A non-destructive approach to investigate the annealing effects on the optical and electrical properties of SnO2:F/SiCxOy low emissivity (Low-E) films via spectroscopic ellipsometry has been established. Using a four-layer model for the SnO2:F/SiCxOy films with various annealing times at 600 degrees C, the structural parameters and optical constants were evaluated, presenting an insight to the mechanisms in the deterioration of Low-E performance during annealing. The ellipsometric-derived results show that the roughness layer is decreasing when heating at 600 degrees C and supposed to give rise to defects and strain variations, contributing to decreased conductivity. However, the diffusion sodium ions from the substrate contribute little to the deterioration of electrical properties during annealing. More intuitively, two key parameters involved in the Drude dispersion law, plasma frequency and collision frequency, were also carried out to evaluate the electrical properties of SnO2:F, and one modified semi-empirical equation is proposed to relate the Drude parameters to emissivity. (C) 2013 Elsevier B.V. All rights reserved.