极紫外光刻投影系统中高反膜厚度一般约300 nm，远大于13.5 nm的工作波长，光能并不能完全穿透膜层入射到基底，从而引入数倍于波长的额外光程差，降低系统成像质量。从能量调制的角度提出了一种基于能量守恒定律的多层膜等效工作界面模型，将光学薄膜中复杂的物理光学过程等效地转换为简单直观的几何光学过程，获取可被常用光学设计软件识别的数据，进而实现对有膜光学系统的分析。利用该模型对不同系统进行了分析优化，获得了一套可实现衍射受限成像的有膜系统方案，证明了基于能量守恒的等效工作界面的有效性，指导后续系统的装调，为多次反射系统的分析提供了一种方法。

The thickness of multilayer coatings in extreme ultraviolet lithography (EUVL) projection system is about 300 nm which is much greater than the work wavelength of 13.5 nm. The most energy can not punch the substrate and optical path difference of dozens of wavelength is induced. Then the image degrades. A model named equivalent work surface (EWS) is built up for coating analysis based on the principle of energy conservation. From the point of erengy modulation, the EWS model transforms the complex physical optics into brief and intuitive geometrical optics, getting recognizable data for commercial softwares. Finally with the aid of EWS, a diffraction-limited virtually-coated system is confirmed, proving the significance of the EWS model. The model can be used for the direction of following alignment and multi-reflection system optimization and coating analysis.