Analysis of variable scale surface roughness on Si(111): a comparative Brewster angle, ellipsometry and atomic force microscopy investigation

Brewster angle analysis (BAA) and single wavelength ellipsometry (SWE) were used to investigate the optical response of Si(111), exposed to subsequent 40% NH4F etching steps, each persisting for 20 s. During native oxide layer etchback and anisotropic etching of the silicon substrate, ultrasmall variations were accurately observed. Contact mode atomic force microscopy (CM AFM) was performed to describe the scale dependence of roughness analysis and to correlate optical and micro-topographical information. It can be shown that BAA and SWE are of comparable sensitivity with respect to variations in film thickness and surface roughness. Quantitative analysis, however, leads to new insights into the information obtainable from the optical methods. BAA data, i.e. the Brewster angle and the reflectance at the Brewster angle, change each in a unique direction, if a clean and smooth surface slightly deteriorates. Ellipsometry, however, shows more complicated variations of the data depending on the concurrent presence of small and long correlation length surface roughness. A combination of both methods allows separating and quantification of these roughness contributions.