Ph.D. Proposal Presentation by
Wednesday, October 19, 2005
(Dr. Zhuomin Zhang, Chair)
"Radiative Properties of Silicon Wafers with Microroughness and Thin-Film Coatings"
Knowledge of the bidirectional reflectance distribution function (BRDF) and emissivity of microrough silicon is essential for accurate radiometric temperature measurement in rapid thermal processing of microelectronic devices. The prediction of the BRDF and emissivity is complicated because the microroughness of many silicon surfaces is non-Gaussian and strongly anisotropic. Oxide and other thin-film coatings commonly exist on the wafers, making the problem even more challenging.
This research aims at investigating the radiative properties of silicon with microroughness and thin-film coatings, with an emphasis on the correlation between surface statistics and BDRF. An atomic force microscope (AFM) is employed to measure the surface topography, from which statistical roughness parameters and slope distribution functions can be obtained. Computational algorithms based on the Monte Carlo ray-tracing method are developed to predict the BRDF of silicon and gold-coated silicon surfaces by incorporating the measured two-dimensional topographic data. These models take multiple scattering and the change of the polarization state upon each reflection into consideration. Analytical modeling approaches are also applied to investigate the effect of silicon dioxide coatings of various thicknesses. Experiments are performed with a laser scatterometer at the wavelength of 635 nm for a number of samples. Preliminary results show good agreement between predictions and measurements of BRDF. Further research is proposed to include the coherent scattering effect in the model, to measure the directional-hemispherical properties with an integrating sphere, and to extend the measured spectral region using a monochromator.