AUTOMATIC HIGH SPEED OPTICAL INSPECTION SYSTEM

Methods and apparatus for inspecting surface features of a substrate. In each configuration, at least one TDI sensor is used to image the portions of interest of the substrate, with those portions illuminated either with substantially uniform illumination or critical illumination. In one configuration, a substrate, is compared to the expected characteristic features prestored in a memory. In a second configuration, a first and second pattern in a region of the surface of at least one substrate are inspected by comparing one pattern against the other and noting whether they agree with each other without the prestoring of an expected pattern. This is accomplished by illuminating at least the two patterns, imaging the first pattern and storing its characteristics in a temporary memory, then imaging the second pattern and comparing it to the stored characteristics from the temporary memory. Here, the comparison reveals whether the two patterns agree or not. Then the comparisons continue sequentially with the second pattern becoming the first pattern in the next imaging/comparison sequence against a new second pattern. Each time the comparison is performed, it is noted whether or not there has been agreement between the two patterns and which two patterns where compared. After all of the patterns are sequentially compared, the bad ones are identified by identifying those that did not compare with other patterns in the test process. This inspection technique is useful for doing die-to-die inspections, as well as repeating pattern inspections within the same die. A variation of the second configuration uses two TDI sensors to simultaneously image the first and second patterns, thus eliminating the need for the temporary memory. In this configuration, the two patterns are simultaneous imaged and compared, then additional patterns are compared sequentially, in the same manner with the results of the comparisons and the pattern locations stored determine which patterns are bad when the inspection of all patterns is completed.