Diamond thin film and method for manufacturing diamond thin film

Abstract

To provide a diamond thin film formed by a CVD method and high in slidability.SOLUTION: A diamond thin film has 0.001 or more and 2.0 or less of the relative ratio of oxygen concentration in the film to hydrogen concentration in the film.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a diamond thin film produced by a plasma CVD method and a method for producing a diamond thin film. [Background technology]

[0002] Conventionally, it is known that diamond thin films are manufactured using a filament CVD apparatus or a microwave surface wave plasma CVD apparatus, as shown in, for example, Patent Document 1.

[0003] When using a filament CVD apparatus, a metal wire with a high melting point is placed above the substrate on which the diamond thin film is to be formed. When this metal wire is heated, the thermoelectrons released decompose the raw material gas to produce the diamond thin film.

[0004] In the case of using a microwave surface wave plasma CVD device, a plasma containing the raw material gas is generated by applying a high frequency current, and the diamond thin film is produced from the activated gas.

[0005] These manufacturing methods are known to mainly generate active atomic hydrogen in the plasma, which acts to remove non-diamond components with sp1 and sp2 bonds, allowing diamond components with sp3 bonds to grow primarily. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2022-191959 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, diamond thin films produced using a filament CVD apparatus have a G band that is stronger than the diamond peak in Raman spectroscopy, resulting in diamond thin films with low crystallinity.

[0008] In addition, when a diamond thin film is manufactured using a microwave surface wave plasma CVD apparatus, the crystal grain size becomes large if the diamond thin film is manufactured in a high temperature environment of, for example, 500°C or higher. On the other hand, when coating a diamond thin film on a substrate such as a tool, it is necessary to apply compressive stress to the diamond thin film, and a high temperature environment of, for example, 500°C or higher is required to apply compressive stress to the diamond thin film. However, if the crystal grain size of the diamond thin film is large, the sliding properties of the diamond thin film decrease.

[0009] As a result of extensive research, the present inventors have found for the first time that the tribological properties of a diamond thin film can be improved by incorporating oxygen within a prescribed range into a highly crystalline diamond thin film.

[0010] The present invention has been made to solve the above problems, and has as its main object to provide a diamond thin film which is formed by a CVD method and has high sliding properties. [Means for solving the problem]

[0011] That is, the diamond thin film according to the present invention is characterized in that the relative ratio of the oxygen concentration in the film to the hydrogen concentration in the film is 0.001 or more and 2.0 or less.

[0012] With this structure, the diamond thin film contains oxygen within the above relative ratio range, so that the slidability of the diamond thin film can be improved. Specifically, when the above-mentioned relative ratio is less than 0.001, the oxygen concentration is low or the hydrogen concentration is high, so that the decrease in oxygen concentration contributes more to the decrease in the sliding properties of the diamond thin film than the increase in hydrogen concentration due to the decrease in crystal grain size. Also, when the above-mentioned relative ratio is greater than 2.0, the oxygen concentration is high or the hydrogen concentration is low, so that the decrease in hydrogen concentration due to the increase in crystal grain size contributes more than the increase in oxygen concentration, so that the surface roughness of the diamond thin film increases and the sliding properties of the diamond thin film decrease. Therefore, in order to improve the sliding properties of the diamond thin film, it is necessary to contain oxygen within the above-mentioned relative ratio range.

[0013] A specific embodiment of the diamond thin film is one in which the oxygen concentration is 1000 ppm or more and 10000 ppm or less.

[0014] A specific embodiment of the diamond thin film is one having a film thickness of 0.1 μm or more and 5.0 μm or less.

[0015] In order for the diamond in the diamond thin film to have various crystal grain sizes, it is necessary to adjust the hydrogen concentration in the diamond thin film. Therefore, in the diamond thin film, the hydrogen concentration is preferably 5000 ppm or more and 250000 ppm or less. With this configuration, diamond thin films having crystal grains of various sizes can be manufactured, from small to large. This effect is particularly noticeable within the above-mentioned numerical range.

[0016] The diamond thin film preferably has a surface roughness of 0.01 μm or more and 1.0 μm or less. With this configuration, diamond thin films with surfaces ranging from smooth to rough can be manufactured.

[0017] The method for producing the diamond thin film is characterized in that a raw material gas containing C, H and O is supplied into a vacuum vessel in which a substrate is placed, an antenna is placed inside or outside the vacuum vessel, and the antenna has a conductor element and a capacitance element electrically connected in series with each other, thereby generating an inductively coupled plasma in the vacuum vessel by passing a high-frequency current through the antenna, and a diamond thin film is synthesized on the substrate at a temperature range of 500°C to 1200°C by a plasma CVD method using the generated inductively coupled plasma. With this configuration, the diamond thin film is synthesized in the temperature range of 500°C to 1200°C, making it possible to obtain a diamond thin film with a grain size of 50 nm or less, as well as a diamond thin film with high crystallinity and high compressive stress. Furthermore, within the above temperature range, a diamond thin film containing oxygen within the above-mentioned relative ratio range is formed, so that the slidability of the diamond thin film can be improved. Effect of the Invention

[0018] According to the present invention thus configured, it is possible to provide a diamond thin film which is formed by a CVD method and has high slidability. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing a schematic configuration of a film forming apparatus according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a diagram showing the gas composition range of the source gas supplied in the film forming apparatus and the method for producing a diamond thin film according to the embodiment; [Diagram 3] FIG. 2 shows Raman scattering spectra of samples synthesized in the examples. [Figure 4] FIG. 13 is a graph showing the oxygen concentration and hydrogen concentration in the film of a sample synthesized in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, a diamond thin film and a method for manufacturing a diamond thin film according to an embodiment of the present invention will be described with reference to the drawings. Note that, in any of the drawings shown below, in order to make it easier to understand, some parts may be omitted or exaggerated and drawn in a schematic manner. The same components are given the same reference numerals and the description thereof will be omitted as appropriate.

[0021] <Device configuration> The diamond thin film F of this embodiment is formed on a substrate W by a plasma CVD method using an inductively coupled plasma P, using a film forming apparatus 100 which is a plasma CVD apparatus, as shown in FIG.

[0022] Specifically, in the diamond thin film F of this embodiment, the grain size is preferably 50 nm or less, and more preferably 30 nm or less. The film thickness of the diamond thin film F is preferably 0.1 μm or more and 5.0 μm or less. Furthermore, the surface roughness is preferably 0.01 μm or more and 1.0 μm or less in terms of arithmetic mean roughness.

[0023] In the diamond thin film F of this embodiment, in order to improve the sliding properties of the diamond thin film F, the relative ratio of the oxygen concentration in the film to the hydrogen concentration in the film is preferably 0.001 or more and 2.0 or less. More specifically, the oxygen concentration in the film is preferably 1000 ppm or more and 10000 ppm or less. Also, the hydrogen concentration in the film is preferably 5000 ppm or more and 250000 ppm or less.

[0024] The film-forming apparatus 100 for producing the above-mentioned diamond thin film F and the method for producing the diamond thin film F will be described below.

[0025] The substrate W in this embodiment is a plate-like member made of a material suitable for forming the diamond thin film F. The substrate W may be made of, for example, glass, plastic, silicon, metals such as iron, titanium, copper, and cemented carbide, other alloy materials such as tool steel, SiC, GaN, AlN, BN, diamond, and other materials, but is not limited thereto.

[0026] The substrate W has a rectangular or circular shape in plan view. The length of the substrate W can be, for example, 20 cm or more or 50 cm or more, but is not limited thereto. The substrate W may also be, for example, a plurality of small chip-shaped substrates of about 1 mm, 5 mm, or 10 mm arranged with the same length or area. The substrate W is not limited to a plate shape, and may also be columnar, perforated, or porous. It may also have a complex shape, such as a tool such as a drill or end mill.

[0027] The substrate W may be subjected to a surface treatment such as a scratching treatment or a seeding treatment. For example, when the substrate W is silicon, the substrate W may be subjected to a scratching treatment or a seeding treatment in which the substrate W is immersed in alcohol together with diamond fine particles and an ultrasonic treatment is used to form irregularities on the surface. For example, when the substrate W is a cemented carbide alloy, the substrate W may be immersed in an acidic solution such as a nitric acid solution to remove Co from the substrate, or the substrate W may be subjected to an alkaline solution such as diluted NaOH to treat the surface of WC (tungsten carbide) particles, and then the seeding treatment may be performed as described above.

[0028] 1, the film forming apparatus 100 includes a vacuum vessel 2 that is evacuated and into which a gas G is introduced, a gas supply mechanism 7 that supplies the gas G to the vacuum vessel 2, a linear antenna 3 disposed in the vacuum vessel 2, and a high-frequency power supply 4 that applies a high-frequency wave to the antenna 3 for generating an inductively coupled plasma P in the vacuum vessel 2. In the film forming apparatus 100, a high-frequency current IR flows through the antenna 3 by applying a high-frequency wave from the high-frequency power supply 4 to the antenna 3, and an inductive electric field is generated in the vacuum vessel 2, generating the inductively coupled plasma P.

[0029] The vacuum vessel 2 is a vessel made of metal such as SUS or aluminum, and its interior is evacuated to a vacuum by a vacuum exhaust device 6. In this example, the vacuum vessel 2 is electrically grounded. The vacuum exhaust device 6 is equipped with a pressure regulator 61 such as a valve that adjusts the pressure inside the vacuum vessel 2. By controlling this pressure regulator 61, the pressure inside the vacuum vessel 2 during plasma generation can be adjusted, for example, to a pressure of 7 Pa or more and 100 Pa or less.

[0030] A gas G such as a source gas is introduced into the vacuum chamber 2 via a plurality of gas inlets 21 arranged in a direction along, for example, a flow rate regulator (not shown) and the antenna 3.

[0031] In addition, a substrate holder 8 for holding a substrate W is provided in the vacuum vessel 2, and a heater 81 for heating the substrate W is provided in the substrate holder 8. The substrate holder 8 does not need to be electrically connected to the vacuum vessel 2. The film forming apparatus 100 of this embodiment may have a function of adjusting the potential of the generated inductively coupled plasma, for example, in the range of +100V to -100V, by applying a bias voltage from a bias power supply 9 to the substrate holder 8. The bias voltage applied is, for example, a negative DC voltage, but is not limited thereto. By using such a bias voltage, for example, the energy when positive ions in the plasma P are incident on the substrate W can be controlled, and the crystallinity of the film formed on the surface of the substrate W can be controlled.

[0032] The gas supply mechanism 7 supplies gas G, such as a source gas, into the vacuum vessel 2 through the gas inlet 21. The gas supply mechanism 7 is configured to supply gas G downward from the gas inlet 21 provided on the upper wall of the vacuum vessel 2. This gas supply mechanism 7 is configured to supply a source gas containing at least C (carbon), H (hydrogen), and O (oxygen), and specifically, is configured to supply H2 gas, CH4 gas, and CO2 gas as source gas. Note that the gas supply mechanism 7 may be configured to supply any other gas as source gas in addition to or instead of H2 gas, CH4 gas, and CO2 gas, as long as it is configured to supply a source gas containing C, H, and O into the vacuum vessel 2.

[0033] The gas supply mechanism 7 is configured to supply H2 gas, CH4 gas, and CO2 gas at any flow rate. The gas supply mechanism 7 of this embodiment is configured to adjust the flow rate of each gas so that the ratio of the concentration of O atoms to the total concentration of O atoms and H atoms (O / (O+H)) in the source gas containing H2 gas, CH4 gas, and CO2 gas is, for example, 5 at% or more and 45 at% or less.

[0034] The gas supply mechanism 7 is configured to supply a catalytic gas at an arbitrary flow rate into the vacuum chamber 2 together with the raw material gas. This catalytic gas functions as a catalyst during plasma generation, and promotes the decomposition of the raw material gas. Specifically, the gas supply mechanism 7 is configured to supply the catalytic gas so that the ratio of the catalytic gas to the total flow rate of all gases supplied into the vacuum chamber 2 (here, the total flow rate of the raw material gas and the catalytic gas) is, for example, 50% to 95%, preferably 70% to 90%. Specifically, examples of this catalytic gas include rare gases such as Ar gas, He gas, and Ne gas.

[0035] The antenna 3 is disposed above the substrate W in the vacuum chamber 2 so as to follow the surface of the substrate W. In this embodiment, a plurality of linear antennas 3 are disposed in parallel so as to follow the substrate W (e.g., substantially parallel to the surface of the substrate W). In this manner, plasma P with good uniformity can be generated over a wider range, and therefore a larger substrate W can be processed.

[0036] The number of antennas 3 is not limited to multiple and may be only one. When multiple antennas 3 are provided, the number is preferably an even number (e.g., 2, 4, 6, etc.). When multiple antennas 3 are provided, in order to avoid radio wave interference, the spacing between the antennas 3 is preferably 5 cm or more, more preferably 10 cm or more, and even more preferably 15 cm or more. On the other hand, in order to deposit a uniform diamond thin film F, the spacing between the antennas 3 is preferably 25 cm or less.

[0037] As shown in FIG. 1, the vicinity of both ends of the antenna 3 penetrates a pair of opposing side walls 2a, 2b of the vacuum vessel 2. An insulating member 11 is provided at each portion where both ends of the antenna 3 penetrate to the outside of the vacuum vessel 2. Both ends of the antenna 3 penetrate each insulating member 11, and the penetration portion is vacuum-sealed by, for example, a packing 12. The antenna 3 is supported via the insulating member 11 in a state in which it is electrically insulated from the opposing side walls 2a, 2b of the vacuum vessel 2. The gap between each insulating member 11 and the vacuum vessel 2 is also vacuum-sealed by, for example, a packing 13. The material of the insulating member 11 is, for example, ceramics such as alumina, quartz, or engineering plastics such as polyphenylene sulfide (PPS) and polyether ether ketone (PEEK).

[0038] The antenna 3 is a so-called LC antenna having an L section which serves as an inductor and a C section which serves as a capacitor. Specifically, the antenna 3 has at least two tubular metallic conductor elements 31 (hereinafter, metal pipes 31), a tubular insulating element 32 (hereinafter, insulating pipe 32) which is provided between adjacent metal pipes 31 and insulates the metal pipes 31, and a capacitor 33 which is a capacitive element provided between adjacent metal pipes 31 and electrically connected in series with them. The conductor elements 31 function as the L section, and the capacitor 33 functions as the C section.

[0039] In this embodiment, the number of metal pipes 31 is three, and the number of insulating pipes 32 and capacitors 33 is two each. Note that the antenna 3 may have four or more metal pipes 31, in which case the number of insulating pipes 32 and capacitors 33 is one less than the number of metal pipes 31.

[0040] The material of the metal pipe 31 is, for example, but not limited to, copper, aluminum, an alloy thereof, stainless steel, etc. The antenna 3 may be hollow and a coolant such as cooling water may be flowed therein to cool the antenna 3.

[0041] In the present embodiment, the insulating pipe 32 is formed from a single member, but is not limited to this. The material of the insulating pipe 32 is, for example, alumina, fluororesin, polyethylene (PE), engineering plastic (e.g., polyphenylene sulfide (PPS), polyether ether ketone (PEEK), etc.).

[0042] Furthermore, the portion of the antenna 3 located inside the vacuum vessel 2 is covered with a straight tubular insulating cover (antenna protection tube) 10. Both ends of this insulating cover 10 are supported by insulating members 11. Note that it is not necessary to seal between both ends of the insulating cover 10 and the insulating members 11. This is because even if gas G enters the space inside the insulating cover 10, the space is small and the travel distance of electrons is short, so that plasma P is not normally generated in the space. Note that the material of the insulating cover 10 is, for example, quartz, alumina, fluororesin, silicon nitride, silicon carbide, silicon, etc.

[0043] By providing the insulating cover 10, it is possible to prevent the charged particles in the plasma P from entering the metal pipe 31 that constitutes the antenna 3, thereby preventing an increase in plasma potential caused by charged particles (mainly electrons) entering the metal pipe 31 and also preventing the metal pipe 31 from being sputtered by the charged particles (mainly ions), resulting in metal contamination of the plasma P and the substrate W.

[0044] The length of the antenna 3 is, for example, preferably 20 cm or more, more preferably 50 cm or more, and even more preferably 100 cm or more. On the other hand, from the viewpoint of ensuring the strength of the insulating pipe 32, the length of the antenna 3 is preferably 1000 cm or less, and more preferably 500 cm or less.

[0045] 1, the antenna 3 has a power feeding end 3a to which high frequency power is fed in the antenna direction (longitudinal direction X) and a grounded end 3b which is grounded. Specifically, at both ends of the longitudinal direction X of each antenna 3, the portion extending outward from one of the side walls 2a or 2b becomes the power feeding end 3a, and the portion extending outward from the other side wall 2a or 2b becomes the grounded end 3b.

[0046] Here, a high frequency is applied to the power supply end 3a of each antenna 3 from a high frequency power supply 4 via a matching device 41. The frequency of the high frequency is 400 kHz or more and 100 MHz or less, for example, a common 13.56 MHz, but is not limited to this. For example, it may be 27.12 MHz, 40.68 MHz, 60 MHz, etc.

[0047] <Method of manufacturing diamond thin film> Next, a method for producing the diamond thin film F using the above-mentioned film forming apparatus 100 will be described.

[0048] First, the substrate W is set on the substrate holder 8 in the vacuum chamber 2 of the film forming apparatus 100, and the vacuum chamber 2 is evacuated by the vacuum exhaust device 6. Then, the substrate W is heated by the heater 81.

[0049] (Supply of raw gas) Next, the gas supply mechanism 7 supplies H2 gas, CH4 gas, and CO2 gas as raw material gases at a predetermined flow rate into the vacuum vessel 2. In the manufacturing method of the diamond thin film F of this embodiment, the flow rates of H2 gas, CH4 gas, and CO2 gas are adjusted so that the atomic ratio of O atoms, C atoms, and H atoms in the raw material gases is within the shaded range shown in the composition ternary diagram (CHO diagram) of Figure 2. The atomic ratio of each atom is explained below.

[0050] (ratio of oxygen and hydrogen atoms) In the raw material gas to be supplied, the flow rates of H gas, CH gas, and CO gas are controlled so that the ratio of the concentration of O atoms to the total concentration of O atoms and H atoms contained therein (O / (O+H)) is preferably 5 at% or more and 45 at% or less, more preferably 5 at% or more and 10 at% or less.

[0051] (ratio of oxygen and carbon atoms) In the raw material gas to be supplied, the flow rates of H2 gas, CH4 gas, and CO2 gas are controlled so that the ratio of the concentration of C atoms to the total concentration of O atoms and C atoms contained therein (C / (O+C)) is preferably 45 at% or more and 70 at% or less.

[0052] (ratio of carbon to hydrogen atoms) In addition, the flow rates of H gas, CH gas, and CO gas are controlled so that the ratio of the concentration of H atoms to the total concentration of C atoms and H atoms (H / (C+H)) in the supplied raw material gas is preferably 60 at% or more and 95 at% or less, more preferably 90 at% or more and 95 at% or less.

[0053] (Catalyst gas supply) Furthermore, the gas supply mechanism 7 supplies a catalytic gas such as Ar gas into the vacuum vessel 2 together with the raw material gas. The flow rate of the catalytic gas to be supplied is preferably 50% or more and 95% or less, more preferably 70% or more and 90% or less, relative to the total flow rate of all gases supplied to the vacuum vessel 2. By setting the flow rate of the catalytic gas to be supplied within this range, it is possible to transfer energy from, for example, Ar, which is easily ionized, to CH4 during film formation, and generate a large amount of C2 radicals, which are likely to generate diamond. As a result, the ratio of the emission intensity of C2 radicals to the emission intensity of Hα radicals can be set to 30% or more and 300% or less in the emission spectrum of the inductively coupled plasma to be generated.

[0054] (Pressure inside the vacuum vessel) Then, while the source gas and catalyst gas are being introduced by the gas supply mechanism 7, the pressure inside the vacuum chamber 2 is adjusted by the pressure regulator 61 to be 7 Pa or more and 100 Pa or less, more preferably 10 Pa or more and 50 Pa or less.

[0055] (Plasma generation and diamond thin film deposition) Then, with the flow rates of the raw material gas and catalyst gas adjusted as described above and the pressure inside the vacuum chamber 2 adjusted, high frequency power is supplied from the high frequency power source 4 to the antenna 3. This generates an induced electric field inside the vacuum chamber 2, generating an inductively coupled plasma P, and forming a diamond thin film F on the substrate W. The frequency of the high frequency power is 13.56 MHz. The power density of the supplied high frequency power is 1.4 W / cm.2 The power density is 1000W / cm 2 Less than 100W / cm is preferable. 2 Less than 50W / cm is more preferable. 2 The following is even more preferred:

[0056] Here, it is necessary to synthesize diamond thin film F at a temperature of 500°C or higher and 1200°C or lower. This ensures that the relative ratio of the oxygen concentration in the diamond thin film F to the hydrogen concentration in the film is 0.001 or higher and 2.0 or lower. When synthesizing a carbon-based thin film containing diamond with a grain size of 50 nm or less, the raw material gas to be supplied must be hydrogen-rich and at 500°C or higher. If diamond thin film F is synthesized at a temperature higher than 1200°C, it will turn into graphite, making it impossible to synthesize a diamond thin film in the first place, and the above relative ratio will be violated.

[0057] When the diamond thin film F was manufactured by setting the temperature of the substrate W to 500°C or higher and 1200°C or lower as described above and laser Raman spectroscopy (325 nm excitation) was performed, -1 The optical phonon peak of diamond observed near the wavelength of 1550 cm -1 The intensity of the optical phonon peak of the G band observed in the vicinity of the wavelength of 100 nm is between 1 and 5 times that of the optical phonon peak of the G band observed in the vicinity of the wavelength of 100 nm, and a diamond thin film F with high crystallinity is produced.

[0058] <Example> The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples, and may be modified within the scope of the above and below-described aims, and all such modifications are within the technical scope of the present invention.

[0059] In the examples, samples were formed on substrates by changing the composition of the source gas, the pressure of the vacuum vessel 2, and the flow rate ratio of Ar gas by the plasma CVD method using the above-mentioned film formation apparatus 100. The flow rate of the source gas, the composition of the source gas, the flow rate ratio of Ar gas, the pressure inside the vacuum vessel 2, the frequency of the supplied high frequency power, the power density of the supplied high frequency power, and the substrate temperature during the manufacture of the samples are as follows: Flow rate of H2 gas in the raw gas: 20sccm Flow rate of CH4 gas among raw gases: 3sccm Flow rate of CO2 gas in the raw gas: 4sccm Ratio of O atom concentration to the total concentration of O atoms and H atoms in the source gas (O / (O+H)): 13% Ar gas flow rate: 82% Pressure inside the vacuum chamber: 15Pa Frequency of supplied high frequency power: 13.56MHz -Power density of supplied high frequency power: 1.4W / cm 2 ·Substrate temperature: 800℃

[0060] Diamond thin film F was produced under the above conditions, and the grain size of diamond contained in diamond thin film F was evaluated by a transmission electron microscope (TEM). As a result, the grain size of diamond thin film F was about 10 nm.

[0061] The crystallinity of the produced sample was evaluated by laser Raman spectroscopy (325 nm excitation). The Raman scattering spectrum obtained for the sample is shown in FIG. 3. As shown in FIG. 3, the sample had a peak at 1333 cm -1 The optical phonon peak of diamond is observed near the wavelength of 1550 cm -1 The intensity of this peak is approximately three times that of the G-band optical phonon peak observed near the wavelength of 1000 nm. Therefore, it was confirmed that diamond thin film F with high crystallinity can be produced.

[0062] In addition, the thickness of the diamond thin film F was evaluated by observing the cross section of the sample with a scanning electron microscope (SEM), and was found to be 1.2 μm. Therefore, it was confirmed that the thickness was within the range of 0.1 μm to 5.0 μm.

[0063] At the above film thickness, the oxygen and hydrogen concentrations in the film were evaluated by secondary ion mass spectrometry (SIMS). The oxygen and hydrogen concentrations in the diamond thin film F are shown in Figure 4. As shown in Figure 4, in the film depth range of 0.1 μm to 1.2 μm, the relative ratio of the oxygen concentration to the hydrogen concentration in the film was about 0.04. The oxygen concentration in the film was about 4.0×10 20 atm / cm 3 The hydrogen concentration in the film is about 1.0×10 22 atm / cm 3 Therefore, it was confirmed that the diamond thin film F contains oxygen within the above-mentioned relative ratio range.

[0064] Furthermore, the sliding properties of the produced samples were evaluated using a reciprocating friction tester.

[0065] In addition, the surface roughness of the manufactured sample was evaluated by a laser microscope. The substrate W was subjected to a surface treatment, and it is known that the roughness after film formation varies depending on the surface roughness during the surface treatment. In this example, in the case of a substrate having a rough surface during the surface treatment (for example, a surface roughness during the surface treatment of 0.03 μm or more and 0.06 μm or less), the surface roughness after film formation was 0.23 μm or more and 0.60 μm or less, and in the case of a substrate having a flat surface during the surface treatment (for example, a surface roughness during the surface treatment of 0.02 μm or more and 0.03 μm or less), the surface roughness after film formation was 0.03 μm or more and 0.60 μm or less. Therefore, it was confirmed that the surface roughness after film formation was within the range of 0.01 μm or more and 1.0 μm or less.

[0066] <Effects of this embodiment> According to this embodiment, the diamond thin film F is produced in a temperature range of 500°C or more and 1200°C or less, so that oxygen can be contained in the diamond thin film F such that the relative ratio of the oxygen concentration in the film to the hydrogen concentration in the film is in the range of 0.001 or more and 2.0 or less, thereby improving the sliding properties of the diamond thin film F.

[0067] Specifically, when the above-mentioned relative ratio is less than 0.001, the oxygen concentration is low or the hydrogen concentration is high, so that the decrease in oxygen concentration contributes more to the decrease in the sliding properties of the diamond thin film than the increase in hydrogen concentration due to the decrease in crystal grain size. Also, when the above-mentioned relative ratio is greater than 2.0, the oxygen concentration is high or the hydrogen concentration is low, so that the decrease in hydrogen concentration due to the increase in crystal grain size contributes more than the increase in oxygen concentration, so that the surface roughness of the diamond thin film increases and the sliding properties of the diamond thin film decrease. Therefore, in order to improve the sliding properties of the diamond thin film, it is necessary to contain oxygen within the above-mentioned relative ratio range.

[0068] Furthermore, since the diamond thin film F is produced in a temperature range of 500°C or higher and 1200°C or lower using an inductively coupled plasma generated by passing a high frequency current through an LC antenna, it is possible to obtain a diamond thin film F having a grain size of 50 nm or less, more preferably a grain size of 30 nm or less, and it is also possible to obtain a diamond thin film F having high crystallinity and high compressive stress.

[0069] Furthermore, according to this embodiment, the hydrogen concentration of the diamond thin film F is not less than 5000 ppm and not more than 250000 ppm, so that diamond thin films F with small crystal grain sizes and large crystal grain sizes can be manufactured.

[0070] Moreover, according to this embodiment, the surface roughness of the diamond thin film F is 0.01 μm or more and 1.0 μm or less, so that diamond thin films F with surfaces ranging from smooth to rough can be manufactured.

[0071] <Other embodiments> The film forming apparatus 100 of the present invention is not limited to the above embodiment.

[0072] For example, in the film forming apparatus 100 of the above embodiment, the antenna 3 for generating the inductively coupled plasma is disposed inside the vacuum chamber 2, but this is not limited thereto. The film forming apparatus 100 of other embodiments may have a structure in which the antenna 3 is disposed outside the vacuum chamber 2.

[0073] It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, it will be understood by those skilled in the art that the above-described exemplary embodiments are specific examples of the following aspects. [Explanation of symbols]

[0074] 100 Plasma CVD equipment 2...Vacuum container 3. Antenna 7 Gas supply mechanism F Diamond thin film W...Base material P...Plasma

Claims

1. A diamond thin film having a relative ratio of oxygen concentration in the film to hydrogen concentration in the film of 0.001 to 2.

0.

2. 2. The diamond film according to claim 1, wherein the oxygen concentration is 1000 ppm or more and 10000 ppm or less.

3. 2. The diamond film according to claim 1, having a film thickness of 0.1 μm or more and 5.0 μm or less.

4. 2. The diamond film according to claim 1, wherein the hydrogen concentration is 5,000 ppm or more and 250,000 ppm or less.

5. 5. The diamond thin film according to claim 1, having a surface roughness of 0.01 μm or more and 1.0 μm or less.

6. Supplying a source gas containing C, H, and O into a vacuum chamber in which a substrate is placed; an antenna disposed inside or outside the vacuum vessel, the antenna having a conductor element and a capacitance element electrically connected in series with each other, to generate an inductively coupled plasma within the vacuum vessel by passing a high-frequency current through the antenna; The method for producing a diamond thin film comprises synthesizing a diamond thin film on the substrate at a temperature in the range of 500° C. to 1200° C. by a plasma CVD method using the generated inductively coupled plasma.

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