Synthesis of Diamond Films with Low Defects

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The synthesis of diamond films with paramagnetic defects as low as possible was performed using a radio-frequency (13.56 MHz) plasma CVD apparatus and an infrared-radiation heater. We tried to synthesize diamond films under various conditions using a mixture gas of ethyl alcohol and carbon trifluoride (CHFィイD23ィエD2) diluted with hydrogen. Next, we synthesized (100)-textured diamond films on (100)-silicon substrates from a source gas of methane and hydrogen using microwave plasma CVD method, because we considered that a reduction of defects can be realized if the films are composed of textured diamond grains with a large size as possible. As a result of various evaluations of these films, the following facts were clarified.1. When ethyl alcohol and carbon trifluoride are used, diamond films can be obtained at a low-deposition temperature of 350 ℃ in a range of trifluoride concentration between 0.1 and 0.6%.2. A high-quality film without nondiamond components can be obtained at deposition temperatures of 400 to 500 ℃. When carbon tetrafluoride was used, the highest-quality film was obtained at 550 ℃. Thus we realized a considerable reduction of deposition temperature by the use of the trifluoride.3. The lowest value of paramagnetic defect density is 7 x 10ィイD117ィエD1 cmィイD1-3ィエD1. This value is comparable to that in the film grown by using the tetrafluoride.4. In the textured films, the size of crystal-grain increases and the density of grain-boundary decreases with increasing the film thickness. Thereby, the density of paramagnetic defects decreases, but it is higher by about one order of magnitude compared with that in the untextured films with high quality.5. The textured films are subjected to a compressive stress. The density of paramagnetic defects is assumed to be increased by this stress.