Excitation Mechanisms and Sheath Dynamics in Capacitively Coupled Radio‐Frequency Oxygen Plasmas

Abstract

Phase resolved optical emission spectroscopy (PROES) was used to determine the spatio-temporal behavior of excitation rates in rf sheaths of capacitively coupled plasmas at 13.56 MHz. The plasmas were ignited in pure oxygen at pressures from 20 to 100 Pa and rf powers from 10 to 100 W. The spatial and phase resolved excitation rates have shown four characteristic patterns, which differing in their spatial and temporal position.PIC-MCC simulations of the oxygen capacitively coupled radio-frequency discharge were used to get a detailed microscopic description of the dynamic processes in rf plasmas. The PIC-MCC simulations reproduced the excitation patterns observed in experiment quite well and allowed to identify the underlying physics.Three excitation patterns appearing in front of the powered electrode were found to be due to electron impact dissociative excitation of molecular Oxygen, whereas the fourth pattern very close to the powered electrode is attributed to collisions of the positive ions with the background gas.

Dynamics and Electronegativity of Oxygen RF Plasmas

“…Thereby, the temporally averaged axial profiles of charged particles are shown in figure 8(b). 7 Axially and rf phase resolved excitation rate X for the corresponding atomic oxygen emission at 844.6 nm in oxygen rf plasma [3,16]: Agreement of significant excitation pattern between (a) PROES measurement and (b) FMC at low rf power, as well as (c) PROES measurement and (d) PIC-MCC simulation at high rf power, respectively. Hence the electronegativity is of about 26.…”

“…The Gaussian beam propagation theory is applied for the microwave free space propagation. Using the optical transition at 844 nm or 777 nm of atomic oxygen, the spatio-temporal pattern of the excitation rates provide detailed information on the rf sheath dynamics and the origin of the excitation due to different mechanisms of the electron heating or the excitation by fast heavy particles species within the rf cycle (74 ns) at a temporal resolution of 1.5 ns, [3,16,17]. The resolution of the microwave interferometer is optimized for measuring line integrated electron densities down to 5 × 10 13 m −2 .…”

“…Furthermore, the electronegative plasmas have been applied in many plasma technologies, e.g. Furthermore, the phase-resolved optical emission spectroscopy (PROES) was applied to study the rf sheath dynamics and electron heating [3]. Currently, the application of non-thermal plasmas at atmospheric pressure in life science is a hot topic [10].…”

Excitation Patterns and Heating Mechanisms During E-H-Mode Transition in Inductively Coupled RF Oxygen Discharges

“…The phase resolved optical emission spectroscopy was applied to study extensively the E-H-mode transition, as it has been done in hydrogen [3]. In particular, the optical emission of atomic oxygen at 844 nm was measured spatial and phase resolved by a gated ICCD camera [4]. The measured emission patterns were radially averaged and the relative excitation rates were calculated considering the natural life time and the quenching rates [4].…”

“…In particular, the optical emission of atomic oxygen at 844 nm was measured spatial and phase resolved by a gated ICCD camera [4]. The measured emission patterns were radially averaged and the relative excitation rates were calculated considering the natural life time and the quenching rates [4]. Four different excitation patterns are distinguished and assigned to different electron heating mechanisms.…”