Offner补偿器的结构设计与装调

Design and tolerance analysis of Offner compensator

针对90nm节点光刻投影镜头中使用的非球面存在高次项,且与理想球面偏离量较大的特点,基于像差补偿理论,设计了一种三片式结构的Offner补偿器来实现非球面的高精度检测。采用等量轴向球差补偿非球面各阶系数的方法,主动引入一定量的轴向球差,补偿光线在非球面法线方向的偏离量。结果表明,初级像差和高级像差可很好地平衡,使剩余像差很小;MTF远远超过衍射极限;系统工作波长为632.8nm,F数为1.64,均方波差RMS<λ/1250;系统轴向像差<0.47μm,满足基本干涉成像条件;各方面指标均满足高精度检测补偿器的设计要求。最后,根据现有检测装置的精度对所设计的结果进行了公差分析,给出了较宽松的公差容限。公差分配后,系统综合残余波像差<0.00727λ,满足系统装调精度要求。

To test precisely the aspheric surface in a 90 nm nodal point lithography projecting lens,an Offner compensator with three pieces of lenses is presented based on the aberration theory.The equal quantity of spherical error is introduced to compensate all orders of aspheric coefficients and a certain quantity of axial spherical aberration is brought in to compensate the deviation of aspheric surface in a normal direction.The results indicate that primary and high order aberrations are balanced well,therefore the residual aberration is small enough.Furthermore,the design wavelength is 632.8 nm,the MTF exceeds diffraction limit,and the wavefront error（RMS）is less than λ/1 250.As the F-number can achieve 1.64 and the longitudinal aberration is lower than 0.47 μm,the system can satisfy the basic image formation condition.Finally,a loosen distribution of the tolerance is presented based on the accuracy of measuring apparatus.Analysis results show that the total residual wave aberration of the system is less than 0.007 27λ,which satisfies the requirement of assembling accuracy.