Improvement of tool reliability and uptime is a current focus in development of extreme ultraviolet lithography. The lifetime of collection mirrors for extreme ultraviolet light in tin-based plasma light sources is limited considerably by contamination with thick tin deposits that cannot be removed sufficiently fast by plasma etching. For tin droplet splats sticking to large substrates, we have developed and compared several efficient cleaning techniques based on cryogenic cooling. A silicon carbide substrate and different silicon wafer samples with up to 6 inch diameter with the surface uncoated, multilayer-coated, unstructured and grating-structured were tested. After tin dripping onto heated samples, embrittlement of droplet contamination is induced in-situ by stresses during phase transformation, following the initiation of tin pest with seed crystals of gray tin. Conversion of initially adhesive deposits to loose gray tin has been reached in less than 24 hours on all tested surfaces by continuous cooling with cold nitrogen vapor to temperatures in the range of -30 to -50 °C. Alternatively, stress-initiated tin-removal by delamination of beta-Sn droplet splats has been attained via contraction strain induced by strong cooling to temperatures of around -120 °C. Profilometry has been used to analyze the bottom side of tin droplet splats removed from a grating-structured wafer. The in-situ tin cleaning techniques give results comparable to fast ex-situ cleaning that has been achieved either by sample immersion in liquid nitrogen or by splat removal after CO2 snowflake aerosol impact using a hand-held jet-nozzle. The implementation of the in-situ phase-conversion concept for the cleaning of collector mirrors in commercial light sources for lithography is discussed.

中文翻译：

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低温清洁与极紫外光收集相关的表面上的锡滴污染

提高工具可靠性和正常运行时间是目前极紫外光刻技术发展的重点。锡基等离子光源中极紫外光收集镜的寿命受到厚锡沉积物的污染而受到很大限制，这些锡沉积物无法通过等离子蚀刻足够快地去除。对于粘附在大型基板上的锡滴飞溅，我们开发并比较了几种基于低温冷却的有效清洁技术。测试了碳化硅衬底和直径高达 6 英寸且表面未涂层、多层涂层、非结构化和光栅结构化的不同硅晶片样品。在锡滴到加热的样品上后，相变过程中的应力会在原位引起液滴污染的脆化，继锡害虫与灰锡晶种开始。通过用冷氮气蒸汽持续冷却至 -30 至 -50 °C 的温度，所有测试表面在不到 24 小时内就将最初的粘合剂沉积物转化为松散的灰色锡。或者，通过强冷却至 -120 °C 左右的温度引起的收缩应变，通过 β-Sn 液滴碎片的分层来实现应力引发的锡去除。轮廓测量法已用于分析从光栅结构晶片上去除的锡滴碎片的底部。原位锡清洗技术的结果可与通过将样品浸入液氮中或使用手持式喷嘴在 CO2 雪花气溶胶撞击后去除飞溅来实现的快速异位清洗相媲美。