Nitride semiconductor substrate and method for producing same

Abstract

To provide a nitride semiconductor substrate capable of suppressing warpage defect by a plastic deformation in an epitaxial growth or a device process in the case of manufacturing a nitride semiconductor substrate by using a silicon signal crystal substrate, and provide a manufacturing method of the same.SOLUTION: In a nitride semiconductor substrate, a nitride semiconductor thin film is formed on a front surface of a silicon single crystal substrate having a front surface and a back surface. The silicon single crystal substrate includes at least on the front surface and the back surface, a carbon diffusion layer having a carbon concentration higher than that of a bulk part of the silicon single crystal substrate by implantation of carbon, and the carbon concentration of the carbon diffusion layer is 5E+16atoms / cm3 or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a nitride semiconductor substrate and a method for manufacturing the same. [Background technology]

[0002] In order to reduce the size and cost of high-frequency devices, development is underway to integrate devices such as antennas, amplifiers, switches, and filters. As frequencies become higher, circuits become more complex and the materials used in the devices become more diverse, including silicon CMOS, devices using III-V semiconductors and nitride semiconductors, and filters using piezoelectric materials.

[0003] It is believed that the substrates underlying these devices will be suitable for use in single crystal silicon wafers, which are available in large diameter wafers at low cost. In particular, single crystal silicon substrates with high resistance and low oxygen content, which have little change in resistivity due to thermal donors, are suitable for use in high frequency devices.

[0004] However, high-resistivity, low-oxygen single crystal silicon substrates have poorer mechanical properties than low-resistivity CZ substrates, and are prone to plastic deformation due to dislocation extension. In particular, when growing GaN on single crystal silicon substrates, stress due to differences in lattice constants and thermal expansion coefficients can easily cause increased warping and plastic deformation, so stress reduction is being carried out by adjusting growth conditions and using relaxation layers.

[0005] For example, in Patent Document 1, a wafer with less warpage and cracks is fabricated by using an intermediate layer of a gallium nitride compound semiconductor that is periodically laminated multiple times to relieve stress. However, there is a concern that fabricating a complex intermediate layer will lengthen the growth time and reduce the degree of freedom in design.

[0006] Furthermore, Patent Document 2 discloses a technology for obtaining high-strength silicon single crystal wafers by carbon doping at the bulk crystal stage and then performing RTA. However, it is difficult to obtain crystals with a controlled carbon concentration, and there are concerns about a decrease in yield.

[0007] In addition, in Patent Document 3, a step of removing the surface layer is added after carbon doping by RTA. The step of removing the surface layer raises concerns about defects and contamination due to etching residues, and therefore a method for growing a mirror-like GaN epitaxial layer without removing the surface layer is desired. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2012-79952 A [Patent Document 2] WO2004 / 008521 publication [Patent Document 3] JP 2021-008386 A Summary of the Invention [Problem to be solved by the invention]

[0009] In order to improve high frequency characteristics of high frequency devices, it is necessary to reduce the parasitic capacitance of the device, its supporting substrate, and the surrounding package. If a high-resistivity silicon single crystal substrate that does not generate thermal donors is used for the supporting substrate and package to reduce the parasitic capacitance, it is thought that the characteristics will be improved and there will be a cost advantage.

[0010] On the other hand, device manufacturing involves processes such as epitaxial growth on a substrate, heat treatment, and bonding, during which stress is generated in the substrate due to differences in lattice constants and thermal expansion coefficients between different materials. However, high-resistivity, low-oxygen substrates have the disadvantage that they are more susceptible to plastic deformation when dislocations are generated, compared to normal low-resistivity substrates. When plastic deformation occurs, the wafer becomes significantly distorted and cannot be restored to its original shape, which can lead to warping abnormalities and poor bonding.

[0011] The present invention has been made to solve the above-mentioned problems, and has an object to provide a nitride semiconductor substrate and a manufacturing method thereof that can suppress warpage defects due to plastic deformation during epitaxial growth or device processing when a nitride semiconductor substrate is manufactured using a silicon single crystal substrate. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides A nitride semiconductor substrate comprising a silicon single crystal substrate having a front surface and a back surface, the nitride semiconductor thin film being formed on the front surface of the substrate, The silicon single crystal substrate has a carbon diffusion layer on at least the front surface and the back surface, in which carbon is implanted to have a higher carbon concentration than a bulk portion of the silicon single crystal substrate, and the carbon concentration of the carbon diffusion layer is 5E+16 atoms / cm 3 The above nitride semiconductor substrate is provided.

[0013] Such a nitride semiconductor substrate can suppress warpage defects caused by plastic deformation during epitaxial growth or device manufacturing steps when a nitride semiconductor substrate is manufactured using a silicon single crystal substrate.

[0014] The silicon single crystal substrate has a resistivity of 100 Ωcm or more and an oxygen concentration of 7E+17 atoms / cm 3 It is preferable that the following is true:

[0015] According to the present invention, even when a silicon single crystal substrate having high resistivity, low oxygen concentration, and low mechanical strength is used, a nitride semiconductor wafer in which plastic deformation and warpage are suppressed can be obtained.

[0016] The carbon diffusion layer preferably has a thickness of 1 μm or more.

[0017] In such a nitride semiconductor substrate, the carbon concentration in the region of at least 1 μm on the front and back sides is 5E+16 atoms / cm 3As a result, it is possible to more reliably prevent the propagation of dislocations in the silicon single crystal substrate and prevent plastic deformation.

[0018] It is also preferable that an Al layer is provided between the surface of the silicon single crystal substrate and the nitride semiconductor thin film.

[0019] By providing an Al layer on the growth surface side of the silicon single crystal substrate, the adhesion between the silicon single crystal substrate and the epitaxial layer can be improved.

[0020] In this case, the thickness of the Al layer is preferably 1 to 5 nm.

[0021] If the thickness is 5 nm or less, the unevenness of the Al layer is small, and the surface roughness of the nitride semiconductor layer grown thereon is also small. Also, if the thickness is 1 nm or more, the surface of the silicon single crystal substrate is sufficiently covered, and the adhesion of the nitride semiconductor thin film can be further improved.

[0022] In the present invention, A method for manufacturing a nitride semiconductor substrate, comprising forming a nitride semiconductor thin film on a surface of a silicon single crystal substrate having a front surface and a back surface, the method comprising the steps of: (1) providing a silicon single crystal substrate having a front surface and a back surface; (2) Injecting carbon into at least the front surface and the back surface of the silicon single crystal substrate by an RTA method to obtain a carbon concentration of 5E+16 atoms / cm 3 The above-mentioned step of forming a carbon diffusion layer; (3) growing a nitride semiconductor thin film containing gallium nitride by vapor phase epitaxy on the surface of the silicon single crystal substrate on which the carbon diffusion layer is formed. The present invention provides a method for producing a nitride semiconductor substrate, comprising the steps of:

[0023] In this way, the manufacturing method of injecting a high concentration of carbon into a silicon single crystal substrate by the RTA method does not hinder single crystallization as occurs in the method of doping with carbon during the growth of the silicon single crystal, and makes it possible to relatively easily and reliably manufacture nitride semiconductor wafers in which plastic deformation and warping are suppressed.

[0024] In the step (1), the silicon single crystal substrate to be prepared is a silicon single crystal substrate having a resistivity of 100 Ωcm or more and an oxygen concentration of 7E+17 atoms / cm 3 It is preferable that the following is used:

[0025] According to the present invention, even when a silicon single crystal substrate having high resistivity, low oxygen concentration, and low mechanical strength is used, a nitride semiconductor wafer in which plastic deformation and warpage are suppressed can be manufactured.

[0026] In the step (2), the carbon diffusion layer preferably has a thickness of 1 μm or more.

[0027] With such a thickness, the propagation of dislocations in the silicon single crystal substrate can be more reliably prevented, and therefore a nitride semiconductor wafer with reduced warpage can be easily manufactured.

[0028] In addition, between the steps (2) and (3), it is preferable to carry out a step (2') of forming an Al layer on the surface of the silicon single crystal substrate on which the carbon diffusion layer is formed, by using trimethylaluminum (TMA) at a temperature of 900°C or less.

[0029] In this way, the Al layer can be easily formed, and a nitride semiconductor substrate with improved adhesion of the epitaxial layer can be manufactured.

[0030] At this time, in the step (2'), the thickness of the Al layer is preferably set to 1 to 5 nm.

[0031] If the thickness is 5 nm or less, the unevenness of the Al layer is reduced, and the surface roughness of the nitride semiconductor layer grown on it is also reduced. Also, if the thickness is 1 nm or more, the surface of the silicon single crystal substrate is sufficiently covered, further improving the adhesion of the nitride semiconductor thin film. Effect of the Invention

[0032] As described above, the present invention can provide a nitride semiconductor substrate and a manufacturing method thereof that can suppress warpage defects due to plastic deformation during epitaxial growth or device processing when the nitride semiconductor substrate is manufactured using a high-resistance, low-oxygen silicon single crystal substrate. Furthermore, by forming an Al layer as an intermediate layer on the epitaxial growth surface of the substrate, the adhesion with the nitride semiconductor thin film can be further improved. [Brief description of the drawings]

[0033] [Figure 1] 1 is a schematic diagram showing an example of a nitride semiconductor substrate of the present invention. [Diagram 2] 1 is a schematic diagram showing an example of a silicon single crystal substrate used in the present invention. [Diagram 3] 1 is a schematic diagram showing an example of a nitride semiconductor thin film used in the present invention. [Figure 4] 1 is a graph showing changes in substrate curvature during growth of nitride semiconductor thin films in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] As described above, there has been a demand for the development of a nitride semiconductor substrate and a manufacturing method thereof that can suppress warpage defects due to plastic deformation during epitaxial growth or device processing when a nitride semiconductor substrate is manufactured using a silicon single crystal substrate.

[0035] As a result of extensive investigations into the above-mentioned problems, the inventors have found that a silicon single crystal substrate having carbon implanted into its surface by an RTA method can suppress plastic deformation during the growth of a nitride semiconductor thin film, and have completed the present invention.

[0036] That is, the present invention provides a nitride semiconductor substrate having a nitride semiconductor thin film formed on the surface of a silicon single crystal substrate having a front surface and a back surface, the silicon single crystal substrate having a carbon diffusion layer on at least the front surface and the back surface into which carbon is implanted to have a higher carbon concentration than a bulk portion of the silicon single crystal substrate, and the carbon concentration of the carbon diffusion layer is 5E+16 atoms / cm 3 The nitride semiconductor substrate is as described above.

[0037] The present invention also provides a method for producing a nitride semiconductor substrate, in which a nitride semiconductor thin film is formed on the surface of a silicon single crystal substrate having a front surface and a back surface, the method comprising the steps of: (1) preparing a silicon single crystal substrate having a front surface and a back surface; (2) implanting carbon into at least the front surface and the back surface of the silicon single crystal substrate by an RTA method to obtain a carbon concentration of 5E+16 atoms / cm 3 The method for manufacturing a nitride semiconductor substrate includes the steps of: (1) forming a carbon diffusion layer as described above; and (2) growing a nitride semiconductor thin film containing gallium nitride by vapor phase growth on the surface of the silicon single crystal substrate on which the carbon diffusion layer is formed.

[0038] The present invention will be described in detail below, but the present invention is not limited thereto.

[0039] <Nitride semiconductor substrate> As shown in Fig. 1, a nitride semiconductor substrate 100 of the present invention is a silicon single crystal substrate 1 having a front surface 1a and a back surface 1b, on which a nitride semiconductor thin film 3 is formed. An Al layer 2 may be provided as an intermediate layer between the front surface 1a of the silicon single crystal substrate 1 and the nitride semiconductor thin film 3. As shown in Fig. 2, the silicon single crystal substrate 1 of the present invention has, at least on the front surface 1a and the back surface 1b, a carbon diffusion layer 12 having a higher carbon concentration than that of a bulk portion 11 of the silicon single crystal substrate 1 due to implantation of carbon, and the carbon concentration of the carbon diffusion layer 12 is 5E+16 atoms / cm 3 That's all.

[0040] Silicon single crystal substrate To reduce parasitic capacitance, the silicon single crystal substrate should preferably have a resistivity of 100 Ωcm or more and an oxygen concentration of 7E+17 atoms / cm 3 The silicon single crystal substrate is as follows: Before carbon is implanted, the silicon single crystal substrate is preferably a low-oxygen, high-resistance silicon single crystal substrate that is less affected by thermal donors in order to reduce leakage current through the substrate, particularly one produced by the FZ method, but a high-resistance, low-oxygen silicon single crystal substrate produced by the CZ method is also acceptable.

[0041] In addition, the carbon concentration on the front and back is 5E+16atoms / cm 3 A substrate with the above carbon diffusion layer is used. The carbon diffusion layer may also be formed on the side of the substrate. The carbon concentration is 5E+16 atoms / cm 3 If the carbon concentration is less than 100%, the effect of suppressing plastic deformation during epitaxial growth cannot be obtained. There is no particular upper limit to the carbon concentration in the carbon diffusion layer. 3 It can be as follows:

[0042] The thickness of the carbon diffusion layer is not particularly limited, but may be, for example, 1 μm or more. There is also no particular upper limit to the thickness, but may be, for example, 20 μm or less, preferably 10 μm or less, and more preferably 5 μm or less.

[0043] The method for producing the carbon diffusion layer is not particularly limited, but it is preferable to produce it by a method in which heat treatment is performed in an atmosphere containing a hydrocarbon using the RTA method.

[0044] A trap rich layer that reduces the carrier lifetime may be formed on the surface of the silicon single crystal substrate. The method of formation is not particularly limited, but the trap rich layer can be formed by ion implantation or irradiation with ionizing radiation such as electron beams, X-rays, and gamma rays.

[0045] Al layer In the nitride semiconductor substrate of the present invention, an Al layer may be provided as an intermediate layer. The Al layer acts as a buffer layer inserted to improve the crystallinity and control stress of the nitride semiconductor thin film (device layer). By forming an Al layer mainly composed of Al on the surface (upper surface) of a silicon single crystal substrate into which carbon has been implanted by the RTA method, the crystallinity and crystal morphology of the nitride semiconductor thin film (epitaxial layer) are improved, and adhesion is increased to more reliably prevent peeling of the epitaxial layer.

[0046] The thickness of the Al layer is preferably 1 to 5 nm. If the thickness is 5 nm or less, the unevenness of the Al layer is small, and the surface roughness of the nitride semiconductor layer grown thereon is also small. If the thickness is 1 nm or more, the surface of the silicon single crystal substrate is sufficiently covered, and the adhesion of the nitride semiconductor thin film can be further improved.

[0047] Nitride Semiconductor Thin Film The nitride semiconductor thin film is formed on a silicon single crystal substrate or an Al layer by vapor phase growth such as thermal CVD, MOVPE, MBE, vacuum deposition, or sputtering. For the nitride semiconductor thin film, nitrides such as GaN, AlN, InN, AlGaN, InGaN, AlInN, and AlScN, and III-V group semiconductors can be used. The film thickness is not particularly limited, but can be designed to suit the device, for example, 1 to 10 μm.

[0048] For example, in a high mobility transistor (HEMT) structure, as shown in Fig. 3, a nitride semiconductor thin film (device layer) 3 is composed of gallium nitride (GaN) 31 and an electron supply layer 32 made of AlGaN formed thereon. To improve device characteristics, the nitride semiconductor thin film is preferably a crystal with few crystal defects and few impurities such as carbon and oxygen, and is preferably fabricated at 900°C to 1350°C using the MOVPE method.

[0049] Gallium nitride has a lattice constant difference of 17% and a thermal expansion coefficient difference of 116% with respect to Si(111) single crystal, and thus stress is applied to the thin film and substrate during growth at high temperatures. In addition, since the wafer is heated to 1000°C or higher during growth, when stress is applied to the wafer, it does not break brittle but shows ductility, generating dislocations and causing plastic deformation. However, in the present invention, carbon is injected into the front and back surfaces to prevent the progression of dislocations in the silicon single crystal substrate and prevent plastic deformation. By preventing plastic deformation, warpage abnormalities can be reduced and yield can be improved. In addition, since the substrate can withstand stress, the thickness of the epitaxial layer can be increased, improving the freedom of device design.

[0050] <Method of Manufacturing Nitride Semiconductor Substrate> The nitride semiconductor substrate of the present invention can be produced by a method for producing a nitride semiconductor substrate of the present invention, which includes the following steps (1) to (3), and, if necessary, the following step (2′).

[0051] Process (1) Step (1) is a step of preparing a silicon single crystal substrate having a front surface and a back surface. The silicon single crystal substrate prepared in this step is not particularly limited, but for example, as described above, a silicon single crystal substrate having a small parasitic capacitance, a resistivity of 100 Ωcm or more, and an oxygen concentration of 7E+17 atoms / cm 3 The following silicon single crystal substrates can be used: The silicon single crystal may be produced by either the FZ method or the CZ method, with the FZ method being more preferred.

[0052] Process (2) In step (2), carbon is implanted into at least the front and back surfaces of the silicon single crystal substrate by the RTA method to obtain a carbon concentration of 5E+16 atoms / cm 3 This completes the process of forming the carbon diffusion layer.

[0053] The conditions of the RTA treatment in this step are not particularly limited as long as carbon can be injected into the front and back surfaces of the silicon single crystal substrate. The atmosphere in the RTA treatment can be, for example, a mixed atmosphere containing a hydrocarbon gas and Ar. The temperature and time of the RTA treatment can be, for example, a temperature of 1100°C or higher and a silicon melting point or lower, and 10 seconds or higher and 150 seconds or lower.

[0054] Process (2') Between steps (2) and (3), a step (2') of forming an Al layer on the surface of the silicon single crystal substrate on which the carbon diffusion layer has been formed may be performed using trimethylaluminum (TMA) at a temperature of 900° C. or less. The thickness of the Al layer may be, for example, 1 to 5 nm.

[0055] In this process, in order to form an Al layer on the surface of the silicon single crystal substrate, trimethylaluminum is introduced as the Al raw material while keeping the inside of the furnace at a high temperature, and the flow rate and time are adjusted to obtain the desired film thickness. There is no particular limitation on the carrier gas, but hydrogen can be used, for example.

[0056] Process (3) The step (3) is a step of growing a nitride semiconductor thin film containing gallium nitride by vapor phase epitaxy on the surface of the silicon single crystal substrate on which the carbon diffusion layer has been formed.

[0057] In this process, a device layer made of a nitride semiconductor thin film containing gallium nitride is fabricated by vapor phase growth such as thermal CVD, MOVPE, MBE, vacuum deposition, and sputtering. For the thin film, nitrides such as GaN, AlN, InN, AlGaN, InGaN, AlInN, and AlScN, and III-V group semiconductors can be used. The film thickness is, for example, 1 to 10 μm and can be designed according to the device.

[0058] During epitaxial growth, TMAl can be used as the Al source, TMGa as the Ga source, and NH3 as the N source. The carrier gas can be N2 and / or H2, and the process temperature can be about 900 to 1350°C.

[0059] In this process, stress is applied to the silicon single crystal substrate, but since the carbon diffusion layer described above is formed on the surface of the silicon single crystal substrate, the propagation of dislocations in the silicon single crystal substrate can be prevented, and plastic deformation can be prevented. Therefore, in the present invention, a nitride semiconductor substrate with small warpage can be manufactured. EXAMPLES

[0060] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0061] Example 1 A silicon single crystal substrate was prepared by the FZ method, which had a resistivity of 100 Ωcm or more and was free of added oxygen.

[0062] The silicon single crystal substrate was heat-treated by the RTA method to implant carbon on the front and back surfaces. The heat treatment was performed at 1250°C for 10 seconds in an atmosphere of CH4 and Ar, implanting a carbon concentration of 5E+16 atoms / cm in the surface layer of the silicon single crystal substrate. 3 A carbon diffusion layer of 1 μm was formed.

[0063] A nitride semiconductor thin film was epitaxially grown by MOVPE on a silicon single crystal substrate with a high carbon concentration on the surface. The growth temperature was 1000-1200°C, and an epitaxial layer of the nitride semiconductor with a total thickness of 2.8μm was grown. The specific manufacturing method is shown below.

[0064] [1] Introduction into the reactor After the silicon single crystal substrate was introduced into the reaction furnace of the MOVPE apparatus, the furnace was filled with nitrogen gas and the gas inside the furnace was evacuated.

[0065] [2] The process of cleaning the substrate surface in a furnace The substrate was heated in a reaction furnace to clean the surface of the substrate. The cleaning temperature was 1050°C, the pressure in the furnace was 50 mbar, and the cleaning was performed for 10 minutes while a mixed gas of hydrogen, nitrogen, ammonia, etc. was supplied to the furnace.

[0066] [3] Al layer formation process Next, to form an Al layer on the substrate, trimethylaluminum was introduced as the Al source while keeping the furnace at a high temperature, and the flow rate and time were adjusted to achieve a film thickness of 2 nm. Hydrogen was used as the carrier gas.

[0067] [4] Step of growing epitaxial layer Next, epitaxial growth of a nitride semiconductor thin film was performed at a furnace pressure of 50 mbar and a substrate temperature of 1120°C. Trimethylaluminum (TMAl) was used as the Al source, trimethylgallium (TMGa) as the Ga source, and ammonia (NH3) as the N source. First, AlN was grown with the TMAl flow rate at standard conditions of 0.24 L / min (240 sccm) and the NH3 flow rate at 2.0 L / min (2000 sccm). Hydrogen was used as the carrier gas for TMAl, TMGa, and NH3. In the same manner, the flow rates of TMAl, TMGa, and NH3, as well as the growth temperature and growth time, were set to grow a buffer layer and a gallium nitride layer.

[0068] By producing the GaN epitaxial substrate in this way, we were able to obtain a high-quality GaN epitaxial substrate on a high-resistance, low-oxygen silicon single crystal substrate in which thermal donors are unlikely to be generated. -1 The change in the carbon concentration of the silicon single crystal substrate is shown in Fig. 4. 3 It was found that the provision of the carbon diffusion layer described above prevented the substrate from plastically deforming during growth. In addition, the amount of warping after growth was 41 μm, which was about 1 / 5 of that in Comparative Example 1 described later.

[0069] Example 2 A nitride semiconductor substrate was manufactured in the same manner as in Example 1, except that the heat treatment conditions for the silicon single crystal substrate by the RTA method were 1250°C for 30 seconds in an atmosphere of CH4 and Ar. At this time, the carbon concentration of the carbon diffusion layer was 8E+16 atoms / cm 3 The amount of warpage after growth was 39 μm, which shows that plastic deformation was suppressed.

[0070] Example 3 A nitride semiconductor substrate was manufactured in the same manner as in Example 1, except that the heat treatment conditions for the silicon single crystal substrate by the RTA method were 1300°C for 10 seconds in an atmosphere of CH4 and Ar. At this time, the carbon concentration of the carbon diffusion layer was 2E+17 atoms / cm 3 The amount of warping after growth was 35 μm, which shows that plastic deformation was suppressed.

[0071] Comparative Example 1 A GaN epitaxial layer was grown under the same conditions as in Example 1, except that the step of injecting carbon into the surface layer by the RTA method in Example 1 was not performed. As can be seen from Figure 4, the substrate was plastically deformed during growth. The amount of warping after growth was 213 μm.

[0072] Comparative Example 2 A nitride semiconductor substrate was manufactured in the same manner as in Example 1, except that the heat treatment conditions for the silicon single crystal substrate by the RTA method were 1225°C for 10 seconds in an atmosphere of CH4 and Ar. At this time, the carbon concentration of the carbon diffusion layer was 2E+16 atoms / cm 3 The amount of warpage after growth was 192 μm, and it was confirmed that when the carbon concentration in the carbon diffusion layer is low, plastic deformation cannot be suppressed.

[0073] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0074] 1...silicon single crystal substrate, 1a...front surface, 1b...back surface, 11...bulk portion, 12...carbon diffusion layer, 2...Al layer, 3...nitride semiconductor thin film, 31...gallium nitride, 32: electron supply layer; 100: nitride semiconductor substrate.

Claims

1. A nitride semiconductor substrate comprising a silicon single crystal substrate having a front surface and a back surface, the nitride semiconductor thin film being formed on the front surface of the substrate, The silicon single crystal substrate has a carbon diffusion layer on at least the front surface and the back surface into which carbon is implanted, the carbon concentration of which is higher than that of a bulk portion of the silicon single crystal substrate, and the carbon concentration of the carbon diffusion layer is 5E+16 atoms / cm ３ A nitride semiconductor substrate characterized by the above.

2. The silicon single crystal substrate has a resistivity of 100 Ωcm or more and an oxygen concentration of 7E+17 atoms / cm ３ 2. The nitride semiconductor substrate according to claim 1, characterized in that:

3. 3. The nitride semiconductor substrate according to claim 1, wherein the carbon diffusion layer has a thickness of 1 [mu]m or more.

4. 4. The nitride semiconductor substrate according to claim 1, further comprising an Al layer between the surface of the silicon single crystal substrate and the nitride semiconductor thin film.

5. 5. The nitride semiconductor substrate according to claim 4, wherein the Al layer has a thickness of 1 to 5 nm.

6. A method for manufacturing a nitride semiconductor substrate, comprising forming a nitride semiconductor thin film on a surface of a silicon single crystal substrate having a front surface and a back surface, the method comprising the steps of: (1) providing a silicon single crystal substrate having a front surface and a back surface; (2) Injecting carbon into at least the front surface and the back surface of the silicon single crystal substrate by an RTA method to obtain a carbon concentration of 5E+16 atoms / cm ３ The above-mentioned step of forming a carbon diffusion layer; (3) A step of growing a nitride semiconductor thin film containing gallium nitride by vapor phase epitaxy on the surface of the silicon single crystal substrate on which the carbon diffusion layer is formed.

2. A method for producing a nitride semiconductor substrate comprising the steps of:

7. In the step (1), the silicon single crystal substrate to be prepared has a resistivity of 100 Ωcm or more and an oxygen concentration of 7E+17 atoms / cm ３ 7. The method for producing a nitride semiconductor substrate according to claim 6, wherein the following is performed:

8. 8. The method for producing a nitride semiconductor substrate according to claim 6, wherein in the step (2), the carbon diffusion layer has a thickness of 1 [mu]m or more.

9. 9. The method for producing a nitride semiconductor substrate according to claim 6, further comprising the step of: (2') performing a step of forming an Al layer on the surface of the silicon single crystal substrate on which the carbon diffusion layer has been formed, using trimethylaluminum (TMA) at a temperature of 900° C. or less, between the steps (2) and (3).

10. 10. The method for producing a nitride semiconductor substrate according to claim 9, wherein in the step (2'), the thickness of the Al layer is set to 1 to 5 nm.

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