Homogeneous gas-phase nucleation in silane pyrolysis

Abstract

Dilute and particle free mixtures of silane in the range of 100 ppm to 10% by volume in different carrier gases were decomposed thermally in a tube reactor. The onset of homogeneous nucleation was determined as a function of temperature and silane concentration for each carrier gas using a CNC with a detection limit of ca 0.01 μm. The gaseous decomposition by-products, disilane, trisilane and hydrogen were measured simultaneously using gas-phase chromatography. The onset of gas-phase nucleation was found to be inversely proportional to the temperature and influenced by the nature of the carrier gas. In inert gases, no chemical reaction took place between the decomposition products of silane and the carrier gas. In hydrogen, equilibrium displacement with the primary decomposition product (SiH 2) lead to a retardation of particle formation. Thus, the temperatures of onset of gas-phase nucleation was higher for mixtures in hydrogen than for mixtures in inert gases.