Nitride semiconductor substrate and method for manufacturing same

Abstract

Provided is a nitride semiconductor substrate provided with: a silicon substrate having a resistivity of 1000 [Omega] cm or more; or a base substrate provided with a silicon layer having a resistivity of 1000 [Omega] cm or more on the surface thereof; and a group III nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer, the nitride semiconductor substrate being characterized in that the average value of the carbon concentration in the group III nitride semiconductor thin film is 3E + 18 atoms / cm3 or less. As a result, a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity and a method for manufacturing the same are provided.

Description

Technical Field

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

[0002] Group III nitride semiconductors represented by GaN are highly anticipated as next-generation semiconductor materials that surpass the material limits of silicon (Si). GaN can be used to make devices that can operate at high frequencies due to its high saturation electron velocity, and can operate at high output due to its high dielectric breakdown field strength. In addition, it can also be expected to be lightweight or miniaturized, and have low power consumption.

[0003] In recent years, gallium nitride high electron mobility transistors (GaN HEMTs) that can operate at high frequencies and high outputs have attracted attention due to the increase in communication speeds represented by 5G and the accompanying demand for higher outputs. GaN HEMTs used as high-frequency devices are mainly used for GaN epitaxial substrates obtained by forming a GaN epitaxial thin film on a base substrate by metal organic vapor deposition (MOCVD) or the like.

[0004] As the base substrate, a semi-insulating SiC substrate having excellent thermal conductivity may be used. On the other hand, since the semi-insulating SiC substrate is expensive, a silicon substrate which can be manufactured at low cost may be used.

[0005] It is generally known that when a silicon substrate is used as a base substrate of a GaN HEMT for high-frequency applications, it needs to be set to a high resistance to reduce high-frequency losses caused by parasitic capacitance. Patent Documents 1 and 2 record the resistivity of the silicon substrate and the carbon concentration in the epitaxial layer, but do not record anything related to thermal conductivity. Patent Documents 3, 4, and 5 record the carbon concentration and thermal conductivity in the GaN epitaxial layer, but do not record the resistivity and high-frequency characteristics of the silicon substrate.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-245504

[0009] Patent Document 2: WO2011 / 016219

[0010] Patent Document 3: Japanese Patent Application Laid-Open No. 2008-179536

[0011] Patent Document 4: Japanese Patent Application Laid-Open No. 2007-277077

[0012] Patent Document 5: Japanese Patent Application Laid-Open No. 2009-269816 Summary of the invention

[0013] 1. Technical issues to be resolved

[0014] Nitride semiconductor substrates such as GaN epitaxial substrates used for high-frequency applications have the following problems: if the substrate has poor heat dissipation properties (low thermal conductivity), the heat generated by the device cannot be dissipated and cannot be used for a long time, or the operating frequency or input power cannot be increased due to component degradation or temperature resistance problems.

[0015] The use of the GaN epitaxial layer for high-frequency devices depends on the specifications and application of the device and cannot be determined without a definite decision, but it is preferred that the GaN epitaxial layer have a thermal conductivity of 160 W / (m·K) or more.

[0016] Furthermore, it is known that when the carbon concentration is high, the dislocation density of GaN increases and the thermal conductivity deteriorates.

[0017] In addition, the high-frequency loss caused by the increase of parasitic capacitance is also required to be small. If the high-frequency loss is large, the input power needs to be increased, which not only reduces the efficiency of the device but also increases the heat generation.

[0018] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity and a method for manufacturing the same.

[0019] (II) Technical solution

[0020] In order to solve the above technical problems, the present invention provides a nitride semiconductor substrate, which comprises:

[0021] A silicon substrate having a resistivity of 1000 Ω·cm or more, or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more on its surface; and

[0022] epitaxially forming a Group III nitride semiconductor thin film on the silicon substrate or the silicon layer,

[0023] In the nitride semiconductor substrate,

[0024] The average carbon concentration in the Group III nitride semiconductor thin film is 3E+18 atoms / cm 3 the following.

[0025] If a silicon substrate with a resistivity of 1000 Ω·cm or more is used, or a base substrate with a silicon layer with a resistivity of 1000 Ω·cm or more on the surface, the increase of parasitic capacitance can be prevented, thereby suppressing high-frequency loss. In addition, if the average carbon concentration in the III-nitride semiconductor thin film is 3E+18 atoms / cm 3 Then, the dislocation density decreases and the thermal conductivity can be improved. As a result, a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity can be provided.

[0026] In addition, preferably: the base substrate is composed of the silicon layer stacked on a composite substrate formed by stacking multiple layers via a planarization layer, the composite substrate has a supporting structure, a second adhesive layer stacked on the back side of the supporting structure, and a conductive layer further stacked on the back side of the second adhesive layer, the supporting structure includes a polycrystalline ceramic core, a first adhesive layer stacked on the entire polycrystalline ceramic core, and a barrier layer stacked on the entire first adhesive layer, the planarization layer is stacked on the surface of the supporting structure of the composite substrate, and the silicon layer is stacked on the planarization layer.

[0027] With such a base substrate, it is possible to relatively easily provide a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity.

[0028] Furthermore, the Group III nitride semiconductor thin film preferably includes at least one of GaN, AlN, and AlGaN.

[0029] Such a Group III nitride semiconductor thin film can relatively easily provide a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity.

[0030] Furthermore, the film thickness of the Group III nitride semiconductor thin film is preferably not less than 1.0 μm and not more than 5 μm.

[0031] In the present invention, the film thickness of the Group III nitride semiconductor thin film can be set to such a thickness.

[0032] In addition, the present invention provides a method for manufacturing a nitride semiconductor substrate, which comprises the following steps:

[0033] A step (1) of preparing a silicon substrate having a resistivity of 1000 Ω·cm or more, or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more on its surface;

[0034] a step (2) of epitaxially forming a Group III nitride semiconductor thin film on the silicon substrate or the silicon layer,

[0035] The average carbon concentration in the Group III nitride semiconductor thin film is 3E+18 atoms / cm 3 The epitaxial film formation was performed in the following manner.

[0036] If a silicon substrate having a resistivity of 1000 Ω·cm or more or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more is used, and the average carbon concentration in the group III nitride semiconductor thin film is 3E+18 atoms / cm 3The epitaxial film formation method described below can relatively easily produce a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity.

[0037] In the step (2), it is preferred that the average carbon concentration in the group III nitride semiconductor thin film be 3E+18 atoms / cm 3 The film forming temperature was adjusted in the following manner.

[0038] By adjusting the film formation temperature in this way, the carbon concentration in the group III nitride semiconductor thin film can be adjusted relatively easily, thereby manufacturing a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity.

[0039] Furthermore, in the step (1), it is preferred that the base substrate is configured such that the silicon layer is stacked on a composite substrate formed by stacking a plurality of layers via a planarization layer, and the composite substrate is provided with a supporting structure, a second adhesive layer stacked on the back side of the supporting structure, and a conductive layer further stacked on the back side of the second adhesive layer, the supporting structure includes a polycrystalline ceramic core, a first adhesive layer stacked on the entire polycrystalline ceramic core, and a barrier layer stacked on the entire first adhesive layer, the planarization layer is stacked on the surface of the supporting structure of the composite substrate, and the silicon layer is stacked on the planarization layer.

[0040] With such a base substrate, a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity can be manufactured relatively easily.

[0041] Furthermore, it is preferred that the Group III nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer includes any one or more of GaN, AlN, and AlGaN.

[0042] Such a Group III nitride semiconductor thin film can relatively easily manufacture a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity.

[0043] Furthermore, it is preferred that the film thickness of the Group III nitride semiconductor thin film be set to be greater than or equal to 1.0 μm and less than or equal to 5 μm.

[0044] In the present invention, the film thickness of the Group III nitride semiconductor thin film can be made to have such a thickness.

[0045] (III) Beneficial effects

[0046] As described above, according to the present invention, the resistivity of the silicon substrate or the resistivity of the silicon layer of the base substrate having the silicon layer on the surface is set to 1000 Ω·cm or more, and the average carbon concentration in the III-nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer is set to 3E+18 atoms / cm3 Hereinafter, it is possible to provide a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity and a method for manufacturing the same.

[0047] If high-frequency loss is reduced, there are effects such as improved device efficiency, reduced input, and reduced heat generation.

[0048] If the thermal conductivity is increased, the heat dissipation of the substrate will be improved, and the heat generated by the device will be easily dissipated, so that it can be used for a longer time than before, and the durability or temperature resistance of the component may be improved. In addition, the operating frequency or input power may also be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram showing an example of the nitride semiconductor substrate of the present invention.

[0050] Figure 2 FIG. 1 is a schematic diagram showing an example of a base substrate used for the nitride semiconductor substrate of the present invention.

[0051] Figure 3 This is a graph showing the thermal conductivity of the Group III nitride semiconductor thin films of the nitride semiconductor substrates produced in the Examples and Comparative Examples.

[0052] Figure 4 This is a graph showing the second harmonic characteristics of the nitride semiconductor substrates manufactured in the examples and comparative examples.

[0053] Figure 5 This is a graph showing the device surface temperature of the nitride semiconductor substrates manufactured in the example and the comparative example. DETAILED DESCRIPTION

[0054] As described above, there is a demand for the development of a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity and a method for manufacturing the same.

[0055] The inventors of the present application have repeatedly conducted in-depth studies on the above-mentioned technical problems, and as a result, have found that by adjusting the resistivity of the silicon substrate or the resistivity of the silicon layer of the base substrate having a silicon layer on the surface, and the carbon concentration in the III-nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer to a specified range, a nitride semiconductor substrate with low high-frequency loss and high thermal conductivity can be produced, thereby completing the present invention.

[0056] That is, the present invention is a nitride semiconductor substrate, which comprises: a silicon substrate having a resistivity of 1000 Ω·cm or more, or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more on its surface; and a group III nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer, wherein the average carbon concentration in the group III nitride semiconductor thin film in the nitride semiconductor substrate is 3E+18 atoms / cm 3 the following.

[0057] In addition, the present invention is a method for manufacturing a nitride semiconductor substrate, which comprises the following steps: a step (1) of preparing a silicon substrate having a resistivity of 1000 Ω·cm or more, or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more on its surface; a step (2) of epitaxially forming a group III nitride semiconductor thin film on the silicon substrate or the silicon layer so that the average carbon concentration in the group III nitride semiconductor thin film becomes 3E+18 atoms / cm 3 The epitaxial film formation was performed in the following manner.

[0058] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0059] [Nitride semiconductor substrate]

[0060] Here, Figure 1 An example of the nitride semiconductor substrate of the present invention is shown in FIG. Figure 1 The left picture shows an example using a silicon substrate. Figure 1 The right figure shows an example in which a silicon layer is stacked on the surface of a base substrate. Figure 1 In the left figure, the nitride semiconductor substrate 100 is formed by epitaxially forming a group III nitride semiconductor thin film 102 on a silicon substrate 101 having a resistivity of 1000 Ω·m or more, and the average carbon concentration in the group III nitride semiconductor thin film 102 is 3E+18 atoms / cm 3 The epitaxial film is formed in the following manner. Figure 1 In the right figure, the nitride semiconductor substrate 100 has a silicon layer 104 with a resistivity of more than 1000 Ω·cm stacked on the surface of the base substrate 103, and a III-nitride semiconductor thin film 102 is formed by epitaxial film formation on the silicon layer 104, and the average carbon concentration in the III-nitride semiconductor thin film 102 is 3E+18 atoms / cm 3 It is obtained by epitaxial film formation in the following manner.

[0061] If a silicon substrate with a resistivity of 1000 Ω·cm or more is used, or a base substrate with a silicon layer with a resistivity of 1000 Ω·cm or more on the surface, the increase of parasitic capacitance can be prevented, thereby suppressing high-frequency loss. In addition, if the average carbon concentration in the III-nitride semiconductor thin film is 3E+18 atoms / cm 3 Then, the dislocation density decreases and the thermal conductivity can be improved. As a result, a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity can be provided.

[0062] If high-frequency loss is reduced, there are effects such as improved device efficiency, reduced input, and reduced heat generation.

[0063] If the thermal conductivity is increased, the heat dissipation of the substrate will be improved, and the heat generated by the device will be easily dissipated, so that it can be used for a longer time than before, and the durability or temperature resistance of the component may be improved. In addition, the operating frequency or input power may also be increased.

[0064] The upper limit of the resistivity is not particularly limited, and can be, for example, 8000 Ω·cm or less.

[0065] The lower limit of the average value of the carbon concentration is not particularly limited, and can be set to 1E+15 atoms / cm 3 above.

[0066] Silicon substrate or base substrate

[0067] As described above, the substrate for epitaxially growing the III-nitride semiconductor thin film may be a silicon substrate or a base substrate having a silicon layer on its surface. <111> The silicon substrate has a diameter of 150 mm and a thickness of 675 μm. The crystal orientation must be <111> , but there is no problem even if there is a deviation angle of several degrees. In addition, the aperture and substrate thickness are not limited to this.

[0068] Alternatively, if the surface layer is provided with a crystal orientation of <111> There is no problem even if the substrate as a whole is not single-material silicon but a laminated substrate having a layer structure.

[0069] In addition, the resistivity of the silicon substrate or the resistivity of the surface silicon layer can be adjusted to 1000 Ω·cm or more. The doping element at this time is not limited, and therefore the conductivity type is not limited.

[0070] Furthermore, there is no particular limitation on the thickness of the substrate. Sometimes the SEMI standard thickness is used (675 μm for a 6-inch (150 mm) substrate, 725 μm for an 8-inch (200 mm) substrate, and 775 μm for a 12-inch (300 mm) substrate) or sometimes a substrate of 1 mm, 1.15 mm, 1.5 mm, etc. is used.

[0071] (Base substrate)

[0072] like Figure 2 As shown, the base substrate 2 used for epitaxial film formation is, for example, composed of a silicon layer 1 stacked on a composite substrate 3 formed by stacking multiple layers via a planarization layer 4. The composite substrate 3 has a supporting structure 8, a second adhesive layer 9 stacked on the back side of the supporting structure 8, and a conductive layer 10 further stacked on the back side of the second adhesive layer 9. The supporting structure 8 includes a polycrystalline ceramic core 5, a first adhesive layer 6 stacked on the entire polycrystalline ceramic core 5, and a barrier layer 7 stacked on the entire first adhesive layer 6. The planarization layer 4 is stacked on the surface of the supporting structure 8 of the composite substrate 3, and the silicon layer 1 is stacked on the planarization layer 4.

[0073] With such a base substrate 2 , it is possible to relatively easily provide a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity.

[0074] Here, the polycrystalline ceramic core 5 is, for example, a sintered body of aluminum nitride obtained by sintering at a high temperature of about 1800 degrees using a sintering aid.

[0075] The first adhesive layer 6 and the second adhesive layer 9 are made of, for example, silicon dioxide (SiO 2 ) layer, which is deposited by a low pressure chemical vapor deposition (LPCVD) process. The film thickness can be set to about 100 nm.

[0076] The barrier layer 7 is, for example, a silicon nitride layer which is deposited by an LPCVD process or the like and can have a thickness of about 250 nm.

[0077] The conductive layer 10 is, for example, a polysilicon layer, which is deposited by an LPCVD process and can be set to a thickness of about 300 nm.

[0078] The planarization layer 4 may be made of, for example, tetraethyl orthosilicate (TEOS) or silicon dioxide (SiO 2 ), which is deposited by LPCVD process, etc., and the thickness can be set to about 2000nm.

[0079] For example, the silicon layer 1 is set to have a crystal orientation of <111> The thickness is about 350 nm. The silicon layer 1 can be produced, for example, by the following steps, namely, the so-called ion implantation stripping technique: a step of implanting ions into a silicon substrate, a step of attaching to the planarization layer 4, and a step of stripping off the silicon layer 1 after heat treatment in a manner that a predetermined silicon layer 1 remains. Here, by using a silicon substrate having a resistivity of 1000 Ω·cm or more, the resistivity of the surface silicon layer 1 after attachment can be made to be 1000 Ω·cm or more.

[0080] III-nitride semiconductor thin films

[0081] A Group III nitride semiconductor thin film is formed on the silicon substrate or the silicon layer of the base substrate.

[0082] For example, in an MOCVD reactor, a III-group nitride semiconductor thin film such as AlN, AlGaN, and GaN is epitaxially grown on a composite substrate for growth to produce a nitride semiconductor substrate. The layer structure of the epitaxial layer is adjusted according to the device application, so there is no particular limitation. Sometimes an AlGaN film is not formed or sometimes an AlN film is further formed after the AlGaN film is formed. In addition, a multi-layer AlGaN film with a changed Al composition is sometimes formed.

[0083] Here, the carbon concentration in the group III nitride semiconductor is set to be 3E+18 atoms / cm as the average value when the total film thickness is measured in steps of 10 to 15 nm. 3 the following.

[0084] By doing so, the dislocation density of the epitaxial layer is reduced and the thermal conductivity of the epitaxial layer is improved.

[0085] The III-nitride semiconductor film plays the role of a base layer required to make the device layer stacked thereon high quality, so a certain degree of thickness is required (depending on the purpose of the device, but generally about 1.5 μm or more). On the other hand, if it is too thick, it becomes costly in terms of raw material consumption and film formation time, so it is preferably about 1.0 μm to 5 μm. Due to such a constant thickness, the heat dissipation characteristics of this layer will also have a great impact on the heat dissipation characteristics of the entire substrate. In high-frequency devices, the device layer itself is mostly a few nm to 100 nm, and even if the device layer is only set to low carbon, sufficient heat dissipation cannot be obtained.

[0086] Device Layer

[0087] A device layer can be provided on the surface side of the above-mentioned nitride semiconductor substrate. For example, in the case of HEMT, the device layer can be provided with a structure including a layer (channel layer) that generates a two-dimensional electron gas and has high crystallinity, a layer (barrier layer) that generates a two-dimensional electron gas, and a cap layer as the outermost layer. The barrier layer can use AlGaN having an Al composition of about 20%, and can also use, for example, InGaN, etc., but is not limited thereto. The cap layer can also be provided, for example, as a GaN layer or a SiN layer, but is not limited thereto. In addition, the thickness of these device layers and the Al composition of the barrier layer are changed according to the design of the device. In addition, when the substrate is intended to be used as a template substrate for making bulk GaN by the HVPE method, etc., the device layer can also be omitted.

[0088] [Method for manufacturing nitride semiconductor substrate]

[0089] The nitride semiconductor substrate of the present invention can be manufactured in the following manner. Hereinafter, a method for manufacturing the nitride semiconductor substrate of the present invention will be described.

[0090] <Step (1)> Preparing a silicon substrate or a base substrate

[0091] Step (1) is a step of preparing a silicon substrate having a resistivity of 1000 Ω·cm or more, or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more on its surface. The silicon substrate or base substrate to be prepared may be any of the above-mentioned silicon substrates or base substrates.

[0092] <Step (2)> Step of performing epitaxial film formation

[0093] Step (2) includes the step of epitaxially forming a Group III nitride semiconductor thin film on a silicon substrate or a silicon layer so that the average carbon concentration in the Group III nitride semiconductor thin film becomes 3E+18 atoms / cm 3 The epitaxial film formation step is performed in the following manner.

[0094] In the MOCVD reactor, epitaxial growth of a III-group nitride semiconductor thin film such as GaN, AlN, or AlGaN is performed on the silicon layer 1 of the base substrate 2. As raw materials, TMGa (trimethylgallium) can be used as a Ga source, TMAl (trimethylaluminum) can be used as an Al source, and NH 3 (Ammonia) was used as the N source. The carrier gas was set to N 2 and H 2 , or any one of them, the film forming temperature is set to about 900~1250℃.

[0095] For example, the average carbon concentration in the group III nitride semiconductor thin film is 3E+18 atoms / cm 3 The film forming temperature is adjusted as follows. The amount of carbon doped from the MO raw material varies depending on the film forming temperature, so the carbon concentration can be adjusted cheaply and easily. The film forming temperature is adjusted to adjust the average carbon concentration in the III-nitride semiconductor thin film to 3E+18 atoms / cm 3 As a result, the dislocation density can be reduced, and a nitride semiconductor substrate having high thermal conductivity can be manufactured.

[0096] In addition, a device layer can be formed on the surface layer side of the nitride semiconductor substrate.

[0097] In addition, the fact that the amount of carbon doped from the MO raw material varies depending on the film formation temperature is used to make the average carbon concentration of the entire III-nitride semiconductor thin film 3E+18 atoms / cm 3Hereinafter, the carbon concentration is adopted because it can be adjusted inexpensively and easily, but the method of adjusting the carbon concentration is not limited to this method, and it is of course possible to adjust the carbon concentration by external doping or other methods.

[0098] If a silicon substrate having a resistivity of 1000 Ω·cm or more or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more is used, and the average carbon concentration in the group III nitride semiconductor thin film is 3E+18 atoms / cm 3 By performing the epitaxial film formation manufacturing method as described below, it is possible to relatively easily manufacture a nitride semiconductor substrate having low high-frequency loss and high thermal conductivity.

[0099] Example

[0100] Hereinafter, the present invention will be specifically described using Examples and Comparative Examples, but the present invention is not limited thereto.

[0101] (Examples 1 to 3)

[0102] According to the following procedure, the resistivity of the silicon layer on the surface of the base substrate and the carbon concentration in the group III nitride semiconductor thin film were changed as shown in Tables 1 and 2, thereby manufacturing the nitride semiconductor substrates of Examples 1 to 3.

[0103] (Preparation of base substrate)

[0104] The base substrate for epitaxial film formation is prepared by the following steps.

[0105] Here, a bonding substrate having a silicon surface layer is used instead of a silicon substrate.

[0106] A support structure 8 is provided, a second adhesive layer 9 only bonded to the back side of the support structure 8, a conductive layer 10 further bonded to the back side of the second adhesive layer 9, a planarization layer 4 only bonded to the surface side of the barrier layer 7, and a silicon layer 1 bonded to the planarization layer 4, the support structure 8 includes a polycrystalline ceramic core 5, a first adhesive layer 6 bonded to the entire polycrystalline ceramic core 5, and a barrier layer 7 bonded to the entire first adhesive layer 6 ( Figure 2 ).

[0107] Here, the polycrystalline ceramic core 5 is a sintered body of aluminum nitride obtained by sintering at a high temperature of about 1800 degrees using a sintering aid.

[0108] The first adhesive layer 6 and the second adhesive layer 9 are made of silicon dioxide (SiO 2 ) layer, which is deposited by LPCVD process. The film thickness is set to about 100nm.

[0109] The barrier layer 7 is formed as a silicon nitride layer which is deposited by an LPCVD process or the like and has a thickness of about 250 nm.

[0110] The conductive layer 10 is set as a polysilicon layer, which is deposited by an LPCVD process and is set to a thickness of about 300 nm.

[0111] The planarization layer 4 is made of SiO 2 , which is deposited by LPCVD process, etc., and the thickness is set to about 2000nm.

[0112] The silicon layer 1 is set to have an axial orientation of <111> , with a thickness of about 350nm. The silicon layer 1 is produced by the following steps, namely the so-called ion implantation and stripping technique: a step of implanting ions into a silicon substrate, a step of attaching to a planarization layer 4, and a step of stripping off in a manner that a predetermined silicon layer is retained after heat treatment. Here, by using a silicon substrate with a resistivity of 1000Ω·cm or more, the resistivity of the surface silicon layer after attachment is made to be 1000Ω·cm or more. The actual resistivity is shown in Tables 1 and 2.

[0113] [Table 1]

[0114]

[0115] [Table 2]

[0116]

[0117] (Epitaxial film formation of III-nitride semiconductor thin films)

[0118] The above substrate was used as a base substrate, and epitaxial growth of III-group nitride semiconductor thin films such as AlN, AlGaN and GaN was performed on the silicon layer in an MOCVD reactor. As raw materials, TMG (trimethylgallium) was used as a Ga source, TMA (trimethylaluminum) was used as an Al source, and ammonia was used as a N source. The carrier gas used was H 2 and N 2 .

[0119] Regarding the design of the epitaxial layer at this time, a 150nm AlN layer is set directly above the base substrate, a 250nm AlGaN layer is set on it, and a GaN layer is further formed on it, and the total film thickness of the epitaxial layer is designed to be about 2μm. The film formation temperature is adjusted so that the average carbon concentration of the entire epitaxial layer at this time is 3E+18 atoms / cm 3The following. The film forming temperature of the GaN layer at this time is shown in Tables 1 and 2. The fact that the amount of carbon doped from the MO raw material varies depending on the film forming temperature is utilized, and the carbon concentration can be adjusted cheaply and easily, so it is adopted. In addition, the carbon concentration of the epitaxial layer is measured by SIMS. The carbon concentration measurement of SIMS is measured with a step size of 15~20nm, and the average value is calculated from all the points of the carbon concentration measurement points of the GaN layer after excluding the surface layer where the carbon concentration cannot be correctly measured.

[0120] (Determination of high frequency loss)

[0121] In the nitride semiconductor substrate produced in the above manner, electrodes are formed to implement the measurement of high-frequency loss. The method is as follows: After forming an electrode called a coplanar waveguide on a group III nitride thin film, a high-frequency signal with a fixed frequency is input from the input (IN) side of the electrode, and the intensity of the high-frequency signal output from the output (OUT) side is measured. Ideally, the high-frequency signal is 100% transmitted only in the electrode, but a part of the signal passes through the substrate instead of the electrode and is output from the output side. The signal passing through the substrate is detected as a harmonic component, so the method is to measure the loss to the substrate side by measuring the intensity of the harmonic component. Therefore, the smaller the harmonic signal intensity (since it is a negative value, the larger the absolute value), the more components are transmitted in the electrode, and it can be said to be an ideal substrate. The results are shown in Figure 4 .

[0122] (Determination of thermal conductivity)

[0123] In addition, the thermal conductivity of the GaN epitaxial layer was measured by thermal reflection method. The results are shown in Figure 3 .

[0124] (Comparative Examples 1 to 6)

[0125] As shown in Tables 1 and 2, a nitride semiconductor substrate having the same base substrate and group III nitride semiconductor thin film as in Example 1 is prepared except that the resistivity of the silicon layer on the surface of the base substrate and / or the average carbon concentration of the group III nitride semiconductor thin film are changed as shown in the table.

[0126] Electrodes were formed on the nitride semiconductor substrate in the same manner as in Examples 1 to 3 to measure high frequency loss, and the thermal conductivity of the GaN epitaxial layer was measured by the thermal reflection method. The results are shown in Figure 3 , Figure 4 .

[0127] In addition, in the III-nitride semiconductor thin film structure of the embodiments and comparative examples, since the GaN layer occupies most of the total thickness and becomes the layer that determines the thermal conductivity characteristics of the substrate, it is considered that it is sufficient to understand the carbon concentration of the GaN layer, and only the film formation temperature and carbon concentration results of the GaN layer are shown in Tables 1 and 2.

[0128] In Comparative Examples 1, 2, and 3, although the silicon layer has a carbon concentration of 1000 Ω·cm or more, the carbon concentration of the epitaxial layer is high, and thus the substrate has a low thermal conductivity ( Figure 3 ). Although high-frequency losses are small and there is no need to increase input power, the heat generated cannot be completely dissipated, and malfunction of the device may occur.

[0129] Comparative Examples 4, 5, and 6 have relatively low resistivity of the silicon layer, and thus are substrates with relatively large high-frequency losses ( Figure 4 ). Compared with the embodiment, a larger power is required. Although the thermal conductivity of the epitaxial layer is high, the high temperature operation becomes a degree to which the heat cannot be completely dissipated, and the device operation may fail.

[0130] In the embodiments, any of these problems have been solved, thus demonstrating that the device can be operated at a higher frequency and input power.

[0131] (Measurement of device surface temperature)

[0132] A high frequency device using the substrates of Examples 1, 2, 3, and Comparative Examples 1 to 6 was manufactured, and the voltage V between the source and the drain was DS =28V, input frequency f =3.5GHz, and the device surface temperature was measured after 20 minutes. The results are shown in Figure 5 .

[0133] As shown in the comparative example, it was confirmed that even if either the carbon concentration of the epitaxial layer or the resistivity of the silicon layer was satisfied, the heat generation temperature of the device would rise, and operational failure might occur.

[0134] In addition, since the types and proportions of molecules generated by the decomposition of raw materials change according to the growth temperature, there is a growth temperature range suitable for crystals with good quality and efficiency. In the case of GaN epitaxial layers, 900~1250℃ is more appropriate. Even if the temperature is set to a high temperature blindly, the GaN epitaxial layer will not grow properly.

[0135] In addition, when using other methods to obtain extremely low-carbon GaN epitaxial layers, it is sometimes acceptable to use a substrate with a silicon layer resistivity lower than 1000Ω·cm from the perspective of heat dissipation alone. However, the state of large harmonic components (signal leakage to the substrate) does not change, so it is unacceptable in terms of comprehensive device characteristics.

[0136] In addition, the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and technical solutions having substantially the same structure and producing the same technical effects as the technical concept described in the claims of the present invention are all included in the protection scope of the present invention.

Claims

1. A nitride semiconductor substrate comprising: A silicon substrate having a resistivity of 1000 Ω·cm or more, or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more on its surface; and epitaxially forming a Group III nitride semiconductor thin film on the silicon substrate or the silicon layer, The nitride semiconductor substrate is characterized in that The average carbon concentration in the Group III nitride semiconductor thin film is 3E+18 atoms / cm 3 the following.

2. The nitride semiconductor substrate according to claim 1, wherein: The base substrate is composed of the silicon layer stacked on a composite substrate formed by stacking multiple layers via a planarization layer. The composite substrate has a supporting structure, a second adhesive layer stacked on the back side of the supporting structure, and a conductive layer further stacked on the back side of the second adhesive layer. The supporting structure includes a polycrystalline ceramic core, a first adhesive layer stacked on the entire polycrystalline ceramic core, and a barrier layer stacked on the entire first adhesive layer. The planarization layer is stacked on the surface of the supporting structure of the composite substrate, and the silicon layer is stacked on the planarization layer.

3. The nitride semiconductor substrate according to claim 1, wherein: The group III nitride semiconductor thin film includes any one or more of GaN, AlN, and AlGaN.

4. The nitride semiconductor substrate according to claim 2, wherein: The group III nitride semiconductor thin film includes any one or more of GaN, AlN, and AlGaN.

5. The nitride semiconductor substrate according to any one of claims 1 to 4, characterized in that The film thickness of the Group III nitride semiconductor thin film is greater than or equal to 1.0 μm and less than or equal to 5 μm.

6. A method for manufacturing a nitride semiconductor substrate, characterized in that: It includes the following steps: A step (1) of preparing a silicon substrate having a resistivity of 1000 Ω·cm or more, or a base substrate having a silicon layer having a resistivity of 1000 Ω·cm or more on its surface; a step (2) of epitaxially forming a Group III nitride semiconductor thin film on the silicon substrate or the silicon layer, The average carbon concentration in the Group III nitride semiconductor thin film is 3E+18 atoms / cm 3 The epitaxial film formation was performed in the following manner.

7. The method for manufacturing a nitride semiconductor substrate according to claim 6, wherein: In the step (2), the average carbon concentration in the group III nitride semiconductor thin film is set to 3E+18 atoms / cm 3 The film forming temperature was adjusted in the following manner.

8. The method for manufacturing a nitride semiconductor substrate according to claim 6, wherein: In the step (1), the base substrate is configured to have a structure in which the silicon layer is stacked on a composite substrate formed by stacking a plurality of layers via a planarizing layer, and the composite substrate is provided with a supporting structure, a second adhesive layer stacked on the back side of the supporting structure, and a conductive layer further stacked on the back side of the second adhesive layer, the supporting structure includes a polycrystalline ceramic core, a first adhesive layer stacked on the entire polycrystalline ceramic core, and a barrier layer stacked on the entire first adhesive layer, the planarizing layer is stacked on the surface of the supporting structure of the composite substrate, and the silicon layer is stacked on the planarizing layer.

9. The method for manufacturing a nitride semiconductor substrate according to claim 7, wherein: In the step (1), the base substrate is configured to have a structure in which the silicon layer is stacked on a composite substrate formed by stacking a plurality of layers via a planarizing layer, and the composite substrate is provided with a supporting structure, a second adhesive layer stacked on the back side of the supporting structure, and a conductive layer further stacked on the back side of the second adhesive layer, the supporting structure includes a polycrystalline ceramic core, a first adhesive layer stacked on the entire polycrystalline ceramic core, and a barrier layer stacked on the entire first adhesive layer, the planarizing layer is stacked on the surface of the supporting structure of the composite substrate, and the silicon layer is stacked on the planarizing layer.

10. The method for manufacturing a nitride semiconductor substrate according to claim 6, wherein: The Group III nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer may include at least one of GaN, AlN, and AlGaN.

11. The method for manufacturing a nitride semiconductor substrate according to claim 7, wherein: The Group III nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer may include at least one of GaN, AlN, and AlGaN.

12. The method for manufacturing a nitride semiconductor substrate according to claim 8, wherein: The Group III nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer may include at least one of GaN, AlN, and AlGaN.

13. The method for manufacturing a nitride semiconductor substrate according to claim 9, wherein: The Group III nitride semiconductor thin film epitaxially formed on the silicon substrate or the silicon layer may include at least one of GaN, AlN, and AlGaN.

14. The method for manufacturing a nitride semiconductor substrate according to any one of claims 6 to 13, characterized in that: The film thickness of the Group III nitride semiconductor thin film is set to be greater than or equal to 1.0 μm and less than or equal to 5 μm.

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