Spatial Virtual Linear Motion Datum Technology Based On Real Time Measurement And Motion Adjustment

Spatial linear motion datum is one of the most fundamental and important components to guarantee the motion accuracy of the lithography.Reticle Stage is one of the key subsystems in the step-and-scan lithography.Its high-precision spatial linear motion with constant velocity is the fundament and premise for the subsequent alignment and etching with higher precision.The motion is required to be marker reference point-centerred,with constant attitude and along the design axis.However,current 6-DOF measurement techniques are restricted in the limited precision and noncoincidence with design axis,and 6-DOF motion precision is influenced by vibration disturbance and motion coupling.These two problems are main technical obstacles in spatial motion linear motion of Reticle Stage.The purpose of this paper is to solve those problems above.By analyzing the special 1-DOF large range and 6-DOF high precision measurement and motion requirement of Reticle Stage,a spatial virtual linear motion datum technology based on real time measurement and motion adjustment is proposed,in which the mathematical spatial line corresponding with design axis is directly applied as the measurement and motion reference.With a full model of measurement system,the spatial position of reference point and relative position between it and spatial line are real time measured simultaneously.By combining quasi-zero stiffness and damping suspension and 6-DOF closed-loop control,Reticle Stage could real time track the design axis.This technology could realize the coincidence between spatial linear motion and the design axis,and also guarantee the measurement and motion precision.Firstly,in order to solve the problem of limited precision and noncoincidence with the design axis of 6-DOF measurement,a 6-DOF measurement method based on a full model of unclosed measurement loop is proposed.Beginning with the fundamental principle of measurement with unclosed loop,the changing unclosed part of measurement loop is real time defined,so that the solution error of multi-DOF position in this part could be eliminated.And with comprehensive analysis on structural errors of real measurement system,the solution error of multi-DOF position and influence of structural errors in the closed part of measurement loop could be eliminated.Then a full model of 6-DOF measurement system is established.This model could obtain the spatial position of reference point and relative position between it and spatial line are real time measured simultaneously,and guarantee the measurement precision of reference point and coincidence with the design axis.Secondly,to solve the problem that the vibration disturbance and motion coupling restricting the 6-DOF motion precision of short stroke stage in dual-actuator stage system,a motion technology with quasi-zero stiffness and damping suspension is proposed.Magnetic gravity compensators are designed to balance the gravity of short stroke stage.Based on the equivalent current model,the mathematical model of suspension force and stiffness is established and verified with simulation and experiment.With magnetic gravity compensators,the preliminary magnetic levitation of short stroke stage is realized.Then a 6-DOF kinematic decoupling model and a force decoupling model are established to decouple the 6-DOF motion with respect to the reference point.With analysis on the generation mechanism of parasitic stiffness and damping between short and long stroke stages in real system,the caused position-dependent and velocity-dependent disturbance forces are identified in time and frequency domains,respectively,and compensated by force feedforward method.On the basis above,the quasi-zero stiffness and damping suspension of short stroke stage is realized.This technology could effectively isolate the vibration and eliminate the influence of decoupling model error,so that the motion precision of short stroke stage is significantly enhanced.The experimental results show that that suspension stiffness in horizontal and vertical DOF is lower than 500N/m and 70N/m,and the damping is lower than 0.23Ns/m.The displacement and angle resolution is less than 30 nm and 8?rad.Dual-stage actuator technique is then researched,and a structural design method for 1-DOF long stroke stage is proposed.On the basis of these researches above,the Reticle Stage is developed.And corresponding experiments are designed to test its servo properties in time and frequency domain,displacement and angle resolution in each DOF,6-DOF measurement and motion decoupling ability,motion performance of the dual-actuator stage system,etc.The experimental results could verify the effectiveness of measurement method and motion technique.In order to indirectly test the accuracy and repeatability of the linear motion datum,straightness error of an optical flat is measured and the results are comparison with a commercial Fizeau Interferometer.Finally,the analysis on uncertainty of the linear motion datum is conducted.Results demonstrate that its combined standard uncertainty is 21 nm in a range of 220 mm,and the velocity uniformity is smaller than 2.4%.