Key Techniques Of Linnik Polarization-Sensitive White Light Interferometry In Micro/Nano Measurement

With the demand for the continuously miniaturization and precision of machinery, electronics, optics, material and semiconductor industries, three-dimensional topography, thin-film thickness, internal structure and physical property play an essential role in the research, production and quality control of the developed micro-/nano-stuctures. Therefore, the study of the three-dimensional non-contact measurement system and techniques for the field of the micro-/nano-manufacturing has significant academic value and practical meaning.In this paper, a three-dimensional non-contact measurement system based on the Linnik polarization-sensitive white light interferometry (PSWLI) configuration is proposed and established, and its key techniques are studied. The techniques include the optical autofocus of microscopic system, the automatic search of Linnik white light interferogram, the three-dimensional surface topography and system calibration, the three-dimensional topography of thin-film thickness, the internal stress induced birefringence measurement and the three-dimensional optical coherence microscopy. The overall system configuration, which is modified and expanded based on the traditional Linnik interference configuration, can switch to the appropriate mode according to the different techniques and does not have to disassemble and remove any part of it. Thereby, the developed system has a high flexibility and stability.The main work and the innovation of this thesis are concluded as follows:1. An improved astigmatic autofocus system is embedded in the Linnik PSWLI to make the unique identification of the best focus position of the microscope and thus realizes the fast autofocus of the two interference arms of the Linnik PSWLI. The developed autofocus system has a dynamic range of190(±95) μm, average sensitivity of70mV/μm, average standard deviation of41.6nm, displayed resolution of4.4nm, accuracy of55nm, and autofocus time less than0.3s.2. An automatic search stratege of Linnik white light interferogram of the best fringe contrast by adjusting the optical path difference is proposed under the circumstance that the two interference arms are auto-focused. The automatic search time is2.2min/mm, and the best fringe contrast position obtained by the proposed method does not deviate the ideal one from one cycle of the interference signal at most.3. The three-dimensional surface topography of the mico-/nano-structure is realized by the frequency domain analysis of the interference signal. In accordance with the results of the calibration experiment, the system has a measurement standard uncertainty of±3.6nm, error of the axial measurement accuracy of3.08%, error of the lateral X-direction measurement accuracy of2.69%, error of the lateral Y-direction measurement accuracy of2.16%, practical lateral resolution of1.31 μm and theoretical axial resolution of0.59nm.4. The weighted method of Fourier phase and amplitude for the thin-film thickness measurement is proposed according to the sensitivity analysis. The weighted method combines the advantages of the Fourier phase of high resolution and the Fourier amplitude of high repeatability. The axial resolution of the measurement result achieves nanometer, and the lateral resolution equals to that of the microscope objective.5. Linnik white light interferometer configuration combined with polarization-sensitive detection is used to simultaneously measure the phase retardation distribution, the optical axis orientation, the stress distribution and the reflectance distribution of the internal stress induced birefringence sample. The standard deviations of the phase retardation and the optical axis orientation are less than4°and4.5°, respectively, according to the calibration results of the Berek compensator.6. A five-point-stencil (FPS) based phase shifting algorithm, which has high computation efficiency and small parasitic fringe amount, is proposed to effectively measure the optical coherence microscopic image of a sample. The two major systematic errors, detector nonlinearity and dependence of the PZT phase shifter on the wavelength, are analyzed and the improved methods are discussed.7. An achromatic (geometric) phase shifting interference system and technology are proposed to tackle the aforementioned problem of the dependence of the PZT phase shifter on the wavelength. The developed geometric phase shifter configuration, by which the shifted phase is eight times the rotation angle of the half-wave plate, has the largest magnification of the phase shifting and the best achromatism. This part is the extension of the study.