2001 Volume 18 Issue 3 Pages 169-
A diamond is considered as a bright prospect material for semiconductors because of its wide band gap, high electron and positive-ion mobility and negative electron affinity. Many researches on the syntheses of diamond thin film have been performed, which utilize plasma chemical vapor deposition (CVD) method. But the detail mechanism of the synthesis of diamond have not been clarified yet, because the natural convection causes the disturbance to understand the phenomena related to the CVD processing under normal gravity. A diagnostic study of hydrogen-methane plasma was applied to the CVD experiments utilizing the 4.5 s drop shaft at Toki in Gifu and 10.0 s drop shaft facility at Kamisunagawa in Hokkaido. The plasma temperature was estimated based on the two-line radiance ratio method as a function of the position from anode. We also examined the delay time, which is taken to generate discharge plasma after adding high-voltage between electrodes. Moreover the pattern formation of the positive column and low-frequency fluctuation of plasma (0～50 Hz) that has been hardly focused on in the past study on plasma was examined.We found that (a) remarkable differences of the electron temperature of plasma were confirmed between the microgravity and the normal-gravity conditions, (b) the gravity affected the delay time, (c) the low-frequency fluctuation of plasma was affected by gravity level, and (d) the pattern formation dynamics of plasma emission on the anode was sensitive to gravity level.
