Dynamics and Electronegativity of Oxygen RF Plasmas

Abstract

Key words Low pressure rf discharge, oxygen plasma, electron and negative ion density, plasma instability.The capacitively coupled radio frequency plasma at 13.56 MHz in oxygen was systematically studied by 160 GHz Gaussian beam microwave interferometry at high temporal resolution (200 ns) and simultaneous laser photodetachment for electron and negative ion density analysis. Additionally, spatio-temporally resolved electric probe measurements were performed for comparison with microwave interferometry. A high and low electronegative operation mode was found in the asymmetric rf discharge. In the high electronegative mode it was shown the significant role of the metastable excited oxygen molecules in electron attachment and detachment processes. In particular, a temporary electron density increase is observed in the early afterglow of a pulsed rf plasma. The transition between both modes is driven by the rf power and the self-bias voltage, respectively. In connection with the phase resolved optical emission spectroscopy and the study of the electron heating mechanisms the transition into the low electronegative mode at higher rf power shows a relation to the alpha to gamma mode transition. Furthermore, electron density fluctuations are measured over a wide field of processing parameters, e.g. due to the attachment-induced ionization instability. PIC-MCC simulation and fluid model calculation of a symmetric oxygen rf discharge confirm the different electron heating mechanisms and the dominance of negative atomic oxygen ions.

Development of Barrier Discharges: Operation Modes and Structure Formation

“…In order to control the microdischarge the implementation of a third electrode is foreseen, a so-called sliding discharge [41]. In particular, it is planned to investigate the role of negative ions by the laser photodetachment technique [42].…”

E‐H Transition in Argon/Oxygen Inductively Coupled RF Plasmas

“…During the mode transition the positive ion saturation current increases over one order of magnitude from The admixture of oxygen completely changes the whole discharge and these complex plasmas consist of electrons, multiple negative and positive ions, neutral transient and stable molecules. Further, the negative ions can strongly change the plasma dynamics as well as the plasma boundary sheath [51]. In particular, the collisional detachment of the negative ions with metastable oxygen molecules is an essential electron sources [52].…”

Recent Progress in Complex Plasmas

“…The following article by Küllig et al [8] concerns the dynamics and electronegativity of a low-pressure capacitively coupled oxygen rf plasma investigated by experiments and simulations. Two operation modes of the oxygen rf plasma at low and high electronegativity, mainly controlled by the rf power, have been found by detailed analysis of the electron and negative ion density as well as the rf phase resolved optical emission intensity.…”