Synthesis of Low-Defct Diamond Films

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The synthesis of diamond films with defects as low as possible was performed using a capacitively coupled rf (13.56MHz) plasma CVD apparatus and an infrared-radiation heater. The films were prepared at various conditions keeping the total-flow rate of ethyl alcohol and hydrogen at 100 sccm and discharge power at 500 W and varying total-gas pressure, ethyl alcohol concentration, heating temperature and flow rate of added gas. Defects in the films were evaluated by nondiamond components in Raman spectrum and spin density in ESR,and the following results were obtained.(1) When a 0.5% carbon tetrafluoride is added keeping the concentration of ethyl alcohol at 0.5%, a high-quality film without nondiamond components grows even at a low temperature of 350ﾟC.The spin density of this film is 1.6*10^<18> cm^<-3>.(2) The temerature is increased in the above case. The highest-quality film grows at 550ﾟC.The spin density of this film is 5.2*10^<17>cm^<-3>, which is lowest in the present project.(3) When the concentration of ethyl alcohol and the temperature are kept at 1.0% and 350ﾟC,respectively, the highesr-quality film is obtained if a 0.2% carbon tetrafluoride is added. This film has a spin density of 7.3*10^<17>cm^<-3>. In contrast with the above case, the film degrades when the temperature is increased.(4) In the measurement of optical emission spectrescopy for the plasma formed by adding carbon tetrafluoride, an increase in the amount of C_2 and CH radicals is observed when the concentration of ethyl alcohol is 0.5 and 1.0%, respectively.(5) When nitrogen is added into the source gas, reduction in the spin density and the nondiamond component is observed in some cases. For improvement in film quality, nitrogen is not so effective as the carbon tetrafluoride.