Research On Design And Stiffness Characteristics Of Compliant Linear Guiding Mechanism Of Variable Slit System In The Lithography Machine

In the variable slit system of extreme ultra-violet(EUV)lithography machine,the precision control of the exposure area in the optical syst em is realized by the high-precision linear movement of the combined blades.Air flotation guiding mechanism,maglev guiding mechanism and other guiding mechanisms can’t be used in the EUV variable slit system because of the design space constraints and vacuum constraints.The compliant linear guiding mechanism can be applied in the EUV variable slit system due to its advantages of high accuracy,no cooling requirement,no friction,no lubrication requirement,and no cable.The research of compliant linear guiding mechanism with large stroke is very important for the development of EUV lithography machine in China.This research is of great significance for the independent production of chips with high performance in China.Most of the compliant mechanism at current stage are applied in the micro stage and micromanipulator.The stroke of these compliant mechanism is too small to meet the requirement of EUV lithography machine.The stiffness model of compliant mechanism can be used directly to analyze characte ristics of mechanism and guide structural design.The large stroke of compliant mechanism is realized based on the nonlinear large deformation of flexure beams within the given design space.In order to ensure the motion accuracy and stability of the compliant linear guiding mechanism with large stroke,the stiffness of the flexure beam along the working direction needs to be low and the stiffness along non-working directions needs to be high.There is shear deformation along the width direction in the spatial deformation of this kind of flexure beam.However,at present,only spatial bending deformation and torsional deformation can be presented by the 6-DOF stiffness model of the flexure beam under large deformation.The accuracy of the stiffness model can ’t meet requirements when it is used to represent the nonlinear stiffness of the flexure beam in the compliant linear guiding mechanism.To solve this problem,a high-precision 6-DOF nonlinear stiffness modeling method for this type of flexure beam is prop osed in this paper.The application of compliant mechanisms is limited by its resilience force.The negative stiffness compliant mechanism can be applied in the large stroke compliant linear guiding mechanism to compensate resilience force.The stiffness along working direction can be reduced and motion flexibility can be improved by compensating resilience force.A structure of compliant linear guiding mechanism with large stroke(>0.4 L,L is the length of flexure beam)is proposed in this paper.There is a resilience force compensation module in this structure.The static stiffness model of the compliant linear guiding mechanism is established and analyzed based on the nonlinear stiffness model of the flexure beam.The stiffness characteristics of mechani sm is analyzed based on the stiffness model.The main work of this paper is as following:(1)A new high-precision stiffness modeling method is proposed.The 6-DOF nonlinear stiffness model of the flexure beam with large deformation is established.This method can be applied to establish the stiffness model of the flexure beam(w/L>0.4,t/w<0.1;w is the width of the flexure beam,t is the thickness of the flexure beam)with low stiffness along the working direction and high stiffness along non-working directions(ratio of stiffness along non-working directions to stiffness along working direction is larger than 50).The accuracy of spatial nonlinear stiffness is ensured by introducing shear deformation characterization term to the stiffness along the width direction.In this paper,a multi-element global model of flexure beam with large deformation(>0.4 L)is established.The flexure beam is discretized into multiple flexure elements with equal length by the multi-element global model.The deformation of every flexure element is within the range of small deformation(<0.1 L).The 6-DOF constitutive relation of spatial flexure beam element is modified based on Timoshenko flexure beam theory.The differential equations are established based on the space coordinate transformation matrix and the curvature,torsion expressions.The analytical expressions of the flexure beam element 6-DOF stiffness is obtained.The 6-DOF stiffness model of the flexure beam under large deformation can be obtained by introducing the flexure beam element stiffness into the multi-element global model.The influence of structural parameters on the stiffness of flexure beam is analyzed based on the theoretical stiffness model.Finally,the accuracy of this method is verified by finite ele ment simulation.The error between simulation results and theoretical results is less than 2.5%.(2)A structural scheme of compliant linear guiding mechanism with large stroke(>0.4 L)is designed.The system coupling error is eliminated in principle scheme based on the symmetric structure.The large stroke is realized based on the series structure.The motion stability of the system is enhanced based on the multi-layer structure.The motion flexibility of the system is enhanced based on the negative stiffness mechanism.The 6-DOF stiffness model of the compliant linear guiding mechanism is established by the discretization model based on the nonlinear spatial beam element.The overall 6-DOF stiffness model of the mechanism is obtained by introducing the pr oposed high-precision stiffness model of large deformation flexure beam under large deformation.The influence of the compliant linear guiding mechanism structural parameters on the stiffness along working direction of the mechanism is analyzed based on th e nonlinear stiffness model.A design method of structural parameters is proposed based on the analysis results.The negative stiffness structural parameters of the compliant linear guiding mechanism obtained by this method can achieve the best resilience force compensation effect in the whole stroke.The performance of the designed mechanism can meet various system requirements.(3)A compliant linear guiding mechanism is developed and its characteristics are verified by experiments.The stiffness along th e working direction and the bearing direction(Z-axis)of the compliant linear guiding mechanism in the whole stroke are tested.The error between the experimental and theoretical results of the stiffness is less than 6.8%.Compared with the stiffness test results without compensation by the negative stiffness compliant mechanism,the stiffness along working direction is reduced by 97.3% after compensation.The motion flexibility of the system is greatly improved.The motion straightness of the compliant linear guiding mechanism in the whole stroke is tested.The measured straightness error result of the mechanism along the Y direction is 6.9μm and the result along the Z direction motion is 3.8 μm.