Study On The Compensation Technology Of Lens Deformation Caused By Gravity

Generally speaking, in the visible band, when the optical lens aperture issmall, the deformation caused by self-weight is basically negligible for ordinaryoptical system. But in some high-accuracy optical system such as193nmphotolithographic objective lens of which the largest diameter reaches300mm, asingle lens errors caused by gravity deformation can reach tens of nanometers, whichwill seriously affect the imaging quality of the optical system. Therefore, it’s of vitalsignificance to analysis and compensate the lens gravity deformation.In photolithographic objective lens, the working state of optical elements isdifferent from the processing and detection state.It leads to the differentgravity deformation between lens’ up surface and down surface. In order to solve thisproblem,this paper presents a method to compensating lens gravity deformation.Themethod calculates the gravity deformation of lens by finite element analysis softwareand compensates the deformation during the processing stage,so that the lens is veryclose to the ideal surface after the gravity deforming. The ultimate aim of the study isto reduce the gravity effect on the imaging quality of the optical system through thegravitational deformation compensation technique.This paper’s research content mainly includes the following aspects:The engineering analysis method of lens gravity deformation is briefly introduced,among which the analytic method and the numerical analysis method are respectivelyused to calculate the gravity deformation of lens simplified model. The influence ofsize effect on deformation is analyzed and the calculating results through analyticmethod and numerical analysis method are compared, which verify the rationality andfeasibility of engineering analysis method.In order to solve the problem that the gravity deformation of lens up surface isdifferent from that of the down surface,which is caused by the difference between theworking state of optical elements and the processing and detection state inlithography objective system,a method to compensating lens gravity deformation ispresented in this paper.The method calculates the gravity deformation of lens by finiteelement analysis software and compensates the deformation during the processingstage,so that we can get the deviation between the ideal surface and the compensatedsurface.Then the deviation is fitted by Zernike polynomials from which we can know the aberration of the deviation.The effect of gravity deformation on a whole optical system is stuied.The24lenses which form the whole193nm lithography objective system are carried on thegravity deformation analysis and deformation compensation. After adding the residualsurface error without rigid body displacement on the ideal surface of the whole opticalsystem,the influence of gravity deformation on imaging quality of the optical systembefore deformation compensation and after are compared,which verifythe compensation methods presented in this paper is meaningful to improveimaging quality of optical system.