Silicon nitride/silicon oxynitride/silicon dioxide thin film multilayer characterized by variable angle spectroscopic ellipsometry

Variable angle spectroscopic ellipsometry (VASE) was used to nondestructively characterize a silicon nitride (Si₃N₄)/silicon oxynitride (SiO_xN_y)/silicon dioxide (SiO₂) thin film multilayer structure, in which Si₃N₄ and SiO_xN_y layers were deposited by plasma enhanced chemical vapor deposition and low‐pressure chemical vapor deposition, respectively. The measured VASE spectra (3500–8200 Å) were analyzed with an appropriate multilayer fitting model, in which the SiO_xN_y layer was modeled, in the Bruggeman effective medium approximation (EMA), to be a physical mixture of two distinct phases, SiO₂ and Si₃N₄. Remarkably good agreement between the measured spectra and the model calculations was obtained, indicating that the EMA and the fitting model were appropriate for the data analysis. As a result, the three layer thicknesses, compositions, and the optical constants of SiO_xN_y layer at several spots across the sample were determined. The thickness values obtained by VASE were in very good agreement with those measured by cross‐sectional transmission electron microscopy.