10 nm以下光刻技术牵引极紫外(EUV)光刻物镜向超高数值孔径(NA)、组合倍率设计形式发展,物镜系统的入射角和入射角范围因此急剧增大,传统规整膜和横向梯度膜难以满足该类物镜系统反射率及像质要求。为此,提出了横纵梯度膜组合法,用横向梯度膜提高反射率,用纵向梯度膜提高反射率均匀性,并补偿横向梯度膜引入的像差。应用该方法对一套NA为0.50的组合倍率EUV光刻物镜进行膜层设计,设计结果表明,在保证系统成像性能不变的情况下,平均每面反射镜的反射率大于60%,各反射镜的反射峰谷值均小于3.5%,满足光刻要求,验证了横纵梯度膜组合法的可行性。

High numerical aperture (NA) projection objectives with anamorphic magnification are demanded for extreme ultraviolet (EUV) lithography down to 10 nm resolution, which results in extreme increase of incident angle and incident angle range of objective lens system. Traditional normalized multilayer film and laterally graded multilayer film cannot satisfy the requirement of reflectivity and image quality in the projection objectives. A method combining laterally graded multilayer film with depth graded multilayer film is presented. The laterally graded multilayer film is used to increase the reflectivity and the depth graded multilayer film is used to enhance the reflectivity uniformity and compensate the wavefront aberration introduced by the laterally graded multilayer film. The method is used to design the multilayer film of an anamorphic magnification EUV lithographic objective with NA of 0.50. The results show that the average reflectivity of each mirror is higher than 60% and the reflectivity peak-to-valley value of each mirror is less than 3.5% with imaging performance unchanged. Which satisfies the lithographic requirement, and verifies the feasibility of this method.