A novel improved layered effective medium approximation for ellipsometric parameters of microrough surfaces

In this work, we proposed an improved layered model to fit the spectroscopic ellipsometry (SE) parameters of the solid material with rough surfaces in ellipsometric measurements. The improved layered model extracted the spatial distribution of volume fraction in rough surfaces. Then a relatively authentic spatial distribution of optical constants was obtained from effective medium approximation (EMA) in rough surfaces. Besides, the finite-difference time-domain (FDTD) method and rigorous coupled-wave analysis (RCWA) were utilized to calculated the precision of the layered model to fit the SE parameters of Gauss microrough surfaces with different optical constants and characteristic parameters (correlation length ζ and root mean square σ). It has been found that the layered model will have a good fitness to the SE parameters of Gauss microrough surfaces when the thickness of layered model is proportional to σ²/ζ. However, it should be noticed that the fitness precision of layered model to the SE parameters of Gauss rough surfaces will decline when optical thickness becomes large so that the effective layer is opaque to light.