Methods for growing diamond layers

Abstract

The present invention is a method for growing a diamond layer via microwave plasma CVD, said method being characterized by comprising a step for disposing a substrate 2 inside a reaction vessel 1 of a microwave plasma CVD device 10, a step for introducing a raw material gas (reaction gas) 6 into the reaction vessel 1, and a step for irradiating a surface of the substrate 2 with microwave plasma to grow a diamond layer on the surface of the substrate 2, wherein, in the step for growing the diamond layer, the substrate 2 is moved in a direction parallel to the surface of the substrate 2, and / or the irradiation position of the microwave plasma is moved in a direction parallel to the surface of the substrate 2. This method provides a large-diameter diamond substrate.

Description

Technical Field

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[0001] The present invention relates to a method for growing a diamond layer and a microwave plasma CVD apparatus. In particular, the present invention is a technology related to artificial diamond growth on a semiconductor substrate, and more specifically, relates to a diamond growth method and an apparatus therefor when growing diamond by CVD (Chemical Vapor Deposition) on a silicon substrate.

Background Art

[0002] Diamond is expected to be applied to various semiconductor elements and electronic devices due to its excellent physical property values such as high hardness, good thermal conductivity, high carrier mobility, and wide bandgap. For these semiconductor element and electronic device applications, artificially synthesized diamond is used. There are two methods for synthesizing diamond: a method of growing using ultra-high pressure and vapor phase growth. In applications to semiconductors, vapor phase growth (CVD growth) has attracted attention because large diameters can be obtained (Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] CVD growth is a method in which a substrate is mounted inside a reaction tube, and a source gas (reaction gas) and a carrier gas are flowed under normal pressure or reduced pressure, and the source gas (reaction gas) is decomposed and activated by thermal decomposition or plasma to grow on the substrate. While methods such as microwave plasma, DC plasma, and the hot filament method using tungsten filaments are employed for diamond growth, the microwave plasma method is attracting attention for single crystal growth. Microwave plasma growth is a method of growing single-crystal diamond by irradiating a substrate with microwaves to decompose and activate the raw material gas (reaction gas).

[0005] Figure 5 is an explanatory diagram of a conventional microwave plasma CVD apparatus. As shown in Figure 5, the conventional microwave plasma CVD apparatus 110 has a reaction vessel 101 in which a silicon substrate (substrate to be coated) 102 can be placed. The reaction vessel 101 is designed to allow for reduced pressure inside.

[0006] A reaction gas introduction pipe 109 is attached to the wall, allowing reaction gas 106 to be introduced inside. Reaction gas 106 is, for example, a mixture of hydrogen gas and methane gas.

[0007] A microwave introduction tube 104 connected to a microwave generator 105 (2.45 GHz) is mounted on the ceiling, allowing microwave plasma to be irradiated directly downwards.

[0008] A plate-shaped stage (substrate heating) 103 is positioned on the bottom side. The surface of the stage 103 is parallel to the direction perpendicular to the direction directly below. The surface of the stage 103 is also designed to accommodate a silicon substrate 102.

[0009] A silicon substrate 102 is placed on the surface of stage 103. As can be seen from Figure 5, there are limitations on the substrate diameter because, in principle, there are limitations on the area that can be irradiated with microwaves.

[0010] Diamond substrates have attracted attention due to their heat dissipation properties, and microwave plasma growth is the growth method for single-crystal substrates. However, due to limitations in the area that can be irradiated with plasma, it has been impossible to produce large diameters such as 300 mmφ. Therefore, forming large-diameter diamond substrates is a challenge. This invention was made to solve the above problems and aims to provide a method for growing a diamond layer with a large diameter and a microwave plasma CVD apparatus. [Means for solving the problem]

[0011] The present invention has been made to achieve the above objective, and provides a method for growing a diamond layer by microwave plasma CVD, comprising the steps of: placing a substrate in a reaction vessel of a microwave plasma CVD apparatus; introducing a raw material gas (reaction gas) into the reaction vessel; and irradiating the surface of the substrate with microwave plasma to grow a diamond layer on the surface of the substrate, wherein in the step of growing the diamond layer, the substrate is moved in a direction parallel to the surface of the substrate, and / or the irradiation position of the microwave plasma is moved in a direction parallel to the surface of the substrate.

[0012] This method of growing diamond layers allows for the formation of large-diameter diamond layers. More specifically, when growing diamond on a large-diameter silicon substrate, the large-diameter silicon substrate is placed on the stage of a microwave plasma growth apparatus, and growth is carried out by introducing a raw material gas (reaction gas) while irradiating it with microwaves, while moving the stage at predetermined time intervals. This makes it possible to grow large-diameter single-crystal diamond layers even with a microwave plasma CVD apparatus. Furthermore, growth occurs in the vertical (lateral) direction in areas with high plasma density, and growth proceeds horizontally in areas with low plasma density, which also contributes to reducing defects. Furthermore, as specified, the substrate may be moved in a direction parallel to the surface of the substrate, and / or the irradiation position of the microwave plasma may be moved in a direction parallel to the surface of the substrate. In any case, it is possible to fix the plasma irradiation position and move the substrate, or conversely, to fix the substrate and move the microwave plasma irradiation position (where the microwave plasma density is high) in the X and Y directions, or to move both the substrate and the irradiation position. In any case, it is possible to grow large-diameter single-crystal diamonds.

[0013] In this case, the diamond layer growth method described above can be adopted, characterized in that, after the step of growing the diamond layer, the substrate on which the diamond layer has been grown is transferred into the reaction vessel of a hot filament CVD apparatus, and diamond is further grown on the diamond layer by the hot filament CVD method.

[0014] This makes it possible to increase the thickness of the large-diameter diamond layer. By further growing the substrate grown by the microwave plasma CVD method using a hot filament CVD apparatus capable of large-diameter growth, it becomes possible to grow even thicker diamonds on the large-diameter substrate. More specifically, while the diamond film grown by the microwave plasma CVD method is sufficient, to grow it even thicker, instead of growing it with microwave plasma alone, it is possible to grow diamonds across the entire large-diameter substrate by introducing methane and hydrogen as gases into the reaction vessel of a hot filament diamond growth apparatus, passing an electric current through a filament such as tungsten placed on the substrate to heat and decompose the gases, and growing diamonds on the substrate.

[0015] In this case, the method for growing a diamond layer as described above can be adopted, characterized in that a silicon substrate is used as the substrate.

[0016] Accordingly, when an integrated circuit is formed on a silicon substrate on which a diamond layer is formed, the diamond layer can be used as a heat sink layer.

[0017] The present invention also provides a microwave plasma CVD apparatus used for a method of growing a diamond layer, which is characterized by comprising a mechanism for moving the substrate in a direction parallel to the surface of the substrate and / or a mechanism for moving the irradiation position of the microwave plasma.

[0018] According to such a microwave plasma CVD apparatus, a large-diameter diamond layer can be formed. More specifically, with an apparatus having such a mechanism, even a microwave plasma CVD apparatus can grow a single-crystal diamond with a large diameter.

[0019] At this time, the above-described microwave plasma CVD apparatus can be further characterized by comprising a mechanism for heating the substrate.

[0020] Thereby, the growth of a large-diameter diamond layer can be promoted.

Effects of the Invention

[0021] As described above, according to the method for growing a diamond layer of the present invention, it is possible to form a large-diameter diamond layer by the microwave plasma CVD method. In particular, in the present invention, a single-crystal large-diameter diamond layer can be grown by the microwave plasma CVD method. Also, according to the microwave plasma CVD apparatus of the present invention, a large-diameter diamond layer can be formed.

Brief Description of the Drawings

[0022] [Figure 1] It is an explanatory diagram of the microwave plasma CVD apparatus of the present invention. [Figure 2] It is an explanatory diagram of a hot filament CVD apparatus used for the method of growing a diamond layer of the present invention. [Figure 3A] This is the Raman peak of a diamond film grown by the diamond layer growth method of the present invention (microwave plasma method only). [Figure 3B] This is a surface optical microscope image of a diamond film grown by the diamond layer growth method of the present invention (microwave plasma method only). [Figure 4A] This is the Raman peak of a diamond film grown by the diamond layer growth method of the present invention (microwave plasma method + thermal filament method). [Figure 4B] This is a surface optical microscope image of a diamond film grown by the diamond layer growth method of the present invention (microwave plasma method + thermal filament method). [Figure 5] This is a diagram illustrating a conventional microwave plasma CVD apparatus. [Modes for carrying out the invention]

[0023] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0024] As described above, there was a need for a diamond layer growth method and microwave plasma CVD apparatus capable of forming a large-diameter diamond layer, particularly a single-crystal diamond layer, on a large-diameter silicon substrate.

[0025] As a result of diligent research into the above-mentioned problems, the present inventors have discovered that a diamond layer can be formed on a large-diameter silicon substrate by a method for growing a diamond layer using microwave plasma CVD, comprising the steps of: placing a substrate in a reaction vessel of a microwave plasma CVD apparatus; introducing a raw material gas (reaction gas) into the reaction vessel; and irradiating the surface of the substrate with microwave plasma to grow a diamond layer on the surface of the substrate, wherein in the step of growing the diamond layer, the substrate is moved in a direction parallel to the surface of the substrate, and / or the irradiation position of the microwave plasma is moved in a direction parallel to the surface of the substrate. This method allows for the formation of a large-diameter diamond layer, particularly a single-crystal diamond layer, on a large-diameter silicon substrate, thus completing the present invention.

[0026] The diamond layer growth method and microwave plasma CVD apparatus according to the first embodiment of the present invention will be described below with reference to Figure 1.

[0027] (First Embodiment) (Microwave plasma CVD apparatus) Figure 1 shows an explanatory diagram of the microwave plasma CVD apparatus of the present invention. As shown in Figure 1, the microwave plasma CVD apparatus 10 of the present invention has a reaction vessel 1 in which a large-diameter silicon substrate 2 can be placed. The reaction vessel 1 is approximately circular in plan view, but the shape of the reaction vessel 1 is not limited to this, and may be approximately rectangular in plan view. The reaction vessel 1 is designed to allow for reduced pressure inside. Note that the left-right direction of the paper is considered the X direction, and the direction perpendicular to the paper is considered the Y direction.

[0028] A reaction gas introduction pipe 9 is attached to the wall, allowing reaction gas 6 to be introduced inside. Reaction gas 6 is, for example, a mixture of hydrogen gas and methane gas.

[0029] A microwave introduction tube 4 connected to a microwave generator (2.45 GHz) 5 is mounted on the ceiling, allowing microwave plasma to be irradiated directly downwards.

[0030] A plate-shaped (X,Y direction movable substrate heating) stage 7 is positioned on the bottom side. The surface of the stage 7 is parallel to the direction perpendicular to the direction directly below. The surface of the stage 7 is also capable of accommodating a large-diameter silicon substrate 2. Furthermore, the stage 7 is equipped with a mechanism that allows it to move in the X and Y directions, and a mechanism that can heat the large-diameter silicon substrate (film-deposited substrate) 2 placed on its surface.

[0031] A large-diameter silicon substrate 2 is placed on the surface of stage 7. For example, the large-diameter silicon substrate 2 was prepared by preparing a 300 mm (111) diameter boron-doped high-resistance single-crystal silicon substrate, grinding the surface with an #8000 grinding wheel (average particle size of abrasive grains 2-4 μm) to roughen the silicon surface and introduce damage, which then served as a nucleus for diamond growth.

[0032] (Methods for growing diamond layers) Next, we will explain the method for growing diamond layers. The present invention relates to a method for growing a diamond layer, particularly a single-crystal diamond layer, using a microwave plasma CVD method. The process includes: placing a substrate in the reaction vessel of a microwave plasma CVD apparatus (substrate placement step); introducing a raw material gas (reaction gas) into the reaction vessel (raw material gas (reaction gas) introduction step); and irradiating the surface of the substrate with microwave plasma to grow a diamond layer on the surface of the substrate (diamond layer growth step).

[0033] (Board placement process) First, as shown in Figure 1, a large-diameter silicon substrate 2 is placed on the surface of a plate-shaped stage 7 located on the bottom side of the reaction vessel 1 of the microwave plasma CVD apparatus 10.

[0034] (Raw material gas (reaction gas) introduction process) Next, the inside of reaction vessel 1 is depressurized, and then reaction gas 6 is introduced into it through the reaction gas introduction pipe 9.

[0035] (Diamond layer growth process) Next, a microwave plasma is irradiated onto the surface of the large-diameter silicon substrate 2 to grow a diamond layer on its surface. When growing the diamond layer, the large-diameter silicon substrate 2 is moved in a direction parallel to the surface of the large-diameter silicon substrate 2, and / or the irradiation position of the microwave plasma is moved in a direction parallel to the surface of the substrate. This allows the locally generated microwave plasma to be uniformly irradiated onto the surface of the large-diameter silicon substrate, and a large-diameter diamond layer can be uniformly formed on the surface of the large-diameter silicon substrate. Furthermore, moving the substrate in a direction parallel to its surface is not limited to translating the substrate in the XY direction, but also includes rotational movements such as rotation and revolution. Furthermore, the preferred moving speed is, for example, about 1 to 50 mm / min when moving the substrate in the X and Y directions, and about 1 to 100 rpm when moving it by rotation.

[0036] Furthermore, it is preferable to heat the large-diameter silicon substrate 2 when growing the diamond layer. This can promote growth.

[0037] (Regarding the evaluation) The diamond layer is evaluated, for example, by Raman spectroscopy, surface optical microscopy, and X-ray diffraction at multiple points within the plane of a large-diameter diamond layer. This allows for the determination of the crystallinity and surface homogeneity of the large-diameter diamond layer.

[0038] (Second embodiment) First, the hot filament CVD apparatus used for growing the diamond layer in the second embodiment of the present invention will be described with reference to Figure 2.

[0039] (Hot filament CVD apparatus) Figure 2 shows an explanatory diagram of the hot filament CVD apparatus used in the diamond layer growth method of the present invention. As shown in Figure 2, the hot filament CVD apparatus 20 used in the diamond layer growth method of the present invention has a reaction vessel 1 in which a large-diameter silicon substrate 2 with a thin diamond layer formed on its surface can be placed. The reaction vessel 1 is designed to allow for reduced pressure inside.

[0040] A reaction gas introduction pipe 9 is installed in the ceiling, allowing reaction gas 6 to be introduced into the interior. Reaction gas 6 is, for example, a mixture of hydrogen gas and methane gas.

[0041] At the bottom of the ceiling, spaced apart, a linear filament 8 is attached directly below the reaction gas introduction pipe 9, parallel to the underside of the ceiling. The heating temperature of the filament 8 is, for example, 2200°C. The filament 8 is, for example, tungsten, but is not limited to this. The shape of the filament is not limited to a linear shape; it may also be a mesh.

[0042] (Methods for growing diamond layers) Next, a method for growing a diamond layer according to the second embodiment will be described. The diamond layer growth method according to the second embodiment is a method of further growing a diamond layer on a diamond layer formed by the diamond layer growth method according to the first embodiment using a hot filament CVD apparatus. In other words, the diamond layer growth method according to the second embodiment includes, in addition to the substrate placement step, raw material gas (reaction gas) introduction step, and diamond layer growth step of the diamond layer growth method according to the first embodiment, a step of placing a substrate in the reaction vessel of a hot filament CVD apparatus (substrate placement step) and a step of further growing the diamond layer using a hot filament CVD apparatus (additional diamond layer growth step).

[0043] (Board placement process) A large-diameter silicon substrate 2, on which a thin diamond layer, particularly a single-crystal diamond layer, is formed on its surface by the diamond layer growth method according to the first embodiment, is placed in the reaction vessel of a hot filament CVD apparatus with the diamond layer facing the ceiling.

[0044] (Diamond layer addition growth process) The inside of reaction vessel 1 is depressurized, and then the filament 8 is heated to a predetermined temperature. Subsequently, a reaction gas 6, consisting of a mixture of hydrogen gas and methane gas, is introduced into the reaction gas introduction tube 9.

[0045] At the bottom of the ceiling, a linear filament 8 is installed parallel to the underside of the ceiling, spaced apart and directly below the reaction gas introduction tube 9. As a result, the reaction gas 6 ejected from the reaction gas introduction tube 9 is heated by the filament 8 and collides with the thin diamond layer formed on the surface of the large-diameter silicon substrate 2. This allows for the further growth of the diamond layer. [Examples]

[0046] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0047] (Example 1) A 300mm (111) diameter boron-doped high-resistance single-crystal silicon substrate was prepared, and the surface was roughened by grinding with an #8000 grinding wheel (average particle size of abrasive grains 2-4 μm) to introduce damage and serve as a nucleus for diamond growth. This substrate was introduced into a microwave plasma growth apparatus, and growth was carried out using 2.45 GHz microwaves at 1500 W, with an H2 flow rate of 10 SLM, a CH4 concentration of 3%, a substrate temperature of 850°C, and a pressure of 60 Torr., while moving the irradiation position at a speed of 10 mm / min. As a result, we were able to form a large-diameter diamond layer. Subsequently, Raman measurements and surface optical microscope images were observed at multiple locations within the plane of the large-diameter diamond layer. Figures 3A and 3B show the results at any single location. As shown in Figure 3A, diamond growth was confirmed. Furthermore, as shown in Figure 3B, high crystallinity was observed. In other words, Raman peaks were confirmed at every location, and surface optical microscope images were observed.

[0048] (Example 2) The substrate from Example 1 (the substrate on which the diamond was grown) was placed in a hot filament apparatus, and growth was carried out 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. As a result, we were able to increase the thickness of the large-diameter diamond layer. Subsequently, Raman measurements and surface optical microscope images were observed at multiple locations within the plane of the large-diameter diamond layer. Figures 4A and 4B show the results at any single location. As shown in Figure 4A, diamond growth was confirmed. Furthermore, as shown in Figure 4B, high crystallinity was observed. In other words, Raman peaks were confirmed at every location, and surface optical microscope images were observed.

[0049] As described above, according to the embodiments of the present invention, it was possible to form a large-diameter diamond layer with high crystallinity.

[0050] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. A method for growing a diamond layer by microwave plasma CVD, comprising the steps of: placing a substrate in a reaction vessel of a microwave plasma CVD apparatus; introducing a raw material gas (reaction gas) into the reaction vessel; and irradiating the surface of the substrate with microwave plasma to grow a diamond layer on the surface of the substrate, wherein in the step of growing the diamond layer, the substrate is moved in a direction parallel to the surface of the substrate, and / or the irradiation position of the microwave plasma is moved in a direction parallel to the surface of the substrate. A method for growing a diamond layer, characterized in that, after the step of growing the diamond layer, the substrate on which the diamond layer has been grown is transferred into the reaction vessel of a hot filament CVD apparatus, and further diamonds are grown on the diamond layer by the hot filament CVD method.

2. The method for growing a diamond layer according to claim 1, characterized in that a silicon substrate is used as the substrate.

Images