Scanning projection grating moire topography

One problem with moire topography for 3D surface metrology is the so-called 2(pi) -ambiguity limiting the maximum step height difference between two neighboring samples points to be less than half the equivalent wavelength of moire fringes. To cope with the ambiguity problem, a special scheme of scanning moire technique is proposed by resorting to the frequency domain fringe analysis that is in fact originated from white light scanning interferometry. This new more principle of 3D measurement allows determining the absolute height of the surface without information on absolute fringe orders so that largely stepped surfaces are measured with a great improvement in accuracy.