Research On Ultraprecision Adjustment Mechanism With Slit Diaphragm Flexures For Optical Elements

As the core component of lithography,the development of projection lens represents the development of lithography technology.The main features of the development of projection lens are bigger field of view,higher resolution,the more lens,of coure,more complex system.One of the ways to improve the resolution of lithography is to increase the numerical aperture of the projection objective and improve the image quality of the objective.With the improvement of the resolution of the lithography system,the image quality requirements of the lithography objective lens increases sharply.In order to achieve the strict image quality requirements of the lithography system,the image quality adjustment of the lithography lens needs to be done by the micro displacement mechanism,and the precision of the micro displacement mechanism is often required to reach the nanometer level.This paper aimed at the requirement of the high NA immersion optical system for the objective lens adjustment mechanism.A new kind of slit diaphragm flexures structure is proposed by studying the ultra-precision adjusting mechanism of optical element.The ultraprecision adjusting mechanism with slit diaphragm flexures for optical element is designed,and the related theoretical analysis,simulation and experiment are finished.The main work of this paper includes:1.The Conceptual Design of Slit Diaphragm FlexureFirstly,the slit diaphragm flexure of a×b type is proposed,where ‘a’ represents the number of the curved beams in the radial direction,the connection type of the curved beams is in series.‘b’ represents the number of the curved beams in the circumferential direction,the connection type of the curved beams is in parallel.Different types of slit flexible structures are designed by changing the number of arc-shaped rectangular section beams and the connection mode.2.The Theoretical Analysis of the Slit Diaphragm FlexureThe physical model of slit diaphragm flexure is established.Based on the stress function of elastic mechanics,the stiffness formulas of the adjustment mechanism are derived.3.Optimal Design of the Adjustment MechanismTo ensure the adjustment mechanism with high guidance accuracy,high adjustment accuracy and compact structure,the slit diaphragm flexure is optimized.The stiffness ratio between the radial and axial direction is set as the objective function,the dimension parameters of the curved beam are set as the variables.4.Design and Simulation of the Adjustment MechanismAn adjustment mechanism for lithography objective lens is designed,including the drive device,frame(internal and external frame and slit diaphragm flexure),connector,flexible support,etc.First,the slit diaphragm flexure is simulated,and the simulation value of rigidity is compared with the theoretical analytical value.The results show that the error between the theoretical value and simulation value of the axial stiffness is 6.07%,and 8.33% for the radial stiffness,which indicates the validity of the stiffness calculation.The effect of the adjusting force acts on the surface figure of the optical element is also analyzed,including the effect of axial and tilt adjustment on the surface figure of the optical element.5.Experimental Study on Adjustment MechanismThe experimental platform of adjustment mechanism with slit diaphragm flexure is built up.The PI actuators are used to drive the adjustment mechanism,and the closedloop control system is established with the capacitive sensor.The adjustment precision and the guidance accuracy of the adjustment mechanism are tested respectively.