极紫外光刻掩模缺陷暗场检测系统优化设计
Optimization Design of Dark Field Detection System for Mask Defects of Extreme Ultraviolet Lithography

为了确保基于Schwarzschild结构的极紫外光刻掩模缺陷检测系统的成像质量，本文应用等效工作面法对其进行了优化设计。将传统光学设计方法得到的Schwarzschild放大系统的优化设计反射面视为由多层膜和裸镜面形共同构成，应用多层膜的等效工作面法反演出最佳裸镜面形。设计结果表明，考虑多层膜的Schwarzschild非球面系统全视场调制传递函数达到衍射极限水平，系统两裸镜的最大面形梯度分别为5.9 μm和10.2 μm，适合检测和加工。本文为添加多层膜的光学成像系统能够达到衍射极限水平提供了一种具有较强实用性的设计方法，避免了多层膜严重降低系统成像质量的问题。
In order to ensure the image quality of mask defects detection system based on Schwarzschild structure for extreme ultraviolet lithography, the equivalent working surface model is used to optimize the optical design. The optimal reflector of Schwarzschild amplification system obtained by traditional optical design method is regarded as the combination of multilayers and bare mirror surface, and the optimal bare mirror surface is obtained by using equivalent working surface model of multilayers. The design results show that the full field modulation transfer function of the Schwarzschild aspheric system with multilayers reaches the diffraction limit level, and the maximum surface gradient of the two bare mirrors is 5.9 μm and 10.2 μm, respectively, which is suitable for the system detection and processing. We provided a practical design method for the optical im-aging system with multilayers to reach the diffraction limit level, and our method avoids the problem that the imaging quality of the ideal system is seriously reduced by the multilayers.