Method for producing diamond thin film and apparatus for producing diamond thin film

Abstract

This method for producing a diamond thin film involves synthesizing a diamond thin film on a base material through a plasma CVD method, wherein a raw material gas containing C, H, and O is supplied to a vacuum vessel in which the base material is disposed, high-frequency current is applied to an antenna that is disposed inside or outside the vacuum vessel and that has a conductor element and a capacitive element which are electrically connected to each other in series to generate inductively coupled plasma inside the vacuum vessel, and the generated inductively coupled plasma is used for the plasma CVD method. When the diamond thin film is being synthesized, the plasma has the following characteristics: the electron temperature is 1.0 eV or more and 2.0 eV or less; the electron density is 1.0 × 1011cm-3 or more and 1.0 × 1012cm-3 or less; and the ion saturation current is 1.0 × 10-4 A or more and 1.0 × 10-2 A or less.

Description

Diamond thin film manufacturing method and diamond thin film manufacturing device

[0001] The present invention relates to a method for producing a diamond thin film synthesized using a plasma CVD method, and to an apparatus for producing a diamond thin film.

[0002] Conventionally, methods for producing diamond thin films synthesized using the CVD method have been known, such as those using a filament CVD apparatus, a microwave resonator type plasma CVD apparatus, a microwave surface wave plasma CVD apparatus (e.g., Patent Document 1), or a radio frequency inductively coupled plasma (RF-ICP) type plasma CVD apparatus using a coiled electrode (e.g., Patent Document 2).

[0003] In the manufacturing method 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, and when this metal wire is heated, the thermoelectrons emitted decompose the raw material gas to produce the diamond thin film.

[0004] In addition, in a manufacturing method using a plasma CVD apparatus that utilizes microwaves or a plasma CVD apparatus that utilizes high frequency, a plasma containing a raw material gas is generated by applying a high frequency current, and a diamond thin film is synthesized using the activated gas.

[0005] These manufacturing methods are known to mainly generate active atomic hydrogen in the plasma, which acts to remove sp1- or sp2-bonded non-diamond components, allowing sp3-bonded diamond components to grow primarily.

[0006] JP 2013-40408 A JP 2003-55087 A

[0007] However, when using the above-mentioned plasma CVD device to synthesize diamond, due to the constraints of device configuration, diamond can only be synthesized in a small area.For example, if the filament is lengthened to synthesize diamond in a large area, when plasma is generated, the filament may not be able to withstand its own weight and may break.In addition, microwaves such as 2.45GHz or 915MHz are used, but due to the problem of resonance wavelength, plasma size cannot be increased.

[0008] Furthermore, when synthesizing a diamond thin film, graphite or diamond-like carbon (DLC) is synthesized simultaneously with diamond, which deteriorates the film quality of the diamond thin film. As a result of intensive research, the inventors of the present application have found for the first time that the deterioration of the film quality of the diamond thin film can be suppressed when the electron temperature, electron density, and ion saturation current, which indicate the plasma characteristics when synthesizing a diamond thin film, are within predetermined ranges.

[0009] The present invention has been made to solve the above problems, and its main object is to synthesize a diamond thin film over a wider area and to prevent deterioration of the film quality of the diamond thin film.

[0010] That is, the method for producing a diamond thin film according to the present invention is a method for producing a diamond thin film, which comprises supplying a source gas containing C, H, and O into a vacuum vessel in which a substrate is placed, generating inductively coupled plasma in the vacuum vessel by passing a high frequency current through 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, and synthesizing a diamond thin film on the substrate by a plasma CVD method using the generated inductively coupled plasma, and the plasma characteristics when synthesizing the diamond thin film include an electron temperature of 1.0 eV to 2.0 eV, an electron density of 1.0×10 １１ cm －３ Above 1.0 x 10 １２ cm －３ or less, and the ion saturation current is 1.0 × 10 －４ A or above 1.0 x 10 －２ A or less.

[0011] This configuration uses an antenna having a conductor element and a capacitance element electrically connected in series with each other, so that compared to configurations using conventional plasma CVD apparatuses, plasma is generated more uniformly in the longitudinal direction of the antenna, allowing diamond thin films to be synthesized over a wider area. Furthermore, when the plasma characteristics are within the above-mentioned numerical ranges, diamond thin films are synthesized with appropriate electron quantities and electron temperatures, preventing deterioration of the diamond thin film quality. Specifically, if the electron temperature exceeds the upper limit, electron collisions with the substrate increase, causing the substrate temperature to rise too much, potentially resulting in the synthesis of graphite. On the other hand, if the electron temperature is below the lower limit, the source gas will not be sufficiently dissociated, resulting in the synthesized thin film becoming a DLC film with many sp bonds or sp2 bonds. Therefore, the electron temperature must be within the above-mentioned numerical range. Furthermore, for the same reasons as the electron temperature, the electron density must also be within the above-mentioned numerical range in order to prevent the synthesis of graphite or DLC films. Here, in the synthesis of diamond thin films, ionized carbon species (C ２＋ , C.H. ３ ＋ , C.H. ＋ (e.g., etc.) exist. As a result, two phenomena occur simultaneously: (1) secondary nuclei are generated on the diamond due to the collision of ionic carbon species with the growth surface, and (2) the growth of the diamond thin film is inhibited by the ionic carbon species. To synthesize a diamond thin film while suppressing these two phenomena, it is necessary to control the ion saturation current within the above-mentioned numerical range. Specifically, if the ion saturation current is greater than the upper limit, the frequency of collision of ionic carbon species with the substrate increases, and the inhibition of the growth of the diamond thin film by the ionic carbon species becomes greater. As a result, the growth rate of the diamond thin film decreases or the film quality of the diamond thin film deteriorates. On the other hand, if the ion saturation current is less than the lower limit, the ionic carbon species necessary for the growth of the diamond thin film are not present on the surface of the substrate in sufficient quantities, and the growth rate of the diamond thin film decreases. Therefore, the ion saturation current must be within the above-mentioned numerical range.

[0012] A specific example of the antenna is a linear antenna having a longitudinal length of 30 cm or more. With this configuration, it is possible to synthesize a diamond thin film over a wider area and more uniformly in the longitudinal direction than with a configuration using a conventional plasma CVD apparatus.

[0013] In addition, a specific embodiment of the method for producing a diamond thin film is one in which the distance between the antenna and the substrate is 100 mm or less. With this configuration, uniform plasma is generated in the vacuum chamber in the longitudinal direction of the antenna, and the diamond thin film can be synthesized uniformly along the longitudinal direction of the antenna.

[0014] The method for producing a diamond thin film applies a bias voltage to the substrate, and preferably applies a negative bias voltage of -100V or less to the substrate and a positive bias voltage of 100V or less to the substrate. With this configuration, by applying a bias voltage to the substrate, it is possible to control the energy of positive ions in the plasma when they are incident on the substrate, thereby controlling the crystallinity of the film formed on the surface of the substrate. Specifically, by applying a negative bias voltage of -100V or less to the substrate, the formation of diamond growth nuclei is promoted, and by applying a positive bias voltage of 100V or less, the growth of the diamond thin film can be promoted.

[0015] The source gas preferably further contains a rare gas selected from Ar, He, and Ne. With this configuration, it is possible to facilitate the decomposition of components contained in the gas that are difficult to decompose, such as carbon dioxide.

[0016] In order to produce a diamond thin film using a high frequency wave instead of a microwave, the high frequency current has a frequency of 400 kHz or more and 100 MHz or less.

[0017] A diamond thin film manufacturing apparatus for synthesizing a diamond thin film on a substrate by a plasma CVD method using inductively coupled plasma includes a vacuum vessel in which the substrate is placed and a source gas containing C, H, and O is supplied, an antenna disposed inside or outside the vacuum vessel and having a conductor element and a capacitance element electrically connected in series with each other, and a high frequency power supply for applying high frequency to the antenna to generate inductively coupled plasma within the vacuum vessel, and the plasma characteristics within the vacuum vessel when synthesizing the diamond thin film include an electron temperature of 1.0 eV or more and 2.0 eV or less, an electron density of 1.0×10 １１ cm －３ Above 1.0 x 10 １２ cm －３ or less, and the ion saturation current is 1.0 × 10 －４ A or above 1.0 x 10 －２ A or less. With this configuration, it is possible to obtain the same effects as those of the above-mentioned method for producing a diamond thin film.

[0018] According to the present invention configured as described above, it is possible to synthesize a diamond thin film over a wider area and to prevent deterioration of the film quality of the diamond thin film.

[0019] 1 is a diagram showing a schematic configuration of a film deposition apparatus according to an embodiment of the present invention, and a diagram showing a gas composition range of a source gas supplied in the film deposition apparatus and a method for manufacturing a diamond thin film according to the embodiment.

[0020] A film forming apparatus and a method for manufacturing a diamond thin film according to an embodiment of the present invention will be described below with reference to the drawings. Note that in all of the drawings shown below, some details may be omitted or exaggerated for clarity. Identical components will be given the same reference numerals and their explanations will be omitted where appropriate.

[0021] <Apparatus Configuration> The film forming apparatus 100 of this embodiment is a plasma CVD apparatus that forms a diamond thin film F on a substrate W by a plasma CVD method using an inductively coupled plasma P.

[0022] 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, or the like, but is not limited to these.

[0023] The substrate W has a rectangular or circular shape in a 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 to this. 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.

[0024] The substrate W may also be subjected to a surface treatment such as a scratching treatment or a seeding treatment. For example, if the substrate W is silicon, it may be immersed in alcohol together with diamond fine particles and subjected to a scratching treatment or a seeding treatment in which unevenness is formed on the surface by ultrasonic treatment. For example, if the substrate W is a cemented carbide, it may be immersed in an acidic solution such as a nitric acid aqueous solution to remove Co from the substrate, or the surface of WC (tungsten carbide) particles may be treated with an alkaline solution such as diluted NaOH, and then the seeding treatment described above may be performed.

[0025] 1 , the film formation 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 within the vacuum vessel 2, and a high-frequency power supply 4 that applies a high-frequency wave to the antenna 3 to generate an inductively coupled plasma P within the vacuum vessel 2. In this film formation apparatus 100, when a high-frequency wave is applied from the high-frequency power supply 4 to the antenna 3, a high-frequency current IR flows through the antenna 3, an inductive electric field is generated within the vacuum vessel 2, and the inductively coupled plasma P is generated.

[0026] 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.

[0027] A gas G such as a source gas is introduced into the vacuum vessel 2 via, for example, a flow rate regulator (not shown) and a plurality of gas inlets 21 arranged in a direction along the antenna 3 .

[0028] A substrate holder 8 for holding a substrate W is provided within the vacuum chamber 2, and a heater 81 for heating the substrate W is provided within the substrate holder 8. The substrate holder 8 does not necessarily have to be electrically connected to the vacuum chamber 2. The film forming apparatus 100 of this embodiment may have a function for adjusting the potential of the generated inductively coupled plasma, for example, within a range of +100 V to −100 V, by applying a bias voltage from a bias power supply 9 to the substrate holder 8. The applied bias voltage is, for example, a negative DC voltage, but is not limited thereto. Such a bias voltage can, for example, control the energy of positive ions in the plasma P when they are incident on the substrate W, thereby controlling the crystallinity of a film formed on the surface of the substrate W.

[0029] The gas supply mechanism 7 supplies gas G, such as a source gas, into the vacuum vessel 2 through a gas inlet 21. The gas supply mechanism 7 is configured to supply the gas G downward from the gas inlet 21 provided on the upper wall of the vacuum vessel 2. The gas supply mechanism 7 is configured to be able to supply a source gas containing at least C (carbon), H (hydrogen), and O (oxygen), and specifically, H ２ Gas, CH ４ Gas and CO ２ The gas supply mechanism 7 is configured to be able to supply a source gas containing C, H, and O into the vacuum chamber 2. ２Gas, CH ４ Gas and CO ２ In addition to or instead of the gas, any other gas may be configured to be supplied as a source gas.

[0030] The gas supply mechanism 7 is ２ Gas, CH ４ Gas and CO ２ The gas supply mechanism 7 of this embodiment is configured to supply the gases at any desired flow rate. ２ Gas, CH ４ Gas and CO ２ The source gas is configured to be supplied by adjusting 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 contained therein (O / (O+H)) is, for example, 5 at % or more and 45 at % or less.

[0031] The gas supply mechanism 7 is also configured to supply a catalyst gas into the vacuum chamber 2 at a desired flow rate along with the source gas. This catalyst gas functions as a catalyst during plasma generation and promotes decomposition of the source gas. Specifically, the gas supply mechanism 7 is configured to supply the catalyst gas so that its proportion of the total flow rate of all gases supplied into the vacuum chamber 2 (here, the total flow rate of the source gas and the catalyst gas) is, for example, 50% to 95%, preferably 70% to 90%. Specific examples of this catalyst gas include rare gases such as Ar gas, He gas, and Ne gas.

[0032] 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 (for example, 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 larger substrates W can be processed.

[0033] The number of antennas 3 is not limited to multiple, and may be just one. When multiple antennas 3 are provided, the number is preferably an even number (for example, 2, 4, 6, etc.). When multiple antennas 3 are provided, 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, in order to avoid radio wave interference. 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.

[0034] As shown in FIG. 1 , the vicinity of both ends of the antenna 3 penetrates a pair of opposing side walls 2 a, 2 b of the vacuum vessel 2. Insulating members 11 are provided at the portions 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 portions are vacuum-sealed by, for example, packings 12. The antenna 3 is supported via the insulating members 11 in a state in which it is electrically insulated from the opposing side walls 2 a, 2 b of the vacuum vessel 2. The gap between each insulating member 11 and the vacuum vessel 2 is also vacuum-sealed by, for example, packings 13. The insulating members 11 are made of, for example, ceramics such as alumina, quartz, or engineering plastics such as polyphenylene sulfide (PPS) and polyether ether ketone (PEEK).

[0035] The antenna 3 is a so-called LC antenna having an L portion that serves as an inductor and a C portion that serves as a capacitor. Specifically, the antenna 3 includes at least two tubular metal conductor elements 31 (hereinafter referred to as metal pipes 31), tubular insulating elements 32 (hereinafter referred to as insulating pipes 32) that are provided between adjacent metal pipes 31 to insulate the metal pipes 31, and capacitors 33 that are capacitive elements that are provided between adjacent metal pipes 31 and electrically connected in series with the conductor elements 31 and capacitors 33. The conductor elements 31 function as the L portion, and the capacitors 33 function as the C portion.

[0036] 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 be configured to 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.

[0037] 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 refrigerant such as cooling water may be passed through it to cool the antenna 3.

[0038] In this embodiment, the insulating pipe 32 is formed from a single member, but is not limited to this. The insulating pipe 32 may be made of a material such as alumina, fluororesin, polyethylene (PE), or engineering plastic (such as polyphenylene sulfide (PPS) or polyether ether ketone (PEEK)).

[0039] Furthermore, the portion of the antenna 3 located inside the vacuum vessel 2 is covered by 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 plasma P is not normally generated in the space. Note that the insulating cover 10 can be made of, for example, quartz, alumina, fluororesin, silicon nitride, silicon carbide, silicon, or the like.

[0040] By providing the insulating cover 10, it is possible to prevent charged particles in the plasma P from entering the metal pipe 31 that constitutes the antenna 3, thereby preventing an increase in plasma potential due to charged particles (mainly electrons) entering the metal pipe 31 and preventing the metal pipe 31 from being sputtered by charged particles (mainly ions), which would cause metal contamination of the plasma P and the substrate W.

[0041] The length of the antenna 3 in the longitudinal direction is preferably 30 cm or more, more preferably 50 cm or more, and even more preferably 100 cm or more, from the viewpoint of synthesizing the diamond thin film F over a wider area. 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.

[0042] Furthermore, the distance between the antenna 3 and the substrate W is preferably 100 mm or less, and more preferably 40 mm or more and 60 mm or less, in order to generate uniform plasma P in the longitudinal direction of the antenna 3 inside the vacuum chamber 2. Here, if the distance between the antenna 3 and the substrate W is too close, the electron density and electron temperature will increase, causing graphitization of the thin film, and therefore it is preferable that the distance between the antenna 3 and the substrate W is a predetermined distance.

[0043] 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. Specifically, at both ends of each antenna 3 in the longitudinal direction X, the portion extending outward from one of the side walls 2a or 2b serves as the power feeding end 3a, and the portion extending outward from the other side wall 2a or 2b serves as the grounded end 3b.

[0044] 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 box 41. The frequency of the high frequency is 400 kHz or more and 100 MHz or less, for example, the common frequency of 13.56 MHz, but is not limited to this. For example, it may be 27.12 MHz, 40.68 MHz, 60 MHz, etc.

[0045] <Method for Manufacturing Diamond Thin Film> Next, a method for manufacturing the diamond thin film F using the above-described film forming apparatus 100 will be described.

[0046] 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, and the temperature of the substrate W is preferably set to 100° C. or higher and 1200° C. or lower.

[0047] (Supply of Source Gas) Next, H as a source gas is supplied by the gas supply mechanism 7. ２ Gas, CH ４ Gas and CO ２ The gas is supplied at a predetermined flow rate into the vacuum chamber 2. In the method for producing the diamond thin film F of this embodiment, the atomic ratio of O atoms, C atoms, and H atoms in the source gas is adjusted to fall within the shaded range shown in the composition ternary diagram (C-H-O diagram) of FIG. ２ Gas, CH ４ Gas and CO ２ The flow rate of each gas is adjusted. The atomic ratio of each atom is explained below.

[0048] (Ratio of Number of Oxygen and Hydrogen Atoms) In the raw material gas to be supplied, 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. ２ Gas, CH ４ Gas and CO ２ The gases are supplied while controlling their respective flow rates.

[0049] (Ratio of Number of Oxygen and Carbon Atoms) In the raw material gas to be supplied, 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. ２ Gas, CH ４ Gas and CO ２ The gases are supplied while controlling their respective flow rates.

[0050] (Ratio of Number of Carbon and Hydrogen Atoms) In the raw material gas to be supplied, the ratio of the concentration of H atoms to the total concentration of C atoms and H atoms contained therein (H / (C+H)) is preferably 60 at % or more and 95 at % or less, more preferably 90 at % or more and 95 at % or less. ２ Gas, CH ４ Gas and CO ２ The gases are supplied while controlling their respective flow rates.

[0051] (Supply of catalytic gas) Furthermore, a catalytic gas such as Ar gas is supplied into the vacuum chamber 2 together with the raw material gas by the gas supply mechanism 7. The flow rate of the supplied catalytic gas is set so that the ratio of the total flow rate of all gases supplied to the vacuum chamber 2 is preferably 50% or more and 95% or less, more preferably 70% or more and 90% or less. By setting the flow rate of the supplied catalytic gas in this range, it is possible to prevent the ionization of gases that are easily ionized, such as Ar, into CH during film formation. ４ C, which transfers energy to ２ This allows the generation of a large number of radicals. As a result, in the emission spectrum of the generated inductively coupled plasma, the C ２ The ratio of the radical emission intensity can be set to 30% or more and 300% or less, more preferably 90% or more and 250% or less.

[0052] (Pressure in Vacuum Chamber) Then, while the raw material gas and catalyst gas are introduced by the gas supply mechanism 7, the pressure in 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.

[0053] (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 supply 4 to the antenna 3. This generates an inductive 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 0.1 W / cm. ２ More than 0.5 W / cm is preferable. ２ More preferably, 1 W / cm or more ２ More preferably, the power density is 1000 W / cm. ２ Preferably, 100 W / cm or less ２ More preferably, 50 W / cm or less ２ The following is even more preferred:

[0054] Here, in order to prevent the synthesis of graphite or DLC when synthesizing the diamond thin film F, it is necessary to set the plasma characteristics within the following numerical ranges. When the plasma characteristics are within the following numerical ranges, the crystallinity of diamond in the diamond thin film F is increased, and deterioration of the film quality of the diamond thin film F is prevented. The plasma characteristics referred to here are the electron temperature Te, electron density ne, and ion saturation current I ｉｓ Electron temperature Te: 1.0 eV≦Te≦2.0 eV Electron density ne: 1×10 １１ cm －３ ≦ne≦1×10 １２ cm －３ Ion saturation current I ｉｓ : 1×10 －４ A≦I ｉｓ ≦1×10 －２ A

[0055] 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 modifications can be made within the scope of the above and below-described aims, and all such modifications are within the technical scope of the present invention.

[0056] In the examples, samples were formed on substrates in the following three examples and two comparative examples by plasma CVD using the above-described film formation apparatus 100. The pressure in the vacuum chamber 2, the input power, the distance between the substrate and the antenna, the frequency of the supplied high-frequency power, and the plasma characteristics during the production of the samples were as follows:

[0057] Example 1 Pressure inside the vacuum chamber 2: 15 Pa Input power: 3.0 kW Distance between the substrate W and the antenna 3: 50 mm Frequency of supplied high frequency power: 13.56 MHz Electron temperature Te: 1.5 eV Electron density ne: 7.5×10 １１ cm －３ Ion saturation current I ｉｓ : 6 x 10 －４ A

[0058] Example 2 Pressure inside the vacuum chamber 2: 15 Pa Input power: 3.0 kW Distance between the substrate W and the antenna 3: 30 mm Frequency of supplied high frequency power: 13.56 MHz Electron temperature Te: 1.98 eV Electron density ne: 7.28×10 １１ cm －３ Ion saturation current I ｉｓ : 1.03 x 10 －３ A

[0059] Example 3 Pressure inside the vacuum chamber 2: 15 Pa Input power: 4.0 kW Distance between the substrate W and the antenna 3: 30 mm Frequency of supplied high frequency power: 13.56 MHz Electron temperature Te: 1.01 eV Electron density ne: 9.8×10 １１ cm －３ Ion saturation current I ｉｓ : 2.3 x 10 －３ A

[0060] Comparative Example 1 Pressure in vacuum chamber 2: 15 Pa Input power: 2.0 kW Distance between substrate W and antenna 3: 50 mm Frequency of supplied high-frequency power: 13.56 MHz Electron temperature Te: 1.99 eV Electron density ne: 1.08×10 １１ cm －３ Ion saturation current I ｉｓ : 9.89 x 10 －５ A

[0061] Comparative Example 2 Pressure in vacuum chamber 2: 30 Pa Input power: 2.0 kW Distance between substrate W and antenna 3: 10 mm Frequency of supplied high-frequency power: 13.56 MHz Electron temperature Te: 1.6 eV Electron density ne: 2.66×10 １２ cm －３ Ion saturation current I ｉｓ : 3.70 x 10 －３ A

[0062] where the electron temperature Te, the electron density ne, and the ion saturation current I ｉｓ was measured by a Langmuir Probe, which is a known plasma measuring instrument.

[0063] In Example 1, the crystallinity of the synthesized sample was evaluated by laser Raman spectroscopy (excitation at 325 nm). －１ The optical phonon peak of diamond observed in the vicinity of the wavelength of 1550 cm －１ This indicates that the intensity is 2.5 times higher than the G-band optical phonon peak observed near the wavelength of 1000 Å. This confirms that it is possible to synthesize diamond thin films with high diamond crystallinity.

[0064] In Example 2, the crystallinity of the synthesized sample was evaluated by laser Raman spectroscopy (325 nm excitation). －１ The optical phonon peak of diamond was detected near the wavelength of 1550 cm －１ Since no optical phonon peak in the G band, which is observed near the wavelength of , was detected, it was possible to confirm that a diamond thin film could be synthesized.

[0065] In Example 3, the crystallinity of the synthesized sample was evaluated by laser Raman spectroscopy (325 nm excitation). －１ The optical phonon peak of diamond was detected near the wavelength of 1550 cm －１ Since no optical phonon peak in the G band, which is observed near the wavelength of , was detected, it was possible to confirm that a diamond thin film could be synthesized.

[0066] In Comparative Example 1, the type of the synthesized sample was evaluated by Raman spectroscopy (325 nm excitation). As a result, the diamond peak (1330 cm －１ ~1335cm －１ ) was not detected, and the D band (1340 cm －１ ~1380cm －１ ) and G band (1510 cm －１ ~1560cm －１ ) was detected, it was confirmed that the synthesized sample was a DLC film, not a diamond thin film.

[0067] In Comparative Example 2, the type of the synthesized sample was evaluated by Raman spectroscopy (325 nm excitation). As a result, the diamond peak (1330 cm －１ ~1335cm －１ ) was not detected, and the G band (1580 cm ) derived from graphite was not detected. －１ ~1620cm －１ ) was detected, confirming that the synthesized sample was graphite, not a diamond thin film.

[0068] From the above, the plasma characteristics when synthesizing a diamond thin film are as follows: electron temperature is 1.0 eV or more and 2.0 eV or less, and electron density is 1.0 × 10 １１ cm －３ Above 1.0 x 10 １２ cm －３ or less, and the ion saturation current is 1.0 × 10 －４ A or above 1.0 x 10 －２ It was confirmed that when the crystallinity is A or less, a diamond thin film with high diamond crystallinity can be synthesized.

[0069] <Effects of this embodiment> According to this embodiment, an antenna 3 is used that has a conductor element 31 and a capacitive element electrically connected in series with each other, so that, compared to a configuration using a conventional plasma CVD apparatus, a uniform plasma P is generated in the longitudinal direction of the antenna 3, and a diamond thin film F can be synthesized over a wider area.

[0070] Furthermore, when the plasma characteristics are within the above numerical ranges, the diamond thin film F is synthesized with the electron temperature Te and electron density ne in an appropriate state, thereby preventing deterioration of the film quality of the diamond thin film F. Specifically, if the electron temperature Te is greater than the upper limit, electron collisions with the substrate W increase, causing the temperature of the substrate W to rise too much, which may result in the synthesis of graphite. On the other hand, if the electron temperature Te is less than the lower limit, the source gas does not dissociate sufficiently, and the synthesized thin film becomes a DLC film with many sp bonds or sp2 bonds. Therefore, the electron temperature Te must be within the above numerical range. Furthermore, for the same reason as the electron temperature Te, the electron density ne must also be within the above numerical range in order to prevent the synthesis of graphite or the synthesis of a DLC film. Here, in the synthesis of the diamond thin film F, ionized carbon species (C ２＋ , C.H. ３ ＋ , C.H. ＋ As a result, two phenomena occur simultaneously: (1) secondary nuclei are generated on the diamond due to the collision of ionic carbon species with the growth surface, and (2) the growth of the diamond thin film F is inhibited by the ionic carbon species. In order to synthesize the diamond thin film F while suppressing these two phenomena, the ion saturation current I ｉｓ It is necessary to control within the above numerical range. Specifically, the ion saturation current I ｉｓ When the ion saturation current I is greater than the upper limit, the frequency with which the ionic carbon species collide with the substrate W increases, and the ionic carbon species significantly inhibit the growth of the diamond thin film F. As a result, the growth rate of the diamond thin film F decreases, or the film quality of the diamond thin film F deteriorates. On the other hand, ｉｓ If the ion saturation current I is less than the lower limit, the ionic carbon species necessary for the growth of the diamond thin film F will not be present in sufficient quantity on the surface of the substrate W, and the growth rate of the diamond thin film F will decrease. ｉｓ must be within the above numerical range.

[0071] Furthermore, according to this embodiment, the antenna 3 has a length of 30 cm or more in the longitudinal direction and is linear, so that a diamond thin film F can be synthesized over a wider area and more uniformly in the longitudinal direction compared to a configuration using a conventional plasma CVD apparatus.

[0072] Other Embodiments The film forming apparatus 100 of the present invention is not limited to the above-described embodiment.

[0073] In addition to this embodiment, the method for manufacturing the diamond thin film F may also be one in which a bias voltage is applied to the substrate W, and a negative bias voltage of −100 V or less is applied to the substrate W, and a positive bias voltage of 100 V or less is applied to the substrate W.

[0074] As a result, by applying a bias voltage to the substrate W, it is possible to control the energy of the positive ions in the plasma P when they are incident on the substrate W, thereby controlling the crystallinity of the film formed on the surface of the substrate W. Specifically, first, a negative bias voltage of -100 V or less is applied to the substrate, which promotes the formation of diamond growth nuclei, and after the diamond nuclei have been formed, a positive bias voltage of 100 V or less is applied, which promotes the growth of the diamond thin film F.

[0075] In the film formation 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 limiting. In other embodiments of the film formation apparatus 100, the antenna 3 may be disposed outside the vacuum chamber 2.

[0076] 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.

[0077] According to the present invention, it is possible to synthesize a diamond thin film over a wider area and to prevent deterioration of the film quality of the diamond thin film.

[0078] REFERENCE SIGNS LIST 100: Film forming apparatus 2: Vacuum vessel 3: Antenna 7: Gas supply mechanism F: Diamond thin film W: Substrate P: Plasma

Claims

1. A method for producing a diamond thin film, comprising: supplying a raw material gas containing C, H, and O into a vacuum vessel in which a substrate is placed; generating an inductively coupled plasma in the vacuum vessel by passing a high-frequency current through 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; and synthesizing a diamond thin film on the substrate by a plasma CVD method using the generated inductively coupled plasma, wherein the plasma characteristics when synthesizing the diamond thin film are: an electron temperature of 1.0 eV or more and 2.0 eV or less; and an electron density of 1.0 x 10 １１ cm －３ Above 1.0 x 10 １２ cm －３ and the ion saturation current is 1.0×10 －４ A or higher 1.0 x 10 －２ A method for producing a diamond thin film, the diamond thin film having a thickness of 100 nm or less.

2. The method for producing a diamond film as set forth in claim 1, wherein the antenna is linear and has a length of 30 cm or more in the longitudinal direction.

3. The method for producing a diamond film according to claim 1, wherein the distance between the antenna and the substrate is 100 mm or less.

4. The method for producing a diamond thin film according to claim 1, wherein the method comprises applying a bias voltage to the substrate, wherein a negative bias voltage of -100V or less is applied to the substrate, and a positive bias voltage of 100V or less is applied to the substrate.

5. The method for producing a diamond thin film according to claim 1, wherein the source gas further contains a rare gas selected from the group consisting of Ar, He and Ne.

6. A method for producing a diamond thin film according to any one of claims 1 to 5, wherein the high frequency of the high frequency current has a frequency of 400 kHz or more and 100 MHz or less.

7. A diamond thin film manufacturing apparatus for synthesizing a diamond thin film on a substrate by a plasma CVD method using an inductively coupled plasma, comprising: a vacuum vessel in which the substrate is placed and a raw material gas containing C, H, and O is supplied; an antenna disposed inside or outside the vacuum vessel and having a conductor element and a capacitance element electrically connected in series; and a high-frequency power source for applying a high frequency to the antenna for generating an inductively coupled plasma in the vacuum vessel, wherein the plasma characteristics in the vacuum vessel when synthesizing the diamond thin film are: an electron temperature of 1.0 eV or more and 2.0 eV or less, and an electron density of 1.0 x 10 １１ cm －３ Above 1.0 x 10 １２ cm －３ and the ion saturation current is 1.0×10 －４ A or higher 1.0 x 10 －２ Diamond thin film manufacturing equipment that is A or below.