Adsorption of chlorine on TiSi₂: application to etching and deposition of silicide films

The interaction of Cl₂ with polycrystalline TiSi₂ has been investigated by temperature programmed desorption to better understand the role of adsorbed chlorine in the etching of TiSi₂ films and in the chemical vapor deposition of TiSi₂ from TiCl₄ and SiH₄. Five different desorption states were observed in response to Cl₂ adsorption over a wide exposure range, including the products TiCl₄, SiCl₄, and SiCl₂. The sticking probability for Cl₂ and the desorption kinetics for the products were incorporated into a quantitative model for TiSi₂ etching. The predicted etch rates matched closely those measured in an etching reactor operated under typical processing conditions. Etch rates of 200 angstrom/s were obtained at 600 K with p_Cl(2) of 5 × 10^-4 Torr. These rates are an order of magnitude higher than those obtained using plasma-based systems, while the Cl₂ pressure is at least an order of magnitude lower. Coadsorption studies with SiH₄ were performed to examine the inhibition effects of surface chlorine during silicide CVD and the role of surface titanium in adsorbate bonding.