Abstract
A theory is presented which predicts the effect of surface roughness on the ellipsometric parameters of reflected light. This theory is valid for low values of gradient of the surface roughness and large values of the lateral correlation length of roughness. The theory is based on geometrical optics and provides an expression for the ratio of p-polarised to s-polarised reflectance which is very similar to that which was obtained by previous workers using scattering theory. It is found, for the first time, that a theory which is valid for long correlation length shows some similarity with results using the effective medium approximation. This geometrical theory also adds further weight to the argument that long-range roughness has only a very small effect on the ellipsometric parameters as measured by typical ellipsometers. An inconsistency in the differentiation of reflectivity with respect to surface roughness out of the plane of specular reflectance, as carried out by previous workers in the field, is pointed out.