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In order to maintain the dynamic stability of a Deep Ultra-Violet(DUV) lithographic projection objective,a kinematic supporting structure which is able to eliminate the effects of temperature change and external strain is designed.The lens surface deformation due to temperature variation and external strain is studied.Firstly,the theoretical formula for the compliance of a supporting seat is derived,then the radial compliance of the supporting seat is calculated by using the derived formula and is compared with the results of the whole supporting seat from a Finite Element Analysis(FEA) analysis.The lens surface profile variation due to temperature change and external strain is analyzed and the supporting structure is compared with a 3-point glue supporting structure.The calculated results indicate that the absolute difference between the radial compliance obtained from the derived formula and the FEA simulation is within 2.2%,RMS values of the optical surfaces are less than 0.36 nm with a 0.1 ℃ temperature rise,and the RMS values of the optical surfaces are less than 0.05 nm for a manufacturing tolerance is 5 μm.Compared with the 3-point glue suporting method,the kinematic supporting structure can eliminate the effect of temperature change and outside strain on the lens surface. |
