Studies on characteristics of neutral and metastable neutral atom in high density argon plasmas by using laser induced fluorescence and scattering

Abstract

In this dissertation, studies on characteristics of high density Argon plasma by using laser induced fluorescence (LIF) and scattering are addressed. By using laser scattering, anomalous temporal evolution of pressure in inductively coupled plasmas is shown. By using laser-induced fluorescence, characteristics of argon metastable neutral density with electron density and pressure are discussed and the method is applied to Helicon plasmas where very high electron density at low pressure and significant neutral depletion exists. Rayleigh scattering and Thomson scattering for measuring neutrals and electrons are applied. Specifically we describe the results in the dissertation as follows: The temporal measurement of gas pressure in inductive coupled plasma revealed that there is an interesting anomalous evolution of gas pressure in the early stage of plasma ignition and extinction: a sudden gas pressure change and its relaxation of which time scales are about a few seconds and a few tens of second, respectively, were observed after plasma ignition and extinction. This phenomenon can be understood as a combined result between the neutral heating effect induced by plasma and the pressure relaxation effect for new gas temperature. The temporal measurement of gas temperature by laser Rayleigh scattering and the time dependent calculations for the neutral heating and pressure relaxation are in good agreement with our experimental results. This result and physics behind are expected to provide a new operational perspective of the recent plasma processes of which time is very short, such as a plasma enhanced atomic layer deposition/etching, a soft etch for disposal of residual by-products on wafer, and light oxidation process in semiconductor manufacturing. The measurement of argon metastable state density in inductively coupled plasma by using laser induced fluorescence revealed that there are both normal and abnormal evolution of metastable state density with electron...