Atomic Oxygen Densities in Pulsed Inductively Coupled Plasmas: Laser Spectroscopy and Energy Resolved Actinometry

Plasma processing of semiconductors allows high-precision etching of nanoscale-sized features and as a result the computational power of devices has continued to increase. However, defects that arise during manufacturing greatly impact their performance. Better control over the plasma species is desired to reduce these, and active monitoring of the plasma during manufacturing will lead to improved optimisation over the production of key reactive species as well as early detection of process drift. While Two-photon Absorption Laser Induced Fluorescence (TALIF) spectroscopy can accurately measure atomic densities with high spatial and temporal resolution, implementing it as a routine industrial method is challenging. As such, this thesis was motivated by the need to develop compatible diagnostics for practical use within the semiconductor manufacturing industry. Energy Resolved Actinometry (ERA) is a passive approach and has previously been used to provide reliable information in atmospheric and capacitively-coupled plasmas. Consequently, its viability was further tested under a different operating regime in a low pressure, pulsed inductively coupled plasma at high powers to recreate processing conditions of interest in a modified Gaseous Electronics Conference reference cell.

This thesis studies the production of atomic oxygen since it is chemically similar to commonly used etch gases, but is much easier to model and use experimentally. TALIF was used to first determine these densities over a range of pressures (10-50 Pa), applied powers (400-1000 W), helium-oxygen admixtures (10-20%), and pure O2 to provide benchmark values. Moreover, it was also used to determine the gas temperature over these conditions through comparison of the fluorescence between the O(3PJ) levels, and was necessary for calculations used in ERA. Consequently, the passive optical method was employed to also measure these values, with helium emission investigated to provide an alternative line-ratio giving more reliable measurements. As a result, good qualitative and quantitative agreement were found between the two diagnostics, with the potential to be more easily implemented onto various industrial plasma sources for better characterisation of the plasma during processing.