A fundamental investigation into electron beam induced deposition
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Electron beam induced deposition (EBID) is a maskless, direct-write nanofabrication technique. It is capable of very high resolution and deposition of a wide variety of materials. It is a widely used technique for nanoprototyping and has several current applications in industry including the repair of photolithographic masks for integrated circuit (IC) production. Despite the widespread usage of EBID, the fundamental mechanisms which govern the process are not sufficiently well understood. In this thesis, an experimental-based investigation is undertaken in order to obtain a greater understanding of fundamental factors which govern the EBIED process and particularly those factors not accounted for by current models of EBIED. A world-class and possibly unique experimental apparatus is developed which allows quantitative EBID experimentation. The conclusions reached demonstrate the importance of a previously neglected fundamental aspect of EBID: the adsorption kinetics of precursor molecules. The findings have significant importance for EBID and the sister technique of electron beam induced etching (EBIE). The first chapter presents a thorough general background and introduction to electron beam induced etching and deposition (EBIED) and literature review with a focus on EBID. Chapter two discusses theoretical aspects of EBIED and current models. Chapter three is a record of the apparatus and experimental procedures which were developed and can be considered as a recipe for reliable EBID experimentation. Experiments were performed as a function of substrate temperature in chapters four and five. The results which were not predicted by current models of EBID demonstrate the effect of activated chemisorption. A new model is developed which correctly predicts the generic temperature dependence of the EBID process. Activated chemisorption is found to allow simultaneous high purity and high growth rates of EBID deposits. FEBID at high Ts with TEOS precursor was found to result in complex unexpected growth and mechanisms involving diffusion, electron beam induced heating (EBIH) and charging are presented and discussed to explain this growth in chapter five. Chapter six involves TEOS EBID with gas mixing. The growth rate was found to be significantly enhanced or suppressed with O2 or Ar mixing respectively. A new mechanism (termed LAOCVD) is proposed to explain O2 mediated purity and EBID rate enhancement with organosilane precursors as reported in literature and demonstrated by my results. The effects of EBID system parameters are characterised and explained in the appendix.
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