Polarized light scattering techniques for surface wafer inspection

Laser light scattering is used in semiconductor manufacturing to inspect product and process-witness wafers for particulate contaminants, defects, and roughness. Typically, a laser beam is focused onto the wafer surface, and one or more large optics collect light scattered from the surface. As the laser beam is scanned over the wafer surface, background signal is associated with microroughness, while excursions from the background are associated with localized scattering sources, such as particles or subsurface defects. The use of multiple detectors allows some discrimination amongst different classes of light scattering events. The polarization of scattered light carries with it information, which can substantially improve the ability of these instruments to characterize the light scattering sources. This information is often not fully utilized by these instruments. While the incident laser beam is usually polarized in a manner to accentuate a specific scattering source, analysis of polarization of the resulting scattered light is rarely performed. This summary will outline results, which have shown how the polarization can be used to identify scattering sources.