Diamond substrate and method for manufacturing diamond substrate

Abstract

The present invention is a diamond substrate 100 characterized by comprising: a substrate 1; a 3C-SiC layer 3 grown on the substrate 1; and a single crystal diamond layer 4 grown on the 3C-SiC layer 3. The diamond substrate is also characterized by having pores formed at a density of 0.001 to 10 pores / μm 2 on the substrate side at the interface between the substrate 1 and the 3C-SiC layer 3. As a result of this configuration, an inexpensive diamond substrate having a large diameter can be provided.

Description

Diamond substrate and method for manufacturing diamond substrate

[0001] The present invention relates to a diamond substrate and a method for manufacturing a diamond substrate.

[0002] Diamond has excellent physical properties, such as high hardness, good thermal conductivity, high carrier mobility, and a wide band gap, and is therefore expected to be applied to various semiconductor elements and electronic devices. Artificially synthesized diamonds are used for these semiconductor element and electronic device applications. Diamond synthesis can be performed using two methods: ultra-high pressure growth and vapor phase growth. For semiconductor applications, vapor phase growth (CVD growth) has attracted attention because it can produce large-diameter substrates (see, for example, Patent Documents 1 to 3).

[0003] Examples of methods for obtaining large-diameter substrates include direct wafering, which involves combining diamond substrates and growing the sidewalls as they are grown, as described in Non-Patent Document 1, and the mosaic method, which involves laying out small single-crystal diamond substrates of a few millimeters square and growing them by CVD. These methods aim to obtain large-diameter substrates from single-crystal diamond by homoepitaxial growth. Since you start with diamonds of a few millimeters square, it takes time to increase the diameter.

[0004] Furthermore, Patent Document 4 discloses a method in which microneedles are grown on a diamond substrate and then diamond is grown on the microneedles, which prevent damage to the wafer.

[0005] Meanwhile, methods for heteroepitaxial growth on substrates other than diamond are also being actively researched. As an example, Patent Document 5 discloses a step-flow heteroepitaxial growth method on an off-axis substrate such as sapphire. This method has the advantage that diamond peels off from the substrate as it grows.

[0006] As another technique, Patent Document 6 describes a method for manufacturing a single crystal diamond substrate having a diameter of 100 mm or more and 300 mm or less, which includes the steps of preparing a cubic or hexagonal semiconductor single crystal other than diamond, dividing the semiconductor seed substrate into a plurality of child substrates, forming diamond nuclei on each of the divided child substrates, arranging the child substrates in the same arrangement as before division so that the gap between the child substrates is 20 μm or less to form base substrates, depositing a single crystal diamond layer on the base substrate, and separating at least a portion of the single crystal diamond layer from the base substrate.

[0007] Furthermore, Patent Document 7 describes a method for forming a single crystal diamond film, in which a single crystal silicon substrate having a (100) or (111) plane orientation is prepared, a 3C-SiC single crystal film is converted into diamond nuclei by microwave plasma CVD in a carbon-containing atmosphere, and a single crystal diamond film is grown on the single crystal silicon substrate by microwave plasma CVD.

[0008] JP 2001-354491 A JP 2004-176132 A JP 2006-143561 A JP 2018-58743 A WO 2022 / 138788 Specification JP 2022-168623 A JP 2023-082528 A

[0009] Chayahara et al., "Large-scale and wafer-making technology using microwave plasma CVD," Synthesiology, Vol. 3, No. 4 (2010), p. 272.

[0010] As described above, a wide variety of methods have been proposed for forming diamond substrates. However, (1) in homoepitaxial growth, the original substrate size is currently small, making it difficult to increase the diameter, (2) in heteroepitaxial growth, a relatively expensive substrate such as sapphire is required, and (3) although the growth of 3C-SiC uses a silicon substrate, it is possible to increase the diameter, but due to the difference in the linear expansion coefficient between silicon and diamond (Si<111>: 2.6×10 －６ / °C, diamond: 0.8 x 10 －６ / °C), and cracking during cooling. (4) In the case of heteroepitaxial growth, how to form the seed crystal for the diamond single crystal has been a problem that has prevented the production of a large diameter diamond at low cost.

[0011] The present invention has been made to solve the above problems, and has as its object to provide an inexpensive, large-diameter diamond substrate. Another object of the present invention is to provide a method for manufacturing a diamond substrate that can produce an inexpensive, large-diameter diamond substrate.

[0012] The present invention has been made to achieve the above object, and comprises a substrate, a 3C-SiC layer grown on the substrate, and a single-crystal diamond layer grown on the 3C-SiC layer, and the substrate side of the interface between the substrate and the 3C-SiC layer is provided with a density of more than 0.001 to 10 / μm ２ The present invention provides a diamond substrate having pores formed therein at a density of 1000 .mu.m.sup.2.

[0013] With such a diamond substrate, the numerous voids formed on the substrate side at the interface between the substrate and the 3C-SiC layer prevent damage to the diamond substrate due to the difference in linear expansion coefficient between the substrate and the diamond layer, making it possible to produce a diamond substrate with a large diameter.

[0014] Furthermore, with such a diamond substrate, the surface of the 3C-SiC layer can be used as a diamond seed crystal, eliminating the need for special seed formation. Furthermore, films with multiple functions can be formed at once. This makes the diamond substrate inexpensive.

[0015] In this case, the substrate may be a single crystal silicon substrate with a surface orientation of (111).

[0016] This is advantageous for growing a 3C-SiC layer on the substrate.

[0017] The present invention has been made to achieve the above object, and includes a 3C-SiC growth step of growing a 3C-SiC layer on a substrate, and forming a 3C-SiC layer on the substrate side at an interface between the substrate and the 3C-SiC layer at a density of more than 0.001 to 10 particles / μm ２and a diamond layer growing step of growing a single-crystal diamond layer on the 3C-SiC layer.

[0018] According to this method for manufacturing a diamond substrate, the large number of voids formed on the substrate side at the interface between the substrate and the 3C-SiC layer prevent damage to the diamond substrate due to the difference in linear expansion coefficient between the substrate and diamond, making it possible to manufacture diamond substrates with large diameters.

[0019] Furthermore, with this method for manufacturing a diamond substrate, the surface of the 3C-SiC layer can be used as a diamond seed crystal, eliminating the need for special seed formation. Furthermore, films with multiple functions can be formed at the same time. This allows for inexpensive manufacturing of diamond substrates.

[0020] In this case, the substrate may be a single crystal silicon substrate having a surface orientation of (111).

[0021] This is advantageous for growing a 3C-SiC layer on the substrate.

[0022] In this case, in the 3C-SiC growth process, Si in the single crystal silicon substrate is diffused into the 3C-SiC layer as a raw material for SiC, and the traces of the diffused Si are left as vacancies, so that the 3C-SiC growth process and the vacancy formation process can be carried out simultaneously.

[0023] This allows the formation of voids while growing a single-crystal 3C-SiC layer over the entire surface of the substrate.

[0024] As described above, the diamond substrate of the present invention can provide a diamond substrate that is inexpensive and has a large diameter. Furthermore, the method for manufacturing a diamond substrate of the present invention can manufacture a diamond substrate that is inexpensive and has a large diameter.

[0025] 1 shows a diamond substrate according to an embodiment of the present invention; 2 shows a flow diagram of a method for manufacturing a diamond substrate according to an embodiment of the present invention; 3 shows the results of Raman measurement of the diamond substrate of Example 1, where (a) shows the Raman spectrum and (b) shows a microscope image of the surface of the diamond layer; 4 shows the results of Raman measurement of the diamond substrate of Example 2, where (a) shows the Raman spectrum and (b) shows a microscope image of the surface of the diamond layer.

[0026] The present invention will be described in detail below, but the present invention is not limited thereto.

[0027] As mentioned above, there is a need for inexpensive, large-diameter diamond substrates.

[0028] As a result of intensive research into the above-mentioned problems, the present inventors have discovered a method for manufacturing a diamond-forming device comprising: a substrate; a 3C-SiC layer grown on the substrate; and a single-crystal diamond layer grown on the 3C-SiC layer; ２ The inventors have found that a diamond substrate characterized by having voids formed at a density of 1000 nm can be used to produce a diamond substrate that is inexpensive and has a large diameter, and have completed the present invention.

[0029] As mentioned above, there has also been a demand for a method of manufacturing a diamond substrate that is inexpensive and capable of manufacturing a large-diameter diamond substrate.

[0030] As a result of extensive research into the above-mentioned problems, the present inventors have discovered a method for growing a 3C-SiC layer on a substrate, and a method for forming a 3C-SiC layer on the substrate side at an interface between the substrate and the 3C-SiC layer, the method comprising: ２ The present inventors have found that inexpensive large-diameter diamond substrates can be manufactured by a method for manufacturing a diamond substrate, which method comprises the steps of: forming vacancies at a density of 3C-SiC; and growing a diamond layer on the 3C-SiC layer.

[0031] The following description will be given with reference to the drawings. First, a diamond substrate according to an embodiment of the present invention will be described with reference to FIG.

[0032] As shown in FIG. 1, the diamond substrate 100 comprises a substrate 1 , a 3C—SiC layer 3 , and a single-crystal diamond layer 4 .

[0033] Substrate 1 supports 3C-SiC layer 3 and single-crystal diamond layer 4, and serves as a base for growing 3C-SiC layer 3. Substrate 1 is preferably a single-crystal silicon substrate. In particular, a single-crystal silicon substrate with a (111) surface orientation is advantageous for growing 3C-SiC layer 3 on the substrate.

[0034] The thickness of the substrate 1 is not particularly limited, but is preferably such that warping of the diamond substrate 100 is small when the 3C-SiC layer 3 and the single-crystal diamond layer 4 are grown, and that the substrate can be put into a device formation apparatus when forming a device on the diamond substrate 100. Furthermore, a larger diameter of the substrate 1 is preferable because the larger the diameter of the single-crystal diamond layer 4 can be made.

[0035] The 3C-SiC layer 3 is an intermediate layer that serves as a base when the single crystal diamond layer 4 is grown, and is a single crystal layer of 3C-SiC grown on the substrate.

[0036] When the substrate 1 is a silicon single crystal substrate, the thinner the 3C-SiC layer 3, the more it can suppress warping of the diamond substrate 100 due to lattice mismatch with silicon. On the other hand, the thicker the 3C-SiC layer 3, the more it functions as an intermediate layer between the single crystal diamond layer 4 and the substrate 1, making the diamond substrate 100 less likely to crack when the single crystal diamond layer 4 is grown.

[0037] Therefore, the thickness of the 3C-SiC layer 3 may be appropriately selected within a range that allows both suppression of warpage and the function as an intermediate layer, and is, for example, less than 100 nm, preferably less than 70 nm. The diameter of the 3C-SiC layer 3 is, for example, approximately the same as that of the substrate 1, but may also be smaller than that of the substrate 1.

[0038] The single-crystal diamond layer 4 is a layer of single-crystal diamond, and is grown on the 3C-SiC layer 3. The thicker the single-crystal diamond layer 4, the higher the height of the device that can be formed. On the other hand, the thinner the single-crystal diamond layer 4, the less likely warping or cracking of the diamond substrate 100 will occur, so the thickness can be selected appropriately taking into consideration the height of the device to be formed and the suppression of warping or cracking of the diamond substrate 100.

[0039] The diameter of the single crystal diamond layer 4 is, for example, approximately the same as that of the 3C—SiC layer 3 , but may be smaller than that of the 3C—SiC layer 3 .

[0040] Here, the diamond substrate 100 has a density of more than 0.001 to 10 particles / μm on the substrate 1 side at the interface between the substrate 1 and the 3C—SiC layer 3. ２ The porous layer 2 has pores (microbubbles, microneedles) formed at a density of 1000 MPa.

[0041] In this way, by providing the vacancy layer 2 on the substrate 1 side at the interface between the substrate 1 and the 3C—SiC layer 3, it is possible to alleviate the lattice mismatch between the substrate 1 (e.g., silicon) and the single-crystal diamond layer 4, and to prevent damage to the diamond substrate 100 due to the difference in linear expansion coefficient between the substrate 1 and the single-crystal diamond layer 4. This allows the diameter of the diamond substrate 100 to be increased.

[0042] Furthermore, with such diamond substrate 100, the surface of 3C-SiC layer 3 can be used as a seed crystal when growing single-crystal diamond layer 4, eliminating the need for special seed formation. Furthermore, films with multiple functions can be formed at once. This makes diamond substrate 100 inexpensive.

[0043] However, the density of the pores in the pore layer 2 is 0.001 pores / μm ２ If the density is less than 10 / μm, the density is too low and the stress caused by the difference in the linear expansion coefficient is not sufficiently alleviated. ２ If it exceeds this value, the density of vacancies may become too high to support the 3C—SiC layer 3 and the single-crystal diamond layer 4 .

[0044] Therefore, the density of the pores in the pore layer 2 is more than 0.001 to 10 pores / μm ２ The more preferable density is 0.002 to 1 particle / μm ２ The depth (thickness) of the void layer 2 is not particularly limited, but is, for example, about 1 μm from the interface between the substrate 1 and the 3C—SiC layer 3. The size of the voids is also not particularly limited, but is, for example, about 10 nm to 5000 nm in maximum width. This concludes the description of the diamond substrate 100 according to an embodiment of the invention.

[0045] Next, a method for manufacturing the diamond substrate 100 according to an embodiment of the present invention will be described with reference to FIG.

[0046] First, a substrate 1 is prepared (S1 in FIG. 2). As shown in FIG. 2, a silicon substrate can be used as the substrate 1. However, a single-crystal silicon substrate having a (111) surface orientation is particularly advantageous for growing a 3C—SiC layer 3 on the substrate. Therefore, the following description will be given using a single-crystal silicon substrate having a (111) surface orientation as the substrate 1.

[0047] Next, in the 3C-SiC growth step, a 3C-SiC layer 3 is grown on the substrate 1, and in the pore formation step, pores are formed on the substrate 1 side at the interface between the substrate 1 and the 3C-SiC layer 3 at a density of more than 0.001 to 10 pores / μm ２ The pores are formed at a density of 1000 .mu.m (S2 in FIG. 2).

[0048] In the 3C-SiC growth step, it is essential to grow a single crystal of the 3C-SiC layer 3 , and in the void formation step, it is necessary to provide a large number of voids in the substrate 1 directly below the 3C-SiC layer 3 .

[0049] The first method of forming voids while growing the 3C-SiC layer 3 is to form a large number of irregularities in the substrate 1 in advance, and then grow the 3C-SiC layer 3 on the irregularities, thereby turning the concave portions of the irregularities into voids, but it may be difficult to form a single-crystal 3C-SiC layer 3 over the entire surface of a substrate 1 having such a surface. Therefore, it is preferable to use a flat substrate 1 and adjust the growth conditions for the 3C-SiC layer 3 to perform the void formation step simultaneously with the 3C-SiC growth step.

[0050] Specifically, in the 3C-SiC growth process, it is preferable to diffuse Si in the single crystal silicon substrate 1 into the 3C-SiC layer 3 as a raw material for SiC, and leave vacancies where the Si has diffused, thereby simultaneously carrying out the 3C-SiC growth process and the vacancy formation process.

[0051] More specifically, the surface of the substrate 1 is carbonized, and then a raw material gas such as trimethylsilane is supplied as a Si source while adjusting the film formation conditions, thereby forming a 3C-SiC layer 3, and at the same time, Si in the single crystal silicon substrate is diffused into the 3C-SiC layer 3 as a SiC raw material, thereby forming vacancies.

[0052] In this way, when vacancies are formed by diffusing Si in a single crystal silicon substrate having a surface orientation of (111) into the 3C-SiC layer 3, the shape of the vacancies reflects the surface orientation and is triangular (triangular pit) when viewed from above the substrate 1.

[0053] The density of the pores in the pore layer 2 is more than 0.001 to 10 pores / μm ２ If the density is lower than this, stress relaxation due to differences in linear expansion coefficients may be insufficient, and if the density is higher than this, the 3C—SiC layer 3 and the single-crystal diamond layer 4 may not be supported.

[0054] Furthermore, these triangular voids are formed because Si from the substrate 1 is used as the Si source material when growing the 3C-SiC layer 3, and as the 3C-SiC layer 3 grows and becomes thicker, Si cannot diffuse from the underlying silicon single crystal substrate 1 to the surface of the 3C-SiC layer 3.

[0055] Therefore, when the Si in the substrate 1 is diffused into the 3C-SiC layer 3 as a raw material for SiC, and the traces of the diffused Si are made into vacancies, the upper limit of the density is set to 10 / μm ２ It is practically difficult to make it larger.

[0056] Specifically, the film formation conditions for adjusting the density of vacancies are as follows: ２ For example, when other film formation conditions are the same, the vacancy density increases as the flow rate of the carrier gas increases.

[0057] Next, as required, as shown in FIG. 2, seed crystal growth (seeding treatment) is carried out before the growth of the single crystal diamond layer 4 (S3 in FIG. 2).

[0058] Finally, a single-crystal diamond layer 4 is grown on the 3C-SiC layer 3 (S4 in FIG. 2, diamond layer growth step). Specifically, for growing a large-diameter single-crystal diamond as in the present invention, methane (CH ４ Although a hot filament CVD apparatus using a raw material such as silicon dioxide is suitable, even a microwave plasma CVD apparatus can be used to grow a diamond substrate 100 with a large diameter.

[0059] The diamond substrate 100 can be manufactured by the above process, but the manufactured diamond substrate 100 can also be separated at the void layer 2 into the substrate 1, the 3C-SiC layer 3 and the single-crystal diamond layer 4 by applying an external force to the void layer 2, for example.

[0060] Thus, according to the method for manufacturing the diamond substrate 100 of the present invention, when artificially growing diamond on the substrate 1, in particular growing a single crystal diamond layer 4 on the silicon single crystal substrate 1 by CVD (chemical vapor deposition), a 3C-SiC layer 3 is used as an intermediate layer, and a vacancy layer 2 is provided on the substrate 1 side at the interface between the substrate 1 and the 3C-SiC layer 3, thereby making it possible to manufacture a diamond substrate 100 with a large diameter at low cost.

[0061] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0062] Example 1 A boron-doped high-resistivity single crystal silicon substrate having a diameter of 150 mm and a surface orientation of (111) was prepared as substrate 1, and a 3C-SiC layer 3 was grown to a thickness of 70 nm using a low-pressure CVD apparatus. The specific growth conditions for 3C-SiC layer 3 at this time were as follows:

[0063] First, 1080°C / 60 seconds H ２ After removing the native oxide film by baking, the silicon surface was carbonized with propane while increasing the temperature from 700°C to 1100°C at a rate of 1°C / sec, and then heated at 1080°C for 10 minutes in trimethylsilane (carrier gas H ２The flow rate was 10 slm to grow the 3C-SiC layer 3 to a thickness of 70 nm, and simultaneously form the void layer 2. The density of the voids (triangular pits) at this time was 0.002 pieces / μm ２ It was.

[0064] The substrate was introduced into a microwave plasma growth apparatus, and microwaves of 2.45 GHz were applied at 1500 W and ２ Flow rate: 10SLM, CH ４ The single-crystal diamond layer 4 was grown under the conditions of a concentration of 3%, a substrate temperature of 850°C, and a pressure of 60 Torr (7999.34 Pa). The temperature of the substrate stage was adjusted so that the substrate temperature was within the range of 850°C±5°C within the plane.

[0065] The substrate surface was then measured by Raman scattering spectroscopy, and a peak corresponding to diamond was obtained in the Raman spectrum shown in Figure 3(a). Furthermore, when the surface was observed with a Raman microscope, grown crystals were observed, as shown in Figure 3(b). This confirmed the growth of a single-crystal diamond layer 4.

[0066] Example 2 A boron-doped high-resistivity single crystal silicon substrate having a diameter of 150 mm and a surface orientation of (111) was prepared, and a 3C-SiC layer 3 was grown to a thickness of 70 nm using a low-pressure CVD apparatus. The specific growth conditions for the 3C-SiC layer 3 at this time were as follows:

[0067] First, 1080°C / 60 seconds H ２ After removing the native oxide film by baking, the silicon surface was carbonized with propane while increasing the temperature from 700°C to 1100°C at a rate of 1°C / sec, and then heated at 1080°C for 10 minutes in trimethylsilane (carrier gas H ２ The 3C-SiC layer 3 was grown to a thickness of 70 nm by flowing a nitrogen gas (100 slm) and the vacancy layer 2 was formed at the same time.

[0068] In this way, the flow rate of the carrier gas in Example 2 was made larger than that in Example 1. At this time, the density of the voids (triangular pits) was 1 / μm ２ and the density was higher than that of Example 1.

[0069] The substrate was introduced into a microwave plasma growth apparatus, and microwaves of 2.45 GHz were applied at 1500 W and ２ Flow rate: 10SLM, CH ４ The single crystal diamond layer 4 was grown under the conditions of a concentration of 3%, a substrate temperature of 850°C, and a pressure of 60 Torr. The temperature of the substrate stage was adjusted so that the substrate temperature was within the range of 850°C±5°C in the plane.

[0070] The substrate surface was then measured by Raman scattering spectroscopy, and the peak corresponding to diamond was obtained in the Raman spectrum shown in Figure 4(a). Furthermore, when the surface was observed with a Raman microscope, grown crystals were observed as shown in Figure 4(b). This confirmed the growth of a single-crystal diamond layer 4.

[0071] (Comparative Example) A boron-doped high-resistivity single crystal silicon substrate having a diameter of 150 mm and a surface orientation of (111) was prepared, and a 3C-SiC layer 3 was grown to a thickness of 70 nm using a low-pressure CVD apparatus. The specific growth conditions for the 3C-SiC layer 3 at this time were as follows:

[0072] First, 1080°C / 60 seconds H ２ After removing the native oxide film by baking, the silicon surface was carbonized with propane while increasing the temperature from 700°C to 1100°C at a rate of 1°C / sec, and then trimethylsilane was flowed at 900°C for 10 minutes to grow a 3C-SiC layer 3 to a thickness of 70 nm.

[0073] In this comparative example, no carrier gas was flowed. The density of the voids (triangular pits) was 0.001 / μm ２ The density was lower than that of Examples 1 and 2.

[0074] The substrate was introduced into a microwave plasma growth apparatus, and microwaves of 2.45 GHz were applied at 1500 W and ２ Flow rate: 10SLM, CH ４The single-crystal diamond layer 4 was grown under the conditions of concentration: 3%, substrate temperature: 850°C, and pressure: 60 Torr. The temperature of the substrate stage was adjusted so that the substrate temperature was within the range of 850°C ± 5°C in the plane. As a result, the single-crystal diamond layer 4 was successfully formed, but cracks occurred during cooling after the film formation.

[0075] As described above, according to the embodiment of the present invention, when growing a single crystal diamond layer 4 on a silicon single crystal substrate 1 by CVD, a 3C-SiC layer 3 is used as an intermediate layer, and a vacancy layer 2 is provided on the substrate 1 side at the interface between the substrate 1 and the 3C-SiC layer 3, thereby making it possible to manufacture a large diameter diamond substrate 100 at low cost.

[0076] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A substrate, a 3C-SiC layer grown on the substrate, and a single crystal diamond layer grown on the 3C-SiC layer, ２ 1. A diamond substrate having voids formed therein at a density of 1000 nm to 1000 nm.

2. The diamond substrate according to claim 1, wherein the substrate is a single crystal silicon substrate having a surface orientation of (111).

3. A 3C-SiC growth step of growing a 3C-SiC layer on a substrate, and a method of forming a 3C-SiC layer on a substrate at an interface between the substrate and the 3C-SiC layer, the method comprising: ２ a void forming step of forming voids at a density of 3C-SiC; and a diamond layer growing step of growing a single crystal diamond layer on the 3C-SiC layer.

4. The method for producing a diamond substrate according to claim 3, wherein a single crystal silicon substrate having a surface orientation of (111) is used as the substrate.

5. A method for manufacturing a diamond substrate as described in claim 4, characterized in that in the 3C-SiC growth process, Si in the single crystal silicon substrate is diffused into the 3C-SiC layer as a raw material for SiC, and the traces of diffused Si are turned into vacancies, thereby carrying out the 3C-SiC growth process and the vacancy formation process simultaneously.

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