电子束光刻(EBL)是一种功能强大的直接写入工具,可提供纳米级的图案化能力,在与蚀刻或剥离等图案转移方法结合使用时,在低体积研发原型制作中特别有用。在模式转移方法中,升空是首选,特别是在研究环境中,因为它具有成本效益和安全,不需要定制的湿/干蚀刻化学,通风柜,和/或复杂的干法刻蚀工具;总而言之,提供方便,“无底切”模式转换使其有用,特别是对于金属层和具有未知蚀刻剂相容性或低蚀刻选择性的独特合金。尽管剥离技术和光学/电子束光刻技术广泛用于微米甚至亚微米尺度,文献中关于具有临界尺寸(CD)的金属结构在10-20nm范围内具有基于剥离的EBL图案的纳米加工的现有报道是分散的,不完整,或者在实验条件方面有很大的不同,这需要系统的流程优化。为了解决这个问题,超出了典型光刻胶数据表中的范围,本文报告了一项全面的研究,以校准亚50nm金属纳米结构的EBL图案化,包括金纳米线和纳米间隙,基于使用双层PMMA作为抗蚀剂堆叠的剥离工艺。EBL中的控制参数,包括暴露剂量,软烘烤温度,发展时间,开发者解决方案,衬底类型,通过200多次EBL运行,对邻近效应(PE)进行了实验研究,通过场发射扫描电子显微镜(FE-SEM)对制造的纳米结构进行成像,以达到11nm的特征尺寸,从而确定最佳工艺条件。
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Electron beam lithography (EBL) stands out as a powerful direct-write tool offering nanometer-scale patterning capability and is especially useful in low-volume R&D prototyping when coupled with pattern transfer approaches like etching or lift-off. Among pattern transfer approaches, lift-off is preferred particularly in research settings, as it is cost-effective and safe and does not require tailored wet/dry etch chemistries, fume hoods, and/or complex dry etch tools; all-in-all offering convenient, \'undercut-free\' pattern transfer rendering it useful, especially for metallic layers and unique alloys with unknown etchant compatibility or low etch selectivity. Despite the widespread use of the lift-off technique and optical/EBL for micron to even sub-micron scales, existing reports in the literature on nanofabrication of metallic structures with critical dimension in the 10-20 nm regime with lift-off-based EBL patterning are either scattered, incomplete, or vary significantly in terms of experimental conditions, which calls for systematic process optimization. To address this issue, beyond what can be found in a typical photoresist datasheet, this paper reports a comprehensive study to calibrate EBL patterning of sub-50 nm metallic nanostructures including gold nanowires and nanogaps based on a lift-off process using bilayer polymethyl-methacrylate as the resist stack. The governing parameters in EBL, including exposure dose, soft-bake temperature, development time, developer solution, substrate type, and proximity effect are experimentally studied through more than 200 EBL runs, and optimal process conditions are determined by field emission scanning electron microscope imaging of the fabricated nanostructures reaching as small as 11 nm feature size.