光逆散乱位相法による微細加工形状計測に関する研究 周期微細溝形状の位相回復

Abstract

A new optical measuring method which can be applied to in-process measurement of micro-machined surface profile with an accuracy of submicrometer order is proposed. The principle of measurement is based on the optical Fourier transform and phase retrieval method. The phase information is retrieved by applying logarithmic Hilbert transform and Fourier series expansion to two Fraunhofer diffraction intensities, which are related to square of the modulus of Fourier transform of object field, with and without an exponential filter at the object plane. In order to verify the validity of the proposed method, first, computer simulations of reconstruction of the fine groove models are performed. Second, the inverse scattering phase measuring system consisting of Fourier transform optical arrangement with an exponential filter is developed. And the measurements of the fine triangular groove with the pitch of 4.75μ m and the height of 0.2μ m which is fabricated by ultra precision diamond turning are carried out. It is found that the proposed measurement method is effective for reconstructing the profile of a submicrometer size workpiece without scanning probe and stylus.