Patterned wafer inspection by high resolution spectral estimation techniques

Abstract

A new self-reference signal processing technique is proposed for detecting the location of irregularities 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. Then a defect-free reference image for comparison with the actual image is produced. Since the technique acquires all the information needed from a single image (in contrast to most existing methods), there is no need for a database image, a scaling or alignment procedure or any a priori knowledge about the repetition period of the patterns. Potential application fields for the proposed method range from the area of wafer and mask defect inspection, which includes inspection of memory chips, shift registers, switched capacitors, CCD arrays, and LCD displays to other areas that deal with repeated structures, such as crystallography. Some results of applying the proposed technique to real images from microlithography are presented.