Methods for diamond growth on silicon substrates and methods for selective diamond growth on silicon substrates.

Abstract

This invention discloses a method for growing diamond on a silicon substrate, characterized by: performing damage on the surface of the silicon substrate such that the Raman shift of the peak value at 520 cm⁻¹ obtained by Raman spectroscopy is 0.1 cm⁻¹ or more; performing surface roughness Sa on the surface of the silicon substrate such that the surface roughness Sa measured by AFM is 10 nm or more; or performing both damage and surface roughness formation on the surface of the silicon substrate as pretreatment, and then growing diamond on the pretreated silicon substrate by CVD. This provides a method for growing diamond on a silicon substrate and a method for selectively growing diamond on a silicon substrate.

Description

[Technical Field]

[0001] This invention relates to a method for diamond growth on a silicon substrate and a method for selective diamond growth on a silicon substrate. [Previous Technology]

[0002] Due to its high hardness, good thermal conductivity, high carrier mobility, and wide bandgap, diamond is expected to be used in various semiconductor / electronic components. Synthetic diamond is already being used in these semiconductor / electronic component applications. There are two methods for diamond synthesis: using ultra-high pressure for growth and chemical vapor deposition (CVD). In semiconductor applications, CVD growth has attracted attention because it can produce large diameter diamonds (Patent Documents 1-3).

[0003] CVD growth is a method in which a substrate is placed inside a reaction tube, and raw material gas and carrier gas flow under atmospheric pressure to reduced pressure. The raw material gas is decomposed / activated by thermal decomposition and plasma, and then grown on the substrate. Diamond growth uses the hot filament method, which uses microwave plasma and DC (direct current) plasma, and filaments such as tungsten. The hot filament method, which can theoretically form large-diameter substrates, has attracted attention when considering its application.

[0004] The hot filament method is an excellent technique for diamond coating and other applications in diamond-growing tools, but it is considered necessary to form a nucleus to grow diamond on a substrate (Patent Document 4). This nucleus formation is particularly important when using a silicon substrate as a diamond growth substrate.

[0005] This growth nucleus is believed to require: immersing the substrate in a solution containing diamond particles and then drying it; immersing the substrate in a solution containing diamond particles and then applying ultrasound; or introducing a gas such as methane for DC plasma treatment, etc. [Previous Art Documents] (Patent Documents)

[0006] Patent Document 1: Japanese Patent Application Publication No. 2001-354491; Patent Document 2: Japanese Patent Application Publication No. 2004-176132; Patent Document 3: Japanese Patent Application Publication No. 2006-143561; Patent Document 4: Japanese Patent Application Publication No. 2013-166692

[0007] Non-patent document 1: Wei Li et. al., "Modeling of the removal mechanism of monocrystalline silicon - based on phase change - dislocation theory and its edge chipping damage during micro - griping", Precision Eng., 71 (2021) 103-118. [Summary of the Invention]

[0008] [Problems to be Solved by the Invention] As described above, large-diameter diamond substrates are attracting attention from the viewpoint of heat dissipation characteristics, etc. Hot filament CVD is a growth method corresponding to large diameters, but it requires seeding as growth nuclei. Besides homoepitaxy, it requires coating diamond particles and ultrasonic treatment, as well as pretreatment using DC plasma. In particular, while coating diamond particles and ultrasonic treatment can be used for large-diameter substrates, it cannot be applied to semiconductor processes due to contamination and particle issues. On the other hand, DC plasma treatment cannot achieve large diameters, such as 300 mm. Furthermore, it is necessary to selectively grow diamond at predetermined locations. This is because diamond is difficult to process due to its high hardness, and if it reaches high temperatures in the presence of oxygen, oxidation occurs, making it difficult to form a film over the entire surface before further processing. This invention was made in view of the above-mentioned problems, and its object is to provide a method for diamond growth on a silicon substrate and a method for selective diamond growth on a silicon substrate using a simplified process while suppressing contamination and particles. [Technical Means for Solving the Problem]

[0009] In order to solve the above-mentioned problems, the present invention provides a method for growing diamond on a silicon substrate, wherein the silicon substrate surface is subjected to damage such that the Raman shift of the peak value of 520 cm⁻¹ obtained by Raman spectroscopy is 0.1 cm⁻¹ or more, the silicon substrate surface is subjected to roughness Sa such that the surface roughness Sa measured by AFM (atomic force microscopy) is 10 nm or more, or both damage and roughness are performed on the silicon substrate surface as pretreatment, and diamond is grown on the silicon substrate after the pretreatment is performed by CVD.

[0010] If such a method of diamond growth on a silicon substrate is adopted, it is possible to obtain large-diameter diamonds with a simple process while suppressing contamination and particles.

[0011] At this point, it is preferable to set the aforementioned CVD method as the hot filament method.

[0012] Using such a CVD method, large-diameter diamonds can be obtained more efficiently.

[0013] Furthermore, the present invention provides a selective diamond growth method on a silicon substrate, wherein, in the above-described diamond growth method on a silicon substrate, only a portion of the surface of the silicon substrate is subjected to the aforementioned damage, only a portion of the surface of the silicon substrate is subjected to the aforementioned unevenness formation, or only a portion of the surface of the silicon substrate is subjected to both the aforementioned damage and unevenness formation as pretreatments, and then diamond is grown on the aforementioned area after the pretreatment is performed by CVD.

[0014] If such a selective diamond growth method is used on a silicon substrate, it is possible to selectively grow large-diameter diamonds with a simple process while suppressing contamination and particles.

[0015] At this point, it is preferable to set the aforementioned CVD method as the hot filament method.

[0016] Using this CVD method, large-diameter diamonds can be grown more efficiently and selectively. [Effects]

[0017] By means of the configuration of the present invention, the parameters of the silicon substrate surface can be controlled by specific values, that is, diamond growth nuclei can be grown, and diamond growth on the silicon substrate can be performed by a simple process without generating pollution and particles.

Implementation Method

[0019] As mentioned above, there has been a prior search for a method for diamond growth on silicon substrates that can suppress contamination and particles.

[0020] After repeatedly conducting research on the problems to be solved as described above, the inventors discovered the following facts and completed the present invention: by applying damage to the surface of a silicon substrate, by forming an uneven surface on the surface of a silicon substrate, or by performing both of these, it is possible to suppress contamination and particles while growing diamond on the silicon substrate.

[0021] In other words, the present invention is a method for growing diamond on a silicon substrate, which involves pretreatment of the silicon substrate surface by performing damage-imparting treatment to achieve a Raman shift of the peak value at 520 cm⁻¹ obtained by Raman spectroscopy of 0.1 cm⁻¹ or more, performing surface roughness Sa formation on the silicon substrate surface to achieve a surface roughness Sa measured by AFM of 10 nm or more, or performing both damage-imparting and surface roughness formation on the silicon substrate surface, and then growing diamond on the silicon substrate by CVD. The pretreatment can be performed on the entire silicon substrate surface or only on a portion of the surface.

[0022] The present invention will now be described in detail, but the present invention is not limited thereto. Embodiments of the present invention will be described with reference to the accompanying drawings.

[0023] [Method for diamond growth on silicon substrate] The method for diamond growth on silicon substrate of the present invention is a method for diamond growth on silicon substrate, wherein the silicon substrate surface is subjected to damage such that the Raman shift of the peak value of 520 cm⁻¹ obtained by Raman spectroscopy is 0.1 cm⁻¹ or more, the silicon substrate surface is subjected to uneven formation such that the surface roughness Sa measured by AFM is 10 nm or more, or both damage and uneven formation are performed on the silicon substrate surface as pretreatment, and then diamond is grown on the silicon substrate after the pretreatment is performed by CVD.

[0024] At this point, it is preferable to set the aforementioned CVD method as the hot filament method.

[0025] Figure 1 shows an example of an embodiment, schematically illustrating a diamond growth method performed by a hot filament method. Methane and hydrogen, serving as reactant gases 4, are introduced into a reaction vessel 1, and a tungsten filament 3 positioned above a silicon substrate (the substrate to be formed) 2 is energized to heat and decompose the reactant gases 4, thereby growing diamond on the silicon substrate 2. The nucleation process on the silicon substrate at this time is explained. If a typical silicon substrate is measured using Raman spectroscopy, a peak value of 520 cm⁻¹ can be obtained. If damage is formed on this silicon substrate, this peak value will shift. Regarding the change in Raman peak value after damage is formed, for example, Non-Patent Literature 1 has reported a comparison between the depth (degree) of the damage and Raman spectroscopy, and revealed that if the degree of damage increases (becomes more severe), the peak value of 520 cm⁻¹ will shift.

[0026] Methods for creating damage on the surface of a silicon substrate include, for example, grinding the surface of the silicon substrate with an abrasive stone. Furthermore, methods for creating roughness on the surface of a silicon substrate include, for example, grinding the surface of the silicon substrate with an abrasive stone. There are methods that create damage or roughness by immersing the substrate in pure water in which diamond particles are dispersed and applying ultrasound. In addition to methods for creating such mechanical damage and roughness, there are also methods that use DC plasma (applying a high voltage to the substrate and ionizing gases such as Ar and methane with plasma) to create damage using ion particles.

[0027] As described above, surface damage can be assessed using Raman shift. A sample with a changed Raman shift is prepared, and diamond is grown using the hot filament method. The result shows that diamond growth is confirmed when the Raman shift is 0.1 cm⁻¹ or more, preferably 0.5 cm⁻¹ or more, as shown in Figure 3, indicating increased damage. There is no particular upper limit to the Raman shift; it can be set, for example, to 2 cm⁻¹ or less. Here, diamond growth is confirmed by Raman measurement and optical microscopy images of the peak value at 1330 cm⁻¹. For example, if a Raman peak value 5 of diamond can be confirmed near 1330 cm⁻¹ as shown in Figure 2, it can be known that diamond has grown. Furthermore, a Raman peak value 6 of carbide (graphite) can be confirmed near 1600 cm⁻¹.

[0028] In the diagram (Figure 1) schematically showing the diamond growth method performed by the hot filament method, methane and hydrogen, which are reactant gases 4, are introduced into the reaction vessel 1, and a tungsten filament 3 disposed on a silicon substrate 2 is energized to heat the reactant gas 4 and decompose it, thereby growing diamond on the silicon substrate 2. As a nucleation process performed on the silicon substrate 2 at this time, a sample is prepared with a change in the surface roughness Sa of the silicon substrate 2 as measured by AFM. Then, after diamond growth is performed by the hot filament method, the results can be confirmed as diamond growth with a surface roughness Sa of 10 nm or more and 50 nm or more, as shown in Figure 4. Here, diamond growth is confirmed by Raman spectroscopy at the peak value of 1330 cm⁻¹ and by optical microscopy images. There is no particular limitation on the upper limit of the surface roughness Sa, and it can be set to, for example, 5000 nm or less.

[0029] AFM measurement can be performed using, for example, the XE-WAFER manufactured by Park Systems.

[0030] In the diagram (Figure 1) schematically showing the diamond growth method performed by the hot filament method, methane and hydrogen, which are the reaction gases 4, are introduced into the reaction vessel 1, and a tungsten filament 3 placed above the silicon substrate 2 is energized to heat the reaction gases 4 and decompose them, thereby growing diamond on the silicon substrate 2. As a nucleation (pretreatment) performed on the silicon substrate 2 at this time, a sample is prepared with changes in the Raman shift of the silicon substrate 2 and the surface roughness Sa measured by AFM. Then, after diamond growth is performed by the hot filament method, the diamond growth is confirmed when the Raman shift after the peak value of 520 cm⁻¹ on the surface of the silicon substrate 2 is 0.1 cm⁻¹ or more, preferably 0.5 cm⁻¹ or more, that is, when the damage is increased, and the surface roughness Sa of the silicon substrate 2 measured by AFM is 10 nm or more and 50 nm or more. Here, the growth of diamond was confirmed by Raman spectroscopy and optical microscopy images, showing a peak at 1330 cm⁻¹.

[0031] [Selective Diamond Growth Method on Silicon Substrate] Furthermore, the present invention provides a selective diamond growth method on a silicon substrate, wherein, in the diamond growth method on the silicon substrate described above, only a portion of the surface of the silicon substrate is subjected to the aforementioned damage induction, only a portion of the surface of the silicon substrate is subjected to the aforementioned unevenness formation, or only a portion of the surface of the silicon substrate is subjected to both the aforementioned damage induction and the aforementioned unevenness formation, as pretreatment, and then diamond is grown on the aforementioned area after the pretreatment is performed by CVD.

[0032] At this point, it is preferable to set the aforementioned CVD method as the hot filament method.

[0033] As described above, surface damage can be evaluated using Raman displacement. A sample (Figure 5) was fabricated on a silicon substrate with a partially altered Raman displacement. Then, diamond growth was performed using a hot filament method. The results showed that selective diamond growth was observed even when the Raman displacement was 0.1 cm⁻¹ or more, indicating increased damage. In Figure 5, a portion 7 of a polishing apparatus was first placed against a silicon substrate 2, and a roughened position 8 and an unpolished position 9 were fabricated. Then, a diamond 10 was CVD-grown on the roughened position 8.

[0034] Here, the growth of diamond is confirmed by Raman spectroscopy and optical microscopy images, with a peak value of 1330 cm⁻¹.

[0035] The method of partially forming damage on the surface can also be performed, for example, by using a partial grinding (sharpening) device to grind (sharpen) only a predetermined position, and by using a method of wet or dry etching after performing photolithography as another method.

[0036] In the diagram (Figure 1) schematically showing the diamond growth method performed by the hot filament method, methane and hydrogen, which are reactant gases 4, are introduced into the reaction vessel 1, and a tungsten filament 3 disposed on a silicon substrate 2 is energized to heat the reactant gas 4 and decompose it, thereby growing diamond on the silicon substrate 2. As a nucleation (pretreatment) performed on the silicon substrate 2 at this time, a sample is prepared in which the surface roughness Sa of the silicon substrate 2, as measured by AFM, is partially changed. Then, after performing the diamond growth method by the hot filament method, the results show that the selective growth of diamond is partially confirmed with a surface roughness Sa of 10 nm or more (Figure 5). Here, the diamond growth is confirmed by Raman spectroscopy with a peak value of 1330 cm⁻¹ and by optical microscopy images.

[0037] The method of partially forming surface roughness can also be, for example, to grind (sharpen) only a predetermined position using a partial grinding (sharpening) device, and can be followed by a wet or dry etching method after performing photolithography as another method.

[0038] In the diagram (Figure 1) schematically showing the diamond growth method performed by the hot filament method, methane and hydrogen, which are the reaction gases 4, are introduced into the reaction vessel 1, and a tungsten filament 3 provided on the silicon substrate 2 is energized to heat the reaction gases 4 and decompose them, thereby growing diamond on the silicon substrate 2. As a nucleation process performed on the silicon substrate 2 at this time, a sample is prepared with changes in the amount of Raman shift of the silicon substrate 2 and the surface roughness Sa measured by AFM. Then, after diamond growth is performed by the hot filament method, the results show that the selective growth of diamond is confirmed when the amount of Raman shift after the peak value of 520 cm⁻¹ measured by Raman measurement is 0.1 cm⁻¹ or more, preferably 0.5 cm⁻¹ or more, that is, when the damage is increased, and the surface roughness Sa of the silicon substrate 2 measured by AFM is 10 nm or more and 50 nm or more (Figure 5). Here, the growth of diamond was confirmed by Raman spectroscopy and optical microscopy images, showing a peak at 1330 cm⁻¹.

[0039] The method of partially creating damage and roughness on the surface can also, for example, use a partial grinding (sharpening) device to grind (sharpen) only a predetermined location, and can be followed by a wet or dry etching method after performing photolithography as another method. [Example]

[0040] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited thereto.

[0041] (Example 1) A high-resistivity single-crystal silicon substrate with a diameter of 300 mm, orientation (111), and boron doped was prepared. Three substrates with different surface states were prepared: a substrate maintained in this state (completed by CMP (chemical mechanical polishing); a substrate ground with a #12000 grinding stone; and a substrate ground with a #3000 grinding stone. Raman spectroscopy was performed on the surface of each substrate, and the peak displacement of silicon from 520 cm⁻¹ was evaluated. The results showed a displacement of 0 cm⁻¹ for CMP, 0.1 cm⁻¹ for #12000 grinding, and 0.5 cm⁻¹ for #3000 grinding. These substrates were placed in a hot filament CVD apparatus and grown for 4 hours under the following conditions: filament temperature: 2200°C, H₂ flow rate: 10 SLM, CH₄ concentration: 3%, substrate temperature: 850°C, and 5 Torr (667 Pa). Raman spectroscopy was then performed to evaluate the diamond growth. As a result, the relationship between the Raman displacement of the silicon substrate and diamond growth can be observed. Diamond growth cannot be observed when the Raman displacement of the silicon substrate is 0 cm⁻¹, but diamond growth can be observed when it is above 0 cm⁻¹ (Figure 3).

[0042] (Example 2) A high-resistivity single-crystal silicon substrate with a diameter of 300 mm, orientation (111), and boron doped was prepared. Three substrates with different surface states were prepared: a substrate maintained in this state (CMP completed); a substrate ground with a #12000 grinding stone; and a substrate ground with a #3000 grinding stone. After roughness measurement of the surface of each substrate by AFM, the roughness Sa was 1 nm for CMP completed, 10 nm for #12000 ground, and 50 nm for #3000 ground. However, Sa = 50 nm (#3000) was confirmed by white interference microscope in a 100 μm field of view due to the low reliability of AFM. These substrates were placed in a hot filament CVD apparatus and grown for 4 hours under the conditions of filament temperature: 2200°C, H2 flow rate: 10 SLM, CH4 concentration: 3%, substrate temperature: 850°C, and 5 Torr (667 Pa). Then, Raman spectroscopy was performed to evaluate diamond growth. The results showed that the relationship between the surface roughness Sa of the silicon substrate and diamond growth could be observed. Diamond growth could not be observed when the surface roughness Sa of the silicon substrate was 1 nm, but it could be observed when it was 10 nm or more (Figure 4).

[0043] (Example 3) A high-resistivity single-crystal silicon substrate with a diameter of 300 mm, orientation (111), and boron doping was prepared. The following sample was prepared: the surface was ground using a partial grinding device with a small #12000 grinding stone, and Raman spectroscopy was performed on the substrate surface. The peak displacement of silicon at 520 cm⁻¹ was 0.1 cm⁻¹. This substrate was placed in a hot filament CVD apparatus and grown for 4 hours under the conditions of filament temperature: 2200 °C, H₂ flow rate: 10 SLM, CH₄ concentration: 3%, substrate temperature: 850 °C, and 5 Torr (667 Pa). Then, Raman spectroscopy was performed to evaluate the diamond growth. As a result, diamond growth was observed only in the partially ground areas on the silicon substrate (Figure 6).

[0044] (Example 4) A high-resistivity single-crystal silicon substrate with a diameter of 300 mm, orientation (111), and boron doped was prepared. The surface was ground using a partial grinding apparatus with a #12000 small grinding stone. The surface roughness of the substrate was measured by AFM, yielding a roughness Sa of 10 nm. This substrate was placed in a hot-filament CVD apparatus and grown for 4 hours under the following conditions: filament temperature: 2200°C, H₂ flow rate: 10 SLM, CH₄ concentration: 3%, substrate temperature: 850°C, and 5 Torr (667 Pa). Then, Raman spectroscopy was performed to evaluate diamond growth. As a result, diamond growth was observed only at the partially ground locations on the silicon substrate (Figure 6).

[0045] (Example 5) A high-resistivity single-crystal silicon substrate with a diameter of 300 mm, orientation (111), and boron doped was prepared. After windowing at a predetermined location using photolithography, etching was performed for 5 minutes using a plasma etching apparatus with CF4 as the etching gas at a flow rate of 100 sscm and a flow rate of 100 Torr (13332 Pa). Then, the resist was removed using oxygen plasma, and the roughness and damage were measured by Raman and AFM. As a result, the roughness Sa obtained by AFM was 15 nm, and the peak shift at 520 cm⁻¹ in the Raman spectrum was 1 cm⁻¹. This substrate was placed in a hot filament CVD apparatus and grown for 4 hours under the conditions of filament temperature: 2200 °C, H₂ flow rate: 10 SLM, CH₄ concentration: 3%, substrate temperature: 850 °C, and 5 Torr (667 Pa). Then, Raman spectroscopy was performed to evaluate the diamond growth. As a result, diamond growth was observed only in a portion of the ground areas on the silicon substrate (Figure 7).

[0046] (Example 6) A high-resistivity single-crystal silicon substrate with a diameter of 300 mm, orientation (111), and boron doped was prepared. After oxidizing the substrate to form a 100 nm silicon oxide film, photolithography was used to create windows only at predetermined locations. Then, etching was performed with a 10% KOH aqueous solution for 5 minutes. The oxide film was then removed with buffered HF, and the roughness and damage were measured by Raman and AFM. As a result, the roughness Sa obtained by AFM was 50 nm, and the peak shift at 520 cm⁻¹ in the Raman spectrum was 1.2 cm⁻¹. This substrate was placed in a hot filament CVD apparatus and grown for 4 hours under the conditions of filament temperature: 2200 °C, H₂ flow rate: 10 SLM, CH₄ concentration: 3%, substrate temperature: 850 °C, and 5 Torr (667 Pa). Then, Raman spectroscopy was performed to evaluate the diamond growth. As a result, diamond growth was observed only in a portion of the ground areas on the silicon substrate (Figure 8).

[0047] Furthermore, the present invention is not limited to the above-described embodiments. The above-described embodiments are merely illustrative, and any embodiment that has a substantially identical structure to the technical concept described in the claims of the present invention and produces the same effect is included within the technical scope of the present invention. [Simplified Explanation of the Diagram]

[0018] Figure 1 is a schematic diagram showing an example of the diamond growth method of the present invention performed by the hot filament method. Figure 2 is a graph showing the Raman peak value of diamond on a silicon substrate. Figure 3 is a graph showing the relationship between the Raman shift of the 520 cm⁻¹ peak value of the silicon substrate and diamond growth. Figure 4 is a graph showing the relationship between the AFM roughness of the silicon substrate and diamond growth. Figure 5 is a flowchart showing an example of a selective diamond growth process performed on a silicon substrate. Figure 6 is a diagram showing the Raman spectrum and optical microscope image of a partially polished silicon substrate after CVD growth. Figure 7 is a diagram showing the Raman spectrum and optical microscope image of a partially dry-etched silicon substrate after CVD growth. Figure 8 is a diagram showing another example of the Raman spectrum and optical microscope image of a partially dry-etched silicon substrate after CVD growth. [Biomaterial Storage]

[0049] Domestic storage information (please note in order of storage institution, date, and number): None. International storage information (please note in order of storage country, institution, date, and number): None.

Claims

1. A method for growing diamond on a silicon substrate, characterized in that: the surface of the silicon substrate is subjected to damage such that the Raman shift of the peak value of 520 cm⁻¹ obtained by Raman spectroscopy is 0.1 cm⁻¹ or more, or the surface of the silicon substrate is subjected to the aforementioned damage and the surface roughness Sa measured by AFM is 10 nm or more, as a pretreatment, and then diamond is grown on the silicon substrate after the pretreatment is performed by CVD.

2. The diamond growth method on a silicon substrate as described in claim 1, wherein the aforementioned CVD method is a hot filament method.

3. A method for selective diamond growth on a silicon substrate, characterized in that: in the method for diamond growth on a silicon substrate as described in claim 1, only a portion of the surface of the silicon substrate is subjected to the aforementioned damage, or only a portion of the surface of the silicon substrate is subjected to the aforementioned damage and the aforementioned unevenness formation, as a pretreatment, and then diamond is grown on the aforementioned area after the pretreatment is performed by CVD.

4. The selective diamond growth method on a silicon substrate as described in claim 3, wherein the aforementioned CVD method is a hot filament method.

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