Deposition of thick doped polysilicon films with low stress in an epitaxial reactor for surface micromachining applications

Abstract

Polysilicon films were deposited in an epitaxial batch reactor at a high deposition rate. The effect of the deposition temperature, total pressure, source gas flow and in situ doping on the deposition rate and morphological and electrical properties of these films was studied. Layers with thicknesses up to 12 μm were deposited on a sacrificial oxide covered with a thin polysilicon nucleation layer, which was formed in a low pressure chemical vapour deposition reactor. The thick polysilicon layers were characterized in terms of the surface roughness, grain growth and concentration and distribution of dopants. The residual stress and stress gradient were also determined. This material was found to be highly suitable for surface micromachining applications because of its low residual stress level, homogeneous doping profile and excellent mechanical properties.