Determination of the surface roughness and refractive index of amorphous As40S60 films deposited by spin coating

Abstract An envelope method, based on the optical reflection spectrum taken at normal incidence, has been successfully applied to the geometrical–optical characterization of thin dielectric films having significant surface roughness. Such a method allows the determination of the average thickness and the refractive index of the films with accuracies better than 1%, as well as the average amplitude of the surface roughness with an accuracy of about 2%. Amorphous As40S60 thin films have been deposited by spin coating, onto glass substrates, from a solution of the bulk material in n-propylamine. Indications of the surface roughness in these films were found from total (specular plus diffuse) reflectance measurements using an integrating sphere, and also from mechanical measurements using a stylus profiler. The latter technique provided a value for the average surface roughness of 20 ± 4 nm, which is in excellent agreement with the optically determined value of 17.4 ± 0.4 nm.