Diamond synthetic method

Abstract: Disclosed herein is a diamond vapor deposition method which can selectively grow high quality diamond on an arbitrary region of a base material at a lower temperature. According to this vapor deposition method, employed is a raw material gas which is prepared by diluting a compound containing carbon atoms such as methane with gaseous hydrogen. This raw material gas is irradiated with a laser beam satisfying at least either a spread angle of 1 x 10⁻² mrad to 5 x 10⁻¹ mrad in oscillation or a half-power band width of 1 x 10⁻⁴ nm to 1 x 10⁻¹ nm with respect to a band width of an oscillation wavelength and having a wavelength 190 nm to 360 nm. Diamond is deposited on the base material from a chemical species generated by such irradiation.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a vapor deposition technique for diamond, and more particularly, it relates to a technique through which high quality diamond can be formed on a base material having a three-dimensionally complicated shape at a low temperature of not more than about 300°C. Description of the Background Art As to the vapor deposition technique for diamond which was started by Derjaguin in 1956 (USSE Inv. Certi. No. 339134, 1958) and Eversole in 1958 (USP Nos. 3030187 and 3030188), further development has been made with the study by Matsumoto et al. in 1982 (Jpn. J. Appl. Phys., 21, 1982, L183). In such development, various low pressure vapor deposition methods such as thermal CVD, plasma CVD, ion beam deposition, optical CVD, laser CVD and the like have been studied for synthesis of diamond. For example, the following is a list of subjects of such a vapor deposition technique for diamond : (1) Improvement in efficiency for film formation (2) Temperature reduction in the deposition process (3) Suppression of damage on the base material (4) Selective growth on a desired region Among these items, temperature reduction in the deposition process and selective growth on a desired region are extremely important subjects for implementing various uses of vapor-deposited diamond. As to techniques of vapor-depositing diamond at lower temperatures, plasma-generating CVD techniques such as dc discharge plasma CVD and microwave plasma CVD can be listed first. In the dc discharge plasma CVD, a diamond film is formed in a range of a relatively low vacuum of 200 to 270 mbar (150 to 200 Torr). at a temperature of about 500°C. Also in relation to the microwave plasma CVD, it has been reported that vapor deposition was carried out at a temperature of about 400°C. In the dc discharge plasma CVD, however, abnormal glow discharge can be carried out only in an extremely limited range on an anode. Therefore, this method is remarkably disadvantageous for selectively growing diamond on a desired region of a base material to be provided with diamond. Also in the microwave plasma CVD, the region allowing formation of diamond is restricted because it is difficult to stably concentrate the discharge on the desired regions of base materials having various threedimensional shapes. Further, a method employing plasma has such a disadvantage that the surface of the base material is damaged by the plasma. Further, while it is possible to attain temperature reduction in a process by employing the aforementioned plasma CVD, awaited is a technique for coating a base material which is weaker against heat, such as plastic, for example, with diamond for implementing various uses of vapor-deposited diamond. In this case, it is necessary to reduce the temperature of the process below 200°C, more preferably below 100°C. On the other hand, there has been studied a technique of employing light for decomposing and exciting a raw material gas, in order to further reduce the temperature of the process. In relation to such a technique, studied are CVD employing ultraviolet radiation from an excimer laser, a mercury lamp, a deuterium lamp or a rare gas lamp, and CVD employing synchrotron radiation (SR), for example, as ultraviolet radiation of shorter wavelength. However, it is difficult to generally carry out the CVD employing SR since an apparatus for emitting synchrotron radiation is extremely high-priced and hard to operate. On the other hand, various methods have been studied as to the CVD employing ultraviolet radiation from an excimer laser or the like. For example, Jaganese Patent Publication No. 3-51675 (1991) discloses a method of irradiating a hydrocarbon reaction gas with high power ultraviolet radiation for decomposing the reaction gas and depositing carbon atoms liberated from the reaction gas on a heated base material. According to this method, a mixed gas of acetylene and hydrogen (acetylene concentration: 10 %) is supplied in a reactor and an Si substrate which is heated to 500°C is irradiated with a KrF excimer laser beam (wavelength: 248 nm) for carrying out vapor deposition, for example. In the prior art disclosing mere employment of an excimer laser beam etc. for photodecomposition, however, it has been impossible to form high quality diamond having sufficient intensity of a diamond peak at 1333 cm⁻¹ in Raman spectrometry. This has been regarded because generally employed ultraviolet radiation such as the excimer laser beam cannot photodecompose H 2, and atomic active hydrogen, which is conceivably an important chemical species for vapor deposition of diamond, is not sufficiently generated. In such a background, a method of additionally generating plasma by dc discharge, RF or microwaves has been developed in a CVD technique of applying a laser beam etc. to photodecomposition. According to this method, it is possible to generate hydrogen atoms and form diamond of relatively high quality at a relatively low temperature. In such a method, on the other hand, it is necessary to generate plasma in a portion which is as close as possible to a substrate in consideration of the mean free path. In order to deposit diamond on a three-dimensional region or a base material, therefore, an apparatus of a considerably complicated mechanism is required for uniformly diffusing atomic hydrogen on the base material surface. In employment of the plasma, further, deterioration of the base material surface is facilitated by the plasma and diamond is disadvantageously formed on an unnecessary position by decomposition of a carbon source in the plasma or the quality of the deposit is extremely reduced by excessive supply of carbon. SUMMARY OF THE INVENTION An object of the present invention is to provide a diamond synthetic method which can sufficiently respond to the particularly important subjects in the current diamond vapor deposition, i.e., temperature reduction in the synthetic process and selective growth on a desired region of a base material, for synthesizing high quality diamond with smaller damage on the base material. A method according to the present invention, which is a method of synthesizing diamond on a base material from the vapor phase using a raw material gas prepared by diluting a compound containing carbon atoms with gaseous hydrogen, comprises a step of irradiating the raw material gas or the base material with a laser beam having a wavelength within a range of 190 nm to 360 nm and satisfying at least one of the following conditions : the spread angle in oscillation is within a range of at least 1 x 10⁻² mrad and not more than 5 x 10⁻¹ mrad or the half-power band width with respect to the band width of the oscillation wavelength is within a range of at least 1 x 10⁻⁴ nm and not more than 1 x 10⁻¹ nm, thereby decomposing the compound and the gaseous hydrogen, and depositing diamond on the base material from the decomposed raw material gas. According to the present invention, a laser source can be prepared from an ArF excimer laser (wavelength: 193 nm), a KrCl excimer laser (wavelength: 222 nm), a KrF excimer laser (wavelength: 248 nm), an XeCl excimer laser (wavelength: 308 nm), an N₂ excimer laser (wavelength: 337 nm) or an XeF excimer laser (wavelength: 353 nm), for example. According to the present invention, coherence of the laser beam is improved. While a laser beam which is oscillated from a laser oscillator generally has a spread angle of about 1 to 3 mrad, such an angle is within a range of at least 1 x 10⁻² mrad and not more than 5 x 10⁻¹ mrad according to the present invention. Further, while the half-power band width with respect to the band width of an oscillation wavelength is 1 to 2 nm in a general laser beam, such half-power band width is within a range of at least 1 x 10⁻⁴ nm and not more than 1 x 10⁻¹ nm according to the present invention. Thus, the band of the laser beam is narrowed according to the present invention. Such improvement of coherence can be attained by a method of using an instable resonator, or a method of amplifying seed light, whose band is narrowed by an etalon, a prism or a grating, with a resonator. According to the present invention, it is preferable to suppress dispersion of energy intensity in a plane which is perpendicular to the optical axis of the laser beam to a level of not more than 10 % of average energy intensity, in order to form homogeneous diamond on a prescribed region of the base material. Such averaging of energy in a section of the laser beam can be attained by a method of combining a prism and a lens for dividing the laser beam into some parts in its section and thereafter reconstructing the same, or a method of cutting a central portion having relatively homogeneous energy distribution by a mask as to the laser beam, for example. According to the present invention, a pulsed laser beam is employed in general. In this case, a high repetition laser oscillator is preferably employed since it is possible to increase the film forming rate by increasing the pulse repetition rate. Further, it is preferable to employ an apparatus which can generate high energy since the film forming rate is improved as the energy density of the laser is increased. According to the present invention, the compound and the gaseous hydrogen contained in the vapor phase are decomposed and excited in the region irradiated with the laser beam, whereby formation of diamond progresses only on this region. Therefore, when an optical path of the laser beam is fixed and the base material is moved, for example, it is possible to form diamond on a portion of the base material which is located under the optical path of the laser beam. In more concrete terms, it is possible to form a homogeneous and flat film on a region of the base material which is irradiated with the laser beam by linearly focusing the laser beam on the base material with a cylindrical lens and uniaxially driving (translating or rotating) the base material, in relation to such driving of the base material. While the base material is driven in the above example, it is also possible to form diamond on an arbitrary region of the base material by moving the laser beam. Thus, according to the present invention, it is possible to grow diamond on an arbitrary region of the base material by simply changing positional relation between the laser beam and the base material. The raw material gas employed in the present invention, which necessarily contains gaseous hydrogen (H₂), can contain an arbitrary compound as the carbon material. According to the present invention, the compound containing carbon atoms can be prepared from an organic compound, such as saturated hydrocarbon such as methane, ethane or propane, unsaturated hydrocarbon such as acetylene, benzene or xylene, alcohol such as methanol or ethanol, ester such as methyl acetate, phenol such as phenol or O-cresol, ether such as ethyl ether, ketone such as acetone, aldehyde such as formaldehyde, or halogenated carbon such as carbon tetrachloride, for example. In selection of such an organic compound for the raw material, it is possible to select an organic compound including no wavelength of the as-employed laser beam in its absorption band, for example. In such selection, it is possible to avoid acetylene etc. having an absorption band at 193 nm and to select saturated hydrocarbon such as methane when an ArF excimer laser (wavelength: 193 nm) is employed, for example. According to the present invention, further, it is possible to add at least one gas selected from the group consisting of helium, argon, krypton, xenon and radon to the raw material gas, in order to facilitate formation of diamond. In addition of such a gas, its concentration is preferably at least about 10 ppm and not more than about 30 %. No effect is attained by addition of the gas if the concentration is not more than about 10 ppm, while concentration of a precursor for forming diamond is so reduced that such addition is in vain if the concentration exceeds about 30 %. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates emission spectra observed upon irradiation with excimer laser beams employed in the present invention and the prior art respectively; Fig. 2 illustrates a Raman spectrum of a film obtained in Example 1 according to the present invention; Fig. 3 illustrates a Raman spectrum of a film obtained in Example 2 according to the present invention; and Fig. 4 illustrates a Raman spectrum in a film obtained according to comparative example. DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical laser beam having a wavelength of about 190 nm to 360 nm is an excimer laser beam. This excimer laser beam is inferior in coherence to other laser beams having large wavelengths. In other words, the excimer laser beam generally has a relatively large spread angle, as well as a certain width as to its oscillation wavelength. In conventional laser CVD, no significance has been found with respect to formation of diamond as to coherence of the as-employed excimer laser beam. However, the inventors have made profound study on CVD using an excimer laser beam, to find that coherence of the laser beam has an extremely important meaning in formation of high quality diamond and it is possible to form high quality diamond at a low temperature by improving coherence of an excimer laser without employing other auxiliary means such as plasma forming means. Fig. 1 shows an emission spectrum which was obtained when a raw material gas (99 % of hydrogen and 1 % of methane) prepared by diluting methane with hydrogen was irradiated with an ArF excimer laser beam having a spread angle of not more than about 5 x 10⁻¹ mrad in oscillation and a half-power band width of not more than about 1 x 10⁻¹ nm with respect to a band width of the oscillation wavelength according to the present invention at (a). Fig. 1 also shows an emission spectrum which was obtained when a raw material gas (99 % of hydrogen and 1 % of acetylene) prepared by diluting acetylene with gaseous hydrogen was irradiated with a generally employed ArF excimer laser beam having a spread angle of about 3 mrad in oscillation and a band width of the oscillation wavelength of about 2 nm according to a conventional method at (b). Referring to Fig. 1, observed at (a) are peaks indicating that a number of chemical species which are important for diamond synthesis are generated upon irradiation with the laser beam according to the present invention, as well as strong emission indicating generation of atomic hydrogen Hβ. On the other hand, observed at (b) is only emission by C₂, with no emission of atomic hydrogen. While a vapor deposition mechanism of diamond has not yet been completely explicated under the present circumstances, it has been clarified through study made by the inventors that atomic hydrogen which is generated by decomposition of gaseous hydrogen has an extremely important action on diamond synthesis. Further, while the inventors have not yet completely explicated the cause for formation of profiles of chemical species which are suitable for diamond synthesis upon irradiation with a laser beam having high coherence as shown at (a) in Fig. 1, it is conceivable that a strong electric field is locally formed to provide a plasma state by improvement in coherence of the laser beam, and that multiple photon absorption/decomposition is facilitated by extremely high energy concentration. In either case, it is possible to decompose the raw material gas also in a wavelength band generally causing no absorption/decomposition, by improving coherence of the excimer laser. When a gas such as helium, argon,neon, krypton, xenon or radon is added to the raw material gas and this raw material gas is irradiated with the laser beam according to the present invention, intensity of its emission spectrum is increased. Thus, it is possible to promote decomposition of the raw material gas by adding such a gas to the raw material gas, thereby improving the formation rate of diamond. Thus, according to the present invention, it is possible to generate chemical species which are suitable for diamond synthesis from the raw material gas by improving coherence of the laser beam, thereby forming high quality diamond at a low temperature. According to the present invention, the spread angle of the laser beam in oscillation is set in the range of about 1 x 10⁻² to 5 x 10⁻¹ mrad, in order to improve coherence of the laser beam. When the spread angle exceeds about 5 x 10⁻¹ mrad, aberration is so increased that required energy density cannot be obtained due to dispersion of energy. On the other hand, it is technically difficult to reduce the spread angle to less than about 1 x 10⁻² mrad, and no sufficient effect is expectable even if the spread angle can be reduced below this value. According to the present invention, further, the half-power band width is set at about 10⁻⁴ to 10⁻¹ nm as to the band width of the oscillation wavelength, in order to improve coherence of the laser beam. It is impossible to sufficiently decompose and excite the raw material gas if the half-power band width exceeds about 10⁻¹ nm, while it is impossible to obtain the energy required for decomposing the raw material gas if the half-power band width is less than about 10⁻⁴ nm. In the present invention, it is to be noted that a compound such as methane having no absorption band for the wavelength of the laser beam can be employed as a carbon source, as hereinabove described. When CVD is carried out with a compound absorbing no laser beam, it is possible to cause decomposition of the carbon material only in a region on which the laser beam is focused and a region close thereto. Therefore, decomposition of the raw material gas progresses in a portion separated from a window for transmitting the laser beam in a chamber for the CVD process, whereby the window is not stained. When a compound having the wavelength of the laser beam in its absorption band, on the other hand, decomposition of the raw material gas is caused everywhere. When absorption/decomposition progresses particularly in the vicinity of the window, sooty products adhere to the window to reduce transmissivity of the window for the laser beam. Finally, no laser beam is supplied with sufficient energy, and no diamond can be synthesized. While an inert gas or gaseous hydrogen may be sprayed onto the inner side of the window in order to solve this problem, this method is not necessarily preferable in consideration of influence by diffusion of the gas. A section of an excimer laser beam generally has a rectangular shape of about 10 mm by 30 mm, with a heterogeneous energy profile in distribution which can be approximated with Gaussian distribution. Namely, the laser energy intensity is high at a central portion and low at a peripheral portion on such a section of the laser beam. This leads to no problem when the laser beam is condensed spotlike, while diamond may be heterogeneously formed when a substrate is irradiated with a laser beam around a condensed point. On the other hand, it is possible to improve accuracy in diamond formation by suppressing energy dispersion in the sectional direction within about 10 % of average energy. Thus, it is possible to substantially eliminate influence exerted by energy dispersion on formation of diamond. The inventors have further found that it is possible to flatly and homogeneously form diamond by simply linearly focusing a laser beam on a base material with a cylindrical lens and uniaxially driving (translating or rotating) the base material. Although the cause for this has not yet been explicated, conceivable is existence of such condition that energy distribution is canceled by unidirectional condensation. As hereinabove described, the following effects can be attained according to the present invention: (1) A large amount of atomic hydrogen can be generated with a laser beam in the vicinity of an irradiated point with no additional apparatus such as plasma generation means, whereby it is possible to form high quality diamond in a simple apparatus. (2) No thermal means is employed while the base material is not additionally heated by generation of plasma dissimilarly to plasma CVD, whereby it is possible to form high quality diamond at a lower temperature such as that of not more than about 300°C, for example, by generating efficiently excited active species on the base material and in a portion extremely close to the base material. (3) The raw material containing carbon atoms can be decomposed/excited with a laser beam of a wavelength allowing no absorption, whereby it is possible to form diamond without staining a window for the laser beam by decomposing the raw material gas only in a region on which the laser beam is focused or a region close thereto. (4) Diamond can be deposited by decomposing the raw material gas in a portion on which the laser beam is condensed, whereby it is possible to form diamond on an arbitrary region of a base material having a complicated shape by three-dimensionally driving the laser beam and the base material. (5) It is possible to obtain a homogeneous and flat diamond film by linearly focusing the laser beam and uniaxially driving the base material. (6) It is possible to freely control the thickness of the diamond film by changing the operation speed for the base material, laser energy density, the laser oscillation pulse number and the like. Example 1 An ordinary vacuum vessel was employed as a chamber for laser CVD, and a raw material gas was prepared from a mixed gas containing 99 % of hydrogen and 1 % of methane. A glass base material was scraped with diamond abrasive grains of #5000 and then stored in the vacuum vessel, which in turn was supplied with the raw material gas under decompression in accordance with a conventional method. Then, the base material was heated with a kanthal heater to about 300°C , and a portion of about 1 mm above the glass base material was irradiated with an XeCl excimer laser beam, which was obtained by amplifying/oscillating seed light whose band was narrowed by a grating and a prism, through a window of fused quartz provided in the vacuum vessel. The current half-power band width of the laser beam measured a Fabry-Pérot interferometer was about 1.0 x 10⁻¹ nm. Further, the laser energy was about 100 mJ. The temperature was measured with a thermocouple. After irradiation with the laser beam for about 1 hour, the base material was taken out from the vacuum vessel and analyzed, whereby the as-formed film exhibited a Raman spectrum shown in Fig. 2. A strong diamond peak (1333 cm⁻¹) was recognized in this spectrum, to prove that a high quality diamond film was obtained. This diamond film had a thickness of about 0.1 µm. Example 2 A base material was prepared from an aluminum base material, and a raw material gas was prepared from a mixed gas containing 99 % of hydrogen and 1 % of methane. The base material was stored in a vacuum vessel, which in turn was supplied with the raw material gas in accordance with a conventional method. Then, an XeF excimer laser beam, which was obtained by amplifying/oscillating seed light whose band was narrowed by a grating and a prism with an instable resonator, was condensed on a portion of about 1 mm above the aluminum base material through a window of fused quartz provided in the vacuum vessel. The current half-power band width of the laser beam measured with a FabryPérot interferometer was about 1.0 x 10⁻⁴ nm. Further, the laser beam had a spread angle of about 5 x 10⁻² mrad and laser energy of about 100 mJ. The temperature was measured with a thermocouple, and the base material was heated to about 200°C with a kanthal heater in CVD. After irradiation with the laser beam for about 1 hour, the base material was taken out from the vacuum vessel and analyzed, whereby a film exhibiting a Raman spectrum shown in Fig. 3 was obtained. This Raman spectrum, which had a strong diamond peak (1333 cm⁻¹), indicated that a high quality di'amond film was formed. The as-obtained diamond film had a thickness of about 0.7 µm. Example 3 An aluminum base material was stored in an ordinary vacuum vessel, which in turn was supplied with a raw material gas containing 99 % of hydrogen and 1 % of methane. The base material was heated with a kanthal heater to about 400°C, and an ArF excimer laser beam which was oscillated with an instable resonator was condensed on a portion of about 1 mm above the heated aluminum base material. At this time, the laser beam exhibited a spread angle of about 1.0 x 10⁻² mrad, with laser energy of about 500 mJ. The temperature was measured with a thermocouple. After irradiation with the laser beam for about 1 hour, the base material was taken out from the vacuum vessel and subjected to Raman spectral analysis, whereby it was proved that a high quality diamond film was formed on the base material. The as-obtained diamond film had a thickness of about 0.1 µm. Example 4 A raw material gas was prepared by adding 5 % of argon gas to the mixed gas containing 99 % of hydrogen and 1 % of methane employed in Example 1, 2 or 3. An aluminum base material was stored in an ordinary vacuum vessel, which in turn was supplied with the raw material gas. Then the base material was heated with a kanthal heater to about 200°C, and an XeCl excimer laser beam, which was obtained by amplifying/oscillating seed light whose band was narrowed by a grating and a prism with an instable resonator, was condensed on a portion of about 1 mm above the heated aluminum base material through a window of fused quartz. The current half-power band width of the laser beam measured with a Fabry-Pérot interferometer was about 1.0 x 10⁻⁴ nm. The laser beam had a spread angle of about 1.0 x 10⁻² mrad, with laser energy of about 100 mJ. The temperature was measured with a thermocouple. After irradiation with the laser beam for about 1 hour, the base material was taken out from the vacuum vessel and analyzed, whereby it was proved that a high quality diamond film was obtained. The diamond film had a thickness of about 1.2 µm. Example 5 A raw material gas was prepared by adding 1 % of helium to a mixed gas containing 99 % of hydrogen and 1 % of methane. An aluminum base material was stored in an ordinary vacuum vessel, which in turn was supplied with the raw material gas in accordance with a conventional method. Then, an ArF excimer laser beam, which was obtained by amplifying/oscillating seed light whose band was narrowed by a grating and a prism with an instable resonator, was condensed on a portion of about 1 mm above the aluminum base material through a window of fused quartz provided in the vacuum vessel. The current half-power band width of the laser beam measured with a Fabry-Pérot interferometer was about 1.0 x 10⁻⁴ nm. Further, the laser beam had a spread angle of about 1.0 x 10⁻² mrad, with laser energy of about 100 mJ. The base material was heated with a kanthal heater to about 200°C, and the temperature was measured with a thermocouple. After irradiation with the laser beam for about 1 hour, the base material was taken out from the vacuum vessel and analyzed, whereby it was proved that a high quality diamond film was formed on the base material. This diamond film had a thickness of about 1.5 µm. Example 6 An aluminum base material was stored in an ordinary vacuum vessel, which in turn was supplied with a raw material gas containing 99 % of hydrogen and 1 % of methane. An ArF excimer laser, which was obtained by amplifying/oscillating seed light whose band was narrowed by a grating and a prism with an instable resonator, was condensed on a portion of about 1 mm above the aluminum base material through a window of fused quartz provided in the vacuum vessel. The laser beam had a spread angle of about 5 x 10⁻² mrad, with a half-power band width, measured with a Fabry-Pérot interferometer, of about 1.0 x 10⁻⁴ nm and laser energy of about 100 mJ. The laser beam was linearly condensed with a cylindrical lens in irradiation. In irradiation with such a laser beam, the aluminum base material was heated with a kanthal heater to about 200°C, and rotated at 60 r.p.m. The temperature was verified with a thermocouple. After irradiation with the laser beam for about 10 minutes, the base material was taken out from the vacuum vessel and analyzed, whereby it was proved that a high quality diamond film was homogeneously formed on a substrate of 60 mm in diameter. The diamond film had a thickness of about 0.5 µm. Example 7 An alumina base material was stored in an ordinary vacuum vessel, which in turn was supplied with a raw material gas containing 99 % of hydrogen and 1 % of methane. The alumina substrate was irradiated with an ArF excimer laser beam, which was obtained by amplifying/oscillating seed light whose band was narrowed by a grating and a prism with an instable resonator and homogenizing its energy profile with a homogenizer prepared by combining a prism and a lens, through a window of fused quartz provided in the vacuum vessel. The current half-power band width of the laser beam measured with a Fabry-Pérot interferometer was about 1.0 x 10⁻⁴ nm. This laser beam had a spread angle of about 5 x 10⁻² mrad, while the difference between maximum and minimum levels of energy distribution observed with a profiler was about 9.5 % of the average energy intensity. The laser energy was about 100 mJ. In irradiation, a convex lens was employed to focus the laser beam to 1 mm by 3 mm square. The aluminum base material was heated with a kanthal heater to about 200°C, and parallelly driven by 10 mm at a constant velocity. The temperature was verified with a thermocouple. After irradiation with the laser beam for 10 minutes, the base material was taken out of the vacuum vessel and analyzed, whereby it was proved that a high quality diamond film was homogeneously formed with a width of 3 mm and a length of 10 mm. This film had a thickness of about 0.5 µm. Example 8 A polyethylene base material was preparatorily scraped with diamond powder having the diameter of 1 - 10 µm. The polyethylene base material was stored in an ordinary vacuum vessel, which in turn was supplied with a row material gas containing 99 % of hydrogen, 0.5 % of methane and 0.5 % of carbon monoxide. The pressure in the vessel was about 54 mbar (40 Torr). The base material was irradiated with an ArF excimer laser beam, which was obtained by amplifying/oscillating seed light whose band was narrowed by a grating and a prism with an instable resonator and homogenizing its energy profile with a homogenizer prepared by combining a prism and a lens. The current half-powder band width of the laser beam measured with a Fabry-Pérot interferometer was about 1.0 x 10⁻⁴ nm. This laser beam had a spread angle of about 5 x 10⁻² mrad. In irradiation, the laser beam was focused to a diameter of 30 µm with a convex lens having a 500 mm focus. The base material was parallely driven by 10 mm at a constant velocity. The film formation was performed at room temperature. The temperature was verified with a thermocouple. The laser energy was about 120 mJ. After irradiation with the laser beam for 10 minutes, the base material was taken out from the vacuum vessel and analyzed, whereby it was proved that a high quality diamond film was homogeneously formed with a width of 3 mm and a length of 10 mm. This film had a thickness of about 0.5 µm. Comparative Example A raw material gas was prepared from a mixed gas containing 99 % of hydrogen and 1 % of acetylene. An Si base material, capable of easily obtaining diamond having relatively excellent crystallinity, was stored in an ordinary vacuum vessel, which in turn was supplied with the raw material gas in accordance with a conventional method. Then, the base material was irradiated with an ArF excimer laser under conditions of a spread angle of about 3 mrad, a half-power band width of about 2 nm, and laser energy of about 100 mJ in accordance with the prior art. At this time, the base material was heated to about 300°C. When the base material was thus irradiated with the laser beam in accordance with the prior art , only sooty products adhered onto the base material, with formation of no diamond. In laser irradiation, dc plasma was added and the substrate temperature was set at a relatively high level of about 700°C, to experimentally synthesize diamond. As the result, a Raman spectrum shown in Fig. 4 was obtained, while a diamond peak at 1333 cm⁻¹ was extremely weak and broad in this spectrum. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: A method of synthesizing diamond on a base material from the vapor phase using a raw material gas prepared by diluting a compound containing carbon atoms with gaseous hydrogen, said method comprising: irradiating said raw material gas or said base material with a laser beam having a wavelength within a range of 190nm to 360nm and satisfying at least one of the following conditions: (1) the spread angle in oscillation is within a range of at least 1 x 10⁻² mrad and not more than 5 x 10⁻¹ mrad (2) the half-power band width with respect to the band width of the oscillation wavelength is within a range of at least 1 x 10⁻⁴ nm and not more than 1 x 10⁻¹ nm thereby decomposing said raw material gas, and depositing diamond on said base material. A method in accordance with claim 1, wherein dispersion of energy intensity in a plane perpendicular to the optical axis of said laser beam is not more than 10 % of average energy intensity. A method in accordance with claim 1, wherein said raw material gas includes at least one gas selected from the group consisting of helium, argon, neon, krypton, xenon and radon. A method in accordance with claim 1, wherein said compound containing carbon atoms is a saturated hydrocarbon. A method in accordance with claim 4, wherein said saturated hydrocarbon is methane. A method in accordance with claim 1, wherein said raw material gas contains methane, hydrogen, and at least one gas selected from the group consisting of helim, argon, neon, krypton, xenon and radon. A method in accordance with claim 1, wherein said base material is moved relatively to said laser beam. A method in accordance with claim 1, wherein said laser beam is linearly focused on said base material and said base material is translated relatively to said laser beam. A method in accordance with claim 1, wherein said laser beam is linearly focused on said base material and said base material is rotated relatively to said laser beam. A method in accordance with claim 1, wherein said base material is heated at a temperature of not more than 300°C. A method in accordance with claim 1, wherein the laser source is selected from the group consisting of an ArF excimer laser, a KrCl excimer laser, a KrF excimer laser, an XeCl excimer laser, an N₂ excimer laser and an XeF excimer laser.

Inventors: FUJIMORI NAOJI C O ITAMI WORKS, OTA NOBUHIRO C O ITAMI WORKS O, WATANABE KENICHI C O ITAMI WOR, FUJIMORI, NAOJI, C/O ITAMI WORKS OF SUMITOMO, OTA, NOBUHIRO, C/O ITAMI WORKS OF SUMITOMO, WATANABE, KENICHI, C/O ITAMI WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1993
Main classification: C23C16
IPC codes: C23C16, C30B25, C30B29