On the Role of the Underlying Microstructure on the Mechanical Properties of Microelectromechanical Systems (MEMS) Materials

Abstract

The microstructure of Low Pressure Chemical Vapor Deposition (LPCVD) Polycrystalline silicon (Polysilicon) thin films was investigated by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and Auger electron spectroscopy (AES). SEM characterization of tensile tested samples showed a brittle like-rupture, along with grooves located at the surface sides of the sample. TEM investigations of as-deposited samples showed equiaxed or fully columnar grains bridging from the bottom to the top of the films. A microstructural coarsening was observed with annealing. In the as-deposited state, the films exhibited a {110} texture as showed by the XRD analysis. The films' top and bottom surfaces were observed to be smooth with a roughness (standard deviation) of about 11nm and 20 nm respectively. A chemical analysis of the thin films showed the presence of carbon and oxygen impurities on the surface and oxygen through the sample as observed in the depth profile. The hypothetical influence of these findings is subsequently discussed in relation to the measured mechanical properties.