Apparatus for synthesizing diamondlike thin film

Abstract: A method of and an apparatus for synthesizing a diamondlike thin film on a substrate, the method comprising the steps of: generating plasma of gas containing hydrocar­ bon gas, in a first vacuum vessel having an inflow portion and an outflow portion for the gas such that the substrate is provided in a second vacuum vessel maintained at a pressure lower, by one figure or more, than that of the first vacuum vessel due to flow resistance of the gas between the outflow portion and the substrate; and irradiat­ ing the plasma onto the substrate by pressure difference between the first vacuum vessel and the second vacuum vessel while an AC power is being applied to at least one of the substrate and an internal electrode provided in the first vacuum vessel.

Description: BACKGROUND OF THE INVENTION The present invention generally relates to an apparatus for synthesizing a diamondlike thin film by using plasma of hydrocarbon gas such that, especially, an excellent diamondlike like thin film can be synthesized also on an insulation substrate in the same manner as on an electrically conductive substrate. A diamond thin film has excellent characteristics of hardness, electric resistent, light transmittance, etc. equivalent to those of diamond and is expected to be applied to wear-resistant protective films for various electronic apparatuses of components and passivation films. Various methods of and apparatuses for synthesizing the diamondlike thin film are known. EP-A-0183254 discloses an apparatus comprising a first vacuum vessel which has an inflow portion and an outflow portion for gas containing hydrocarbon gas, a plasma generating means for converting the gas into plasma in the first vacuum vessel, a second vacuum vessel which is coupled with the first vacuum vessel so as to allow the gas to flow between the first and the second vacuum vessels. The substrate is provided at such a position as to set a pressure in the second vacuum vessel lower than that of the first vacuum vessel. An AC power source is provided for applying an AC potential. This known apparatus further comprises a mesh type electrode which is provided upstream of the substrate in a flow path of the gas between the first vacuum vessel and the second vacuum vessel. In the operation of another known apparatus, where the diamondlike thin film is synthesized also on the mesh type electrode during synthesis of the diamondlike thin film on the substrate, when thickness of the diamondlike thin film synthesized on the mesh type electrode exceeds a predetermined value, the diamondlike thin film is readilly separated from the mesh type electrode and, thus, pieces of the diamondlike thin film separated from the mesh type electrode reach the substrate. In this case, the separated pieces of the diamondlike thin film are undesirably included, as foreign matter, into the diamondlike thin film synthesized on the substrate. SUMMARY OF THE INVENTION Accordingly, an essential object of the present invention is to provide, with view of eliminating the above described inconvenience, an apparatus for synthesizing diamondlike thin film, by which the undesirable inclusion of separated pieces of the diamondlike thin film from the mesh type electrode into the diamondlike thin film synthesized on the substrate is prevented. In order to accomplish this object, according to the present invention there is provided an apparatus for synthesizing a diamondlike thin film on a substrate, comprising a first vacuum vessel which has an inflow portion and an outflow portion for gas containing hydrocarbon gas, a plasma generating means for converting the gas into plasma in said first vacuum vessel, a second vacuum vessel which is coupled with said first vacuum vessel so as to allow the gas to flow between said outflow portion of said first vacuum vessel and said second vacuum vessel and has a pressure lower than that of said first vacuum vessel, said substrate being provided in said second vacuum vessel, a mesh type electrode which is provided upstream of said substrate in a flow path of the gas between said first vacuum vessel and said second vacuum vessel, and a voltage applying means for applying a voltage to said mesh type electrode, characterized by a supply means for continously supplying a clean portion of said mesh type electrode to a front of said substrate. According to the invention, the above mentioned inconvenience is eliminated by providing a supply means for continously supplying a clean portion of the mesh type electrode to a front of the substrate. Namely, since the clean mesh type electrode free from foreign matter confronts the substrate at all times, such a phenomenon does not occure that the separated pieces of the diamondlike thin film are scattered towards the substrate from the mesh type electrode, so that the diamondlike thin film of high quality substantially free from inclusion of foreign matter for a long time can be synthesized on the substrate. A further advantage of the present invention is that a diamondlike thin film of high quality uniform in characteristics and thickness can be stably synthesized on even an insulating substrate at high speed. Furthermore, in the present invention, maintainance operations such as cleaning of the vacuum vessel is not required to be performed substantially, thereby resulting in an improvement of operating condition. Thus, in accordance with the present invention, industrial application of the diamondlike thin film can be extended to wear-resistant protective films for various electronic apparatuses or components, passivation films, etc. BRIEF DESCRIPTION OF THE DRAWINGS This object and features of the present invention will become apparent from the following description taking in conjunction with the preferred embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 is a schematic view of an apparatus for synthesizing a diamondlike thin film according to a first embodiment of the present invention; and Fig. 2 is a schematic view of an apparatus for synthesizing a diamondlike thin film according to a second embodiment of the present invention. DETAILED DESCRIPTON OF THE INVENTION Referring now to the drawings, there is shown in figure 1, an apparatus for synthesizing a diamondlike thin film, according to a first embodiment of the present invention. This apparatus includes a first vacuum vessel 73 and a second vacuum vessel 78. A distal end of the first vaccum vessel 73 is drawn like a nozzle. A mixed gas 75 of methane gas acting as raw material and argon gas acting as auxiliary gas is introduced into the first vacuum vessel 73 from an inflow portion 74. A mesh type internal electrode 76 is provided in the first vacuum vessel 73. The first vacuum vessel 73 is coupled with the second vacuum vessel 78 by a flange such that the first and second vacuum vessels 73 and 78 are evacuated by a vacuum pump 79. A substrate 66 is provided in the second vacuum vessel 78 so as to be disposed in front of an outflow portion 69 of the first vacuum vessel 73. A mesh type electrode 68 is provided between the outflow portion 69 and the substrate 66. The mesh type electrode 68 has a long band-like shape. At the time of synthesis of the diamondlike thin film, the mesh type electrode 68 is displaced in the direction of the arrow A in Fig. 1 by a pair of continuous winding and rewinding rollers 67 acting as an electrode supply means. Thus, a new and clean mesh type electrode free from the diamondlike thin film is supplied in front of a substrate at all times. Hereinbelow, one example of synthesis of the diamondlike thin film in the apparatus is described. A film made of organic photosensitive material is employed as the substrate 66. Initially, the film 66 is loaded on a film transport mechanism 65 in the second vacuum vessel 78. Then, the first and second vacuum vessels 73 and 78 are evacuated to a pressure of 1,33·10⁻³ Pa (1x10⁻⁵ Torr) by the pressure pump 79. Subsequently, the mesh type electrode 68 is displaced in the direction of the arrow A by the continuous winding and rewinding rollers 67 and the film 66 is transported in the direction of the arrow B by the film transport mechanism 65. Thereafter, the mixed gas 75 of methane gas and argon gas is introduced into the first vacuum vessel 73 from the inflow portion 74 and thus, the first vacuum vessel 73 is set at a pressure of 40 Pa (0.3 Torr). Furthermore, a DC potential of -500 V is applied to the mesh type electrode 68 relative to an internal electrode 76 by a DC power source 77. Meanwhile, when an RF power of 170 W is applied to an excitation electrode 71 by an RF power source 72, plasma 70 is generated in the first vacuum vessel 73 such that the diamondlike thin film is synthesized on the film 66. At this time, pressure in the second vacuum vessel 78 is 9,31·10⁻² Pa (7x10⁻⁴ Torr) and no plasma is generated in the second vacuum vessel 78. In this embodiment, when the diamondlike thin film of 0.1 µm in thickness is uniformly synthesized on the film 66 having a length of 100 m and a width of 30 cm by setting feed rate of the mesh type electrode 68 at 0.1 m/min. or more, no foreign matter such as pieces of the diamondlike thin film separated from the mesh type electrode 68 is included into the diamondlike thin film synthesized on the film 66. When this feed rate of the mesh type electrode 68 is too small, inclusion of foreign matter into the diamondlike thin film takes place undesirably. When the diamondlike thin film has been synthesized on a whole face of the film 66 as described above, the first and second vacuum vessel 73 and 78 are communicated with atmosphere and the film 66 is removed from the film transport mechanism 65 such that processing for the next film 66 is started. At this time, the diamondlike thin film has already been synthesized on the mesh type electrode 68. Therefore, it is desirable to replace the used mesh type electrode 68 with a new one. Meanwhile, in this embodiment, the plasma is generated by the RF power source 72 and the excitation coil 71 and ions are removed by the DC power source 77 and the mesh type electrode 68. However, it can also be so arranged that the DC power source and the mesh type electrode serve not only to generate the plasma but to remove ions. Fig. 2 shows an apparatus according to a second embodiment of the present invention. In this apparatus, the mesh type electrode 68 of the apparatus of the first embodiment can be used repeatedly by removing substances adhering to the mesh type electrode 68 such that the diamondlike thin film can be synthesized on the further longer film. Operations of synthesis of the diamondlike thin film in the apparatus of the second embodiment are similar to those of the first embodiment. The apparatus includes removal portions 87 and 87a for removing substances adhering to a mesh type electrode 82. The removal portions 87 and 87a are, respectively, separated from a second vacuum vessel 99 by partition walls 91 and 91a. The partition walls 91 and 91a have openings 92 and 92a for passing the mesh type electrode 82 therethrough, respectively. The removal portions 87 and 87a employ oxygen plasma etching. The removal portions 87 and 87a are, respectively, evacuated by vacuum pumps 88 and 88a simultaneously with evacuation of a first vacuum chamber 94 and the second vacuum vessel 99 by a vacuum pump 102. Subsequently, oxygen gases 83 and 83a are, respectively, introduced into the removal portions 87 and 87a so as to set the removal portions 87 and 87a at a pressure of 13,3 Pa (0.1 Torr). Thereafter, a DC voltage is applied to electrodes 89 and 89a of the removal portions 87 and 87a by DC power sources 90 and 90a so as to generate oxygen plasmas 84 and 84a in the removal portions 87 and 87a, respectively. A number of particles such as oxygen radicals and oxygen ions are present in the oxygen plasmas 84 and 84a and these particles cause vigorous oxidation reaction with carbon, a constituent element of the diamondlike thin film so as to change the carbon into carbon monoxide, carbon dioxide, etc. such that these carbon monoxide, carbon dioxide, etc. are discharged into the removal portions 87 and 87a. Since this oxidation reaction takes place vigorously at the side of positive potential, it is preferable that the mesh type electrode 82 has positive potential relative to the electrodes 89 and 89a as shown in Fig. 2. Configuration and size of the removal portions 87 and 87a and operating conditions of the removal portions 87 and 87a are so set that the diamondlike thin film synthesized on the mesh type electrode 82 is sufficiently removed by the removal portions 87 and 87a. As described above, in this embodiment, the removal portions are provided for effectively removing the diamondlike thin film synthesized on the mesh type electrode 82. Since the mesh type electrode 82 is reciprocated by continuous winding and rewinding rollers 86 and 86a while being cleaned by the removal portions 87 and 87a, a clean portion of the mesh type electrode 82 can be so set as to confront a face of a film 81 at all times. Therefore, it becomes possible to synthesize the diamondlike thin film on the film 81 of large capacity. As a result, in this embodiment, the diamondlike thin film of 0.1 µm in thickness free from foreign matter such as pieces of the diamondlike thin film separated from the mesh type electrode 82 can be uniformly synthesized on the film 81 of 500 m in length and 30 cm in width by setting feed rate of the mesh type electrode 82 at 0.1 m/min. or more. When this feed rate of the mesh type electrode 82 is too small, foreign matter is undesirably included into the diamondlike thin film. Meanwhile, in this embodiment, the second vacuum vessel 99 accommodating the film 81 subjected to synthesis of the diamondlike thin film is separated from the removal portions 87 and 87a by the partition walls 91 and 91a having the openings 92 and 92a for passing the mesh type electrode 82 therethrough, respectively. The partition walls 91 and 91a are primarily designed to prevent such a phenomenon in which oxygen gas in the removal portions 87 and 87a leaks into the second vacuum vessel 99 and thus, adversely affects synthesis of the diamondlike thin film. Therefore, in this case, it is desirable that each of the openings 92 and 92a has a size smaller than a sum of thickness of the mesh type electrode 82 and mean free path of gaseous molecules at pressure in the removal portions 87 and 87a. This size of each of the openings 92 and 92a is not restricted to the above description but can be properly selected in accordance with synthesis conditions of the diamondlike thin film, removal methods employed in the removal portions 87 and 87a, removal conditions of the removal portions 87 and 87a, etc. Meanwhile, the above described oxidation reaction in the removal portions 87 and 87a is promoted by, for example, heating the mesh type electrode 82 with a halogen lamp or the like. Therefore, by providing such heating means in the removal portions 87 and 87a, it is also possible to make the mesh type electrode 82 more compact. Furthermore, in this embodiment, oxygen plasma etching is employed in the removal portions 87 and 87a but instead, plasma etching and ion beam etching which utilize at least one of hydrogen, fluorine and inert elements may also be employed. Furthermore, it can also be so arranged that, for example, a brush made of stainless steel is additionally brought into direct sliding contact with the mesh type electrode 82 so as to mechanically scrape the diamondlike thin film from the mesh type electrode 82. Moreover, in this embodiment, plasma 95 is generated by an RF power source 97 and an excitation coil 96, while ions are removed by a DC power source 101 and the mesh type electrode 82. However, it can also be so arranged that the DC power source 101 and the mesh type electrode 82 not only generate the plasma 95 but remove ions. Meanwhile, also in this embodiment, such gases as ethylene, ethane, butane, benzene, pentane and propane may be used independently or mixedly as the hydrocarbon gas. Furthermore, rare gases such as helium, krypton and xenon or auxiliary gas such as hydrogen may be added to the above described gases used as the hydrocarbon gas. The substrate may be made of electrically conductive material such as stainless steel or insulating material such as plastics, etc. In addition, the substrate may have a solid shape, a platelike shape or a filmy shape.

Claims: An apparatus for synthesizing a diamondlike thin film on a substrate (66; 81), comprising: a first vacuum vessel (73; 94) which has an inflow portion (74) and an outflow portion (69; 100) for gas containing hydrocarbon gas (75; 107); a plasma generating means (71, 72; 96, 97) for converting the gas into plasma (70; 95) in said first vacuum vessel (73; 94); a second vacuum vessel (78; 99) which is coupled with said first vacuum vessel (73; 94) so as to allow the gas to flow between said outflow portion (69; 100) of said first vacuum vessel (73; 94) and said second vacuum vessel (78; 99) and has a pressure lower than that of said first vacuum vessel (73; 94); said substrate (66; 81) being provided in said second vacuum vessel (78; 99); a mesh type electrode (68; 82) which is provided upstream of said substrate (66; 81) in a flow path of the gas between said first vacuum vessel (73; 94) and said second vacuum vessel (78; 99); and a voltage applying means (77; 101) for applying a voltage to said mesh type electrode (68; 82); characterized by a supply means (67; 86, 86a) for continuously supplying a clean portion of said mesh type electrode (68; 82) to a front of said substrate (66; 81). An apparatus as claimed in Claim 1, further comprising: a removal means (87, 87a) for removing the diamondlike thin film synthesized on said mesh type electrode (82), which is separated from said second vacuum vessel (99) by a partition wall (91, 91a) having an opening (92, 92a) for passing said mesh type electrode (82) therethrough; wherein the diamondlike thin film synthesized on said mesh type electrode (82) is removed from said mesh type electrode (82) by said removal means (87, 87a) such that the clean portion of said mesh type electrode (82) is continuously supplied to the front of said substrate (81) by said supply means (86, 86a). An apparatus as claimed in Claim 2, wherein plasma etching utilizing at least one of oxygen, hydrogen, fluorine and inert elements is employed in said removal means (87, 87a). An apparatus as claimed in Claim 2, wherein ion beam etching utilizing at least one of oxygen, hydrogen, fluorine and inert elements is employed in said removal means (87, 87a). An apparatus as claimed in anyone of Claims 1 to 4, wherein said substrate (66; 81) is provided at such a position as to set a pressure in said second vacuum vessel (78; 99) lower, by one figure or more, than that of said first vacuum vessel (73; 94) due to flow resistance of the gas between said outflow portion (69; 100) and said substrate (66; 81).

Inventors: KUROKAWA HIDEO, MITANI TSUTOMU, NAKAUE HIROKAZU, KUROKAWA, HIDEO, MITANI, TSUTOMU, NAKAUE, HIROKAZU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1990
Main classification: C23C16
IPC codes: C23C16, H01J37