Patent ID: 7492449

Claim:
An inspection method, comprising: receiving a reference signal having first surface displacement information, the first surface displacement information corresponding to a non-zero displacement of a first surface known in advance of inspection to have no defects; receiving a target signal having second surface displacement information, the second surface displacement information corresponding to a non-zero displacement of a second surface; determining a correlation coefficient between the first surface displacement information and the second surface displacement information, the correlation coefficient determined according to an equation for r, wherein the equation comprises: r = ∑ n ⁢ ⁢ ( R n - R _ ) ⁢ ( A n - A _ ) ( ∑ n ⁢ ⁢ ( R n - R _ ) 2 ) ⁢ ( ∑ n ⁢ ( A n - A _ ) 2 ) where R n corresponds to the first surface displacement information, R corresponds to a mean of R n , A n corresponds to the second surface displacement information, and Ā is a mean of A n ; determining a modified correlation coefficient, the modified correlation coefficient equal to (1-r 2 ); comparing the determined modified correlation coefficient with a threshold modified correlation coefficient; and indicating whether the inspected object exhibits a defect based on the comparison between the determined modified correlation coefficient and the threshold modified correlation coefficient.