US Patent 7973919 High resolution wafer inspection system

A method for inspecting a region, including irradiating the region via an optical system with a pump beam at a pump wavelength. A probe beam at a probe wavelength irradiates the region so as to generate returning probe beam radiation from the region. The beams are scanned across the region at a scan rate. A detector receives the returning probe radiation, and forms an image of the region that corresponds to a resolution better than pump and probe Abbe limits of the optical system. Roles of the pump and probe beams may be alternated, and a modulation frequency of the pump beam may be changed, to produce more information. Information extracted from the probe signal can also differentiate between different materials on the region.