This experimental study shows that ellipsometry can provide thickness and refractive index measurements of oxide films grown on randomly rough surfaces. The sample roughness ranged from 0.01 to 10 pm, with measuring light of wavelength 0.6328 pm. The calculated values of oxide thickness and refractive index deviate from those on flat reference samples. The deviations are reproducible, so that calibration curves may be established for rough versus smooth samples.
Ellipsometry is employed routinely in the determination of the thickness and refractive index of layers of SiO2 on silicon. Such layers are usually grown on silicon substrates with highly polished surfaces. In photovoltaic technology the characterization of dielectric layers on rough substrates also may be of interest. Rough substrates are produced by the sawing, grinding and etching of silicon wafers. Many polycrystalline semiconductor films are rough, although on a smaller scale than sawed wafers.
In this paper we present the results of an eUipsometric study of SiO2/Si structures whose oxide had been grown on roughened silicon substrates. We find that the values for thickness and refractive index deviate from those determined on flat reference samples. However, the deviations are smooth functions of the roughness, so that the thickness and refractive index still may be determined with the help of calibration data such as those established in our work.
The use of ellipsometry to measure thin films assumes perfectly smooth surfaces. Several workers have addressed the problems encountered