Alignment Of The Initial Position In Multiple-wavelength Microscopic Interferometry Driven By PZT

Multiple-wavelength micro-interferometry is widely used in surface topography measurement of micro-nano elements in scientific research and industry applications.However,with the influence of environmental vibration and the hysteresis and creep behavior of the piezoelectric transducer(PZT),it is difficult to ensure the starting positions are the same when the PZT is controlled with open-loop.The misalignment of the initial positions will influence the measurement accuracy.Therefore,this paper proposes an alignment method of the initial position in multiple-wavelength microscopic interferometry driven by PZT.The main contents are as follows.Firstly,the basic principle of multi-wavelength interference and PZT driving characteristics are analyzed,and a phase shift method to drive the PZT by zigzag with a fallback path is proposed,The structure of the multi-wavelength interference system is designed,and the principle of dual-wavelength,multi-wavelength interferometry and the calculation method of the height of the shape are analyzed.Based on the hysteresis,creep moving features and open-loop,closed-loop control characteristics of the PZT,three different phase-shifting driving methods are analyzed,and a phase shift method to drive the PZT by zigzag with a fallback path is proposed.The method can not only overcome the influence of the creep hysteresis characteristic of PZT on the measurement accuracy,but also improve the phase shift efficiency.Secondly,an alignment method of initial positions of multiple-wavelength is proposed.A high-precision phase extraction algorithm is designed.Two sets of pixel points with phase shifts close to k?+(?/2)+? are selected in a series of interferograms,and then ellipse fitting and phase unwrapping algorithm are used to obtain the total drive phase shift amount and initial phase of each wavelength.Then,according to the multi-wavelength phase shift driving start and end positional relationship,the initial positions of the other wavelengths are moved to coincide with the starting position of the first wavelength to achieve coarse alignment.On the basis of the coarse alignment,the 0-level interference fringes are obtained by using the already-aligned initial phase and the design algorithm is used to finely align the initial phase of the initial position.Then,on the basis of initial phase alignment,a software algorithm is proposed to obtain 0 order interference fringes by using the aligned initial phase.The algorithm USES the phase difference of near wavelength,far wavelength and single wavelength to find all the pixels in the vicinity of 0 optical path,further carry out the initial phase alignment,and finally USES the aligned initial phase to calculate the height of the topography,so as to improve the measurement accuracy of the final surface topography while expanding the height measurement range.Finally,multi-wavelength interferometry experiments are fulfilled and alignment accuracy is analyzed.Based on the analysis of the spectral characteristics of the white light source,three different bandwidth filters were selected,and the multiple-wavelength phase shift driving software based on VC++ was programmed to realize the automatic rotation of multiple wavelengths and synchronous acquisition of corresponding interferograms.The experimental results show that the zigzag with a small voltage fallback drive mode can overcome the PZT driving inertia,and the proposed alignment algorithm can ensure the alignment error of the initial positions of different wavelengths are less than 3.44 nm.