PATTERNED WAFER INSPECTION BY HIGH-RESOLUTION SPECTRAL ESTIMATION TECHNIQUES

A new self-reference signal processing technique is proposed for detec ting the location of irregularities and defects in a periodic two-dime nsional signal or image. Using high-resolution spectral estimation alg orithms, the proposed technique first extracts the period and structur e of repeated patterns from the image. Then a defect-free reference im age for comparison with the actual image is produced. Since the techni que acquires all the information needed from a single image (in contra st to most existing methods), there is no need for a database image, a scaling or alignment procedure or any a priori knowledge about the re petition period of the patterns. Potential application fields for the proposed method range from the area of wafer and mask defect inspectio n, which includes inspection of memory chips, shift registers, switche d capacitors, CCD arrays, and LCD displays to other areas that deal wi th repeated structures, such as crystallography. Some results of apply ing the proposed technique to real images from microlithography are pr esented.