Correlation and convolution filtering and image processing for pitch evaluation of 2D micro- and nano-scale gratings and lattices

We have mathematically explicated and experimentally demonstrated how a correlation and convolution filter can dramatically suppress the noise that coexists with the raster-scanned topographic signals of 2D gratings and lattices with 2-dimensional (2D) perspectives. To realize pitch evaluation, the true peaks’ coordinates have been precisely acquired after detecting the local maxima from the filtered signal, followed by image processing. The combination of 2D filtering, local maxima detection and image processing make up the pitch detection (PD) method. It is elucidated that the pitch average, uniformity, rotation angle and orthogonal angle can be calculated using the PD-method. This has been applied to the pitch evaluation of several 2D gratings and lattices, and the results are compared with the results of using the CG- and FT-method. The differences of pitch averages which are produced using the PD-, CG- and FT-methods are within 1.5 pixels. Moreover, the PD-method has also been applied to detect the dense peaks of Si (111) 77 surface and the HOPG basal plane.