Advanced optical characterization of multilayer lead zirconate titanate films: A spectroscopic ellipsometry approach

Abstract

The intricate preparation processes associated with multilayer Lead Zirconate Titanate (PZT) films may induce variations in optical properties compared to their single-layer counterparts. In this work, a new method for spectroscopic ellipsometry measurements (yielding both ellipsometric parameters and reflectance) of multilayer PZT films across the ultraviolet–visible-near infrared spectral range of 192–1698 nm was proposed. A comparative analysis of three oscillator dispersion models for one-layer PZT film demonstrated that the linear combination model integrating a Psemi-M0 oscillator with a Gaussian oscillator achieved the lowest mean squared error value while employing the minimal number of constituent functions and fitting parameters, which was selected to accurately describe the optical response characteristics of multilayer-film systems. The utilization of two-layer film optical constants as initialization demonstrated enhanced measurement accuracy compared to the one-layer reference. PZT films of varying thicknesses exhibit minimal changes in the refractive index (n) and extinction coefficient (k) within the visible and infrared regions, contrasting with significant variations observed in the ultraviolet band, where thicker films display lower k and higher n. An increase in the number of spin coat/bake/anneal cycles induces Pb volatilization, modifies intrinsic film stress, and alters grain size. These changes lead to compositional deviations and microstructural evolution, ultimately impacting the films' optical properties. The demonstrated approach exhibits promising potential for extending ellipsometric studies to a broader range of complex direct bandgap semiconductor multilayer-film systems.