Modeling radiative properties of silicon with coatings and comparison with reflectance measurements

Abstract

Achieving high-accuracy temperature measurements in rapid thermal processing using radiation thermometry requires knowledge of the optical properties of silicon and related materials, such as silicon dioxide, silicon nitride, and polysilicon. However, available optical property models lack consistency and are not fully validated by experiments at the wavelength and temperature ranges critical to radiation thermometry. A critical survey is given of the existing optical models, with emphasis on the need for extrapolation and validation. Also described is an algorithm for calculating the radiative properties of lightly doped silicon with coatings. The effect of coatings covering one or both sides of a smooth silicon wafer is theoretically studied at room temperature, as well as at elevated temperatures. A spectrophotometer was used to measure the reflectance for selected samples in the wavelength region from 0.5 to 1 mu m at room temperature. The measurements agree well with the predicted reflectance for bare silicon, a silicon wafer with a nitride coating, and wafers with an oxide coating of different thicknesses, whereas a larger deviation of as much as twice the measurement uncertainty is observed for a silicon wafer coated with polysilicon and oxide films.