Optical Characterization of Inhomogeneous Thin Films Deposited onto Non-Absorbing Substrates

Abstract

In this study, a novel approach for characterizing the optical properties of inhomogeneous thin films is presented, with a particular focus on samples exhibiting absorption in some part of the measured spectral range. Conventional methods of measuring the samples only from the film side can be limited by incomplete information at the lower boundary of the film, leading to potentially unreliable results. To address this issue, depositing the thin films onto non-absorbing substrates to enable measurements from both sides of the sample is proposed. To demonstrate the efficacy of this approach, a combination of variable-angle spectroscopic ellipsometry and spectrophotometry at near-normal incidence was employed to optically characterize three inhomogeneous polymer-like thin films. The spectral dependencies of the optical constants were modeled using the Kramers–Kronig consistent model. It was found that it is necessary to consider thin, weakly absorbing transition layers between the films and the substrates. The obtained results show excellent agreement between the fits and the measured data, providing validation of the structural and dispersion models, as well as the overall characterization procedure. The proposed approach offers a method for optically characterizing a diverse range of inhomogeneous thin films, providing more reliable results when compared to traditional one-sided measurements.

Optical characterization of inhomogeneity of polymer-like thin films arising in the initial phase of plasma-enhanced chemical vapor deposition

“…This necessity arises from the fact that, due to absorption in a significant part of our spectral range by the upper part of the film, there is too little information obtainable about the lower part of the film. One way to overcome this limitation would be to measure the films deposited onto non-absorbing substrates [51] . This would enable the possibility to perform measurements from both sides of the samples.…”

“…Further information about the construction of UDM can be found in the reference [50] . The dispersion model describing the response of the polymer-like thin films outlined above was also used in our previous work [51] , where the concrete forms of all contributions can be found.…”