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.