极紫外投影光刻(EUVL)两镜微缩投影物镜通常采用Schwarzschild结构和平场结构。本文分析了这两种结构在EUVL不同发展阶段的设计特点,并依据有限距反射系统像差理论,从解析解出发,设计了两套平场两镜系统,分别用于对分辨力为70nm、无遮拦、环形视场扫描曝光系统及目前研制的EUVL 32nm技术节点小视场曝光系统的研究。系统设计指标满足极紫外投影光刻要求。
To study the two-mirror reduced projection optics for Extreme Ultraviolet Lithography (EUVL), Schwarzschild design form and flat field design form were investigated. An analytic design method for flat field design form was employed. Formulas were set up based on the theory of reflective optics with finite object. The initial design of the two-mirror system free of third order spherical aberration, coma, astigmatism and field curvature were determined. Systems were optimized taking special requirements of EUVL into account. Finally, according to analytic solution, two flat-field imaging systems were designed. It is applied to unobstructed scanning system with 70nm spatial resolution and microfield exposure system for 32nm node. Analysis of design results suggests that the latter can satisfy rigid performance specification of EUVL application.