Digital image processing techniques for patterned-wafer inspection

A new self-reference signal processing technique is proposed for detecting the location of any nonregularities and defects in a periodic two-dimensional signal or image. Using high- resolution spectral estimation algorithms, the proposed technique first extracts the period and structure of repeated patterns from the image to sub-pixel resolution in both directions, and then produces a defect-free reference image for making comparison with the actual image. Since the technique acquires all its needed information from a single image, on the contrary to the existing methods, there is no need for a database image, a scaling procedure, or any a- priori knowledge about the repetition period of the pattern. Results of applying the proposed technique to real images from microlithography are presented.