3D Micro-Profile Measurement using Optical Inverse Scattering Phase Method

Abstract With the advance of the nano-technology, especially micromachining, in-process measurement techniques for micro-machined profiles in the submicron order are increasingly required. However, conventional Scanning Probe Microscopes (SPM) come with numerous problems in applications to in-process measurement. In this paper, we propose a new optical measuring method which can be applied to the in-process measurement of three-dimensional micro-profiles with accuracy in the nanometer order. The optical inverse scattering phase method offers the advantage of measuring a three-dimensional profile within the whole area illuminated by the laser beam simultaneously. No scanning process is required. Employing Fourier phase retrieval algorithm, three-dimensional micro-profiles are reconstructed from only the measured Fraunhofer diffraction intensity. Computer simulations and actual measurements were performed for the verification of the proposed method. The result obtained in the measurement for an ultra precision grid plate, which has rectangular pockets 44nm deep at intervals of 10μm, shows the validity of this method.