Defect detection algorithm for wafer inspection based on laser scanning

A defect detection algorithm for wafer inspection based on laser scanning is presented. Microscopic anomalies, contaminants, and process induced pattern defects result in a two-dimensional (2-D) laser scattering signature, which closely resembles the coherent point-spread-function of the scanning laser beam. This point-spread-function is a 2-D Gaussian in the majority of cases and can be characterized by four parameters. The algorithm fits Gaussian surfaces to sampled data points. Events are accepted or rejected on the basis of how similar the Gaussian parameters are to that of the point-spread-function, known a priori. It is shown that the algorithm achieves a 95% capture for submicron particles and pattern defects on typical logic and array wafer regions. Results demonstrating the algorithm's performance relative to mechanical and electronic noise and to signal resolution are presented.