Intensity shift correction for thin film optical parameter determination

Abstract

In recent years, many approaches have been proposed to extract optical parameters from the spectrum of thin films and have been rapidly adopted in scientific research and industrial applications. In most cases, there are unavoidable intensity shifts in the measured thin film spectra, which lead to measurement errors in the analysis of optical parameters, especially if the instrument is not calibrated. Here we try to solve this problem from an algorithmic point of view and develop a model with a scaling factor to eliminate the effect of the intensity shift in the fitting process. In the fitting process, the scaling factor can be determined from the difference between the envelope of the thin film spectrum and the spectrum of the bare substrate, along with the extraction of optical parameters. By using the scaling factor, it is shown that the thickness results of our model are more consistent over repeated measurements of the same thin film sample than those without the scaling factor. And the standard deviation of the measured thickness decreases by as much as 89% for certain types of experimental configurations. We also characterized the thin film sample using a transmission electron microscope (TEM). A good agreement is observed between the TEM results (700.72 nm) and the results of our model (701.6 nm).