Determination of the SiO_2/Si interface roughness by diffuse reflectance measurements

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Abstract
The problem of determining the roughness of the SiO2/Si interface is treated. A model is used based on the Fresnel formalism and scalar scattering theory. The resulting formulas express the diffuse reflectance as a function of the optical constants of the two materials, the oxide thickness and the rms roughness of the interfaces. Using the roughness values as adjustable parameters, quantitative information about the interface roughness is obtained from the diffuse reflectance spectra for an SiO2/Si double layer. Excellent agreement between calculated and experimental spectra is obtained for an rms roughness of 9.0 nm at the front surface and 2.2 nm at the oxide substrate interface for the case of a low-pressure low-temperature CVD film of SiO2 on Si.