Detection and Identification of Near-Surface Microprecipitates in Silicon Wafers by Laser Scattering Tomography

A nondestructive measurement system for characterizing near-surface (0 to 100 µ m) microprecipitates in silicon wafers using laser scattering tomography has been developed. A near-infrared laser beam (λ=1 µ m) is focused to about 4 µ m in diameter and introduced into the wafer from an inclined direction through the polished surface. The scattered light is also observed from the polished side. The scattered light has a complicated signal, because the scattered light from the near-surface microdefects, that from the haze related to the surface microroughness, and that from the dust on the surface are mixed. By using a polarization analysis method, the scatterings from the haze, dust and microdefects are clearly distinguished. The scattering from the subsurface (0 to 5 µ m) region is also identified as that due to dust and microprecipitates by using a short-wavelength laser (λ=680 nm).