Modeling the radiative properties of semitransparent wafers with rough surfaces and thin-film coatings

Semitransparent materials with rough surfaces and coatings have a wide range of applications. This work incorporates the thin-film optics formulation into the Monte Carlo ray-tracing method to predict the radiative properties of semitransparent wafers, considering the effect of surface roughness and a thin-film coating. Multiple reflections with interference inside the coating are included by assuming the uniform coating thickness. On the other hand, geometric optics is applied to trace the rays at the top and bottom surfaces of the wafer as well as inside the wafer. Instead of generating a random rough surface a priori, a weighted probability density function, based on the surface slope distribution and the projected area, is used to determine the microfacet orientation each time a ray hits the interface. The computational code has been validated against the conservation of energy and the reciprocity principle. The studied examples using Si wafers and either a SiO2 or Au coating demonstrate the strong influence of roughness and coating on the bidirectional and directional-hemispherical radiative properties. This study helps gain a better understanding of the radiative properties of semitransparent wafers with rough surfaces and will have an impact on semiconductor processing.