CHARACTERIZATION OF POLYCRYSTALLINE SILICON THIN-FILM MULTILAYERS BY VARIABLE ANGLE SPECTROSCOPIC ELLIPSOMETRY

Samples of polycrystalline silicon (poly-Si) thin-film multilayers were prepared by low-pressure chemical vapor deposition. Analysis of these samples by cross-sectional transmission electron microscopy (XTEM) revealed large changes in grain size between the undoped-as-deposited and doped-annealed poly-Si layers. Roughness at the top of the poly-Si layers was also observed by XTEM. Non-destructive variable angle spectroscopic ellipsometry (VASE) was used to characterize these structures and to determine the layer thicknesses and compositions. The poly-Si and roughness layers were each modeled as physical mixtures, using the Bruggeman effective medium approximation, and incorporated into the appropriate multilayer fitting models. As a result, layer thicknesses and compositions, as well as the surface and interface roughnesses, were determined. The VASE-obtained thicknesses compared well with those determined by destructive XTEM. The effects on the poly-Si layer microstructure due to doping and annealing were also characterized.