JPH0518795B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method and apparatus for depositing diamond on a substrate from a gas phase. (Prior Art and its Problems) Several methods are conventionally known for synthesizing diamond by thermal decomposition of carbon compound gas. For example, the Journal of Non-Crystalline Solites, published in 1980.
Nou-Crystalline Solids) Volumes 35 & 36, Page 435, the paper uses glass or molybdenum-deposited glass as the substrate, the pressure is 0.9 Torr, the gas flow rate is 0.5 to 7.0 cc per minute, the substrate temperature is 25 to 375 degrees Celsius, and the discharge current is Under the conditions of 0.8~2mA, discharge voltage 300~400V,
It is stated that amorphous carbon film was obtained by decomposing acetylene by direct current glow discharge.
The electrical resistivity of the amorphous carbon film is:
It has a maximum resistance of 10 ¹⁶ Ωcm and is excellent in that it provides an insulating carbon film, but it has the disadvantage that the carbon film will peel off from the substrate if the film thickness exceeds 1 μm or if it is heat treated. Further, when the substrate temperature is high, the carbon film becomes black and graphite-like. Furthermore, it has the disadvantage that a crystalline diamond film cannot be synthesized. Still another method is to generate plasma by microwave discharge or high frequency discharge from a reaction gas under reduced pressure, place a substrate directly in the plasma or during the afterglow of the plasma, and deposit diamond on the substrate. Alternatively, there is a method of synthesizing film-like diamond by bombarding a substrate with ionized carbon, but the former method has the disadvantage that the substrate must be heated to a high temperature in order to obtain a diamond phase. Furthermore, since the substrate is placed in plasma, plasma damage to the substrate is unavoidable. The latter method is an excellent method in that it allows diamond to be synthesized at around room temperature, but it has the disadvantage that the equipment is expensive. Furthermore, since the ions are drawn out in a beam shape, the beam intensity is uneven, making it impossible to obtain a uniform diamond phase over a wide area. In addition, a normal DC glow discharge device is equipped with two electrodes facing each other, and a substrate is placed on one of the electrodes, and a DC voltage is applied between the electrodes to generate a DC glow discharge. The structure is such that a thin film is synthesized on the The above configuration has the drawback that accelerated ions are directly incident on the substrate, causing spatter on the substrate, and atoms constituting the substrate are mixed into the thin film to be synthesized. Furthermore, when an insulating thin film is grown on the substrate,
The disadvantage is that the discharge is difficult to sustain. (Object of the present invention) The purpose of the present invention is to eliminate such conventional drawbacks, and to create a transparent diamond thin film that has a flat surface and strong adhesion to the substrate, and prevents the incorporation of substrate atoms. The object of the present invention is to provide a method and apparatus for synthesizing diamond that can be produced at low temperatures. (Structure of the Invention) That is, the present invention provides a method for forming diamond on a substrate by decomposing and exciting carbon compound gas or vapor in a direct current glow discharge, in which a screen mesh is installed between two opposing electrodes. Then, a DC voltage is applied between one electrode and the screen mesh to generate a DC glow discharge, a substrate is placed on the other independent electrode to which a DC voltage is applied, and a diamond is formed on the substrate. A diamond vapor phase synthesis method is characterized in that the method includes a vacuum chamber to which a gas supply section and a vacuum exhaust system are connected, two electrodes facing each other inside the vacuum chamber, and a substrate is placed on one of the electrodes. This diamond vapor phase synthesis apparatus is equipped with a movable screen mesh between two opposing electrodes. (Detailed Description of Configuration) The present invention solves the problems of the prior art by adopting the above-described configuration. Generally, to synthesize diamond from a gas phase, a gas or vapor of a carbon compound is used as a carbon source. However, the process of diamond precipitation from the gas phase requires artificial manipulation to stabilize a thermodynamically metastable phase. It is obvious that non-diamond carbon will be deposited on the substrate if free carbon atoms are obtained only from the thermal decomposition of the reactant gas. In addition, even in methods that utilize plasma, the process of synthesizing diamond using only a single excitation process lacks energy.
Stable precipitation of diamond requires high temperatures and also results in the production of non-diamond carbon as a by-product. Therefore, in the process of synthesizing diamond from the gas phase, if there is a process that adds more energy to the decomposed and excited species in addition to the process of decomposing and exciting the reaction gas, it is possible to effectively synthesize diamond at low temperatures. . The method of the present invention involves forming a direct current glow discharge region between a screen mesh installed between opposing electrodes with a carbon compound gas or vapor and an electrode with no substrate installed, and forming a direct current glow discharge region between a screen mesh installed between opposing electrodes and an electrode installed on another electrode. By diffusing charge-neutral active species into a charged substrate or by applying an independent potential to the substrate, positively or negatively charged active species are accelerated or decelerated to collide with the substrate. This is a method in which diamond is deposited on a substrate. That is, the principle of the present invention is to first generate active species necessary for vapor phase synthesis of diamond in a DC glow discharge region between a screen mesh and an electrode on which no substrate is installed, and then to generate active species on another electrode. Let it spread to the installed board. Here, in order to prevent glow discharge from occurring between the screen mesh and the electrode on which the substrate is placed, and to accelerate or decelerate positively or negatively charged active species, apply an appropriate potential to the electrode on which the substrate is placed. By colliding these active species on the substrate, chemically stable SP bonds and SP ² bonds are cut, and only diamond with SP ³ bonds is precipitated on the substrate. The collision of the charged active species with the substrate improves the adhesion of the diamond thin film to the substrate. The role of hydrogen in the process of growing diamond is complex, but it is thought that it mainly becomes atomic hydrogen in the plasma, and carbon with SP and SP ² bonds precipitated on the substrate, that is, non-diamond carbon, is converted into hydrocarbons and removed. Therefore, it is thought that using a carbon compound gas or vapor mixed with hydrogen gas as the reaction gas is more effective in removing non-diamond carbon. Conventionally, substrates and synthetic materials that can be used in the DC glow discharge method have been limited to materials with low resistance, ie, conductors or semiconductors, in order to maintain stable glow discharge. In the present invention, DC glow discharge is performed using an electrode without a substrate and a screen.
Since the conditions are such that no glow discharge is generated between the meshes and between the electrodes on which the screen mesh and the substrate are installed, it is possible to use an insulating substrate, which has been difficult in the past. Furthermore, an insulating thin film can also be stably deposited. It is conceivable to mix a rare gas into the carbon compound gas or vapor as a gas that facilitates discharge, but if argon gas, which is particularly easy to discharge, is used, the discharge pressure range can be expanded. Atomic hydrogen is said to play an important role in the method of synthesizing diamond from the gas phase, and diamond can also be efficiently synthesized by mixing hydrogen into the gas or vapor of carbon compounds. . In the method of the present invention, the selection of the distance between the screen mesh to which an appropriate bias voltage is applied and the electrode on which the substrate is placed is decelerated or accelerated;
Diamond synthesis conditions are important because they determine the conditions under which charged active species move in the reaction gas and collide with the substrate, and determine the diffusion state of charge-neutral active species generated within the DC glow discharge region. This is an important factor. Although it is desirable that the distance be short, specifically, it is desirable to install the screen mesh from the center of the opposing electrodes directly above the electrode on which the substrate is installed. Furthermore, control of the screen mesh is also important in order to maintain stable DC glow discharge. That is,
High resistance or insulating substances, which are decomposition products of hydrocarbons, tend to deposit on the screen mesh, clogging the pores of the screen mesh and causing charge accumulation, which can lead to fluctuations in DC glow discharge conditions. Currently, stable growth is prevented, but as in the configuration of the device of the present invention, the screen mesh is moved parallel to the two electrode surfaces facing each other in parallel, so that new surfaces are always created. By directing it toward the electrode, the above-mentioned drawbacks can be eliminated. Various methods can be considered for the moving mechanism, but in consideration of the fact that it can be operated for a long time, two rolls are used, and the screen mesh is wound on one roll and then wound on the other roll. A possible mechanism is possible. Hereinafter, examples of the apparatus and manufacturing process used in the present invention will be explained in detail with reference to the drawings. The surface of the substrate used in the present invention has been cleaned using an etching agent suitable for the substrate as a pretreatment. In the figure, after a cleaned substrate 5 is placed on an electrode 6, the inside of the vacuum chamber 1 is preliminarily evacuated to 10 ^-3 Torr with a rotary pump 9, and heated with a heater 7 to a predetermined temperature. Hydrocarbon gas cylinder 10,
The tanks 13, 14, 15 from the hydrogen gas cylinder 11 or the rare gas cylinder 12 are opened to introduce a predetermined reaction gas into the vacuum chamber 1, and the pressure regulator 8 is used to maintain a predetermined pressure. DC glow discharge is generated by applying an appropriate bias voltage between the grounded screen mesh 3 and electrode 6 so that no glow discharge occurs, and applying a positive or negative DC voltage of several hundred volts to electrode 2. . Bias voltages up to ±100 volts are valid. Screen mesh 3 has two rolls 1
Screen mesh moving mechanism 4 consisting of 6 and 17
can be moved parallel to the electrodes 2 and 6. Furthermore, the screen mesh 3 and the screen mesh moving mechanism 4 can be moved perpendicular to the electrodes 2 and 6 in order to determine the optimum screen mesh position. (Example) A DC glow discharge was generated between a grounded screen mesh by applying a positive or negative DC voltage of several hundred volts to an electrode on which no substrate was installed. The discharge current density was 1 mA/cm ² . A voltage of +100 volts to -100 volts was applied to the substrate. Pressure is 1 Torr, reaction time is 1 hour, temperature
It was kept constant at 200℃. The position of the screen mesh was expressed as a relative value, with the distance between the two electrodes being 100 and the position of the substrate being 0. Table 1 shows the experimental conditions, the identification results using a transmission vortex electron microscope, and the experimental results of the adhesion force using the scratching method. When the screen mesh was fixed, the discharge became unstable and a uniform film could no longer be deposited after several tens of minutes of reaction time, but when the screen mesh was moved at a rate of 5 cm per minute, a uniform interference color appeared over the entire surface of the substrate. A diamond thin film exhibiting the following properties was obtained. Note that a screen mesh of 20 to 100 meshes is appropriate, and in this example, 80 meshes were used.

[Table] (Effects of the present invention) According to the present invention, a diamond thin film was synthesized at a low temperature with a large adhesion force. The adhesion of the film obtained by the conventional method is several tens of grams, so the adhesion force of the film synthesized by the method of the present invention is several times greater, and it can be used as a surface protection film for surface passivation of semiconductor devices, tools, etc. The range of applications has expanded, and its industrial value has further increased. In the conventional DC glow discharge method, it is difficult to use an insulating substrate or to synthesize an insulating thin film, but with the configuration of the device of the present invention, the insulating diamond can be replaced with the insulating quartz glass. It became possible to synthesize diamond on any substrate, whether insulating or non-insulating, using a simple structure called the DC glow discharge method, increasing its industrial value.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an apparatus for carrying out the method of the invention. DESCRIPTION OF SYMBOLS 1... Vacuum chamber, 2... Electrode, 3... Screen mesh, 4... Screen mesh moving mechanism, 5... Substrate, 6... Electrode, 7... Heater, 8... Pressure regulator,
9... Rotary pump, 10... Hydrocarbon cylinder,
11...Hydrogen cylinder, 12...Rare gas cylinder, 13,
14,15...Kotuku, 16,17...Roll.

Claims (1)

[Claims] 1. A method for forming diamond on a substrate by decomposing and exciting a carbon compound gas or vapor in a direct current glow discharge, in which a screen mesh is installed between two opposing electrodes, and one A DC voltage is applied between the electrode and the screen mesh to generate a DC glow discharge, a substrate is placed on the other independent electrode to which a DC voltage is applied, and a diamond is formed on the substrate. A method of vapor phase synthesis of diamond. 2. In a diamond vapor phase synthesis apparatus that includes a vacuum chamber to which a gas supply section and a vacuum exhaust system are connected, and two electrodes facing each other inside the vacuum chamber, and a substrate is placed on one of the electrodes. A diamond vapor phase synthesis apparatus characterized by having a movable screen mesh between two electrodes. 3. The diamond vapor phase synthesis apparatus according to claim 2, wherein the screen mesh is installed in a range from the center of the two electrodes to just above the electrode on which the substrate is installed.