The use of ion beam mixing and rapid thermal annealing in the formation of tungsten and molybdenum silicides

Abstract

Thin films of tungsten or molybdenum were deposited on single crystal silicon and reacted to form silicide layers using either rapid thermal annealing or vacuum furnace annealing. The effect of ion implantation, prior to annealing, on the silicide properties was investigated for several ion species including As +, B + and BF 2 + with ion doses between 10 14 and 10 16 cm -2. The silicide films were characterised using cross-sectional transmission electron microscopy, scanning electron microscopy, secondary ion mass spectrometry and sheet resistivity measurements. Annealing at 1100°C minimised the silicide resistivity and was performed with minimal dopant diffusion by rapid thermal annealing. Ion mixing was found to reduce dramatically the surface roughness of the annealed silicide films with the reaction occurring uniformly across the metal-silicon interface instead of at localised reaction centres. B +, a light ion, was found to be ineffective for smooth film formation. Heavy ions such as As + or P +, or molecular ions such as BF 2 + were found to be effective and their use allowed simultaneous p or n type substrate doping.