Atomic oxygen densities in pulsed inductively-coupled plasmas: Laser spectroscopy & energy resolved actinometry*

Oxygen-containing pulsed Inductively Coupled Plasma (ICP) enable high-precision semiconductor etching with nanoscale features and low substrate damage. Atomic oxygen plays a key role in the plasma-material interactions, and reliable absolute density measurements can improve plasma processing precision. Two-photon Absorption Laser Induced Fluorescence (TALIF) spectroscopy can accurately measure these with high spatial and temporal resolution. However, implementing TALIF as a routine industrial method is challenging. Alternative diagnostics that balance ease of use and accuracy are desired. Energy Resolved Actinometry (ERA) has previously shown to provide reliable information in capacitively-coupled plasmas. In this contribution, the ERA concept has been adapted to different operation regimes of an ICP and also extended to implement Bayesian analysis using different optical emission lines for improved reliability. It is compared with direct TALIF measurements taken in the early afterglow.  Generally, good agreement has been found between the two techniques, promising the potential application of ERA in future real-time process control.