THE EFFECT OF LONG-CORRELATION-LENGTH SURFACE-ROUGHNESS ON THE ELLIPSOMETRIC PARAMETERS OF REFLECTED LIGHT

A theory is presented which predicts the effect of surface roughness o n the ellipsometric parameters of reflected light. This theory is vali d for low values of gradient of the surface roughness and large values of the lateral correlation length of roughness. The theory is based o n geometrical optics and provides an expression for the ratio of p-pol arised 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 th e ellipsometric parameters as measured by typical ellipsometers. An in consistency in the differentiation of reflectivity with respect to sur face roughness out of the plane of specular reflectance, as carried ou t by previous workers in the field, is pointed out.