Patent Application
20090226718
The present invention relates to a carbon film and a carbon film laminate having new properties; an optical device, an optical glass, a lens, a wrist watch, an electronic circuit substrate, a grinding tool, a low-friction protection film, a vehicle engine component, a mechanical component, and a health appliance provided with the same; and a method and apparatus for manufacturing the carbon film and the carbon film laminate.
A carbon-based thin film has various excellent characteristics such as high hardness, thermal conductivity, an electric insulating property, transparency, a high refractive index, chemical resistance, a low friction property, and a low abrasion property. Recently, due to its excellent environmental compatibility and biocompatibility, it has been desired to use a carbon-based thin film as a coating for improving the performance of various substrates. Especially, a diamond-like carbon film and a diamond film are thin carbon-based films having excellent properties, and improvement in the coating technique for enhancing mechanical, optical, and electrical functions of various substrates has been expected. However, at present, diamond-like carbon and diamond have the following problems caused by the characteristics of diamond-like carbon and diamond. Consequently, development of a new carbon film has been desired in order to solve such problems.
In the formation of a carbon film on a substrate, when glass is used as a substrate, it has been expected to be applied for scratch resistance on a surface due to the high hardness thereof, and for optical devices having new functions realized by the high refractive index thereof. For example, a method of forming a micro-crystal diamond (hereinafter simply referred to as MCD) film on a glass substrate by a CVD treatment is already known (for example, see Patent Document 1 and Non-Patent Document 1).
For applying the carbon film to an optical protective film, it has been attempted to utilize the high transmittance of a diamond film. It is known that the transmittance becomes higher as the grain size of the diamond grains coated on the glass surface becomes smaller and the surface roughness becomes smaller.
However, in a conventional CVD treatment, since the formed MCD has a grain size as large as 0.3 μm to several μm, the obtained MCD film lacks surface flatness and satisfactory transmittance cannot be obtained. For improving the transmittance, it is necessary to form a flat surface by grinding, and the cost therefor is one of the obstacles to becoming widespread.
Conventional Nano-Diamond Synthesis Method and Problems Thereof
Therefore, it has been attempted to develop a technique of forming a flat surface without the need of grinding by making the grain size of the diamond grains smaller.
As well known, a gas-phase synthesis of diamond requires the use of a gaseous mixture of a carbon source such as methane (CH4) and hydrogen, and a hydrogen-rich atmosphere in which the concentration of the carbon source is about 1% (or less). For synthesizing a high quality diamond film, the upper limit of the concentration of the carbon source is about 1%. By increasing the concentration of the carbon source, the film growth rate can be increased. However, by increasing the concentration of the carbon source, non-diamond components such as amorphous carbon within the film increase. As a result, transparency deteriorates, thereby causing quality deterioration of the diamond.
Nevertheless, by increasing the concentration of the carbon source, the grain size diamond decreases. In a conventional gas-phase synthesis of nano-crystal diamond, high concentration of the carbon source, which can be said as a requirement of synthesizing low quality diamond, has been used. Further, synthesis by fullerene (C60) and argon in a system containing no hydrogen has also been performed. Representative gas compositions of nano-crystal diamond synthesis by high concentration of carbon source using microwave plasma are exemplified below.
Zuiker et al. of Argonne National Laboratory succeeded for the first time in forming a nano-crystal diamond film having an extremely low coefficient of friction (0.04) by a process using a system of fullerene+Ar and a small amount of hydrogen added thereto, as indicated in item 2 above (see Non-Patent Document 2). Especially, in a carbon source concentration as high as 20% or more, the nucleus formation density can be increased, and it is suggested that a nano-crystal diamond film having an extremely smooth surface can be obtained. However, as described above, such a film is opaque so as to assume a black color. Therefore, this film cannot be utilized in optical application. Moreover, since electrical resistivity is small, the film cannot be used as an insulator. For this reason, there has been desired the development of a carbon film capable of maintaining transparency even when the grain size becomes small and exhibiting electrical insulation, and a method of producing such a carbon film.
When a carbon film coating for a glass-protecting film is used, high adhesion is required. For example, a technique of coating diamond on a glass substrate is disclosed in Patent Document 1. In this document, the coating exhibits good performance in a tape test.
However, for application to coating of front glass of an automobile and coating on a spectacle lens, etc., a coating capable of maintaining higher adhesion as well as high transmittance is required.
Moreover, for optical application to lenses for spectacles, cameras and cinema projectors, it is important that the coating layer has a high refractive index and exhibits no birefringence.
However, when MCD is formed by the CVD method which is a typical coating method, it is extremely difficult to synthesize MCD exhibiting no birefringence due to thermal strain and residual stress. Further, density is likely to be lowered, and the refractive index is usually lowered considerably. Therefore, it has been a problem that MCD coating is not suitable for optical application.
Further, as a carbon-based thin film has high hardness and a low friction/low abrasion characteristic, application of carbon-based thin film coating to sliding portions of mechanical components made of iron or stainless steel has been expected. However, diamond-like carbon film coating and a diamond film are extremely difficult to put to practical use for the following problems. One problem is that carbon atoms as the component element of the film impregnate into the iron substrate, and as a result, the film is not deposited. Another problem is that the substrate becomes brittle. On the other hand, there has been developed a technique of forming an intermediate layer (adhesion-reinforcing layer), which is a thin film of titanium, chromium, or a nitride thereof, on the iron-based substrate prior to the coating of carbon-based thin film. However, there are still problems in that the cost for forming the intermediate layer (adhesion-reinforcing layer) is expensive, and in that the adhesion of the coating is still low. For this reason, there have been demands for development of a method of forming an intermediate layer (adhesion-reinforcing layer) which is simpler and can be performed at a low cost, and an intermediate layer (adhesion-reinforcing layer) with higher adhesion.
Further, when copper is used as a substrate, since a diamond-like carbon and a diamond film exhibit a high electric insulating property, it has been desired to apply a diamond-like carbon film coating or a diamond film coating on an electronic circuit substrate having a copper surface. However, it is extremely difficult to deposit a diamond-like carbon film or a diamond film on a copper surface. Even if it is deposited, there is a big problem in that adhesion of the film to the copper surface is low, and hence, the film is easily delaminated from the surface. For solving this problem, formation of an intermediate layer of titanium or a nitride thereof has been attempted, as in the case of the iron-based substrate described above. However, this also results in a problem with cost or low adhesion. Further, when a CVD method which is a typical method is used for forming, especially, a diamond coating, boron in the atmosphere is easily taken into the film without intentional doping. Therefore, there is a big problem in that the electric insulating property of the diamond coating is lowered.
Further, as a method of coating a carbon film on a plastic substrate, coating of a diamond-like carbon film on a PET bottle has been put to practical use. However, there has been desired the use of plastics with the diamond coating at a higher temperature and the coating of plastics with diamond for optical application. For example, in recent years, 90% or more of spectacle lenses are made of plastics. If it becomes possible to form diamond coated plastic spectacle lenses, it would become possible to manufacture a high functional lens which utilizes properties such as resistance to scratching of the lens and high refractive index of diamond. However, since synthesis of the diamond film requires a temperature as high as at least 600° C., at present, diamond is not suitable as a coating material for plastics.
[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. Hei 10-95694
[Non-Patent Document 1] Diamond and Related Materials Vol. 7, pp. 1639-1646 (1998)
[Non-Patent Document 2] Thin Solid Films Vol. 270, pp. 154-159 (1995)
The invention takes into consideration the above circumstances of carbon films represented by diamond-like carbons and diamond.
Therefore, an object of the present invention is to provide a carbon film and a laminate having optical characteristics of maintaining high transparency even when the grain size becomes smaller, high refractive index and small birefringence; exhibiting an excellent electric insulating property; capable of being coated with good adhesion, irrespective of the type of substrate including iron, copper and plastics; and capable of being formed at a low temperature. Further, another object of the present invention is to provide an optical device, an optical glass, a wrist watch, an electronic circuit substrate, or a grinding tool using the carbon film or the laminate.
The present inventors have made extensive and intensive studies in order to form a carbon film and a laminate having the various characteristics described above. As a result, the present inventors have found that a carbon film and laminate thereof exhibiting excellent performance can be formed by conducting a CVD treatment using a specific apparatus under specific conditions. The present invention has been completed based on these findings.
According to the present application, the following inventions are provided.
<1> A carbon film including: carbon grains having substantially the same grain size in the range of 1 nm to 1,000 nm, and preferably in the range of 2 nm to 200 nm, in the thickness-wise direction of the carbon film; and an amorphous substance for suppressing generation of impurities accompanied by formation of the carbon grains and/or for suppressing growth of the carbon grains, the amorphous substance existing at least on the surfaces of the carbon grains in a grain boundary between the carbon grains and/or gaps between the carbon grains.
<2> The carbon film according to <1>, wherein the carbon grains have an approximate spectrum curve obtained by superimposing a peak fitting curve B at a Bragg angle (2θ±0.5°) of 41.7° and a baseline on a peak fitting curve A at a Bragg angle (2θ±0.5°) of 43.9° in an X-ray diffraction spectrum by a CuKα1 ray, and wherein the peak fitting curve A, the peak fitting curve B, and the baseline are represented by a Pearson VII function, an asymmetric normal distribution function, and a linear function, respectively.
<3> The carbon film according to <2>, wherein the intensity ratio of the peak fitting curve B to the peak fitting curve A is at a minimum 5% and at a maximum 90%.
<4> The carbon film according to any one of <1> to <3>, wherein the impurities accompanied by formation of the carbon grains is amorphous carbon or graphite.
<5> The carbon film according to any one of <1> to <4>, wherein the amorphous substance is at least one member selected from the group consisting of Si, SiO2, Ti, TiO2, HfO2, and ZnO.
<6> The carbon film according to <5>, wherein the amorphous substance exists within the carbon film in the range from 0.01 to 10 at %, and preferably in the range from 0.1 to 10 at %.
<7> The carbon film according to any one of <1> to <6>, wherein the amorphous substance is formed at a furnace temperature in the range from room temperature to 600° C.
<8> The carbon film according to any one of <1> to <7>, which exhibits an average transmittance of 60% or more in the wavelength region of 400 to 800 nm, an electrical resistivity of 1×107 Ωcm or more at 100° C., a refractive index of 1.7 or more at a wavelength of 589 nm, a thermal conductivity of 20 W/mK or more at 25° C., and surface flatness with a surface roughness (Ra) of 20 nm or less.
<9> A carbon film laminate including the carbon film of any one of <1> to <8> deposited on a substrate.
<10> The carbon film laminate according to <9>, which further includes an adhesion-reinforcing layer provided between the substrate and the carbon film for improving adhesion between both.
<11> The carbon film laminate according to <9> or <10>, wherein the substrate is at least one member selected from the group consisting of insulating materials including glass, quartz, and diamond; semiconductors including silicon; conductive materials including iron, stainless steel, molybdenum, aluminum, copper, and titanium; ceramic materials including tungsten carbide, alumina, and boron nitride; and plastic materials including PES, PET, PPS, and polyimide.
<12> The carbon film laminate according to <10>, wherein the adhesion-reinforcing layer includes amorphous Si and/or SiO2.
<13> A method of forming a carbon film including continuously or discontinuously supplying into a chamber of a plasma generation furnace a carbon-containing gas, a hydrogen gas, and a gas which forms an amorphous substance for suppressing generation of an impurity accompanied by formation of carbon grains and/or for suppressing growth of the carbon grains, in a plasma state toward a substrate in a downflow manner, the substrate temperature being in the range of room temperature to 600° C.
<14> The method according to <13>, wherein the amorphous substance is at least one member selected from the group consisting of Si, SiO2, Ti, TiO2, HfO2, and ZnO.
<15> The method according to <13>, wherein the gas for forming the amorphous substance is a silicon-containing gas.
<16> The method according to <15>, wherein the silicon-containing gas is generated by exposing plasma to bulk-like silicon or SiO2.
<17> The method according to <15> or <16>, wherein the concentration of the silicon-containing gas is 10 mol % or less.
<18> The method according to <13>, which further includes adding carbon dioxide.
<19> The method according to <13>, which further includes performing a heat treatment after depositing the carbon film.
<20> A method of forming a carbon film laminate, including: providing a substrate; forming an adhesion-reinforcing layer on said substrate at a furnace temperature within the range of room temperature to 600° C. by a plasma CVD using a surface wave; and forming a carbon film on the adhesion-reinforcing layer by the method of <13>.
<21> A carbon film deposition apparatus including: a plasma-generating unit; a supply unit for generating a silicon-containing gas by exposing plasma to bulk-like silicon or SiO2, and supplying the silicon-containing gas together with source gases including carbon-containing gas and hydrogen in a plasma state toward a substrate in a downflow manner; and a cooling unit for cooling the substrate temperature to a temperature within the range of room temperature to 600° C.
<22> An optical device provided with the carbon film of <1> or the carbon film laminate of <9>.
<23> An optical glass provided with the carbon film of <1> or the carbon film laminate of <9>.
<24>. A wrist watch provided with the carbon film of <1> or the carbon film laminate of <9>.
<25> An electronic circuit substrate provided with the carbon film of <1> or the carbon film laminate of <9>.
<26> A grinding tool provided with the carbon film of <1> or the carbon film laminate of <9>.
<27> A protection film provided with the carbon film of <1> or the carbon film laminate of <9>.
A carbon film and a carbon film laminate according to the present invention have optical characteristics of maintaining high transparency even when the grain size becomes small, a high refractive index, and small birefringence; exhibit an excellent electric insulating property; can be coated with satisfactory adhesion, irrespective of the type of the substrate including iron, copper, and plastics; and can be formed at a low temperature.
As the carbon film and the carbon film laminate according to the invention has the characteristics described above, it can be utilized in a protection film for glass with large area, an optical material with high refractive index, a highly thermal-conductive heat sink, an electrode material, a protection film for a machining tool, a grinding tool, an electron emission material, a low-friction/low-abrasion coating for an engine component, a protection film for chemical resistance, a high frequency device (SAW device), a gas barrier coating material, a tribo-electric material, a protection film of a cover glass for a wrist watch or a mobile telephone, a biocompatible material, a biosensor, etc.
a) is a Raman scattering spectrum of the carbon film of the present invention formed on a borosilicate substrate at a temperature as low as about room temperature (CVD treatment temperature: 40° C.), and
The carbon film according to the invention is a carbon film including: extremely fine carbon grains having substantially the same grain size in a thickness-wise direction of the carbon film; and a substance for suppressing generation of impurities accompanied by formation of the carbon grains and/or for suppressing growth of the carbon grains, said amorphous substance existing at least on the surfaces of the carbon grains in a grain boundary between the carbon grains and/or gaps between the carbon grains.
Specifically, the carbon grains are characterized in that they have substantially the same grain size in the range from 1 nm to 1,000 nm, and preferably in the range from 2 nm to 200 nm, and exist in the thickness-wise direction of the carbon film. Here, the expression “have substantially the same grain size in the range from 1 nm to 1000 nm” means that 51% or more of all the carbon grains have the grain size in the range from 1 nm to 1000 nm. Likewise, the expression “having substantially the same grain size in the range from 2 nm to 200 nm” means that 51% or more of all the carbon grains have the grain size in the range from 2 nm to 200 nm.
The carbon film according to the invention can be obtained by mainly employing a specific production apparatus under specific production conditions. For producing the carbon film, it is necessary to use a surface wave plasma generating apparatus capable of forming a film with a large area. In addition, it is necessary that the surface wave plasma generating apparatus include a supply unit which supplies the substance for suppressing the generation of impurities such as amorphous carbon or graphite accompanied by formation of the carbon grains and/or for suppressing growth of the carbon grains, as well as source gases of the carbon grains such as a carbon-containing gas, a hydrogen gas, and a carbon dioxide gas if necessary, toward a substrate within a chamber in a downflow manner. As the operation conditions, it is necessary to select the concentration and the molar ratio of the source gases, the reaction time, or the like, and to perform the operation at a relatively low temperature.
With respect to a method of producing the carbon film and/or a carbon film laminate according to the present invention, the scheme thereof will be described below with examples. For example, fine diamond grains are adhered to a substrate such as glass, silicon, iron, titanium, copper or plastic by an ultrasonic treatment. Then, in a low-temperature surface wave plasma CVD apparatus, a gas containing 97% hydrogen, 1% carbonic acid gas, 1% methane gas and 1% silane gas is supplied toward the substrate within the chamber in a downflow manner to perform a surface wave plasma treatment under a pressure of 1×102 Pa.
The treatment time is in the range from several hours to several tens of hours and the treatment temperature is in the range from room temperature to 600° C. By the treatment as described above, fine carbon grains having a grain size of 2 to 30 nm are deposited on the substrate surface. By extending the time of the surface wave plasma treatment, carbon grains can be deposited compactly without gaps, to thereby form a film having a thickness of 2 μm or more.
When a copper substrate is used, the fine carbon grains are deposited without adhesion of the fine diamond grains by the ultrasonic treatment. Furthermore, as a result of various film tests with respect to the deposition layer of the fine carbon grains, it was found that the layer exhibited outstanding properties such as a transmittance of 90% or more to visible light when the film thickness is 500 nm, high adhesion to the substrate, a high refractive index (2.1 or more at wavelength of 589 nm), hardly any birefringence, surface flatness with a surface roughness (Ra) of 20 m or less when a film having a thickness of 2 μm is formed, and an electric resistivity as high as 107 Ωcm or more at a temperature of 100° C. As described above, the carbon grains and the carbon film formed by the above-described method have high transparency and high adhesion which a conventional carbon film does not possess, and exhibits excellent performance such that it is capable of being directly coated on an iron-based substrate or a copper substrate.
The carbon film according to the present invention is preferably formed on the above-described substrates.
As the substrate, a conventional substrate may be used, for example, an insulating material such as glass, quartz, or diamond; a semiconductor such as silicon; a metal such as iron, stainless steel, molybdenum, aluminum, copper, or titanium; a ceramic material such as tungsten carbide, alumina, or boron nitride; or a plastic material such as PES, PET, PPS, or polyimide may be used.
Hereinafter, the case where glass is used as a representative example of the substrate will be described. The glass substrate includes, for example, various types of conventional glass such as soda lime glass and borosilicate glass. The thickness of glass is not particularly limited, and is appropriately selected depending on the application of the final product. In general, the thickness is in the range from 100 nm to 0.5 mm.
For forming the carbon film according to the present invention, firstly, nano-crystal diamond grains, cluster diamond grains, or graphite cluster diamond grains are adhered to the glass substrate. Alternatively, adamantane (C10H16), a derivative thereof, or a multimeric compound thereof is adhered to the glass substrate.
Typically, the nano-crystal diamond grains are diamond grains which are produced by explosion synthesis of diamond, or by high temperature/high pressure synthesis of diamond, followed by pulverizing the synthesized diamond; the cluster diamond grains are aggregates of the nano-crystal diamond grains; and the graphite cluster diamond grains are cluster diamond grains which contain large amounts of graphite or amorphous carbon components.
With respect to the nano-crystal diamond, a colloidal solution in which the nano-crystal diamond produced by explosion synthesis is dispersed in a solvent is sold by NanoCarbon Research Institute Co., Ltd., and a nano-crystal diamond powder produced by pulverization or a product in which the powder is dispersed in a solvent is sold by Tomei Diamond Co., Ltd. The average grain size of the nano-crystal diamond grains used in the present invention is in the range from 4 nm to 100 nm, and preferably from 4 nm to 10 nm. The nano-crystal diamond grains are described in detail in, for example, “Hiroshi Makita, New Diamond Vol. 12 No. 3, pp. 8 to 13 (1996).
For adhering the nano-crystal diamond grains to a glass substrate, the nano-crystal diamond grains are dispersed in water or ethanol. At this time, for improving dispersibility, a surfactant (e.g., lauryl sulfate ester sodium salt or sodium oleate) is added. Then, the glass substrate is immersed in the dispersion and cleaned by an ultrasonic cleaner. Subsequently, the substrate is immersed in ethanol and cleaned by the ultrasonic cleaner. Finally, the substrate is taken out and dried.
By performing the above-described operations, a glass substrate having nano-crystal diamond grains adhered to the surface thereof can be obtained. The nano-crystal diamond grains are adhered to the surface of the glass substrate by a physical force in the course of the ultrasonic cleaning operation, which buries a part of the grains in the substrate surface.
The number of the nano-crystal diamond grains adhered to the substrate surface is preferably in the range from 109 to 1012 grains per 1 cm2, and more preferably from 1010 to 1011 grains per 1 cm2. The diamond grains adhered to the glass substrate serve as seed crystals for the growth of the carbon film in the surface wave plasma treatment.
The number of nanocrystal diamond grains adhered to the surface of the glass substrate can be reduced by diluting the concentration of the nano-crystal diamond grains dispersed in the dispersion medium (water, ethanol, etc.). In this manner, it becomes possible to lower the nucleus generation density of the carbon grains in the surface wave plasma treatment and obtain, instead of a continuous film, a discontinuous film composed of aggregates of the carbon grains. In the aggregates, the surface density of the carbon grains can be controlled by the concentration of the nano-crystal diamond grains in the dispersion fluid. The grain size of the carbon grains can be controlled by the surface wave plasma treatment time. Further by making the concentration extremely low, it becomes possible to form an aggregate composed of the carbon grains isolated on the glass substrate. Furthermore, by treating the aggregate with hydrofluoric acid or the like and removing the glass substrate from the aggregate, it becomes possible to obtain only the carbon grains.
As an alternative method of adhering nano-crystal diamond grains to a glass substrate, a method of spin-coating the dispersion of the nano-crystal diamond to the glass substrate and drying can be mentioned. By this method, the same adhesion effect as that in the ultrasonic cleaning method can be achieved.
The cluster diamond grains are agglomerates of the nano-crystal diamond produced by the explosion synthesis method and exhibit excellent transparency. The cluster diamond grains are sold, for example, by Tokyo Diamond Tools Mfg. Co., Ltd. The average grain size of the cluster diamond used in the present invention is in the range from 4 nm to 100 nm, and preferably from 4 nm to 10 nm. The cluster diamond grains are described in detail in, for example, “Hiroshi Makita, New Diamond Vol. 12 No. 3, pp. 8 to 13 (1996).
For adhering the cluster diamond grains to a glass substrate, the cluster diamond grains are dispersed in water or ethanol. At this time, for improving dispersibility, a surfactant (e.g., lauryl sulfate ester sodium salt or sodium oleate) is added. Then, the glass substrate is immersed in the dispersion and cleaned by an ultrasonic cleaner. Subsequently, the substrate is immersed in ethanol and cleaned by the ultrasonic cleaner. Finally, the substrate is taken out and dried.
By performing the above-described operations, a glass substrate having cluster diamond grains adhered to the surface thereof can be obtained. The cluster diamond grains are adhered to the surface of the glass substrate by a physical force in the course of the ultrasonic cleaning operation, which buries a part of the grains in the substrate surface.
The number of the cluster diamond grains adhered to the surface of the glass substrate is preferably in the range from 109 to 1012 grains per 1 cm2, and more preferably from 1010 to 1011 grains per 1 cm2. The diamond grains adhered onto the glass substrate serve as seed crystals for the growth of the carbon film in the surface wave plasma treatment.
The number of cluster diamond grains adhered to the surface of the glass substrate can be reduced by diluting the concentration of the cluster diamond grains dispersed in the disperson medium (water, ethanol, or the like). In this manner, it becomes possible to lower the nucleus generation density of the carbon grains in the surface wave plasma treatment and obtain, instead of a continuous film, a discontinuous film composed of an agglomerate of the carbon grains. In the agglomerate, the surface density of the carbon grains can be controlled by the concentration of the nano-crystal diamond grains in the dispersion fluid. The grain size of the carbon grains can be controlled by the surface wave plasma treatment time. Further by making the concentration extremely low, it becomes possible to form an agglomerate composed of the carbon grains isolated on the glass substrate. Furthermore, by treating the agglomerate with hydrofluoric acid or the like and removing the glass substrate from the agglomerate, it becomes possible to obtain only the carbon grains.
As an alternative method of adhering cluster diamond grains onto a glass substrate, a method of spin-coating the dispersion of the cluster diamond to the glass substrate and drying can be mentioned. By this method, the same adhesion effect as that in the ultrasonic cleaning method can be achieved.
For adhering the graphite cluster diamond grains to a glass substrate, the graphite cluster diamond grains are dispersed in water or ethanol. At this time, for improving dispersibility, a surfactant (e.g., lauryl sulfate ester sodium salt or sodium oleate) is added. Then, the glass substrate is immersed in the dispersion and cleaned by an ultrasonic cleaner. Subsequently, the substrate is immersed in ethanol and cleaned by the ultrasonic cleaner. Finally, the substrate is taken out and dried.
By performing the above-described operations, a glass substrate having graphite cluster diamond grains adhered on the surface thereof can be obtained. The graphite cluster diamond grains are adhered to the surface of the glass substrate by a physical force in the course of the ultrasonic cleaning operation, which buries a part of the grains in the substrate surface.
The number of the graphite cluster diamond grains adhered to the surface of the glass substrate is preferably in the range from 109 to 1012 grains per 1 cm2, and more preferably from 1010 to 1011 grains per 1 cm2. The diamond grains adhered to the glass substrate serve as seed crystals for the growth of the carbon film in the surface wave plasma treatment.
The number of the graphite cluster diamond grains adhered to the surface of the glass substrate can be reduced by diluting the concentration of the graphite cluster diamond grains dispersed in a disperson medium (water, ethanol, or the like). In this manner, it becomes possible to lower the nucleus generation density of the carbon grains in the surface wave plasma treatment and obtain, instead of a continuous film, a discontinuous film composed of an agglomerate of the carbon grains. In the agglomerate, the surface density of the carbon grains can be controlled by the concentration of the graphite cluster diamond grains in the dispersion fluid. The grain size of the carbon grains can be controlled by the surface wave plasma treatment time. Further, by making the concentration extremely low, it becomes possible to form an agglomerate composed of the carbon grains isolated on the glass substrate. Furthermore, by treating the agglomerate with hydrofluoric acid or the like and removing the glass substrate from the agglomerate, it becomes possible to obtain only the carbon grains. Alternatively, when a continuous film is formed on the substrate, an independent film can be obtained by removing the substrate.
As an alternative method of adhering graphite cluster diamond grains to a glass substrate, a method of spin-coating the dispersion of the graphite cluster diamond to the glass substrate and drying can be mentioned. By this method, the same adhesion effect as that in the ultrasonic cleaning method can be achieved.
For adhering adamantane, a derivative thereof, or a multimeric compound thereof on the glass substrate, the adamantane, the derivative thereof, or the multimeric compound thereof is dissolved in a solvent (e.g., ethanol, hexane, or acetonitrile). Then the substrate is immersed in the solution and cleaned by an ultrasonic cleaner. Subsequently, the substrate is taken out and dried. By performing such operations, a glass substrate having the adamantane, the derivative thereof, or the multimeric compound thereof adhered to the surface thereof can be obtained.
Adamantane is a molecule represented by the molecular formula C10H16, and is in the form of a molecular crystal (at room temperature and under atmospheric pressure) exhibiting a sublimation property and having a diamond-like structure. Adamantane is manufactured in the course of petroleum refining. A powder of adamantane, a derivate thereof, and a multimeric compound thereof are sold by Idmitsu Kousan Co., Ltd.
It is possible to reduce the adhesion ratio of the adamantane, the derivate thereof, or the multimeric compound thereof adhered to the substrate surface by diluting the concentration of the adamantane, the derivate thereof, and the multimeric compound thereof to be dissolved in the solvent. In this manner, it becomes possible to lower the nucleus generation density of the carbon grains in the surface wave plasma treatment and obtain, instead of a continuous film, a discontinuous film composed of an agglomerate of the carbon grains. In the agglomerate, the surface density of the carbon grains can be controlled by the concentration of the adamantane, the derivate thereof, and the multimeric compound thereof in the dispersion fluid. The grain size of the carbon grains can be controlled by the surface wave plasma treatment time. Further, by making the concentration extremely low, it becomes possible to form an agglomerate composed of the carbon grains isolated on the glass substrate. Furthermore, by treating the agglomerate with hydrofluoric acid or the like and removing the glass substrate from the agglomerate, it becomes possible to obtain only the carbon grains.
As an alternative method of adhering adamantane, the derivate thereof, and the multimeric compound thereof to a glass substrate, a method of spin-coating a solution of the adamantane, the derivate thereof, and the multimeric compound to the glass substrate and drying can be mentioned. By this method, the same adhesion effect as that in the ultrasonic cleaning method can be achieved.
Next, in the present invention, the glass substrate having the diamond grains, adamantane, the derivative thereof, or the multimetric compound thereof adhered to the surface thereof (hereinafter, simply referred to as the glass substrate) is treated using a microwave plasma CVD apparatus.
The structure of a reactor is illustrated in
In the apparatus illustrated in
Specifically, when the quartz is exposed to the source gases plasmarized by microwaves, a Si gas and an oxygen gas are generated, and are plasmarized together with the source gases. Such plasma has a higher density as it is closer to the quartz tube. The plasma is diffused in substantially the substrate direction. The Si gas and the oxygen gas diffuse and flow downwardly together with the source gases so as to be effectively supplied to the substrate. This supplying is controlled by adjusting the gas pressure within the CVD chamber to control the plasma density so as to control the generation ratio of the Si gas and the oxygen gas. As explained above is the fundamental method of the carbon film depositing apparatus according to the present invention illustrated in
On the other hand, the configuration of a conventional CVD treatment apparatus is illustrated in
In the apparatus illustrated in
As described below, it is desirable that the furnace temperature (temperature of the atmosphere inside the furnace) be low, preferably in the range from room temperature to 600° C., and more preferably in the range from 100° C. to 450° C., so that this amorphous substance is deposited and coated on the grain boundary between the carbon grains and/or the gap between the carbon grains with high density. When the temperature was outside the above-mentioned range, formation of the amorphous substances Si and/or SiO2 were not confirmed. The formation of the amorphous substances and the mechanism of Si and/or SiO2 are as follows. As the temperature is low, Si which is likely to be melted into the carbon grains when the carbon grains are formed is deposited as the amorphous substance Si on the surface of the carbon grains. Si deposited on the surface is deposited on the surface of the grains i.e., the grain boundaries between the carbon grains and/or the gaps between the carbon grains. Alternatively, Si is oxidized by oxygen in the plasma to be deposited and coated as the amorphous substance SiO2. Until now, formation of an amorphous substance such as Si and/or SiO2 by a CVD treatment at a temperature as low as room temperature has been confirmed.
In the present invention, for subjecting a glass substrate to a CVD treatment, it is necessary to perform the CVD treatment at a temperature lower than the distortion point of the glass substrate. Since a typical CVD treatment of diamond is performed under a pressure of 2×103 to 1×104 Pa, the temperature of the glass substrate becomes 800° C. or higher. Therefore, a typical CVD treatment cannot be applied to a glass substrate. For lowering the temperature, it is necessary to perform the plasma treatment under a low pressure.
For this reason, in the present invention, surface wave plasma is generated under a pressure of about 1×102 Pa and utilized in the CVD treatment. The surface wave plasma is described in detail in, for example, “Hideo Sugai, Plasma Electronics pp. 124 and 125 published in 2000 by Ohmusha, Ltd.”. As a result, it became possible to perform the CVD treatment of the glass substrate at a temperature lower than the distortion point of the glass substrate. Moreover, it became possible to generate uniform plasma onto a surface as large as 380 mm×340 mm or more. Such plasma was evaluated by a Langmuir probe (single probe), and the plasma density was found to be 8×1011/cm3. This plasma density exceeds the critical plasma density of 7.4×1010/cm3, which is the requirement of surface wave plasma by microwaves having a frequency of 2.45 GHz. The Langmuir probe method is described in detail in, for example, “Hideo Sugai, Plasma Electronics p. 58 published in 2000 by Ohmusha, Ltd.”.
With respect to the CVD treatment conditions used in the present invention, the temperature is in the range from room temperature to 600° C., and preferably in the range from 100° C. to 450° C., and the pressure is preferably in the range from 5×102 Pa to 5×102 Pa, and more preferably in the range from 1.0×102 Pa to 1.2×102 Pa. The treatment time is in the range from 0.5 hour to 20 hours, and generally in the range from 1 hour to 8 hours. By the above-mentioned treatment time, it becomes possible to obtain a film thickness of about 100 nm to 2 μm.
The source gas (reaction gas) used to perform the CVD treatment is a mixture gas composed of a carbon-containing gas and hydrogen. Examples of the carbon-containing gas include methane, ethanol, acetone, and methanol.
In the carbon-containing gas/hydrogen mixture gas, the concentration of the carbon-containing gas is in the range from 0.5 mol % to 10 mol %, and preferably in the range from 1 mol % to 4 mol %. If the carbon-containing gas becomes larger than the above-mentioned range, a problem may arise in that transmittance is lowered, which is not desirable.
Further, as an additive gas for forming amorphous substance, an amorphous substance forming gas such as a silicon-containing gas including silane or disilane, or a gas containing metals such as titanium, hafnium, and zinc is added to the above-mentioned mixture gas.
These gases function as an amorphous source for suppressing generation of impurities such as amorphous carbon or graphite accompanied by the formation of the carbon grains and/or for suppressing growth of the carbon grains.
The amount of the amorphous substance forming gas (such as silane and/or disilane) within the mixture gas is preferably in the range from 0.1 mol % to 10 mol %, and more preferably in the range from 0.5 mol % to 2 mol %.
Further, as an additive gas, it is preferable that CO2 and/or CO be added to the mixture gas. Such a gas functions as an oxygen source and removes impurities in the CVD treatment.
The amount of CO2 and/or CO within the mixture gas is preferably in the range from 0.5 mol % to 10 mol % of the entire mixture gas, and more preferably in the range from 1 mol % to 4 mol %.
In the present invention, when the glass substrate is subjected to the CVD treatment, in consideration of the adhesion between the glass substrate and the synthesized carbon film, the CVD treatment temperature (substrate temperature) is appropriately adjusted to a temperature lower than the distortion point of the glass, and preferably a temperature of about 300° C. to 450° C. For example, when a soda lime glass substrate is used, since the distortion point thereof is at about 470° C., the CVD treatment temperature is a temperature lower than the distortion point, and preferably a temperature from room temperature to 450° C. Alternatively, when a borosilicate glass such as Pyrex (registered trademark) or the like is used, the CVD treatment temperature is preferably in the range from room temperature to 550° C., and more preferably in the range from 100° C. to 450° C.
According to the present invention, the carbon grains or the carbon film can be formed on a glass substrate. The carbon grains and the carbon film have a remarkable characteristic different from other carbon grains and carbon films such as diamond in that they have an approximate spectrum curve obtainable by superimposing a peak fitting curve B at a Bragg angle (2θ±0.5°) of 41.7±0.5° and a baseline on a peak fitting curve A at a Bragg angle (2θ±0.5°) of 43.9° in an X-ray diffraction spectrum by a Cukα1 ray, as shown in
Further, in a Raman scattering spectrum (excitation light wavelength: 244 nm), a distinct peak is clearly observed near a Raman shift of 1333 cm−1 and the full width at half maximum (FWHM) thereof is in the range from 10 cm−1 to 40 cm−1. Furthermore, the film is excellent in flatness and adhesion and the surface roughness Ra is 20 nm or less. In some cases, the film is extremely flat to exhibit a surface roughness Ra of 3 nm or less. Still further, the film has excellent optical characteristics, such as excellent transparency, a refractive index as high as 2.1 or more, and hardly any birefringence. Still further, the film has an excellent electrical property. Specifically, the film exhibits an extremely high electric insulating property, such that the electrical resistivity is as high as 107 Ωcm or more at 100° C.
When the cross-sectional surface of the film was observed with a high-resolution transmission electron microscope, the following characteristics were confirmed. Crystalline carbon grains having a grain size in the range from 1 nm to several tens of nm are closely formed without gaps. Further, the grain size distribution does not vary (that is, the average grain size is almost the same) at the interface between the film and the substrate, within the film and in the vicinity of the outermost surface of the film. The thickness of the carbon film is preferably in the range from 2 nm to 100 μm, and more preferably in the range from 50 nm to 500 nm. The grain size of the grains is preferably in the range from 1 nm to 100 nm, and more preferably in the range from 2 nm to 20 nm.
The cross-sectional surface of the film was thinned by ion milling, and the film structure and element distribution were observed by a high-resolution transmission electron microscope and electron energy loss spectroscopy (EELS).
With respect to various points within the film, an EELS spectrum was observed in a region of approximately 100 nm. As a result, Si was observed in all of the observed points. Further, it was confirmed that the amount of Si varies depending on the observed point.
Further, for investigating the element distribution in a micro-region, a detailed EELS measurement was performed, and a detailed analysis of the spectrum was performed. In the EELS spectrum, a peak ascribed to Si (silicon) in the vicinity of 120 eV, a signal ascribed to C (carbon) in the vicinity of 300 eV and a signal ascribed to O (oxygen) in the vicinity of 530 eV were significant, and hence, attention was directed to these peak and signals.
From the shape of the peak in the EELS spectrum, Si which is not SiO2, and C exist at Measurement Point 1, SiO2 and C exist at Measurement Point 2, and SiO2 and C exist at Measurement Point 3. Therefore, in the carbon film according to the present invention, it was confirmed that SiO2 exists on the surface of the carbon grains forming the film, and more preferably, SiO2 is formed so as to surround the carbon grains. In the diffraction image illustrated in
The amorphous SiO2 plays an extremely important role in functioning as a substance for suppressing generation of impurities such as amorphous carbon or graphite accompanied by formation of the carbon grains and/or for suppressing growth of the carbon grains.
It was confirmed that an amorphous layer was formed in a region of about 10 nm directly above the substrate. In
According to the method of the present invention, an amorphous SiO2 layer is formed directly above the substrate, and a carbon film layer is formed on the amorphous SiO2 layer. Such a method and effects thereof are realized in the following manner. Source gases including a carbon-containing gas, a hydrogen gas, and a silicon-containing are uniformly supplied toward the chamber in a downflow manner to generate plasma. Further, by using a substrate temperature of preferably 600° C. or lower, and more preferably 450° C. or lower, SiO2, which is deposited more easily than the carbon film at a low temperature, can be deposited on the substrate surface prior to the carbon film. Finally, the carbon film is deposited on the surface of the SiO2 layer. This is one of the most significant effects of the present invention.
The SiO2 layer existing between the substrate and the carbon film serves as an adhesion-reinforcing layer for enhancing adhesion between the substrate and the carbon film. Especially with respect to a substrate such as copper, iron, or tungsten carbide to which a carbon film cannot be directly deposited, or which exhibits a considerably weak adhesion and various capabilities of the carbon film cannot be utilized even if the carbon film is deposited, this technique according to the present invention is considerably simpler and more practical, as compared to a conventional technique of forming an adhesion-reinforcing layer for enhancing adhesion by a conventional process. Furthermore, by the method of the present invention, the adhesion-reinforcing layer and the carbon film can be deposited by the same process. Therefore, adhesion can be considerably improved, as compared to the conventional method.
For investigating how much of the amorphous SiO2 exhibiting the above-described effects was taken into the carbon film, the concentration of silicon and oxygen within the film was measured by secondary ion mass spectroscopy (SIMS).
The silicon content and the oxygen content in the vicinity (0.16 μm) of the center of the thicknesswise direction of the carbon film of
From the above, it was confirmed that the carbon film of
As follows is a description of examples of the present invention, although the scope of the present invention is by no way limited by these examples.
As a substrate, glass (borosilicate glass and soda lime glass) cut out with a size of 300 mm×300 mm was used. Further, for producing a sample to be evaluated, a wafer-like glass substrate with a 4-inch diameter was also used. For increasing the nucleus formation density of the carbon grains to thereby form a uniform film, the substrate was subjected to a pretreatment (treatment of adhering nano crystal diamond grains) prior to formation of a film.
In this pretreatment, a colloidal solution (product name: Nanoamand, manufactured by NanoCarbon Research Institute Co., Ltd) in which nano-crystal diamond grains having an average grain size of 5 mm were dispersed in pure water, a solution in which nano-crystal diamond grains of an average grain size of 30 nm or 40 nm (products name: MD30 and MD40 respectively, manufactured by Tomei Diamond Co. Ltd.) were dispersed in pure water, ethanol in which cluster diamond grains or graphite cluster diamond grains (products name: CD and GCD, respectively; manufactured by Tokyo Diamond Tools Mfg. Co.) were dispersed, or a solution of adamantane, derivatives thereof, or multimeric compounds thereof (manufactured by Idemitsu Kosan Co., Ltd.) was used, and a substrate was immersed therein and treated with a supersonic cleaning apparatus.
Subsequently, the substrate was immersed in ethanol, subjected to supersonic cleaning and dried, or the solution was uniformly applied onto the substrate by spin coating and dried. The uniformity achieved by the pretreatment affects the uniformity of the formed carbon film. In this case, the number of diamond grains adhered to the substrate was from 1011 to 1011 per 1 cm2.
As a source gas, CH4, CO2, silane, and H2 were used, and the concentrations of CH4, CO2 and silane were each set at 1 mol %. The gas pressure within the reaction vessel was set at 1.0 to 1.2×102 Pa (1.0 to 1.2 mbar) which is lower than the pressure used for a typical CVD synthesis of diamond (103 to 104 Pa), and microwave of 20 to 24 kW in total were charged to generate uniform plasma for an area larger than the substrate area (300×300 mm2). At this time, by closely contacting a Mo sample support with a cooling stage and adjusting the distance between the substrate and the antenna, it became possible to maintain the substrate temperature at 450° C. or lower, which is the softening point of soda lime glass, during film formation.
Film formation was performed for 6 to 20 hours under the above-described film forming conditions. A uniform and transparent carbon film was formed on the glass substrate after film formation. The thickness of the film was in the range from 300 nm to 2 μm.
The carbon film was observed by X-ray diffraction. The measurement will be described below in detail. The X-ray diffraction apparatus used was an X-ray diffraction measurement apparatus RINT2100 XRD-DSCII manufactured by Rigaku Corporation, and the goniometer used was Ultima III horizontal goniometer manufactured by Rigaku Corporation. A multi-purpose sample support for thin film standard was attached to the goniometer. The measured sample was a carbon film having a thickness of 500 nm formed on a borosilicate glass substrate having a thickness of 1 mm by the above-described method. The measurement was performed with respect to a piece cut out with a size of 30 mm square together with the glass substrate. As X-ray, copper (Cu) Kα1 ray was used. The voltage and current applied to the X-ray tube were 40 kV and 40 mA, respectively. A scintillation counter was used as an X-ray detector. First, calibration of the scattering angle (2θ angle) was conducted by using a standard silicon sample. Deviation of 2θ angle was no more than +0.02°. Then, the sample to be measured was fixed to the sample support, and the 2θ angle was adjusted to 0°, i.e. a condition under which X-ray directly entered the detector. The X-ray incident direction and the sample surface were adjusted to be in parallel, and a half of the incident X-ray was shielded by the sample. The goniometer was rotated from this state and X-ray was irradiated at an angle of 0.5° relative to the sample surface. The 2θ angle was rotated by 0.02° from 10° to 90° while fixing the incident angle, and the intensities of X-ray scattering from the sample at respective 2θ angles were measured. The computer program used for the measurement was RINT2000/PC software Windows version (registered trademark) manufactured by Rigaku Corporation.
A spectrum of the measured X-ray diffraction is shown in
Meanwhile, it could be seen that the peak for the X-ray diffraction spectrum of the carbon film according to the present invention in
Next, the constitution of the peaks (positions and strength for respective peak components) will be described in detail.
In order to analyze the detailed constitution of the peak at 20 of 43.9° in the X-ray diffraction measurement for the carbon film according to the present invention, analysis was carried out with respect to the 2θ angle in the range from 39° to 48° by using peak fitting. For the fitting of the first peak, a function called Pearson VII function was used. The function is used most generally for representing the profile of a peak obtained in a diffraction method such as X-ray diffraction or neutron diffraction. With respect to the Pearson VII function, see, for example, “Introduction Practice of Powder X-ray Analysis-Introduction to Rietveld Method” (edited by X-ray Analysis Study Conference of Japan Society for Analytical Chemistry, Asakura Shoten, Asakura Publishing Ltd.). On the other hand, as a result of study of various functions, it was found that an asymmetric function can be preferably used for the fitting of the second peak. In this example, an asymmetric normal distribution function (Gaussian distribution function) was used. This function is a normal distribution function having different dispersion (standard deviation) values on the right-hand side and the left-hand side of the peak position, and is one of the simplest functions as a function used for the fitting of an asymmetric peak. Nevertheless, the peak fitting could be performed favorably. Further, a linear function was used as a base line (background) function.
In the actual fitting operation, various computer programs can be used. In this example, ORIGIN version 6, peak fitting module Japanese edition (hereinafter referred to as ORIGIN-PFM) was used. In ORIGIN-PFM, the Pearson VII function is represented as “Pearson 7”, the asymmetric normal distribution function is represented as “BiGauss”, and the linear function is represented as “Line”. The completion requirement for the fitting was defined that the correlation coefficient (“COR”, or “Corr Coef” in ORIGIN-PFM) representing the reliability of the fitting was 0.99 or more.
According to the analysis using the peak fitting, as shown in
X-ray diffraction measurement was performed with respect to many samples of the carbon film according to the present invention. As a result, it was found that a peak with a broad width as shown in
In the analysis method of measuring the X-ray diffraction, it should be noted that fluctuation in the measurement data becomes large when the intensity of the X-ray is small, and hence, a reliable fitting becomes impossible. For this reason, it is necessary to carry out the analysis by the above-described fitting with respect to those having a maximum peak intensity of 5,000 counts or more.
As described above, it became apparent that the carbon film according to the present invention has a broad peak around 2θ of 43.9° as the center in the measurement of X-ray diffraction by CuKα1 rays, and that the peak has a shoulder on the lower angle side. By the analysis using the peak fitting, it was found that the peak could be well approximated by superimposing a first peak according to a Pearson VII function having a center at 2θ of 43.9°, a second peak according to an asymmetric normal distribution function being maximum at 41.7°, and a base line according to a linear function (background).
Analysis by peak fitting was carried out in the same manner for the spectrum of diamond shown in
The carbon film according to the present invention has a characteristic in that the above-described second peak is observed, and has a structure different from that of diamond. The production steps of the carbon film according to the present invention and the result of other measurements were investigated and the structure was studied. The synthesis method of the carbon film used in the present invention has the following remarkable characteristic, as compared to the CVD synthesis method of diamond. Firstly, a typical synthesis of diamond has been carried out at a temperature of at least 700° C. or higher, whereas the carbon film according to the present invention is synthesized at a considerably low temperature. Further, for reducing the grain size of a diamond film, a method in which a rapid growth is performed at a high carbon source concentration (molar ratio of methane gas) contained within the source gas of about 10% has been conventionally used. On the other hand, in the present invention, the carbon source concentration is as low as about 1%. That is, in the method of the present invention, carbon grains are deposited at a low temperature considerably slowly over a long period to form a film. As a result, the carbon grains are deposited in a state where they are almost transformed into diamond. Therefore, a force of promoting deposition of hexagonal diamond (which is carbon crystals more stable than the typical cubic diamond) or deposition of more stable graphite is acted, and hence, it is extremely unstable as the state of crystal deposition. Further, deposited graphite and amorphous carbon-based substance are removed by etching with an excess amount of hydrogen plasma contained in the source gas. By such a deposition mechanism, carbon grains form a structure in which cubic diamond and hexagonal diamond are mixed, and portions removed by etching remain as defects with a considerably high concentration. Such defects include point defects such as atomic vacancy, linear defects such as dislocation, and defects on a unit surface such as lamination defects, which are contained in large amounts. For this reason, the carbon film has a structure in which an X-ray diffraction peak at 43.9° has a shoulder on the lower side angle.
However, the characteristic of the X-ray diffraction peak described above is in association with high functions of the carbon film according to the present invention. Specifically, due to the low rate synthesis at a low carbon source concentration, etching of graphite and graphite-like substances is promoted. Consequently, although the structure contains defects at high concentration, transparency of the carbon film is maintained at a high level. Because the synthesis is performed at a low temperature, the cubic diamond and the hexagonal diamond are mixed, and defects are contained with a high concentration. However, by virtue of the low temperature, carbon can be deposited on an iron-based substrate without immersion into the iron-based substrate, and direct coating on copper becomes possible. Further, by virtue of the low temperature, the size of grains becomes uniformly fine, and hence, thermal strain is extremely small. That is, the structure in which the cubic diamond and the hexagonal diamond are mixed and defects are contained at a considerably high concentration enables the thermal strain to be reduced, thereby resulting in small optical birefringence. Likewise, due to this structure, a considerably high electric insulation property is exhibited.
A Raman scattering spectrum of the carbon film was measured. An ultraviolet excitation spectrometer, NRS-1000UV manufactured by Jasco International Co., Ltd., was used to carry out the measurement and a UV-laser (Ar ion laser 90C FreD manufactured by Coherent Inc.) at a wavelength of 244 μm was used for the excitation light. The power of the laser source was 100 mW, and a beam attenuator was not used. The aperture was set at 200 μm. The measurement was performed with an exposure time of 30 to 60 seconds twice and was integrated to obtain a spectrum. The apparatus was calibrated with single crystal diamond synthesized at high temperature and under high pressure as a standard sample for Raman scattering spectroscopy (DIAMOND WINDOW Type: DW005 for Raman, Material: SUMICRYSTAL, manufactured by Sumitomo Electric Industries Ltd). The peak position of the Raman spectrum of the standard sample was adjusted to a Raman shift of 1333 cm−1. A standard computer software for this apparatus (Spectra Manager for Windows (registered trademark) 95/98 ver. 1.00 manufactured by Jasco International Co., Ltd.) was used to carry out the measurement and the analysis.
A typical measured Raman scattering spectrum is shown in
The cross-sectional surface of the carbon film was observed by a high resolution transmission type electron microscope (HRTEM). The HRTEM apparatus used was H-9000 transmission electron microscope manufactured by Hitachi Ltd. and observation was carried out at an acceleration voltage of 300 kV. Further, a standard fitted sample holder for the HRTEM apparatus was used as a sample holder. The sample for observation was produced by one of the methods (1) slicing the sample by Ar ion milling treatment, (2) slicing the sample by focused ion beam (FIB) fabrication, or (3) delaminating the film surface with a diamond pen and collecting the obtained slice in a microgrid.
An example of the results of observation is shown in
The term “crystallite” refers to a micro-crystal that can be regarded as a single crystal. In general, one grain is constituted of one or plurality of crystallites. From the result of HRTEM observation, it was found that the size (average grain size) of the carbon grains (crystallites) does not differ at the interface with the substrate, within the film, and in the outermost surface, and the size was in the range from 2 to 40 nm.
When it could be regarded that the film was constituted of grains filled with no gaps, the average grain size was calculated in accordance with the following procedures.
The average grain size was determined by taking the average of the grain size of at least 100 different grains (crystallites) in a transmission electron photomicrograph of the cross-sectional surface of a carbon film. In
wherein π represents the ratio of circumference.
Further, the surface density ds of the grain was determined on the basis of the average grain size of the grains by the following formula:
d
s=unit area/(π×(average grain size/2)2)
By determining the surface density of the carbon film according to the present invention in this manner, it was found that the surface density does not differ in the interface, within the film, and in the outermost surface, and is in the range from 8×1010 cm−2 to 4×1012 cm−2.
TEM-EELS Measurement
The cross-sectional surface of the film was thinned by an ion milling treatment to observe the film structure and element distribution with a high resolution transmission electron microscope and electron energy loss spectroscopy (EELS).
With respect to various points within the film, an EELS spectrum was observed in a region of approximately 100 nm. As a result, Si was observed in all of the observed points. Further, it was confirmed that the amount of Si varies depending on the observed point.
Further, for investigating the element distribution in a micro-region, a detailed EELS measurement was performed and a detailed analysis of the spectrum was performed. In the EELS spectrum, a peak ascribed to Si (silicon) in the vicinity of 120 eV, a signal ascribed to C (carbon) in the vicinity of 300 eV and a signal ascribed to O (oxygen) in the vicinity of 530 eV were significant, and hence, attention was directed to these peak and signals.
From the shape of the peak in the EELS spectrum, it was found that Si which is not SiO2, and C exist at Measurement Point 1, SiO2 and C exist at Measurement Point 2, and SiO2 and C exist at Measurement Point 3. Therefore, in the carbon film according to the present invention, it was confirmed that SiO2 is formed so as to surround independent carbon grains. The distribution of such SiO2 is observed anywhere within the film. This characteristic distribution of SiO2 has been realized for the first time by the technique of the present invention. Such a characteristic distribution was not observed in a conventional diamond, a diamond-like carbon film, or the like.
This SiO2 plays an extremely important role in functioning as a substance for suppressing generation of impurities such as amorphous carbon or graphite accompanied by formation of the carbon grains and/or for suppressing growth of the carbon grains.
TEM-EELS Measurement
It was confirmed that an amorphous layer was formed in a region of about 10 nm directly above the substrate. In
According to the method of the present invention, an amorphous SiO2 layer is formed directly above the substrate, and a carbon film layer is formed on the amorphous SiO2 layer. Such a method and effects thereof are realized in the following manner. Source gases including a carbon-containing gas, a hydrogen gas, and a silicon-containing are uniformly supplied toward the chamber in a downflow manner to generate plasma. Further, by using a substrate temperature of preferably 600° C. or lower, and more preferably 450° C. or lower, SiO2, which is deposited more easily than the carbon film at a low temperature, can be deposited on the substrate surface prior to the carbon film. Finally, the carbon film is deposited on the surface of the SiO2 layer. This is one of the most significant effects of the present invention.
The SiO2 layer existing between the substrate and the carbon film serves as an adhesion-reinforcing layer for enhancing adhesion between the substrate and the carbon film. Especially with respect to a substrate such as copper, iron, or tungsten carbide to which a carbon film cannot be directly deposited, or which exhibits a considerably weak adhesion and various capabilities of the carbon film cannot be utilized even if the carbon film is deposited, this technique according to the present invention is considerably simpler and more practical, as compared to a conventional technique of forming an adhesion-reinforcing layer for enhancing adhesion by a conventional process. Furthermore, by the method of the invention, the adhesion-reinforcing layer and the carbon film can be deposited by the same process. Therefore, adhesion can be considerably improved, as compared to the conventional method.
Film Structure
For investigating how much of the amorphous SiO2 exhibiting the above-described effects was taken into the carbon film, the concentration of silicon and oxygen within the film was measured by secondary ion mass spectroscopy (SIMS).
The silicon content and the oxygen content in the vicinity (0.16 μm) of the center of the thicknesswise direction of the carbon film of
From the above, it was confirmed that the carbon film of
The carbon film was observed with a scanning electron microscope (SEM). Specifically, a carbon film having a thickness of about 500 nm was formed on a borosilicate glass substrate having a diameter of 10 cm and a thickness of 1 mm. Then, the substrate was broken and inclined to observe the cross-sectional surface thereof. For preventing charge-up caused by the fact that the glass substrate and the diamond film are insulators, a relatively low acceleration voltage of 1 kV was used to observe the cross-sectional surface thereof at a relatively low magnification factor of about 7000 times. The results of the observation are shown in
The surface of the carbon film was observed by an atomic force microscope (AFM) to evaluate the surface roughness. In this case, for suppressing the effect of the surface roughness of the substrate on the surface roughness of the film as much as possible, the film was formed on a mirror-polished quartz disk (10 mm diameter×3 mm thickness) with a small surface roughness (arithmetic mean height Ra=0.9 to 1.2 nm) and used as a sample to be measured. The AFM apparatus used was a nanoscope scanning probe microscope manufactured by Digital Instruments Corporation, and a canti-lever mono-crystal silicon production rotation probe Tap300 for use in a scanning probe microscope manufactured by Digital Instruments Corporation was used as the canti-lever. A tapping mode was used for the measurement, and observation was carried out at a scanning size of 1 μm and at a scanning rate of 1.0 Hz.
The results of observation of the film surface by an atomic force microscope (AFM) are shown in
The arithmetic average height Ra is described in detail in, for example, “JIS B 0601-2001” or “ISO 4287-1997”.
Transmittance of the carbon film to visible light was measured. As a sample, a carbon film of the present invention formed on a borosilicate glass wafer substrate having a diameter of 10 cm and a thickness of 1 mm was used. As a transmittance measuring apparatus, UV/Vis/NIR Spectrometer Lambda 900 manufactured by Perkin Elmer Inc. was used, and transmittance was measured in a wavelength region from 300 nm to 800 nm. In the measurement, light from a light source was divided into two optical paths, and one path was applied to the sample on which the film was formed and the other path was applied to a glass substrate on which the carbon film was not formed. In this manner, the transmittance spectrum of the sample and that of the glass substrate were simultaneously measured, and the transmittance spectrum of the carbon film itself was determined by subtracting the spectrum of the glass substrate from the spectrum of the sample. For carrying out measurement and analysis, a computer software for measurement and analysis for the apparatus, LV-Winlab ver. X1.7A manufactured by Perkin Elmer Inc., was used.
An example of the measured transmission spectrum of the film is shown in
The refractive index of the carbon film was measured by phase difference measurement. A sample prepared by forming a carbon film of the present invention on a borosilicate glass wafer substrate having a diameter of 10 cm and a thickness of 1 mm and cutting the substrate into about 20 mm square was used. A phase difference measuring apparatus NPDM-1000 manufactured by Nikon Corporation was used as a measuring apparatus, and M-70 was used as a spectrophotometer. A xenon lamp was used as a light source, and Si—Ge was used as a detector. Further, Gramthomson was used as a polarizer and an analyzer, and the number of revolutions of the polarizer was set at 1. Measurement was carried out at an incident angle of 65° and 60°, a measuring wavelength in the range from 350 nm to 750 nm, and a pitch of 5 nm. The spectrum of the measured phase difference Δ and the amplitude reflectivity ψ was compared with calculation models and fitted, so as to approach the measured values (Δ, ψ). The refractive index, the extinction coefficient and the film thickness were determined based on the results of the best fitting between the measured values and the theoretical values. The calculation was carried out on the assumption that each layer of the sample was an isotropic medium.
The birefringence of the carbon film was measured. A sample prepared by forming the carbon film of the present invention on a borosilicate glass wafer substrate having a diameter of 10 cm and a thickness of 1 mm and cutting the substrate into about 20 mm square was used. Measurement was carried out by a phase difference measuring method, and a phase difference measuring apparatus NPDM-1000 manufactured by Nikon Corporation was used as a measuring apparatus, M-70 was used as the spectrophotometer, and a halogen lamp was used as a light source. Si—Ge was used as the detector and Gramthomson was used as a polarizer and an analyzer. The number of revolutions of the polarizer was set at 1, and the measurement was carried out at the at an incident angle of 0°, a wavelength region of 400 nm to 800 nm and a pitch of 5 nm. Further, the dependence on the rotation angle was measured at a wavelength of 590 nm.
Measurement was carried out in the arrangement shown in
Measurement was also carried out in the same manner with respect to the borosilicate glass used as the substrate, and was compared with the glass substrate having the carbon film formed thereon, so as to evaluate the birefringence of the carbon film.
A typical example of the measurement results are shown in
An experiment on the adhesion of the carbon film to the glass substrate was carried out. Samples prepared by forming carbon films having thickness of about 280 nm, 600 nm, and 2.2 μm, respectively, on a borosilicate glass wafer substrate having a diameter of 10 cm and a thickness of 1 mm and cutting respective substrates each into about 20 mm square were used.
With respect to the three samples, a flatwise experiment was carried out to evaluate the adhesion strength. A universal material experiment apparatus, Model 5565 manufactured by Instron Corporation, was used as a measuring apparatus and a crosshead displacement rate method was used as a measurement method. A jig was bonded with an adhesive to each of the sample diamond film and the glass substrate, and an adhesion strength test (flatwise test) was carried out by a crosshead displacement rate method at a measuring temperature of room temperature (23° C.) to obtain a load-displacement diagram. The load upon initial fracture was read from the obtained diagram, and the adhesion strength was evaluated based on a value obtained by dividing the load upon initial fracture by the adhesion area. The experiment was carried out at a speed of 0.5 mm/min. The data processing system “Merlin” manufactured by Instron Corporation was used for the data processing.
As a result of the measurement, it was found that delamination did not occur at the interface between the glass and the carbon film, and delamination occurred at the interface between the adhesive and the jig in all of the samples. Therefore, the adhesion strength between the glass and the film could not be evaluated. However, it was found that the adhesion strength was at least 0.30 MPa or more.
Thus adhesion of the film to the glass substrate was evaluated by a scratch method using a Nano Indenter-scratch option. In the scratch method, the surface of the sample was scratched while applying a load on a diamond tip (in other words, the sample was scratched while indenting the diamond tip therein), and the adhesion was evaluated by the vertical load when the film was delaminated (critical delamination load).
As a measuring apparatus, Nano Indenter XP manufactured by MTS System Corporation was used, and Test Works 4 manufactured by MTS System Corporation, which is a standard computer software for measurement and analysis for the apparatus, was used. XP (diamond Cube corner type) was used as the indenter (tip). Measurement was carried out under conditions of a maximum indentation load in the range from 20 mN to 250 mN, a profile load of 20 μN, a scratch distance of 500 μm, the number of measuring points of 10, a measuring point interval of 50 μm, and a measuring ambient temperature of 23° C. (room temperature).
The maximum indentation load was determined by carrying out an indentation experiment before the scratch experiment, and estimating the load to reach the substrate based on a load-displacement (indentation depth) curve.
The profile load is a load applied to an indenter upon scanning the sample surface with a minute load (profile step) before the scratch experiment in order to detect the shape of the sample surface.
A sample for the measurement prepared by forming the diamond film according to the present invention on a borosilicate glass wafer substrate having a diameter of 10 cm and a thickness of 1 mm and cutting the substrate into about 10 mm square was used. The sample was adhered to a sample support by using a crystal bond (hot melting adhesive) to carry out the measurement.
The scratch experiment was carried out by the following three steps.
First step: surface profile with a minute load
In this step, the surface shape was detected.
Second step: pre-profile→scratch→post profile
In this step, the scratch experiment was carried out while actually applying a load.
Third step: surface re-profile
In this step, the surface property of scratch flaws could be recognized.
The steps were carried out on every measuring point, and the adhesion strength was evaluated as scratch hardness on every measuring point.
H═P/A,
wherein P denotes the vertical load at the delamination position and A denotes the contact area at the delamination starting point. A was estimated as follows:
A=2.5981×ht2/3 (ht: indentation depth at the delamination starting point).
In this manner, the scratch experiment was carried out on 10 measuring points of each sample, and an average of significant measuring results was taken, which was defined as the scratch hardness of the sample. With respect to the sample shown in
In other samples (film thickness: about 280 nm), the carbon film did not delaminate even when the indenter reached the substrate. Thus, these samples exhibited high adhesion such that it could not to be evaluated by this method.
For evaluating the electric characteristic of the carbon film according to the invention, electric resistance measurement and Hall effect measurement were carried out. The measurements will be described below. The electric resistance measuring apparatus and Hall effect measuring apparatus used was Resi Test Model 8310S equipment manufactured by Toyo Corporation. The sample holder used was model VHT manufactured by Toyo Corporation. The measured sample was a carbon film having a thickness of 500 nm formed on a Pyrex (registered trademark) glass substrate having a thickness of 1 mm by the above-described method. Specifically, the measurement was performed with respect to a carbon film cut together with the glass substrate into a size of 4 mm square. As electrodes, Ti was deposited with a thickness of 50 nm in the shape of a circle having a diameter of 0.3 mm by vacuum vapor deposition on four corners of the sample. Further, Pt with a thickness of 50 nm and Au with a thickness of 100 nm were deposited on the Ti electrodes to prevent oxidation of the Ti electrodes. The electrodes were heat-treated in an argon atmosphere at 400° C. for stabilization. The resultant was attached to a sample support made of high resistance alumina, and wiring of a gold wire having a φ of 250 μm was performed by supersonic bonding to the electrode.
Measurement of the electric resistance was carried out in an atmosphere of helium at 1 mbar. Measurement was carried out by raising the temperature by 25° C. from room temperature up to 400° C.
Although determination of the electro-conductivity type by the Hall effect measurement was tried, it could not be determined whether it was p-type or n-type due to the high resistance.
The above-described electrical properties show that the carbon film according to the present invention functions as an excellent electric insulating film.
Formation of the carbon film was tried at a CVD treatment temperature of about room temperature by the technique according to the present invention.
On the other hand,
Carbon films were formed on glass substrates other than the borosilicate glass and substrates other than glass such as metal and plastic. Specifically, the following substrates were used.
Following the surface wave plasma CVD treatment, the carbon film according to the present invention was formed on each of the substrates. The Raman scattering spectra of the films formed on the substrates are shown in
A carbon film was formed on a PPS (polyphenylene sulfide) resin substrate by the method of the present invention. A PPS substrate with a size of 50×50×t2 mm was used. The substrate temperature during the surface wave plasma treatment was 28° C. Following the surface wave plasma CVD treatment, a carbon film was formed on the substrate. The Raman scattering spectrum of the film is shown in
With respect to diamond films formed on the copper substrate and the stainless steel substrate, the adhesion strength was evaluated by a scratch test. Measurement was performed in the same manner as in the evaluation for the scratch hardness by the scratch method using the Nano Indenter scratch option described above. The sample used for the evaluation was a copper substrate having a size of 20×20×t3 mm and a stainless steel (SUS 430) substrate having a size of 20×20×t2 mm each having a diamond film formed thereon. The thickness of the diamond film formed on each of the substrates was about 600 nm. The maximum indentation load in this example was 1 mN for the film on the copper substrate and 10 mN for the film on the stainless steel substrate. Other measuring conditions were the same as those for the method described above.
As a result of the scratch experiment, it was found out that delamination of the film did not occur even when the indenter was indented by 1 μm which was larger than the film thickness, and hence, the evaluation of the adhesion strength was difficult. Nevertheless, since delamination did not occur even at the indentation depth larger than the film thickness, it can be considered that the adhesion was excellent.
A discontinuous carbon film composed of aggregates of carbon grains according to the present invention was formed on a substrate by the method of the present invention. Upon depositing nano diamond grains, cluster diamond grains, graphite cluster diamond grains, adamantane, derivative thereof, or multimeric compounds thereof on a substrate before carrying out the surface wave plasma CVD treatment according to the method of the invention, the deposition density of them to the substrate can be reduced by considerably lowering the concentration thereof to a dispersion medium or a solvent for dispersing or dissolving them. In this manner, the surface density of the nucleus formation generation of diamond upon CVD treatment can be lowered, and formation of a discontinuous film (not a continuous film) on the substrate becomes possible. In this case, the grain size of the carbon grains constituting the discontinuous film can be controlled by the time for the surface wave plasma CVD treatment (wherein the size becomes smaller as the time is shortened, and the size becomes larger as the time is prolonged).
The discontinuous film composed of the carbon grain aggregates shown in
Thermal conductivity of the carbon film according to the present invention formed on the silicon substrate was measured. The thickness of the carbon film was 1 Hm. An optical exchange method was used as a measuring method (with respect to the optical exchange method, see “Calorimetry and Thermal Analysis Handbook” (Japan Society of Calorimetry and Thermal Analysis, JSCTA) edition, Maruzen Co., Ltd.). As a result, a thermal diffusivity of 0.758×10−4 m2/S was obtained at 25° C. Simultaneously, the specific heat and density of the carbon film were measured. By multiplying them with the thermal diffusivity, the thermal conductivity of 137 W/mK of the carbon film according to the present invention was obtained.
As shown in
The carbon film according to the present invention was laminated on glass, and the optical confinement effect was demonstrated. The carbon film according to the present invention was deposited with a thickness of 200 nm on the surface of a typical slide glass (25 mm×75 mm, about 1 mm thickness) to form a laminate.
The carbon film according to the present invention was coated on glass to demonstrate the scratch flaw resistance effect. The carbon film according to the present invention was coated with a thickness of 300 nm on the surface of a borosilicate glass having a diameter of 10 cm and a thickness of 1 mm. Then, it was rubbed with No. 400 sand paper by 800 experimenters. The results are shown in
A carbon film according to the present invention was deposited with a thickness of 300 nm on quartz glass, and a wrist watch provided with the coated quartz glass as a wind proof was formed as shown in
A carbon film according to the invention with a thickness of 500 nm was deposited on a thin aluminum plate having a thickness of 0.3 mm to form a laminate. Further, an electronic circuit pattern was formed with copper on the carbon film to form an electronic circuit substrate.
The carbon film according to the present invention was coated on a glass plate, a silicon substrate, a stainless plate, a copper plate, an aluminum plate, an alumina plate each having a diameter of 10 cm and a thickness of 1 mm, and chemical resistance against various chemicals was investigated. The carbon film according to the present invention was coated with a thickness of 300 nm on each of the substrates. Fluorinated acid, nitric acid, hydrochloric acid, sulfuric acid, hydrogen peroxide solution, and aqueous solution of sodium hydroxide were applied onto the surface coated with the carbon film, and then allowed to stand for 1 hour. As a result, it was found that the carbon film was not eroded by any of the above-described chemicals, and all of the substrates were protected. Thus, it was found that the carbon film according to the present invention is effective as a protection film.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-194628 | Jul 2005 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2006/313315 | 7/4/2006 | WO | 00 | 4/10/2009 |
