Dual wavelength optical metrology using ptychography

We describe an experimental implementation of ptychography to optical metrology, in particular topography measurement, in combination with the dual wavelength method. This is the first published account of the application of the dual wavelength method to ptychography or any other phase retrieval method in order to obtain surface height information over a wide range of scales, from small fractions of a wavelength up to many tens of wavelengths, in reflection mode. Moreover, the work presented here is the first report on the application of lensless reflection mode ptychography. Advantages of the ptychographic dual wavelength method are compared with other optical topography measurement techniques, especially with respect to the experimental procedures and constraints and the analysis of the data. We show that dual wavelength ptychography can remove material-specific phase changes which adversely affect topography measurements using white light profilometry.