INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 34 (2001) 2854–2861 PII: S0022-3727(01)25905-1 Observation of the transition of operating regions in a low-pressure inductively coupled oxygen plasma by Langmuir probe measurement and optical emission spectroscopy Dong-cheol Seo and Tae-hun Chung Department of Physics, Dong-A University, Busan 604-714, Korea Received 19 June 2001 Published 5 September 2001 Online at stacks.iop.org/JPhysD/34/2854 Abstract 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. 1. Introduction Oxygen plasmas have been used widely in various plasma processes such as the surface modification of synthetics, surface cleaning, plasma enhanced chemical vapour deposition of oxide thin films, and photoresist etching (Behle et al 1997, Yun and Tynan 2001). Negative ions are found in electronegative gases such as oxygen, chlorine and fluorocarbons, which are used extensively in discharges for various applications of plasma processing. The presence of negative ions complicates the discharge phenomena. There is considerable scientific and technological interest in electronegative plasmas (Lee and Lieberman 1995, Lee et al 1994) and so in the determination of negative-ion density (Quandt et al 1998, Hayashi and Kadota 1998). The operating regions in electronegative plasmas were classified over the entire control parameter space (Lichtenberg et al 2000). The control parameter space is partitioned by whether the ion flux to the wall or positive–negative ion recombination is the dominant positive ion loss mechanism. The control parameter space consists of parameters, pL (pressure times system length), and n e L (electron density times system length). The discharge properties such as the ratio of the negative-ion density to the electron density, the spatial profile of charged species, and the prevailing particle loss mechanism (recombination-loss-dominated or ion-flux- loss-dominated) also depend on the operating region. Thus, in various regions, the discharge generally exhibits different scalings of the operating parameters. In previous articles we have explored the transitions between operating regions and the scaling behaviour of inductively coupled low-pressure oxygen plasma for a low- power condition (Chung et al 1999) and for a medium- or high-power condition (Seo et al 2001) based on an electrostatic probe method. We observed that there exist transitions of the operating region from the ion-flux-loss-dominated region to the recombination-loss-dominated region with increasing operating pressure, and that experimentally measured scalings of the charged species are in agreement with the predictions of the spatially averaged global model. Because of the 0022-3727/01/182854+08$30.00 © 2001 IOP Publishing Ltd Printed in the UK 2854