US Patent 7161670 Inspection systems using sensor array and double threshold arrangement

A two dimensional sensor array is used to collect light diffracted from the inspected substrate. The signal generated by each individual sensor is passed through a threshold. Those signals which are below the threshold are amplified and are summed up. The summed signal is then passed through a second threshold. Summed signals which pass the second threshold are flagged as indicating suspect locations on the substrate. In the preferred embodiment, the entire circuitry is provided in the form of a CMOS camera which is placed in the Fourier plane of the diffracted light.