A New Method for the Optical Characterization of Inhomogeneous Thin Films Based Only on Spectroscopic Reflection Measurements

摘要

Inhomogeneities in thin films have a large influence on the optical transmission and reflection spectra. If not corrected for, this may lead to too large calculated values for the absorption coefficient or the apparent presence of an absorption band tail, as well as serious errors in the values of the refractive index and film thickness. The effect of thickness variation on the optical reflection spectrum is analyzed in detail. New analytical expressions for the optical reflectance and for the corresponding envelopes are derived. From these expressions, the optical constants, refractive index, n(λ), and extinction coefficient, k(λ), and, finally, average thickness, t, of an inhomogeneous film can be accurately calculated from the upper and lower envelopes of the corresponding shrunk reflection spectrum.