Ion‐backscattering analysis of tungsten films on heavily doped SiGe

摘要

The technique of ion backscattering has been used to obtain information on the reactions taking place at the interface between a sputtered tungsten film and a heavily doped silicon‐germanium alloy substrate. Significant differences were observed for n‐type and p‐type SiGe substrates. In both cases silicon was observed to migrate into the tungsten at temperatures above 650 °C and form a layer of atomic composition, WSi2. There was little or no diffusion of silicon beyond the WSi2 layer for the samples on n‐type substrates, but on p‐type SiGe, silicon diffused through the WSi2 layer to the surface of the tungsten film. Tungsten films on single‐crystal silicon showed small amounts of tungsten‐silicon diffusion and little or no WSi2 formation for anneals at and below 700 °C. Samples with n‐type SiGe substrates exhibited little or no tungsten‐germanium diffusion; whereas, samples on p‐type substrates annealed to 675 °C or higher showed significant migration of tungsten and/or germanium. The oxidation of the sputtered tungsten films was also investigated by ion backscattering. A 1200‐Å‐thick W film was completely converted to tungsten oxide (atomic composition WO3) by annealing at 650 °C, which inhibited WSi2 formation. In addition, the growth of WO3 on a thick W film was observed as a function of time.