High temperature surface Brillouin scattering study of mechanical properties of boron-doped epitaxial polysilicon

A study of the mechanical properties of a boron-doped epitaxial polysilicon layer deposited on a Si (100) substrate specimen has been carried out by surface Brillouin scattering at high temperatures. This type of specimen is widely used in micro-electro-mechanical systems (MEMS). By accumulating spectra with the Rayleigh mode and the Lamb continuum the isotropic elastic constants C44 and C11 were obtained, from which the values of the bulk, shear and Young’s moduli and Poisson’s ratio for the layer were determined over a range of temperatures from 20 °C to 110 °C. By contrast, an examination of the literature on polycrystalline silicon shows that other methods each provide a limited range of the above properties and thus additional experiments and techniques were needed. The SBS method is applicable to other polycrystalline materials such as silicon carbide, silicon nitride, silicon germanium and amorphous diamond that have also been used for MEMS applications.