Stress gradient and structural properties of atmospheric and reduced pressure deposited polysilicon layers for micromechanical sensors

In this paper we report the mechanical and the structural properties of thick polysilicon layers performed by using atmospheric pressure (ATM) and reduced pressure (RP) chemical vapour deposition in order to obtain minimum residual stress and stress gradient for micromachined released structures and minimum surface roughness, avoiding poor mechanical characteristics in the performed sensors. Stress profile analysis was carried out by using Raman spectroscopy. Complementary TEM, XRD and AFM measurements have also been performed to aid the explanation of the experimental results, taking into account the morphology data, defect density, surface roughness, grain size and crystallographic directions. Finally, comparison with the data deduced from mechanical test structures was carried out.