The structure of Si-surfaces has been investigated by elastic lightscattering which provides rapid, contactless, and nondestructive information on any kind of defects like dust, particles, bloom, microscratches and micro etch pits. Moreover we used the diffuse scattered light as a very sensitive method to determine the microroughness of polished Si wafers in the submicron (0.16 μm - 10 μm) range. Using different wavelengths this technique allows to distinguish between superficial and subsurface defects. Angle resolved measurements under wafer rotation (azimuthal scans) demonstrate anisotropic etching behavior. Alkaline solutions (potassium hydroxide) produce a strong anisotropic surface structure on (100)- and (111)-oriented Si wafers. In contrast an acidic etch gives an isotropic and smoother surface. Chemo-mechanical polishing reduces the diffuse scattered light for all scattering vectors by about six orders of magnitude. According to Total Integrated Scattering (TIS) measurements (carried out for calibration) the smoothness of a perfectly polished wafer is below 1 Å (RMS). Polishing leads to regular atomic steps at the surface. If the misorientation is less than 0.1° the existence and regularity of these steps can be proved by this lightscattering method. During subsequent processing steps, however, the smoothness of the polished surface deteriorates in most cases again. It is demonstrated that oxidation and ion implantation increase the lightscattering level substantially due to surface roughening and/or subsurface damage.