor substrate 1 shown in FIG. It is sectional drawing which shows the 1st step of the modification of the manufacturing method of the compound semiconductor substrate 1 in 1st Embodiment of this invention. It is sectional drawing which shows the 2nd step of the modification of the manufacturing method of the compound semiconductor substrate 1 in 1st Embodiment of this invention. It is sectional drawing which shows the structure of the compound semiconductor substrate 1 in the 2nd Embodiment of this invention. It is sectional drawing which shows the 1st step of the manufacturing method of the compound semiconductor substrate 1 in 2nd Embodiment of this invention. It is sectional drawing which shows the 2nd step of the manufacturing method of the compound semiconductor substrate 1 in the 2nd Embodiment of this invention. It is a top view which shows an example of the method of holding a Si substrate 11 in a CVD apparatus in 2nd Embodiment of this invention. It is sectional drawing which shows the structure of the compound semiconductor substrate 1a in 3rd Embodiment of this invention. It is a graph explaining an example of the film forming condition of the AlN film 21 and the GaN film 22 in the 3rd Embodiment of this invention. It is sectional drawing which shows the structure of the compound semiconductor substrate 1b in 4th Embodiment of this invention. It is sectional drawing which shows the 1st step of the manufacturing method of the compound semiconductor substrate 1b in 4th Embodiment of this invention. It is sectional drawing which shows the 2nd step of the manufacturing method of the compound semiconductor substrate 1b in 4th Embodiment of this invention. It is sectional drawing which shows an example of the use method of the compound semiconductor substrate 1 in 5th Embodiment of this invention. In one embodiment of the present invention, it is a photograph of the back surface of the Si substrate during spin etching of the present invention. It is a photograph of the back surface of the Si substrate during wet etching of the comparative example in one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]

FIG. 1 is a cross-sectional view showing the configuration of the compound semiconductor substrate 1 according to the first embodiment of the present invention. FIG. 1 is a cross-sectional view of the SiC film 12 when cut in a plane perpendicular to the surface 12a.

With reference to FIG. 1, the compound semiconductor substrate 1 in the present embodiment includes a Si substrate 11 and a SiC film 12.

The Si substrate 11 has an annular planar shape. The Si substrate 11 includes a front surface 11a, a back surface 11b, and a side surface 11c. The (111) surface is exposed on the surface 11a of the Si substrate 11. The (100) surface or the (110) surface may be exposed on the surface 11a of the Si substrate 11.

The SiC film 12 is formed on the surface 11a of the Si substrate 11 (an example of one main surface of the Si substrate). The SiC film 12 includes a front surface 12a, a back surface 12b, and a side surface 12c. The back surface 12b of the SiC film 12 is exposed in the recess 13 inside the annular Si substrate 11. The SiC film 12 is not formed on the back surface 11b of the Si substrate 11 (an example of the other main surface of the Si substrate), and the back surface 11b of the Si substrate 11 is exposed.

The SiC film 12 has a thickness w of 20 nm or more and 10 μm or less. The thickness w is preferably 1 μm or less, more preferably 500 nm or less. The SiC film 12 is made of single crystal 3C-SiC, polycrystalline 3C-SiC, amorphous SiC, or the like. In particular, when the SiC film 12 is epitaxially grown on the surface of the Si substrate 11, the SiC film 12 is generally made of 3C-SiC.

FIG. 2 is a plan view showing the configuration of the compound semiconductor substrate 1 when viewed from a direction perpendicular to the surface 12a of the SiC film 12 in the first embodiment of the present invention. In FIG. 2, the Si substrate 11 is shown by a dotted line for the purpose of showing the shape of the Si substrate 11, but the Si substrate 11 is not actually visible directly.

With reference to FIG. 2, each of the Si substrate 11, the SiC film 12, and the recess 13 has an arbitrary planar shape. The outer peripheral end of the SiC film 12 is supported by an annular Si substrate 11. As a result, the mechanical strength of the SiC film 12 is reinforced by the Si substrate 11. Each of the Si substrate 11, the SiC film 12, and the recess 13 may have a circular planar shape, for example, as shown in FIG. 2 (a), or may have a rectangular shape as shown in FIG. 2 (b). May have a planar shape of. In FIG. 2B, the Si substrate 11 has a square annular planar shape. Further, as shown in FIG. 2C, each of the Si substrate 11 and the SiC film 12 may have a circular planar shape, and the recess 13 may have a rectangular planar shape. The size of the recess 13 is arbitrary, and may be determined according to the mechanical strength required for the compound semiconductor substrate 1.

Next, the method for manufacturing the compound semiconductor substrate 1 according to the present embodiment will be described with reference to FIGS. 3 to 9.

With reference to FIG. 3, for example, a disk-shaped Si substrate 11 (in which the recess 13 is not formed) is prepared.

With reference to FIG. 4, the Si in the central portion RG1 of the back surface 11b of the Si substrate 11 is then removed. The removal of Si in the central portion RG1 may be performed by mechanically grinding the Si in the central portion RG1 of the Si substrate 11. Further, the removal of Si in the central portion RG1 is performed by forming a photoresist in the region excluding the central portion RG1 on the back surface 11b of the Si substrate 11 and etching the Si in the central portion RG1 using the formed photoresist as a mask. You may.

Further, when increasing the resistance of the mask to the chemical solution used for wet etching of Si, the removal of Si in the central portion RG1 may be performed by the following method.

With reference to FIG. 5, a mask layer 14 made of a silicon oxide film or a silicon nitride film is formed on the entire back surface 11b of the Si substrate 11. Subsequently, a photoresist 15 patterned in a required shape is formed on the mask layer 14.

With reference to FIG. 6, the mask layer 14 is then patterned by wet etching using the photoresist 15 as a mask. As a result, only the outer peripheral portion of the mask layer 14 is left. When the mask layer 14 is made of a silicon oxide film, a hydrofluoric acid solution or the like is used as the chemical solution for wet etching of the mask layer 14. When the mask layer 14 is made of a silicon nitride film, a phosphoric acid solution or the like is used as the chemical solution for wet etching of the mask layer 14. Subsequently, using the patterned mask layer 14 as a mask, Si in the central portion RG1 is removed by wet etching using a chemical solution such as a mixed acid. After that, the photoresist 15 and the mask layer 14 are removed. The photoresist 15 may be removed before the wet etching of Si.

In the step shown in FIG. 3, the step of forming the mask layer 14 shown in FIG. 5 may be omitted by preparing a substrate on which the mask layer 14 is previously formed on the back surface 11b of the Si substrate 11. Further, as the mask layer 14, an oxide film or a nitride film other than the silicon oxide film and the silicon oxide film may be used.

As a result of removing Si from the central portion RG1 with reference to FIG. 7, a recess 13 is formed on the back surface 11b of the Si substrate 11. In FIG. 7, the recess 13 has a depth that does not penetrate the Si substrate 11, and the bottom surface of the recess 13 is made of Si. Due to the presence of the recess 13, the thickness of the central portion of the Si substrate 11 (the length in the vertical direction in FIG. 7) is thinner than the thickness of the outer peripheral portion of the Si substrate 11.

With reference to FIG. 8, after the recess 13 is formed, the SiC film 12 is formed on the surface 11a of the Si substrate 11. The SiC film 12 is formed, for example, by using an MBE (Molecular Beam Epitaxy) method, a CVD (Chemical Vapor Deposition) method, or the like on a base layer made of SiC obtained by carbonizing the surface 11a of the Si substrate 11. Be filmed. Further, the SiC film 12 may be formed only by carbonizing the surface 11a of the Si substrate 11. Further, the SiC film 12 may be formed on the surface 11a of the Si substrate 11 by using an MBE method, a CVD method, or the like. When the SiC film 12 is formed, the SiC film 12 may also be formed on the side surface 11c of the Si substrate 11.

With reference to FIG. 9, the bottom surface RG2 of the recess 13 of the Si substrate 11 is subsequently removed by wet etching. The bottom surface RG2 constitutes a part of the back surface 11b of the Si substrate. As a result of removing Si from the bottom surface RG2, the back surface 12b of the SiC film 12 is exposed on the bottom surface of the recess 13. Further, during this wet etching, Si on the outer peripheral portion RG3 of the back surface 11b of the Si substrate 11 is removed together with Si on the bottom surface RG2. By adopting wet etching, it is possible to suppress damage to the SiC film 12 when the Si substrate is removed. Through the above steps, the compound semiconductor substrate 1 shown in FIG. 1 is completed.

Wet etching of Si on the bottom surface RG2 is performed by moving the Si substrate 11 and the SiC film 12 relative to the chemical solution used for wet etching. To move the Si substrate 11 and the SiC film 12, the Si substrate 11 and the SiC film 12 are rotated without changing the positions of the Si substrate 11 and the SiC film 12, and the positions of the Si substrate 11 and the SiC film 12 are changed. (In other words, the Si substrate 11 and the SiC film 12 are moved), and the Si substrate 11 and the SiC film 12 are rotated while changing the positions of the Si substrate 11 and the SiC film 12. As the chemical solution used for wet etching of Si, for example, a mixed acid containing hydrofluoric acid and nitric acid, an aqueous solution of potassium hydroxide (KOH), or the like is used.

When an alkaline solution such as an aqueous potassium hydroxide solution is used as the chemical solution for wet etching of Si, even the SiC film 12 may be etched through pinholes existing in the SiC film 12 at a low density. In order to prevent the SiC film 12 from being etched and to improve the quality of the SiC film 12, it is preferable to use the above-mentioned mixed acid as a chemical solution for wet etching of Si.

The direction in which the Si substrate 11 and the SiC film 12 are moved during wet etching of Si is arbitrary. However, in order to avoid a situation in which the SiC film 12 is damaged by the pressure received from the chemical solution while the Si substrate 11 and the SiC film 12 are being moved, the SiC film 12 is as described in the first to third methods below. It is preferable to move the Si substrate 11 and the SiC film 12 in a direction in a plane parallel to the surface 12a (plane PL in FIGS. 10 to 12).

10 to 12 are diagrams schematically showing the first to third methods of wet etching of Si according to the first embodiment of the present invention. In the description of FIGS. 10 to 12, the structure immediately before wet etching of Si is referred to as intermediate 2. In the present embodiment, the structure immediately after the process of FIG. 8 corresponds to the intermediate body 2, and in the second embodiment described later, the structure immediately after the process of FIG. 17 corresponds to the intermediate body 2.

With reference to FIG. 10, the first method is a method of removing Si by spin etching. In the first method, the intermediate 2 is fixed to the fixing base HP so that the back surface 11b of the Si substrate 11 faces upward. Then, as shown by the arrow AR1, the fixed base HP is rotated around a rotation axis extending in a direction orthogonal to the back surface 11b. In this way, the chemical solution MA (etching solution) used for wet etching is injected into the back surface 11b of the Si substrate 11 in a state where the intermediate body 2 is rotated without changing the position of the intermediate body 2. The rotation speed of the fixed base HP is set to, for example, about 500 to 1500 rpm.

With reference to FIG. 11, in the second method, the plurality of intermediates 2 are fixed to the fixing base HP in an upright state. Then, a plurality of intermediates 2 are immersed in the chemical solution MA filled in the reaction vessel CS, and the positions of the intermediates 2 are located in the plane PL parallel to the surface 12a of the SiC film 12 as shown by the arrow AR2. The intermediate body 2 and the fixed base HP are rotated while changing the above.

With reference to FIG. 12, in the third method, the intermediate 2 is fixed to the fixing base HP so that the back surface 11b of the Si substrate 11 faces upward. Then, the intermediate 2 is immersed in the chemical solution MA filled in the reaction vessel CS, and the intermediate 2 and the fixing base HP are shown in the plane PL parallel to the surface 12a of the SiC film 12 as shown by the arrow AR3. Is reciprocated on a straight line.

FIG. 13 is an enlarged view of part A in the compound semiconductor substrate 1 shown in FIG. In FIG. 13, the amount of change in the width of the Si substrate 11 is emphasized more than the actual one.

With reference to FIG. 13, the mixed acid containing hydrofluoric acid and nitric acid has an action of isotropically etching Si. Therefore, when Si is wet-etched using a mixed acid containing hydrofluoric acid and nitric acid as a chemical solution, the width d (horizontal length in FIG. 13) of the Si substrate 11 is as a trace from the SiC film 12. It decreases as the distance increases (from the SiC film 12 toward the back surface 11b of the Si substrate 11).

As a modification of the manufacturing method of the present embodiment, as shown in FIG. 14, after forming the SiC film 12 on the surface 11a of the Si substrate 11, as shown in FIG. 15, the back surface 11b of the Si substrate 11 The Si of the central portion RG1 may be removed to form the recess 13, and then the bottom RG2 of the recess 13 may be removed by wet etching.

According to the present embodiment, when the Si substrate 11 is wet-etched, the Si substrate 11 and the SiC film 12 are moved relative to the chemical solution for the wet etching, so that the SiC film is formed during the wet etching of the Si substrate 11. It is possible to prevent a situation in which the SiC film 12 is cracked or the SiC film 12 is peeled off from the Si substrate 11, and the SiC film 12 in the compound semiconductor substrate 1 can be thinned.

The inventor of the present application has found that the cause of cracks in the SiC film 12 or peeling of the SiC film 12 from the Si substrate 11 during wet etching of the Si substrate 11 (during immersion of the Si substrate 11 in a chemical solution) is the Si substrate 11. The chemical solution after the reaction locally stays on the reaction surface (the surface of the portion of the back surface 11b of the Si substrate 11 that reacts with the chemical solution), whereby the etching rate of Si becomes non-uniform, and the reaction surface of the Si substrate 11 It was found that it was to cause roughness. Further, the inventor of the present application, when a mixed acid is used as the chemical solution for wet etching, large bubbles generated by the reaction between the chemical solution and Si locally stay on the reaction surface of the Si substrate 11, and the bubbles are locally retained on the reaction surface of the Si substrate 11. It has been found that the reaction surface of the reaction surface of Si substrate 11 is locally hindered from reacting with the chemical solution, and the reaction surface of the Si substrate 11 is roughened.

When the SiC film 12 is relatively thick (for example, when the thickness is larger than 10 μm), the mechanical strength of the SiC film 12 itself is high, so that the roughness of the reaction surface of the Si substrate 11 has a great adverse effect on the SiC film 12. Does not reach. However, when the SiC film 12 is relatively thin (for example, when the thickness is 10 μm or less, specifically, when it is a thin film (thickness is about several μm) or when it is an ultrathin film (thickness is on the order of 100 nm or less). The roughness of the reaction surface of the Si substrate 11 adversely affects the SiC film 12. That is, the roughness of the reaction surface of the Si substrate 11 applies non-uniform stress to the SiC film 12, and the SiC film is subjected to Si etching. The 12 may be cracked or the SiC film 12 may be peeled off from the Si substrate 11.

Therefore, in the present embodiment, when the Si substrate 11 is wet-etched, the Si substrate 11 and the SiC film 12 are moved relative to the chemical solution for the wet etching, so that the Si substrate 11 is locally on the reaction surface of the Si substrate 11. It is possible to prevent the chemical solution and bubbles from staying after the reaction, and to prevent the reaction surface of the Si substrate 11 from becoming rough. As a result, it is possible to prevent non-uniform stress from being applied to the SiC film 12, and it is possible to reduce the thickness of the SiC film 12.

In particular, when the method of removing Si by spin etching (the first method shown in FIG. 10) is adopted as the method of wet etching of Si, the SiC film 12 is exposed to the chemical solution during the wet etching. Only while the back surface 12b of the SiC film 12 is exposed at the bottom of the recess 13. Further, the surface 12a of the SiC film 12 is not exposed to the chemical solution during the wet etching. Therefore, damage to the SiC film 12 due to the chemical solution can be minimized.

Further, by using a mixed acid as a chemical solution for wet etching of Si, damage to the SiC film 12 by the chemical solution can be suppressed. As a result, the yield of the SiC film 12 can be improved, and the SiC film can be formed in a large area.

[Second Embodiment]

FIG. 16 is a cross-sectional view showing the configuration of the compound semiconductor substrate 1 according to the second embodiment of the present invention. Note that FIG. 16 is a cross-sectional view of the SiC film 12 when cut in a plane perpendicular to the surface 12a.

With reference to FIG. 16, in the compound semiconductor substrate 1 of the present embodiment, the SiC film 12 is formed on the outer peripheral portions of the front surface 11a, the side surface 11c, and the back surface 11b of the Si substrate 11. The outer peripheral portions of the front surface 11a, the side surface 11c, and the back surface 11b of the Si substrate 11 are completely covered with the continuous SiC film 12. The back surface 12b of the SiC film 12 is exposed at the bottom of the recess 13. The thickness of the SiC film 12 is reduced at the end of the outer peripheral portion of the back surface 11b. The portion of the SiC film 12 formed on the surface 11a of the Si substrate has a thickness w of 20 nm or more and 10 μm or less. The thickness w is preferably 1 μm or less, more preferably 500 nm or less.

Next, the method for manufacturing the compound semiconductor substrate 1 according to the present embodiment will be described with reference to FIGS. 17 and 18.

With reference to FIG. 17, a SiC film 12 is formed on the Si substrate 11 shown in FIG. 3 by a CVD method. When forming the SiC film 12, the Si substrate 11 is held so that a part of the raw material gas supplied to the front surface 11a of the Si substrate 11 also wraps around the side surface 11c and the back surface 11b of the Si substrate 11. As a result, the chemical reaction of the raw material gas also occurs on the outer peripheral portions of the front surface 11a, the side surface 11c, and the back surface 11b of the Si substrate 11, and the SiC film 12 continuous on the outer peripheral portions of the front surface 11a, the side surface 11c, and the back surface 11b of the Si substrate 11. Is formed. As a result, Intermediate 2 in the present embodiment is obtained.

With reference to FIG. 18, subsequently, the exposed central portion RG4 of the back surface 11b of the Si substrate 11 is removed by wet etching using the SiC film 12 formed on the outer peripheral portion of the back surface 11b of the Si substrate 11 as a mask. As a result of removing Si from the central portion RG4, a recess 13 is formed on the back surface 11b of the Si substrate. The back surface 12b of the SiC film 12 is exposed on the bottom surface of the recess 13. During this wet etching, Si on the outer peripheral portion of the back surface 11b of the Si substrate 11 covered with the SiC film 12 is not removed. Through the above steps, the compound semiconductor substrate 1 shown in FIG. 16 is completed.

In the step shown in FIG. 17 (step of forming the SiC film 12 by using the CVD method), it is preferable that the Si substrate 11 is held in the CVD apparatus by the following method.

FIG. 19 is a plan view showing an example of a method of holding the Si substrate 11 in the CVD apparatus according to the second embodiment of the present invention.

With reference to FIG. 19, the CVD apparatus includes a holding unit 31 for holding the Si substrate 11. The holding portion 31 includes an annular outer peripheral portion 31a and a plurality of (three in this case) protruding portions 31b provided at equal intervals on the inner peripheral side end portion of the outer peripheral portion 31a. Each of the plurality of projecting portions 31b is linear and projects toward the center of the outer peripheral portion 31a. The Si substrate 11 is placed on the tip of each of the plurality of protrusions 31b so that the surface 11a faces upward. The reaction gas is flowed on the surface 11a of the Si substrate 11 in the direction indicated by the arrow AR4. A part of the reaction gas wraps around the side surface 11c and the back surface 11b of the Si substrate 11 through the space SP between the outer peripheral portion 31a and the plurality of protruding portions 31b. As a result, a continuous SiC film 12 is formed on the outer peripheral portions of the front surface 11a, the side surface 11c, and the back surface 11b of the Si substrate 11.

The configuration and manufacturing method of the compound semiconductor substrate 1 other than the above are the same as the configuration and manufacturing method of the compound semiconductor substrate in the first embodiment. Therefore, those explanations will not be repeated.

According to the present embodiment, the same effect as that of the first embodiment can be obtained. In addition, since the Si substrate 11 can be wet-etched using the SiC film 12 formed around the back surface 11b of the Si substrate 11 as a mask, a recess is formed in the Si substrate 11 in a step separate from the step of forming the SiC film 12. There is no need to form a pattern or form a pattern by lithography. As a result, the compound semiconductor substrate 1 can be manufactured by a simple method, and the compound semiconductor substrate 1 can be manufactured in a short period of time and at low cost.

[Third Embodiment]

FIG. 20 is a cross-sectional view showing the configuration of the compound semiconductor substrate 1a according to the third embodiment of the present invention. FIG. 20 is a cross-sectional view taken along a plane perpendicular to the surface 22a of the GaN film 22.

With reference to FIG. 20, the compound semiconductor substrate 1a in the present embodiment further includes an AlN film 21 and a GaN film 22.

The AlN film 21 is formed on the surface 12a of the SiC film 12 (an example of one main surface of the SiC film). The AlN film 21 is a buffer layer for improving the wettability of the SiC film 12 and the GaN film 22. The AlN film 21 has, for example, a thickness of 5 nm or more and 15 nm or less, preferably a thickness of 5 nm or more and 9 nm or less, and more preferably a thickness of 7 nm or more and 9 nm or less.

The GaN film 22 is formed on the surface 21a of the AlN film 21. The GaN film 22 has, for example, a thickness of 1500 nm or more and 3000 nm or less, preferably 1500 nm or more and 2500 nm or less. The GaN film 22 may have a p-type or n-type conductive type, or at least a part of the GaN film 22 may be doped with C.

Since the configuration of the compound semiconductor substrate 1a other than the above is the same as the configuration of the compound semiconductor substrate 1 in the first embodiment shown in FIGS. 1 and 2, the same members are designated by the same reference numerals. , The explanation is not repeated.

Subsequently, a method for manufacturing the compound semiconductor substrate 1a according to the present embodiment will be described.

First, the compound semiconductor substrate 1 shown in FIG. 1 is obtained by using the same manufacturing method as the manufacturing method in the first embodiment. As an example, the compound semiconductor substrate 1 includes a ring-shaped Si substrate 11 having an outer diameter of 100 mm and an inner diameter of 80 mm, and a SiC film 12 having a thickness of 160 nm formed on the Si substrate 11.

Next, the GaN film 22 is formed on the surface 12a of the SiC film 12 via the ultra-thin AlN film 21. Here, a case where the AlN film 21 and the GaN film 22 are heteroepitaxially grown on the surface 12a of the SiC film 12 by using the MOCVD (Metalorganic Chemical Vapor Deposition) method will be described.

FIG. 21 is a graph illustrating an example of film formation conditions for the AlN film 21 and the GaN film 22 according to the third embodiment of the present invention.

With reference to FIG. 21, the AlN film 21 is cleaned with TMA (trimethylaluminum: Al (CH ₃ ) ₃ ) and then at a temperature of, for example, about 1000 to 1300 ° C. (1200 ° C. in FIG. 21), for example, 1. It is formed in a time of about 60 minutes. As the raw material gas for Al, for example, TMA is used, and as the raw material gas for N, for example, ammonia (NH ₃ ) is used.

After the formation of the AlN film 21, the GaN film 22 is formed at a temperature of, for example, about 900 to 1200 ° C. (1080 ° C. in FIG. 21), for example, about 5 to 200 minutes. As the raw material gas for Ga, for example, TMG (trimethylgallium: Ga (CH ₃ ) ₃ ) is used, and as the raw material gas for N, for example, ammonia is used. By the above steps, the compound semiconductor substrate 1a shown in FIG. 20 is obtained.

In the compound semiconductor substrate 1a, after the GaN film 22 is formed (after the compound semiconductor substrate 1a is completed), the Si substrate 11 may be completely removed by using fluorine or the like. Further, if necessary, an inclined layer (for example, an AlGaN film in which the composition ratio of Al gradually decreases from the AlN film 21 to the GaN film 22) may be provided between the AlN film 21 and the GaN film 22. Good. Further, an intermediate layer (for example, made of an Al film or an AlGaN film) may be provided in the GaN film 22.

Generally, when a GaN film is directly formed on a Si substrate, large warpage and cracks occur due to differences in physical properties (lattice constant and coefficient of thermal expansion) between Si and GaN. In order to avoid such a situation, conventionally, a complicated and thick buffer film has been formed between the Si substrate and the GaN film.

According to the present embodiment, since a part of Si under the SiC film 12 is removed, the adverse effect of the difference in physical properties between Si and GaN on GaN is small. Further, the difference in physical properties between SiC and GaN is smaller than the difference in physical properties between Si and GaN, and the thickness of SiC is smaller than the thickness of Si. Therefore, the adverse effect of the underlying SiC film 12 on the GaN film 22 is small. As a result, a high-quality GaN film 22 with few dislocations and few warpage / cracks can be obtained simply by providing a simple buffer layer (AlN film 21).

Further, a GaN free-standing substrate may be obtained by forming a GaN film 22 as thick as several hundred μm. In this case, the number of defects contained in the GaN film 22 is very small. When the GaN film 22 is formed as thick as several hundred μm, the growth time of the GaN film 22 may be shortened by using the H-VPE (Hydride Vapor Phase Epitaxy) method having a high growth rate. Further, the MOCVD method and the H-VPE method may be combined.

When the compound semiconductor substrate 1a is used for applications such as power devices and high-frequency devices, after the compound semiconductor substrate 1a is completed, a device layer (High Electron Mobility Transistor) layer such as a HEMT (High Electron Mobility Transistor) layer is formed on the surface 22a of the GaN film 22. Specifically, the device layer may include an AlGaN barrier layer, an AlN spacer layer, a GaN cap layer, and the like).

When the compound semiconductor substrate 1a is used for power devices, high-frequency devices, etc., a part of Si under the SiC film 12 is removed, so that an insulating ceramic having high thermal conductivity (AlN, etc.) The SiC film 12 can be directly attached to the heat sink made of the material. As a result, the heat dissipation can be improved, and a device that handles high power can be realized.

Further, when the compound semiconductor substrate 1a is used for the application of a light emitting device such as an LED (Light Emitting Diode), after the compound semiconductor substrate 1a is completed, the surface 22a of the GaN film 22 has a repeating structure of an InGaN layer and a GaN layer. A device layer such as an MQW layer (quantum well layer) including the above and a p-type GaN layer (Mg-doped GaN layer) may be provided.

When the compound semiconductor substrate 1a is used as a light emitting device, a part of Si under the SiC film 12 is removed, so that absorption of visible light by Si can be avoided. As a result, it is possible to extract light from the back surface of the SiC film 12, and it is possible to realize a high-luminance light emitting device.

[Fourth Embodiment]

FIG. 22 is a cross-sectional view showing the configuration of the compound semiconductor substrate 1b according to the fourth embodiment of the present invention. FIG. 22 is a cross-sectional view of the graphene film 25 when cut in a plane perpendicular to the surface 25a.

With reference to FIG. 22, the compound semiconductor substrate 1b in the present embodiment further includes a graphene film 25.

The graphene film 25 is formed on the surface 12a of the SiC film 12 (an example of one main surface of the SiC film). The graphene film 25 may be made of a single-layer graphene film or may be made of a laminated multi-layer graphene film (that is, a graphite film). The graphene film 25 has a thickness of, for example, 0.3 nm or more and 1 μm or less.

Since the configuration of the compound semiconductor substrate 1b other than the above is the same as the configuration of the compound semiconductor substrate 1 in the first embodiment shown in FIGS. 1 and 2, the same members are designated by the same reference numerals. , The explanation is not repeated.

Subsequently, a method for manufacturing the compound semiconductor substrate 1b according to the present embodiment will be described.

First, the structure shown in FIG. 8 is obtained by using the same manufacturing method as the manufacturing method in the first embodiment. As an example, the structure shown in FIG. 8 includes a Si substrate 11 having an outer edge having an outer diameter of 100 mm and an inner diameter of 80 mm, and a SiC film 12 having a thickness of 50 nm formed on the Si substrate 11.

Referring to FIG. 23, then, the compound semiconductor substrate 1 was placed in a container such as a furnace, for example, in an H ₂ atmosphere for one hour heat treatment at a compound temperature of the semiconductor substrate 1 1200 ° C. (annealing) Do. As a result, the bond between the Si atom and the C atom forming the portion 12d (the portion surrounded by the dotted line) close to the surface 12a of the SiC film 12 is decomposed, and the Si atom is eliminated. As a result, only the SiC in the upper portion 12d of the SiC film 12 changes to the graphene film 25.

Instead of changing a part of the SiC film 12 into the graphene film 25, the graphene film 25 may be laminated on the surface 12a of the SiC film 12 by the following method. Specifically, a solvent in which graphene is dispersed is applied to the surface 12a of the SiC film 12 by a method such as spin coating or spray coating. When the spin coating method is used, the structure shown in FIG. 8 is fixed to the fixing base HP (FIG. 10) so that the surface 12a of the SiC film faces upward, and the fixing base HP is rotated. As the solvent in which graphene is dispersed, for example, a graphene flower dispersion such as MEK (methyl ethyl ketone) (polymeric surfactant) [GF9MEK-DS] (manufactured by Incubation Alliance) can be used. After applying a solvent in which graphene is dispersed, heat treatment is performed at 400 ° C. for 20 minutes, for example. As a result, the solvent evaporates, and the hardened graphene film 25 is laminated on the SiC film 12. In this method, the SiC film 12 is not grapheneized.

With reference to FIG. 24, the Si of the bottom surface RG2 of the recess 13 of the Si substrate 11 and the outer peripheral portion RG3 of the back surface 11b of the Si substrate 11 are then removed by wet etching. As a result, the back surface 12b of the SiC film 12 is exposed on the bottom surface of the recess 13. By the above steps, the compound semiconductor substrate 1b shown in FIG. 22 is obtained.

As an alternative manufacturing method of the present embodiment, after removing the bottom surface RG2 of the recess 13 of the Si substrate 11, a part of the SiC film 12 may be changed to the graphene film 25. In this case, since Si atoms are desorbed from both the front surface 12a and the back surface 12b of the SiC film 12, the graphene film 25 is formed on both the front surface 12a and the back surface 12b of the SiC film 12. Further, after removing the bottom surface RG2 of the recess 13 of the Si substrate 11, the graphene film 25 may be formed (laminated) on the surface 12a of the SiC film 12.

In the compound semiconductor substrate 1b, the Si substrate 11 may be completely removed by using fluorine or the like after the graphene film 25 is formed (after the compound semiconductor substrate 1b is completed).

According to the present embodiment, the thin graphene film 25 can be obtained by using the thin SiC film 12 of the compound semiconductor substrate 1 in the first embodiment as a raw material. Since graphene is excellent in mechanical strength and thermal properties, the graphene film 25 plays a role of protecting the SiC film 12 when the compound semiconductor substrate 1b is used as a pellicle film. Graphene in particular has a negative coefficient of thermal expansion. Therefore, when the compound semiconductor substrate 1b is used as the pellicle film, it is possible to avoid a situation in which the pellicle film is bent even if the temperature of the pellicle film is raised by EUV irradiation.

[Fifth Embodiment]

FIG. 25 is a cross-sectional view showing an example of how to use the compound semiconductor substrate 1 according to the fifth embodiment of the present invention.

With reference to FIG. 25, in the present embodiment, the compound semiconductor substrate 1 of the first or second embodiment is used as the pellicle film 100 covering the mask MK. On the surface of the mask MK, a pattern PN for blocking the exposure light and a pellicle frame PF for supporting the pellicle film 100 are provided. The pellicle film 100 is fixed to the pellicle frame PF by adhesion or the like in a state where the mask MK side is the Si substrate 11 and the side opposite to the mask MK is the SiC film 12. The compound semiconductor substrate 1 may be processed according to the shape of the mask MK or the pellicle frame PF, if necessary.

It is also possible to use the compound semiconductor substrate 1b of the fourth embodiment as the pellicle film 100. In this case, the pellicle film 100 is fixed to the pellicle frame PF by adhesion or the like with the mask MK side as the Si substrate 11 and the side opposite to the mask MK as the graphene film 25.

The pellicle film 100 is for preventing exposure troubles caused by foreign matter adhering to the mask MK during exposure focusing on an exposure object (semiconductor substrate or the like). The exposure light passes through the pellicle film 100 and enters the surface of the mask MK, as indicated by the arrow AR5. A part of the exposure light that has passed through the gap of the pattern PN is reflected on the surface of the mask MK and passes through the pellicle film 100. After that, the exposure light is applied to a photoresist (not shown) applied to the surface of the object to be exposed.

Any wavelength can be used as the exposure light, but in order to realize a high resolution lithography technique, the exposure light is UV (Extreme Ultra-Violet) light having a wavelength of several tens of nm to several nm. It is preferable to be used. Since SiC and graphene are chemically stable compared to Si, have high transmittance and high light resistance to EUV light, they are suitable as a pellicle film when EUV light is used as exposure light. .. In particular, by using the compound semiconductor substrate 1 containing the extremely thin SiC film 12 of 20 nm or more and 10 μm or less as the pellicle film 100, as in the compound semiconductor substrate 1 of the first or second embodiment, the transmittance is further increased. Can be realized.

[Example]

The inventor of the present application has attempted to produce a compound semiconductor substrate by the methods of Examples 1 and 2 of the present invention and Comparative Examples described below.

Example 1: A Si substrate having a diameter of 4 inches and a thickness of 525 μm and having a surface composed of (100) planes was prepared. Next, while holding the Si substrate by the method shown in FIG. 19, a SiC film having a thickness of 160 nm was formed on the surface of the Si substrate by the CVD method. The SiC film was made of a 3C-SiC single crystal, and its surface was composed of (100) planes. Further, a SiC film was also formed on the side surface of the Si substrate and the region within 1 cm from the outer peripheral end portion of the back surface of the Si substrate.

Subsequently, a part of the Si substrate was removed by spin etching. Specifically, the Si substrate was rotated at a speed of 1000 rpm, and the chemical solution was injected. A mixed acid called "Si-E" manufactured by Mitsubishi Chemical Corporation was used as the chemical solution. When the dummy Si substrate was etched in advance under the conditions of this spin etching, an etching rate of 25 μm / min was obtained. When the Si substrate was observed during spin etching, as shown in FIG. 26, the growth and retention of bubbles were suppressed, and a very smooth reaction surface was observed. It is presumed that the etching of Si proceeded uniformly.

After performing the above-mentioned spin etching for 21 minutes, pure water was injected into the Si substrate instead of the chemical solution, and the Si substrate was rinsed. The Si substrate was rinsed for 1 minute. As a result, a compound semiconductor substrate was obtained.

When the obtained compound semiconductor substrate was observed, an annular SiC film was formed on the front surface, the side surface, and the outer peripheral portion of the back surface of the Si substrate. On the back surface of the Si substrate, Si was completely removed from the inside of the annular SiC film having a diameter of about 8 cm in a circular recess, and the self-supporting SiC film was exposed at the bottom of the recess. When observed using X-rays, it was confirmed that the SiC film was a single crystal. As a result, a compound semiconductor substrate having a large-area SiC film that was self-supporting (composed of SiC alone) was obtained.

Example 2: A compound semiconductor substrate was produced by the same manufacturing method as in Example 1 of the present invention, except that the thickness of the SiC film was 50 nm instead of 160 nm.

When the obtained compound semiconductor substrate was observed, an annular SiC film was formed on the front surface, the side surface, and the outer peripheral portion of the back surface of the Si substrate. On the back surface of the Si substrate, Si was completely removed from the inside of the annular SiC film having a diameter of about 8 cm, and Si was completely removed, and the self-supporting SiC film was exposed at the bottom of the recess. When observed using X-rays, it was confirmed that the SiC film was a single crystal. As a result, a compound semiconductor substrate having a large-area SiC film that was self-supporting (composed of SiC alone) was obtained.

Comparative Example: A Si substrate was prepared in the same manner as in the example of the present invention, and a SiC film was formed on the surface of the Si substrate. Subsequently, a part of the Si substrate was removed by wet etching by immersing the Si substrate and the SiC film in the chemical solution filled in the container. As the chemical solution, the same one as in the case of the example of the present invention was used. When the Si substrate was observed during the wet etching, as shown in FIG. 27, the growth and retention of bubbles on the reaction surface of the Si substrate were observed. It is presumed that the etching of Si proceeded non-uniformly.

After immersion in the above-mentioned chemical solution for 5 hours, the Si substrate and the SiC film were taken out from the chemical solution, and then rinsed with pure water for 10 minutes. As a result, a compound semiconductor substrate was obtained.

When the obtained compound semiconductor substrate was observed, an annular SiC film was formed on the front surface, the side surface, and the outer peripheral portion of the back surface of the Si substrate. On the back surface of the Si substrate, Si partially remained in the recess inside the annular SiC film. In addition, there was a place where the SiC film was torn in the recess. The self-supporting SiC film was obtained only in a region having a diameter of about 2 mm at the maximum.

[Other]

In the above-described embodiment, the case where Si on the bottom surface of the recess 13 is removed by wet etching has been shown, but in the present invention, the portion removed by wet etching may be at least a part of the other main surface of the Si substrate. The position, size, and shape of the portion to be removed are arbitrary.

In the above-described embodiment, the case where the GaN film 22 or the graphene film 25 is formed on the surface of the SiC film 12 has been shown, but when another film is formed on the surface of the SiC film, the film is different from the SiC film. It should be.

The above embodiments can be combined with each other. For example, by combining the second embodiment and the third embodiment, the outer peripheral portions of the front surface 11a, the side surface 11c, and the back surface 11b of the Si substrate 11 are completely covered with the continuous SiC film 12. The GaN film 22 may be formed on the compound semiconductor substrate 1 that is present.

Further, by combining the second embodiment and the fourth embodiment, the outer peripheral portions of the front surface 11a, the side surface 11c, and the back surface 11b of the Si substrate 11 are completely covered with the continuous SiC film 12. The graphene film 25 may be formed on the compound semiconductor substrate 1. In this case, immediately after the step shown in FIG. 17, a part of the SiC film 12 is changed to the graphene film 25 (or the graphene film 25 is laminated on the surface 12a of the SiC film 12), and then the step shown in FIG. 18 is performed. Will be implemented.

Further, a modified example of the manufacturing method of the first embodiment shown in FIGS. 14 and 15 and the fourth embodiment may be combined. In this case, a part of the SiC film 12 is changed to the graphene film 25 immediately after the step shown in FIG. 14 (or the graphene film 25 is laminated on the surface 12a of the SiC film 12), and then the step shown in FIG. 15 is performed. Will be implemented.

The embodiments and examples described above should be considered in all respects as exemplary and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1,1a, 1b Compound semiconductor substrate 2 Intermediate 11 Si substrate 11a Si substrate front surface 11b Si substrate back surface 11c Si substrate side surface 12 SiC film 12a SiC film surface 12b SiC film back surface 12c SiC film side surface 12d SiC film 13 Concave part 14 Mask layer 15 Photoresist 21 AlN film 21a AlN film surface 22 GaN film 22a GaN film surface 25 Graphene film 25a Graphene film surface 31 Holding part 31a Outer part of holding part 31b Protruding part of holding part 100 Pellicle Membrane CS Reaction Vessel HP Fixing Base MA Chemical Solution MK Mask PF Pellicle Frame PL A plane parallel to the surface of the SiC film PN pattern RG1 Central part of the back surface of the Si substrate RG2 Bottom surface of the recess of the Si substrate RG3 Outer circumference of the back surface of the Si substrate Part RG4 Si Substrate back surface exposed central part Space between the outer peripheral part and a plurality of protruding parts in the SP holding part

Claims (17)

A Si substrate with an annular planar shape and
A SiC film formed on one main surface of the Si substrate and having a thickness of 20 nm or more and 10 μm or less is provided.
The SiC film is a compound semiconductor substrate that is not formed on the other main surface of the Si substrate. The compound semiconductor substrate according to claim 1, wherein the width of the Si substrate decreases as the distance from the SiC film increases when viewed in a cross section cut in a plane perpendicular to the surface of the SiC film. The compound semiconductor substrate according to claim 1 or 2, further comprising a film different from SiC formed on one main surface of the SiC film. The compound semiconductor substrate according to claim 3, wherein the film different from SiC is made of graphene, graphite, or GaN. A pellicle film using the compound semiconductor substrate according to any one of claims 1 to 4. The process of forming a SiC film on one main surface of a Si substrate,
A step of removing at least a part of the other main surface of the Si substrate by wet etching is provided.
A method for producing a compound semiconductor substrate, in which the Si substrate and the SiC film are relatively moved with respect to a chemical solution used for wet etching in a step of removing at least a part of the other main surface of the Si substrate. Claim that in the step of removing at least a part of the other main surface of the Si substrate, the Si substrate and the SiC film are moved in a direction in a plane parallel to one main surface of the SiC film. 6. The method for producing a compound semiconductor substrate according to 6. In the step of removing at least a part of the other main surface of the Si substrate, the chemical solution used for the wet etching is applied to the other main surface of the Si substrate in a state where the Si substrate and the SiC film are rotated. The method for producing a compound semiconductor substrate according to claim 7, wherein the compound semiconductor substrate is injected. Further comprising a step of forming a recess having Si as a bottom surface in the central portion of the other main surface of the Si substrate.
The method for producing a compound semiconductor substrate according to any one of claims 6 to 8, wherein the SiC film is exposed on the bottom surface of the recess in the step of removing at least a part of the other main surface of the Si substrate. The compound according to claim 9, wherein after the step of forming the recess in the central portion of the other main surface of the Si substrate, the step of forming the SiC film on the one main surface of the Si substrate is performed. Manufacturing method of semiconductor substrate. The compound according to claim 9, wherein after the step of forming the SiC film on the one main surface of the Si substrate, the step of forming the recess in the central portion of the other main surface of the Si substrate is performed. Manufacturing method of semiconductor substrate. In the step of forming the recess in the central portion of the other main surface of the Si substrate, the Si substrate uses a mask layer made of an oxide film or a nitride film formed on the other main surface of the Si substrate as a mask. The method for producing a compound semiconductor substrate according to any one of claims 9 to 11, wherein the central portion of the other main surface is removed by wet etching. In the step of forming the SiC film, the SiC film is formed on the one main surface and side surface of the Si substrate and the outer peripheral portion of the other main surface of the Si substrate.
In the step of removing at least a part of the other main surface of the Si substrate, the other of the Si substrate is masked by the SiC film formed on the outer peripheral portion of the other main surface of the Si substrate. The method for producing a compound semiconductor substrate according to any one of claims 6 to 8, wherein the main surface is removed. The compound semiconductor substrate according to any one of claims 6 to 13, wherein a mixed acid containing hydrofluoric acid and nitric acid is used as the chemical solution used for the wet etching in the step of removing at least a part of the other main surface of the Si substrate. Manufacturing method. 6. To any of claims 6 to 14, further comprising a step of forming a GaN film on one main surface of the SiC film after the step of removing at least a part of the other main surface of the Si substrate. The method for manufacturing a compound semiconductor substrate according to the description. The method for producing a compound semiconductor substrate according to any one of claims 6 to 14, further comprising a step of changing a part of the SiC film into a graphene film or a graphite film. The method for producing a compound semiconductor substrate according to any one of claims 6 to 14, further comprising a step of laminating a graphene film or a graphite film on one main surface of the SiC film.