| abstract |
The invention concerns on-line electro-optical detection of wafer defects by illuminating a continuously moving wafer with a light pulse from a pulsed laser and imaging the moving wafer onto a focal plane assembly formed as a continuous surface of photo-detectors at the focal plane of the optical imaging system. The laser pulses are of duration significantly shorter than the pixel dwell time, such that there is effectively no image smear during the wafer motion. A fiber optical illumination delivery system, which reduces the effects of source coherence, is described. Other aspects of the system include a system for compensating for variations in the pulse energy of a Q-switched laser output, methods for auto- focusing of the wafer imaging system, and methods for removal of repetitive features of the image by means of Fourier plane filtering, to enable easier detection of wafer defects. |