Research On Mechanism And Correction Of Color Deviation For White Light Interference Fringes

The white light microscopic interferometry,which combines white light interferometry with microscopic imaging technology,can realize the measurement of microcosmic three-dimensional morphology.Because of a series of advantages,like fast,non-contact,high precision,it has been widely concerned for many years.Ideally,the center of the white light interference signal is the zero-order fringe with the largest contrast,and the two sides of the zero-order fringe are symmetrical color fringes.However,in the actual assembly process,it is difficult to ensure that the reference arm and the test arm match perfectly,and the dispersion will be inevitably introduced to make the two sides of the zero-order fringe asymmetric,resulting in color deviation,which will affect the morphology measurement.In this paper,based on the intensity expression of white light interference fringes and the optical path structure of Mirau interference microscopic objective,three reasonable sources of color deviation errors are given.On the basis of the theory of double beam interference,the models are established for the two error sources of the thickness difference between the reference plate and the splitter plate and the inclination of the reference plate.According to the interference signal evaluation method proposed,the influence of the above two error sources on the shape of interference signals is quantitatively analyzed.Then the effect of color deviation on the accuracy of surface restoration is studied,therefore an original polygon is set,a series of interferograms are generated according to the color deviation models to simulate the scanning process,Fourier transform method and eight-step phase shifting algorithm are used to reconstruct surface morphology to obtain restoration error.According to the size of restoration error,the anti-dispersion performance of the two algorithms is compared and the tolerance of the maximum thickness difference between the reference plate and the splitter plate and the maximum inclination of the reference plate are given.The error source of phase change of reflected light on metal surface is studied,the situation that may cause restoration is discussed,and the corresponding correction method is proposed.Finally,the experiment verifying the influence of error source of color deviation on the interference fringes and restoration accuracy is done,the 90.5nm standard step and the amplitude-type computational-generated holography(CGH)are selected as the test objects,and the test results are compared with the simulation analysis to verify the correctness of the theoretical model and the correction method.