Zhang Yaqin, Wu Rengmao, Zheng Zhenrong
Appl Opt. 2014 Nov 1;53(31):7296-303. doi: 10.1364/AO.53.007296.
Off-axis illumination (OAI) is a promising resolution-enhancement technology in optical lithography. This paper aims to provide some practical OAI solutions for optical lithography by using freeform surfaces. An integrated Monge-Ampère (MA) equation method is presented here to find these solutions. By this method, the OAI design is converted into a nonlinear boundary problem for the elliptic MA equation. Then, the L Monge-Kantorovich theory is used to find an initial design for the iterative scheme of the MA method. The prescribed OAI patterns are successfully achieved with energy efficiency of more than 99.9% and relative standard deviation of irradiance of less than 0.009. Smooth freeform surfaces that are much easier to fabricate are obtained, and the achieved OAI designs have large tolerance to the spread angle of the collimated beam. This may be a significant step toward a practical technique for OAI design in optical lithography.
离轴照明（OAI）是光学光刻中一种很有前景的分辨率增强技术。本文旨在通过使用自由曲面为光学光刻提供一些实用的OAI解决方案。本文提出了一种集成的蒙日 - 安培（MA）方程方法来找到这些解决方案。通过这种方法，OAI设计被转化为椭圆型MA方程的非线性边界问题。然后，利用L蒙日 - 康托罗维奇理论为MA方法的迭代方案找到初始设计。成功实现了规定的OAI图案，能量效率超过99.9%，辐照度相对标准偏差小于0.009。获得了更易于制造的光滑自由曲面，并且所实现的OAI设计对准直光束的发散角具有较大的容差。这可能是迈向光学光刻中OAI设计实用技术的重要一步。
