深紫外双层金属光栅偏振器的设计与分析

Design and analysis of bilayer metallic grating polarizer in deep ultraviolet band

193 nm波长浸没式步进扫描投影光刻机是实现45 nm及以下技术节点集成电路制造的核心装备.增大数值孔径是提高光刻分辨率的有效途径,而大数值孔径曝光系统的偏振性能严重影响光刻成像质量.光刻机曝光系统偏振参数的高精度检测是对其进行有效调控的前提.基于光栅的偏振检测技术能实现浸没式光刻机偏振检测装置的小型化,满足其快速、高精度在线检测的需求,该技术中的关键部件是结构紧凑且偏振性能良好的光栅.本文基于反常偏振效应和双层金属光栅对TE偏振光的透射增强原理,采用严格耦合波理论和有限时域差分方法,设计了一种双层金属光栅偏振器.计算了该偏振器的初始结构参数,并通过数值仿真得到了其偏振性能关于各光栅参数的变化关系.仿真结果表明,中间层高度是影响TE偏振光透射增强的主要因素;垂直入射时TE偏振光的透过率可达到56.8%,消光比高达65.6 dB.与现有同波段金属光栅偏振器相比,所设计的光栅偏振器在保证高透过率的同时,消光比提升了四个数量级.

The 193-nm immersion step-and-scan projection lithography tool is the most critical equipment in the highvolume manufacturing of integrated circuit with 45nm technology nodes and beyond.With the increase of numerical aperture(NA)of the projection lens,the resolution of lithography tool can be enhanced effectively.However,the polarization effect of the optics in an exposure system is more significant in high NA immersion lithography,which influences the lithographic imaging quality greatly.Thus,the polarization parameters of the immersion exposure system should be controlled-accurately for ensuring the lithographic imaging quality.With the advantages of miniaturization and high-accuracy online detection,the grating is applied to the polarization detection of the immersion lithography tools.A bilayer metallic grating polarizer with compact structure and excellent polarization performance is designed based on the inverse polarization effect and transmission enhancement effect on TE-polarized light.Rigorous coupled-wave theory and finite-different time-domain method are used to design the bilayer metallic grating polarizer.The former is used for analyzing the initial structure parameters of the grating,and the latter is used for acquiring the cross-sectional electromagnetic field of the structure.The initial parameters of the grating are calculated based on the surface plasmons resonance and Fabry-Perot-like theory.The influence of geometrical parameters of the grating on its polarization performance is analyzed.The simulation results show that the enhancement of TE-polarized light transmittance is mainly modulated by the middle layer height of the grating.Firstly,the TE-polarized light transmission is enhanced by the standing wave in the bottom medium cavity,and further enhanced by the top optical funnel formed.However,the transmission suppression of TM-polarized light is mainly caused by the low frequency mode of charge movement formed by surface plasmons.For the designed grating polarizer,the transmittance of TE-polarized light is 56.8%,and the extinction ratio is 65.6 dB at normal incidence.Comparing with previous metal grating polarizer,the extinction ratio of the designed grating is increased by four orders of magnitude.