INFLUENCE OF TEMPERATURE-GRADIENTS ON PARTIAL PRESSURES IN A LOW-PRESSURE CHEMICAL-VAPOR-DEPOSITION REACTOR

Measurements and calculations of the influence of temperature gradient s on the partial pressures of the gas species in a cold-wall chemical- vapor-deposition reactor are presented. The experiments were performed at low pressures (300-500 Pa total pressure) and gas mixtures consist ing of hydrogen, nitrogen, and tetrafluoromethane. The partial pressur es were determined by Raman spectroscopy. The Soret effect (or thermal diffusion) has a large influence on the partial pressures of heavy ga ses in the vicinity of the heated wafer. In some cases a decrease in p artial pressure of 20% compared to the inlet partial pressures was obs erved. Numerical calculations were performed to predict the behavior o f the gas mixture. For mixtures under investigation the gas temperatur es as well as the changes in partial pressures due to the Soret effect were predicted correctly.