J. Qiu, D. F. Ran, Y. B. Liu, L. H. Liu

Investigation of ellipsometric parameters of 2D microrough surfaces by FDTD

Applied Optics 55 (2016) 5423-5431

Ellipsometry is a powerful method for measuring the optical constants of materials and is very sensitive to surface roughness. In previous ellipsometric measurement of optical constants of solid materials with rough surfaces, researchers frequently used effective medium approximation (EMA) with roughness already known to fit the complex refractive index of the material. However, the ignored correlation length, the other important parameter of rough surfaces, will definitely result in fitting errors. Hence it is necessary to consider the influence of surface roughness and correlation length on the ellipsometric parameters Delta (phase difference) and Psi (azimuth) characterizing practical systems. In this paper, the influence of roughness of two-dimensional randomly microrough surfaces (relative roughness sigma/lambda ranges from 0.001 to 0.025) of silicon on ellipsometric parameters was simulated by the finite-difference time-domain method which was validated with experimental results. The effects of incident angle, relative roughness, and correlation length were numerically investigated for two-dimensional Gaussian distributed randomly microrough surfaces, respectively. The simulated results showed that compared with the smooth surface, only tiny changes of the ellipsometric parameter Delta could be observed for microrough silicon surface in the vicinity of the Brewster angle, but obviously changes of Psi occur especially in the vicinity of the Brewster angle. More differences between the ellipsometric parameters of the rough surface and smooth surface can been seen especially in the vicinity of the Brewster angle as the relative roughness sigma/lambda increases or correlation length tau decreases. The results reveal that when we measure the optical constants of solid materials by ellipsometry, the smaller roughness, larger correlation length and larger incident wavelength will lead to the higher precision of measurements. (C) 2016 Optical Society of America

Cited Articles

1. Franta D., Ohlídal I.,
   Ellipsometric parameters and reflectances of thin films with slightly rough boundaries,
   Journal of Modern Optics 45 (1998) 903–934