Study On The Rapid Mold-change And Phase-lock Technology Of Fabry-perot Interferometry Displacement Measurement System

With the rapid development of high-tech industry,the size of chips and the size of very-large-scale integrated circuits is getting smaller and smaller.Therefore,the requirements for displacement resolution and positioning accuracy of aligning system in high-end lithography machine are also getting higher and higher.And higher requirements for displacement metrology are also put forward.Theoretically,the measurement resolution of Fabry-Perot laser interferometry can reach sub-nanometer level or even picometer and without the nonlinear error.Besides Fabry-Perot laser interferometry is traceable.So Fabry-Perot laser interferometer has always been the focus of measurement research.The measurement process of Fabry-Perot interferometer needs laser mold-change.If this process is complex and slow,it will lead in measurement error.Therefore,this thesis conducting a study on the rapid moldchange and phase-locking technique of Fabry-Perot laser interferometry,aiming at establishing Fabry-Perot laser interferometry micro-displacement measurement system that can quickly measure the micro-displacement.Firstly thesis analyzes and summarizes the research status of micro-displacement or small size measurement at home and abroad,describes the principle of Fabry-Perot laser micro-displacement measurement.Aiming at the shortcomings of Fabry-Perot laser interferometry at the present stage,thesis put forward rapid mold-change and phase-locking technique scheme of the micro-displacement system.Secondly the optical path of the Fabry-Perot laser interferometry micro-displacement measuring system is designed and built.The program of the Fabry-Perot cavity transmission light intensity acquisition and conversion is designed based on VC # and data acquisition card,which achieved fast counting of the quantity of interference gradation in the process of displacement measurement.Then the program of scanning laser frequency and locking the frequency of resonant cavity is designed.Finally,the result of the displacement measurement is given by combining the counting result of the interference gradation change with the change quantity of laser frequency.In order to verify the feasibility of the Fabry-Perot laser micro-displacement measurement system,the thesis performed the following experiments:(1)The calibration experiment of the transmission light intensity acquisition module is designed.After the AD acquisition card is calibrated,the conversion error at the peak of light intensity is reduced from 8.4% to 0.1%.(2)System stability test experiment,the experiment measured the average of transmission light intensity peak spacing is 158.4nm,the difference with the theoretical is 0.2nm.And the result of laser frequency locking stability experiment show that the frequency drift is less than 8MHz,indicating that this system is stable;(3)The displacement measurement experiment,the average error of the return value from the PI nano-positioning platform is less than 2.2nm.(4)The comparison experiment with commercial laser interferometer.The experimental results show that the nonlinear error of this commercial laser interferometer is ±2.0nm.