Low Temperature Chemical Vapor Deposition of Silicon-rich Tungsten Silicide Films from Tungsten Hexafluoride - Disilane Pre-activated Mixtures

Abstract

Abstract Kinetics of chemical vapor deposition (CVD) of silicon-rich tungsten silicide films from WF6/Si2H6 mixtures was investigated as a function of the configuration of a hot-wall tubular reactor. The step coverage within micron-sized trenches was analyzed to determine the overall sticking probability, which is the ratio between the film-forming species deposited on a surface and the flux of that species to the surface. The overall sticking probability was found in the range 0.01 - 0.30 as the deposition temperature was varied from 120 to 360°C. The activation energy was 25 kJ/mol. These sticking probabilities were lower than those for CVD of tungsten silicide film from WF6/SiH4 mixtures, which yielded better step-coverage profiles. The extinction temperature, Tex, below which no deposition was observed, ranged from 70 ‹ Tex ‹ 80°C. Tex = 70°C corresponded to an inner reactor diameter, d, of 22 mm, and Tex = 80°C corresponded to d = 11 mm. The dependence of Tex on d strongly suggests that radical chain reactions are involved in the CVD process. The reaction producing active intermediate species occurs in the gas phase and these active species are consumed on the surface of the reactor wall. Therefore, the volume to surface ratio of the reactor may be the key factor to control Tex, and an increase in d leads to a decrease in Tex. For Tex = 80°C, pre-heating of the gas phase can be used to induce the chain reaction and increase the silicon content in the tungsten silicide films.