基于纳米压印技术的全硅介质超透镜的制备工艺研究

传统的光学共聚焦系统往往通过增加一定数量的光学透镜或者使用不同材料的光学透镜组合来实现多波长共聚焦，使得系统具有较大的体积和重量。超透镜作为二维平面亚波长微元结构组成的光学超构表面，通过设计其微元结构的相位和偏振等可实现传统透镜组的聚焦和成像功能，在高度集成化、微型化和便携式的光学共聚焦系统中展现出了巨大的应用潜力。

本文根据传输相位原理和超透镜聚焦相位分布公式设计了一种由矩形纳米硅柱构成的全硅介质超透镜，该透镜可以在波长为10.6 μm的x线偏振光和波长为9.3 μm的y线偏振光入射时实现共聚焦。超透镜整体为边长30 mm的正方形，由4840×4840个全硅介质微元结构按照周期性排列组成，其中矩形硅柱的长宽在1.5～5 μm范围内变化，高度固定为6.8 μm，排列周期为6.2 μm。根据几何参数，本文通过激光直写光刻技术和感应耦合等离子体刻蚀技术制备了超透镜样品，激光共聚焦显微镜对结构的表征结果表明加工符合设计要求。

由于纳米压印技术在光学超构表面产业化方面展现出的巨大潜力，本文对紫外光固化纳米压印技术和感应耦合等离子体刻蚀技术转移超透镜图案的工艺进行了重点研究。综合分析了压印过程中压印胶的流变和填充机理以及脱模过程中力与界面的相互作用，并提炼出压印胶厚度、压印力、压印时间、固化时间、脱模方式以及脱模速度等关键因素对压印工艺进行综合设计，成功把超透镜图案从硅模版转移到了压印胶PixNIL-ST2上。

因为PixNIL-ST2中含有TiO₂，本文选择了Cl₂/BCl₃作为残胶层刻蚀气体并确定刻蚀参数，该条件下其对PixNIL-ST2的刻蚀速率约为2.09 nm/s，然后使用深硅刻蚀工艺对PixNIL-ST2进行刻蚀测定了PixNIL-ST2对硅的刻蚀选择比约为7，最后借助这两个工艺对转移到压印胶层中的超透镜结构进行逐层刻蚀得到了全硅介质超透镜。

超透镜的聚焦和成像实验结果表明经本文所研究的纳米压印工艺制备得到的超透镜具有良好的光场会聚能力和长红外成像能力，本文的研究工作可以为光学超构表面的实际工程应用提供一定的理论依据和技术支持。

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