Optical inverse scattering phase method for nano-in-process measurement of microsurface profile

Measurement techniques of processed micro surface profiles have been increasingly required in the production of microstructures. Especially the demands on evaluating the dimensional characteristics ofmicrostructure components by in-situ and inprocess measurement are quite high. In this paper, we propose an optical measurement method that can be applied to the inprocess measurement of micro surface profile with an accuracy in the nanometer order. Surface profiles are reconstructed by measuring two intensity images, Fraunhofer diffraction pattern of coherently illuminated work surface and an optical microscope image. In this method, the whole illuminated surface can be measured at one time and no scanning process is imposed, and measurement is not likely to be affected by vibration and tilt of work. Such features are advantageous for in-process measurements. Numerical simulations based on Maxwell's equations and the theory ofFourier optics were performed for the verification ofthe proposed method. The results obtained here demonstrate that nanometer accuracy is achievable. An instrument is designed and developed, and an example of experimentally measured Fraunhofer diffraction intensity of an ultra precision grid plate standard which has rectangular pockets 44nm deep at intervals of lOim is presented.