A filter to selectively block light from passing through the filter and to selectively permit light to pass through the filter. The filter includes an array with a plurality of individually addressable filter elements. Each filter element is selectively settable to have a variable transmittance to the light of between substantially zero percent and substantially one hundred percent. In this manner, the filter according to the present invention provides areas that pass only a portion of the light, and thus can block the light using patterns other than just an abrupt on/off filtering. By so doing, the filter is able to dramatically reduce, and in some embodiments eliminate, the light ringing that typically accompanies such on/off filters.

A cylindrical mirror or lens is used to focus an input collimated beam of light onto a line on the surface to be inspected, where the line is substantially in the plane of incidence of the focused beam. An image of the beam is projected onto an array of charge-coupled devices parallel to the line for detecting anomalies and/or features of the surface, where the array is outside the plane of incidence of the focused beam. For inspecting surface with a pattern thereon, the light from the surface is first passed through a spatial filter before it is imaged onto the charge-coupled devices. The spatial filter includes stripes of scattering regions that shift in synchronism with relative motion between the beam and the surface to block Fourier components from the pattern. The spatial filter may be replaced by reflective strips that selectively reflects scattered radiation to the detector, where the reflective strips also shifts in synchronism with the relative motion.

A compact and versatile multi-spot inspection imaging system employs an objective for focusing an array of radiation beams to a surface and a second reflective or refractive objective having a large numerical aperture for collecting scattered radiation from the array of illuminated spots. The scattered radiation from each illuminated spot is focused to a corresponding optical fiber channel so that information about a scattering may be conveyed to a corresponding detector in a remote detector array for processing. For patterned surface inspection, a cross-shaped filter is rotated along with the surface to reduce the effects of diffraction by Manhattan geometry. A spatial filter in the shape of an annular aperture may also be employed to reduce scattering from patterns such as arrays on the surface.

A dark field surface inspection tool and system are disclosed herein. The tool includes an illumination source capable of scanning a light beam onto an inspection surface. Light scattered by each inspection point is captured as image data by a photo detector array arranged at a fourier plane. The images captured are adaptively filtered to remove a portion of the bright pixels from the images to generate filtered images. The filtered images are then analyzed to detect defects in the inspection surface. Methods of the invention include using die-to-die comparison to identify bright portions of scattering patterns and generate unique image filters associated with those patterns. The associated images are then filtered to generate filtered images which are then used to detect defects. Also, data models of light scattering behavior can be used to generate filters.