Stresses in TaSix films sputter deposited on polycrystalline silicon

Abstract

Stress in thin TaSi_x films sputtered on polycrystalline silicon was studied as a function of temperature. A dual laser‐beam apparatus was used to measure wafer curvature in situ. Stress was studied in the TaSi₂/undoped polysilicon structure, in TaSi₂ on polysilicon doped with either phosphorus, arsenic, or boron, and in films with a deposited Si/Ta ratio of more than 2. Several observations of stress‐temperature behavior in TaSi₂ were made. Tensile stress in TaSi₂/undoped polysilicon increases to 1.2×10¹⁰ dyn/cm² at 450 °C during the postdeposition anneal, decreases to near 0 at 900 °C, and linearly increases as temperature is subsequently lowered. Both doping and stoichiometry affected the stress‐temperature behavior. N‐type dopants decreased tensile stress and boron did not. Raising the Si/Ta ratio increased tensile stress at high temperatures. The stress‐temperature measurements were combined with results from other characterization techniques to draw conclusions about the influence of temperature on the film. TaSi₂ compound formation was found to occur at less than 400 °C in these films.