Study On Wafer Exchange Technology Based On Coplanar Equilibrium Of Parallel Compliant Mechanism

The wafer exchange is defined as the transportation of wafer between transportation mechanism and workpiece table.Its characteristics of stability,accuracy and rapidity ensure lithography process to be safe,stable and efficient.The stability characteristic can avoid wafer broken.The accuracy characteristic can meet the requirement of alignement.The rapidity characteristic is related to throughput.Compliant mechanism smoothly and continuously exchanges,and improves performance and reliability.However,the complex motion and the different attitudes of interface increase the difficulty of mechanism design,attitude analysis and motion control.Therefore,the stability,accuracy and rapidity of wafer exchange are difficult to realize.And the application of compliant mechanism is restricted in lithography.This dissertation aims to solve the problem of the stability,accuracy and rapidity of wafer exchange in lithography.In this dissertation,the compliance model of parallel compliant mechanism is studied.Based on the analysis of the coplanar equilibrium of interface,the method of wafer attitude calculation is proposed.And the minimum region plane fitting method is used to provide the interface information.The stability and accuracy of wafer exchange are achieved.T he time optimization and precision positioning method is proposed in amplitude limiting.And the rapidity of wafer exchange is realized.The main research contents of this dissertation are described as followings:In order to solve the problem that simple flexible element model can not describe the compliance of compliant mechanism and the change of wafer attitude,the compliance model of global mechanism is established.Based on the screw theory,the eigencompliance of compliance matrix is analyzed.Structural parameters are optimized to meet the requirements of stability.A solving method of wafer attitude is proposed based on the coplanarity of parallel compliant mechanism.After analyzing the mechanism of coplanarity equilibrium,equilibrium equations and geometric constraint equations are established to solve wafer attitude accurately.Simulation results show that parallel compliant mechanism can greatly reduce wafer tilt caused by the difference of interface height,and adjust the inclination of interfaces to realize coplanarity,and eliminate stress concentration caused by point contact,and make wafer exchange more stable.Experimental results show that the deviation between experiment result and theoretical analysis result is less than 0.2mrad,and the validity and effectiveness of attitude calculation method are verified.In order to solve the problem that the exact solution of minimum region and the efficient processing of a large number of discrete points are difficult to be considered in plane fitting of interfaces,a new method of reduced constraint region and convex hull edge is proposed.This method reduces the searching range of the edge by the constraint area of plane normal vector,and obtains the geometric characteristic point and the minimum region exact solution by convex hull projection method.To test the validity of the method,a number of test data set s including those published in the literature and new large data sets of the actual measurements are solved.Simulation results show that the proposed method can obtain the minimum region solution which is equal to or better than existing algorithms,and can deal with a large number of convex hull data with high efficiency and reliability,and realize the minimum region exact solution of interface,and ensure the accuracy of the wafer exchange.In order to solve the problem that the balance among optimal time and high precision and the limit of control amplitude is difficult,the motion model of parallel compliant mechanism is established.A zero-phase error tracking and constraint deadbeat control method is proposed.Amplitude is controlled by modifying the number of control beats,and the control quantity of each beats is solved by nonhomogeneous linear equations.The tracking performance of control system is improved by increasing the zero phase error tracking feedforward.Simulation results show that input voltage amplitude is limit to 6V.100?m step takes 8ms which includes 4 sampling periods,and step response is accurate and stable,and control system has a good tracking performance.Finally,an experimental platform is built,and the performance of mechanism and wafer exchange are experimented.Experimental results show that parallel compliant mechanism can achieve 1?m resolution near the exchange position,8ms step response time with a stroke of 100?m,which is 59.4% shorter than traditonal method,and 2?m position error.New control method takes 0.454 s for wafer exchange,which is 9.9% shorter than that of the traditional method.The validity and effectiveness of the proposed method are verified,and the rapid and high-precision wafer exchange is realized.