Method for producing diamond

Abstract

[Problem] The purpose of the present invention is to produce diamond on a dissimilar substrate using an epitaxial growth method. [Solution] This method is characterized by comprising: a step for spraying diamond particles onto a substrate that has a crystal plane composed of a (111) plane; a step for causing carbon constituting the diamond particles to form a solid solution in the substrate so that the crystal planes of the diamond particles stop at the (111) plane; and a step for epitaxially growing the diamond particles using a CVD device.

Description

Method for producing diamond

[0001] The present invention relates to a method for producing diamond by an epitaxial growth method.

[0002] Diamond is expected as a semiconductor material because it has a large band gap, high insulation and excellent thermal conductivity. However, large-sized diamond has not been obtained so far, and large-diameter diamond substrates are required.

[0003] Non-Patent Document 1 describes that, using a hot filament CVD apparatus, a large amount of diamond powder is seeded on a nickel substrate having crystal planes of (100) plane and (111) plane, and heated to 1100°C in a hydrogen atmosphere to melt Ni-C-H at the interface of the nickel substrate, and then grow a diamond film at 900°C. However, since the melting temperature is as high as 1100°C or higher, and the diamond growth process is subsequently performed at 900°C, the temperature change may cause detachment of diamond particles, formation of graphite, and the like.

[0004] Oriented diamond films grown on nickel substrates,W.Zhu, et al. Appl. Phys. Lett. 1993, 63(12), 1640-1642Anisotropic diamond etching through thermochemical reaction between Ni and diamond in high - temperature water vapour,M. Nagai,et al,Sci.Rep. 2018,8:6687

[0005] An object of the present invention is to produce diamond on a heterogeneous substrate by using an epitaxial growth method.

[0006] The present invention relates to a method for producing diamond, characterized by comprising the steps of: scattering diamond particles on a substrate having (111) crystal planes; solid dissolving carbon constituting the diamond particles in the substrate such that the crystal planes of the diamond particles stop at the (111) planes; and epitaxial growth using a CVD apparatus.

[0007] We focused on the fact that when diamond particles are scattered on a substrate whose crystal planes consist of (111) planes and heated under predetermined conditions, the carbon constituting the diamond particles solid-solves in the substrate, but this solid-solution stops at the diamond (111) planes. For example, Non-Patent Literature 2 describes that when the (100) diamond surface is etched with nickel, the diamond (111) planes are exposed on the bevel.

[0008] The step of solid-solving the carbon into the substrate is preferably carried out under a hydrogen atmosphere or an inert gas mixed hydrogen atmosphere. If the temperature for solid-solving the carbon is too low, the solid-solving of carbon into the substrate will be slow and impractical, and if the temperature is too high, the difference in solid-solving rates depending on the crystal orientation will be lost, and there is a risk that it will not stop at the (111) plane. Therefore, the temperature for solid-solving the carbon into the substrate is preferably 800°C or higher and less than 1100°C. Preferably, it is 850°C or higher and 1050°C or lower, and more preferably 900°C or higher and 1000°C or lower. Examples of substrates that exhibit such a carbon solid-solving reaction include Ni, Pt, Co, Ti, Mo, W, Cu, Fe and their alloys.

[0009] When diamond particles are scattered on a substrate with (111) crystal planes, and the carbon constituting these diamond particles dissolves in the substrate, this carbon solid solution reaction stops at the diamond (111) plane. This allows for the formation of high-density crystal nuclei necessary for epitaxial growth on the substrate, enabling the manufacture of diamonds using dissimilar substrates. As a result, diamond substrates that are larger in diameter and less expensive than conventional ones can be obtained, and are expected to have applications in quantum technology and other fields.

[0010] A schematic diagram of the process according to the present invention is shown. An SEM image of a diamond obtained by the process according to the present invention is shown. The Raman spectrum of a diamond obtained by the process according to the present invention is shown. The X-ray diffraction pattern of a diamond obtained by the process according to the present invention is shown. An SEM image of a diamond grown on a substrate without carbon solid solution is shown.

[0011] The diamond manufacturing process according to the present invention will be explained with reference to Figure 1. When diamond particles (DP) are scattered on a (111) substrate, the crystal orientation of the DP becomes random, as shown in the schematic diagram in Figure 1(a). Focusing on one of these DPs, an enlarged view is shown in Figure 1(a-1). In this DP, the diamond (100) plane is in contact with the substrate surface. When heat treatment is performed in a hydrogen atmosphere or an inert gas mixed hydrogen atmosphere in this state, the DP begins to solid dissolve carbon in the (111) substrate, and stops when the diamond (111) plane comes into contact with the substrate surface. The progress of this carbon solid dissolution is shown in Figure 1(a-2). As the carbon solid dissolution progresses and the diamond (111) plane comes into contact with the substrate, the carbon solid dissolution stops as shown in Figure 1(a-3). The same carbon solid dissolution occurs in the other DPs, and the randomly oriented DPs become in a state where each (111) plane is in contact with the substrate surface. This state is shown in Figure 1(b). Subsequently, the diamond grows through epitaxial growth, and this state is shown in Figure 1(c).

[0012] As an example of a single-crystal substrate with (111) crystal planes, we manufactured diamond using a Ni substrate and will explain the process. (1) Using a microwave plasma CVD (MPCVD) apparatus, diamond particles (DP) with a particle size of approximately 1 μm were scattered onto the substrate, and then diamond crystal nuclei were formed under the following conditions: ・Hydrogen flow rate: 100 [sccm] ・Substrate temperature: 975 [°C] ・Time: 15 [min] ・Pressure: 10 [kPa] (2) Next, epitaxial growth was carried out using an MPCVD apparatus under the following conditions: ・Hydrogen flow rate: 100 [sccm] ・Methane flow rate: 2 [sccm] ・Substrate temperature: 975 [°C] ・Time: 5 [hr] ・Pressure: 10 [kPa]

[0013] Figure 2 shows the surface SEM image of the diamond obtained above, and Figure 3 shows the Raman spectrum. Figure 4 shows the X-ray diffraction (XRD) pattern. From the SEM image, diamonds with characteristic triangular and hexagonal shapes of (111) were confirmed, and the Raman spectrum also confirmed that they were diamonds. From the XRD pattern, the alignment of the orientation of the Ni substrate and the diamond (Dia) was also confirmed. In this invention, crystal nuclei can be formed at 800°C or higher and less than 1100°C, and diamonds can be manufactured by epitaxial growth at the same temperature.

[0014] As a comparative example, when the above diamond particles were scattered on a Ni substrate and grown in an MPCVD apparatus, the diamond particles grew larger, but remained randomly oriented as shown in Figure 5.

[0015] This invention allows for the formation of crystal nuclei necessary for epitaxial growth at high density on the substrate, making it possible to obtain diamond substrates with larger diameters and lower costs than conventional methods.

Claims

1. A method for producing diamond, comprising the steps of: scattering diamond particles on a substrate having (111) crystal planes; solid-solving carbon constituting the diamond particles into the substrate such that the crystal planes of the diamond particles stop at the (111) planes; and epitaxial growth using a CVD apparatus.

2. The method for producing diamond according to claim 1, characterized in that the step of solid-solving the carbon in the substrate is carried out under a hydrogen atmosphere or under an inert gas mixed hydrogen atmosphere.

3. The method for producing diamond according to claim 1, characterized in that the step of solid-solving the carbon in the substrate is carried out under conditions of a temperature of 800°C or higher and less than 1100°C.

4. The method for producing diamond according to any one of claims 1 to 3, characterized in that the substrate is one of Ni, Pt, Co, Ti, Mo, W, Cu, Fe, or an alloy thereof.

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