EFFECTS OF AR+ SPUTTERING AND THERMAL ANNEALING ON OPTICAL SCATTER FROM SI(100) AND SI(111)

The applications of crystalline silicon in imaging detectors and other devices motivate an interest in the ''macroscopic'' optical properties of Si surfaces, including reflective scatter. The types of substrate preparation procedures typically employed in Si surface studies can significantly affect the optical scatter at visible wavelengths. Specifically, surface cleaning via sputtering with 500 eV Ar+ ions followed by annealing at approximately 8 50-degrees-C can increase optical scatter by more than two orders of magnitude. Similar results are obtained through thermal cycling of the Si sample to about 1000-degrees-C. For the results reported herein, scattered light measurements were made in situ in an ultrahigh vacuum system. The incident radiation had a wavelength of 590 nm. The scattering geometry used a detection angle 45-degrees from the specular direction. The measured increase in scatter depends strongly on the sample treatment history. A simple model is proposed to account for these observations. The model is based on standard descriptions of classical optical scatter, combined with defect and impurity diffusion on Si surfaces and step bunching.