Observation of the transition of operating regions in a low-pressure inductively coupled oxygen plasma by Langmuir probe measurement and optical emission spectroscopy

In inductively coupled low-pressure oxygen plasmas, planar Langmuir probes were used to determine the variation of the plasma parameters (positive and negative ion densities, electron density, electron temperature) with applied pressure (1-40 mTorr) and power (1-800 W). Simultaneous optical emission spectra were obtained. The relative abundance of the species was estimated from the intensities of the two spectral lines from excited oxygen atoms and molecular oxygen ions. In conjunction with the Langmuir probe data, the scaling behaviours of the charged and neutral species were investigated. A change of scaling behaviour in charged and neutral species densities which was due to the transition from the ion-flux-loss-dominated region to the recombination-loss-dominated region was observed by Langmuir probe measurement and optical emission spectroscopy.