Subsurface quality of polished SiO2 surface evaluated by quasi-Brewster angle technique

As a surface-sensitive optical method, the quasi-Brewster angle technique is extended to evaluate the subsurface qualities of quartz crystal and fused silica. By measuring the ellipsometry parameters at λ = 900 nm with variable incidence angle, a fitting process is executed using a proper subsurface nanostructure with an exponential porosity distribution. The fitting results predict the surface and subsurface information which are in good agreement with that of the Zygo interference microscope measurements and etching methods. In addition, the shift characteristics of phase change at the Brewster angle of such crystal and non-crystal material are compared and demonstrated.