Research On Modeling And Calibration Method Of High-precision Grating Displacement Measurement System

Independence of information science & technology industry is significant for our nation,and localization of lithography machine is one of many necessary chains.Heterodyne grating interferometry is an important measurement technique for precision positioning of the wafer stage of lithography machine.At present,domestic research in this field is mainly focused on the research and development of key equipment,such as lasers with ultra-high wavelength stability,high subdivision number and low noise phase processing boards,large-size high-line-density two-dimensional diffraction gratings,etc.The research of heterodyne grating interferometry technology in measurement modeling and error compensation,especially the error analysis and compensation of heterodyne grating interferometry system,is still lacking.Therefore,this article focuses on the key issues of measurement model and calibration that need to be solved in heterodyne grating interferometry,and studies the modeling of measurement models and the method of verifying model solution errors.Based on the in-depth analysis of heterodyne laser interferometer error compensation methods,study the calibration method of heterodyne grating interferometer.The specific content is as follows:1.Modeling and simulation verification of heterodyne grating interferometer measurement system.Based on the principle of laser Doppler frequency shift,a mathematical model for calculating the displacement of the reading head of the grating interferometer from the laser phase difference is established;according to the structural layout of the measurement system,based on the spatial geometry theory,a position model describing the relationship between the position of the wafer stage and the displacement of the read head is completed;Then according to the principle of equal displacement,a six-degree-of-freedom displacement measurement model of the wafer stage is established.In the error analysis of the measurement model,the model-in-the-loop simulation method is used to verify the solution error of the measurement model,and the model solution error is less than 0.1nm.Aiming at the influence of the uncertainty of the installation error on the calculation error of the measurement model,an estimation method of the installation error threshold of the grating interferometer is proposed.Model-in-the-loop simulation is used to analyze the optimal combination of multiple read head combinations,and finally the switching strategy and switching model between different read head combinations are given for the smooth switching of the read heads.2.Construction of experimental platform for heterodyne grating interferometer.In response to the error compensation requirements of the grating interferometer,an experimental platform for the grating interferometer was built.A structural layout in which the heterodyne laser interferometer and the heterodyne grating interferometer can simultaneously measure the position of the six degrees of freedom of the hexapod microrobot is designed.After experimental testing,the actual resolution of the laser interferometer is 0.154 nm,and the resolution of the grating interferometer is 0.2nm.The short-term repeatability of the laser interferometer is less than 0.5nm,and the repeatability of the grating interferometer reaches 3nm.3.Error compensation method and experiment of heterodyne laser interferometer.Based on the measurement axis layout of the laser interferometer,this paper presents a9-axis laser interferometer displacement measurement model.The zero position of the hexapod microrobot was used to test the zero-return error of the laser interferometer,and the coordinate system of the hexapod microrobot was used as a reference to complete the rough calibration of the laser interferometer coordinate system.The laser interferometer rotation,scanning tilt,and mirror-type calibration methods based on Rz and Ry measurement redundancy are studied.Experimental verification shows that the calibration residual of the laser interferometer measurement value is about 150 nm,which is consistent with the positioning error of the hexapod microrobot.4.Error compensation method and experiment of heterodyne grating interferometer.This article deeply analyzes the sources of heterodyne grating interferometer errors,including instrument errors,environmental errors,model errors,installation errors and switching errors.Taking the measurement data of the laser interferometer as a reference,the zero-return error of the grating interferometer was tested,and the self-gain of the grating interferometer and the non-orthogonal coordinate system were compensated.Using the redundant measurement axis of the grating interferometer,the method of compensating for the non-uniformity error of the displacement of the read head is studied.After experimental testing,the residual of the non-uniformity error compensation is less than0.1nm,and the compensation model of the displacement of the reading head is not uniform.