Infrared optical constants of silicon dioxide thin films by measurements of R and T

Optical constants [n,k] of 30–300 nm SiO2 films, thermally grown on c-Si substrates, are obtained numerically from [R,T] data. The calculations are done at each wavelength, no a priori assumptions regarding dispersion relations are needed. The technique also provides the film thickness, whose values agree with ellipsometric measurements. The optical constants are compared to those of bulk fused silica glass (FSG) and are found to differ in subtle but important ways. The principal absorption band due to the Si–O TO stretching vibrations, and measured by the e″ (imaginary dielectric) band, is slightly greater in magnitude and 12 cm−1 narrower for the film than for the bulk material. We interpret this to indicate a simpler strain field within the film compared to the bulk material. We find, however, that the integrated intensities are identical, indicating similar densities. We show that the shift in peak position of the absorbance band with changes in film thickness is almost entirely an optical thin film e...