Relating mechanical testing and microstructural features of polysilicon thin films

Polycrystalline silicon thin films (polysilicon) have been deposited on single crystalline silicon substrates, and square and rectangular windows have been etched into these substrates using standard micromachining techniques. Pressure-displacement curves of the resulting polysilicon membranes have been obtained for these geometries, and this data has been used to determine the elastic constants E and nu. The microstructural features of the films have been investigated by transmission electron microscopy (TEM) and x-ray diffraction. The grains were observed to be columnar and were found to have a [011] out-of-plane texture and a random in-plane grain orientation. A probabilistic model of the texture has been used to calculate the bounds of the elastic constants in the thin films. The results obtained from bulge testing (E = 162 +/- 4 GPa and nu = 0.20 +/- 0.03) fall in the wide range of values previously reported for polysilicon and are in good agreement with the microsample tensile measurements conducted on films deposited in the same run as the present study (168 +/- 2 GPa and 0.22 +/- 0.01) and the calculated values of the in-plane moduli for [110] textured films (E = 163.0 - 165.5 GPa and nu = 0.221-0.239).