Sensitive optical probes for low pressure plasmas

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This project falls within the EPSRC Plasma and Lasers research area. It will utilise cavity ringdown spectroscopy (CRDS) as a high-resolution experimental technique to investigate trace species within low pressure plasmas. Low pressure plasmas are of high technological interest for micro/nanoelectronics, semiconductors and catalysis, and have secondary multidisciplinary applications in medicine and agriculture. Within the micro/nanoelectronics and semiconductor industries, there is demand for etch processes with atomic level precision and high material selectivity, only possible with plasma enhanced processes. The acceleration of ions towards surfaces is key to high speed chemical vapour deposition and precise etching processes. Utilising plasmas in these technological applications allows otherwise inaccessible conditions to be acheived and significantly reduces the energy cost of maintaining the required conditions, contributing to improved environmental sustainability. Research on the fundamentals behind plasma processing is still limited and enhanced knowledge of ion energy and velocity angular distribution is needed. In particular, the 2022 Plasma Roadmap highlights the lack of knowledge of neutral and ionic species fluxes and emphasises the importance that this knowledge is gained. Therefore, the more complete understanding of plasma characteristics and ion spatial distributions near surfaces which this project will provide will be paramount to advancements within these fields of technology. Previous work on this project within the last year has investigated characteristics of nitrogen plasma. In particular, novel experimental methods were established to quantify the spatial variation of species number densities within the plasma, including within the sheath and pre-sheath regions. This project will continue this work, optimising these methods, and including investigations into other technologically important processing gases such as argon and oxygen. In addition, the ability to manipulate the sheath and presheath regions of the plasma will be investigated through the application of novel rf waveforms and electrode biasing in the plasma chamber, which will also lead to better control of the ion energies impinging on key surfaces. Experimental results obtained will be compared to theoretical models established within the group with the assistance of knowledge from industrial partners, Lam Research Inc. (US), who are global experts within the semiconductor industry and are heavily involved in developing the next generations of fabrication processes for 3D architecture on the nanometre scale. Lam are world leading semiconductor foundry equipment developers, using knowledge of plasma enhanced processes, including chemical vapour deposition, atomic layer deposition, and plasma etching, to produce precise, high performance equipment with the ability to achieve high-aspect ratio features required for micro-electromechanical applications within the industry. This research aligns with the EPSRC's strategies as a discovery research project within mathematical and physical sciences. The outcomes of this project not only will transform our understanding of low pressure plasmas, particularly ion and radical fluxes towards surfaces, but also enable the optimisation of plasma enhanced processes. Once optimisations are implemented on an industrial scale, substantial energy efficiency improvements and cost reductions could be expected, both contributing to a greener future and supporting economic growth within the industry.