Ionic Liquid Ion Sources: the Flexible Ion Beam

离子束蚀刻技术是一种广泛应用的技术，为完成微制造部件的原位光刻提供了有价值的工具。传统的镓液态金属离子源（LMIS）是目前应用最广泛的聚焦离子束刻蚀方法，该方法通过施加强静电场从液态金属表面提取镓离子。LMIS提供直接的、不可抗拒的三维图形，但在蚀刻速率、蚀刻分辨率和应用方面，一种离子类型的选择是有限的。离子的性质极大地影响了所得到的蚀刻纳米和微结构的物理和化学性质，限制了潜在的应用领域。在这个项目中，我们建议研究离子液体离子源（ILIS）作为蚀刻的替代离子束源的应用。通过使用有机“离子液体”分子来产生离子，从根本上规避了LMIS的限制——可用离子类型的数量非常有限。离子液体由分子阳离子和阴离子在溶液中离子键合而成，高电场可以从中提取出高度单分散的分子离子的高度准直光束。目前已知超过5000种室温离子液体，具有广泛不同的性质和大小的离子，这提供了一个巨大的变化在带电的物种被发射，允许一个定制的选择离子（大或小，化学反应或惰性，能够离子注入与否，等等）。这导致了离子束源更大的灵活性，例如允许使用大离子液体分子离子的高蚀刻率，然后切换到较小的分子离子（通过简单的离子液体变化），导致更准确的最终蚀刻。我们的目的是研究应用离子液体离子源蚀刻材料衬底的潜力。我们开发了一种新型离子液体离子源，它可以产生高能量的单分散离子束，使用的离子液体被证明可以产生良好的蚀刻能力。我们的目标是证明它可以提供传统液态金属离子源的替代品，同时研究使ILIS设备运行的基本现象。在这个项目中有三个主要的主题将被调查。首先对用于微加工的离子液体离子源进行了系统的分析。研究已经证明了该技术的前景，但仅限于有限的方面，并没有充分研究其广泛的潜力。我们将完成对该技术的系统研究，提供全面的数据集，以突出该技术可以特别有利的地方。其次，需要对离子液体离子源的工作原理有更深入的了解。光源可以产生高度单分散的光束，但影响光束输出的参数（液体特性、光源设计）尚不完全清楚。我们将运用理论和模拟技术，辅以羽流的实验分析，以更好地了解正在发生的过程。这将反馈到源的设计中。第三，从上述分析中吸取的教训将使我们能够生产专门为蚀刻过程设计的离子液体离子源，而不是在项目开始时使用的航天器推进离子推进器的改编。

The use of ion beams for etching is a widely applied technique, providing a valuable tool for completing in situ lithography of micro manufactured components. Today conventional gallium Liquid Metal Ion Sources (LMIS) is the most well appleid focused ion beam etching method, in which gallium ions are extracted from a liquid metal surface through the application of a strong electrostatic field. LMIS offer direct, resistless, three dimensional patterning, but the choice of one ion type is limiting, both in terms of etching rate, etching resolution, and application. The properties of the ion influences significantly the physical and chemical nature of the resulting etched nano and microstructures, limiting the potential application areas. In this project, we propose to investigate the application of an Ionic Liquid Ion Source (ILIS) as an alternative ion beam source for etching. These fundamentally circumvent the limitation of LMIS - the very limited number of ion types available - through using an organic 'ionic liquid' molecule to create the ions. An ionic liquid consists of molecular cations and anions bonded ionically in solution, from which a high electric field can extract a very collimated beam of highly monodisperse molecular ions. Currently over 5000 room temperature variants of ionic liquids are known, with widely varying properties and size of ions, which offer a vast variation in the charged species being emitted, allowing for a bespoke selection of ions (big or small, chemically reactive or inert, capable of ion implantation or not, etc.). This leads to much greater flexibility of the ion beam source, for example allowing for high etching rates using a large ionic liquid molecrular ion, and then switching to a smaller molecular ion (by simple ionic liquid variation), resulting in more accurate final etching.We aim to investigate the potential of applying an ionic liquid ion source to the etching of material substrates. We have developed a novel ionic liquid ion source that produces a high-energy monodisperse ion beam, using an ionic liquid demonstrated to produce good etching capability. We aim to demonstrate that it can offer an alternative to conventional liquid metal ion sources, whilst investigating the fundamental phenomena that enable ILIS devices to operate.There are three main subjects that will be investigated in this project. Firstly a systematic analysis of ionic liquid ion sources for micro fabrication will be completed. Studies have demonstrated the promising nature of the technique, but to a limited aspect and not fully investigating its wide potential. We will complete a systematic study of the technique, providing a comprehensive data set which will highlight where the technique can be particularly advantageous. Secondly there is a need for greater understanding of how the ionic liquid ion source operates. The source can produce a highly monodisperse beam, but the parameters that affect this beam output (liquid properties, source design) are incompletely understood. We will apply theoretical and simulation techniques complimented by experimental analysis of the plume to greater understand the processes that are occurring. This will feed into the design of the source.Thirdly the lessons learnt from the above analysis will allow us to produce a ionic liquid ion source designed specifically for etching processes, rather than an adaptation of spacecraft propulsion ion thrusters that will be used at the start of the project.