Exploring thermal surface chemistry inherent in focused electron beam induced deposition (FEBID) towards an optimal control of nanofabrication

聚焦电子束诱导沉积（FEBID）是一种用于制造纳米材料和器件的最先进的工具。它依赖于当这些前体被投配到由紧密聚焦的电子束扫描的表面上时，挥发性金属络合物的电子诱导分解。然而，需要进一步改进FEBID以实现关于存款生长和组成的最佳控制。特别是，迄今为止对FEBID的基本理解是基于这样一种简化的观点，即吸附的前体分子保持完整，直到它遇到撞击、背散射或二次电子，这些电子将使前体解离，从而使撞击部位的材料分解。因此，前体的电子驱动反应被认为是存款形成的决定性步骤。这忽略了类似于化学气相沉积（CVD）的热化学可有助于存款生长，并因此抵消电子束对沉积的空间控制，从而导致存款成分和形状的不受控制的变化。因此，本项目的目的是提供一个基本的理解之间的电子驱动和热表面化学的FEBID前体的过渡。该项目的新奇在于，在特高压条件下使用表面科学工具系统地研究了存款形成过程中固有的化学性质，但研究的表面是FEBID存款的代表，因此与存款增长有关。电子辐照导致的存款表面的反应性是特别令人感兴趣的。杂配体前体的使用将使我们能够研究如何通过替换络合物中的选定配体来控制反应。所提出的研究的观点是三方面的：（1）洞察到FEBID前体的热表面化学的生长存款将允许设计前体和工艺条件，抑制热表面反应，从而使排他性控制存款形成的电子束。研究结果将指导开发具有存款形状和成分最佳控制的新型FEBID工艺。(2)反应性表面如何诱导前体解离以及这如何取决于前体结构的基本见解与通过电子束诱导表面活化（EBISA）诱导自催化存款生长的纳米纤维工艺相关。这将拓宽可用于具有EBISA定义的空间选择性的热沉积的前体的范围，使得更大种类的材料变得可获得。(3)特定FEBID前体在生长存款表面上表现出自限性解离吸附的条件的知识将提供关于将精确逐层沉积（类似于电子增强原子层沉积（EE-ALD）工艺）集成到空间选择性FEBID工艺中的指导。

Focused electron beam induced deposition (FEBID) is a state-of-the-art tool for fabrication of nanoscale materials and devices. It relies on the electron-induced decomposition of volatile metal complexes when these precursors are dosed onto a surface that is scanned by a tightly focused electron beam. However, further improvement of FEBID is needed to achieve optimal control with respect to deposit growth and composition. In particular, the fundamental understanding of FEBID is so far based on the simplified view that an adsorbed precursor molecule remains intact until it encounters an impinging, backscattered, or secondary electron that will dissociate the precursor and thus immobilize material at the site of impact. The electron-driven reaction of the precursor is thus considered as decisive step in deposit formation. This neglects that thermal chemistry akin to chemical vapor deposition (CVD) can contribute to deposit growth and thus counteract the spatial control of deposition by the electron beam leading to uncontrolled variations of the deposit composition and shape. Therefore, the aim of this project is to provide a fundamental understanding of the transition between electron-driven and thermal surface chemistry of FEBID precursors. The novelty of the project is that the chemistry inherent in deposit formation is systematically studied using surface science tools under UHV conditions but on surfaces that are representative of FEBID deposits and thus relevant to deposit growth. The reactivity of the deposit surface as a result of electron irradiation is of particular interest. The use of heteroleptic precursors will allow us to study how the reactions can be controlled by replacing selected ligands within the complex. The perspectives of the proposed research are threefold: (1) Insight into the thermal surface chemistry of FEBID precursors on the growing deposit will allow to devise precursors and process conditions that suppress thermal surface reactions and thus enable exclusive control of deposit formation by the electron beam. The results will guide the development of novel FEBID processes with optimal control of deposit shape and composition. (2) Fundamental insight in how a reactive surface induces precursor dissociation and how this depends on the precursor architecture is relevant to nanofabrication processes that induce autocatalytic deposit growth by electron beam induced surface activation (EBISA). This will widen the range of precursors that can be used for thermal deposition with spatial selectivity defined by EBISA so that a larger variety of materials becomes accessible. (3) Knowledge of conditions under which specific FEBID precursors exhibit self-limiting dissociative adsorption on the surface of a growing deposit will provide guidance with respect to the integration of precise layer-by-layer deposition, akin to an electron-enhanced atomic layer deposition (EE-ALD) process, into spatially selective FEBID processes.