2000 Volume 26 Issue 6 Pages 749-753
Achieving a uniform film thickness profile over a substrate has been difficult in CVD-Al2O3 coating processes. Although this problem can be solved by H2S-doping to the source gas mixture, AlCl3/CO2/H2, the role of H2S in the mechanisms of the CVD coating have not been clarified. In this study, the effects of H2S-doping on the improvement of the uniformity of a coated layer is studied, focusing on the particles generated in the gas phase. It is found in the measurement of gasborne particles that the number concentration of particles larger than 200 nm in diameter is reduced dramatically by the H2S-doping. The concentration is over 108 particles/m3 when no H2S is doped, while it is less than 106 particles/m3 at 0.20% doping. The improvement of the coating by H2S-doping is concluded to be caused by a size reduction of particulate matters of the Al2O3 precursors that leads to an increase of the diffusivity.