On the role of metastable states in low pressure oxygen discharges

Abstract

Abstract.We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 to explore the spatiotemporal evolution of the electron heating mechanism in a capacitively coupled oxygen discharge in the pressure range 10 -200 mTorr. The electron heating is most significant in the sheath vicinity during the sheath expansion phase. We explore how including and excluding detachment by the singlet metastable states O 2 (a 1 ∆ g ) and O 2 (b 1 Σ + g ) influences the heating mechanism, the effective electron temperature and electronegativity, in the oxygen discharge. We demonstrate that the detachment processes have a significant influence on the discharge properties, in particular for the higher pressures. At 10 mTorr the time averaged electron heating shows mainly ohmic heating in the plasma bulk (the electronegative core) and at higher pressures there is no ohmic heating in the plasma bulk, that is electron heating in the sheath regions dominates.

The Influence of Secondary Electron Emission and Electron Reflection on a Capacitively Coupled Oxygen Discharge

“…Furthermore, when operating at low pressure, the electron heating within the discharge is due to a hybrid drift-ambipolar-mode (DA-mode) and α-mode, and while operating at higher pressures, the discharge is operated in a pure α-mode [26,27]. We have also shown that detachment by the singlet molecular metastable states is the process that has the most influence on the electron heating process in the higher pressure regime, while it has almost negligible influence at lower pressures [22][23][24].…”

“…The driving frequency is assumed to be 13.56 MHz. These are the parameters used in our earlier works using oopd1 [20][21][22]24,27] and in the work of Lichtenberg et al [9] using the xpdp1 code. The discharge electrode separation is assumed to be small compared to the electrode diameter so that the discharge can be treated as one dimensional.…”

“…In recent years, the oxygen reaction set in the oopd1 code was improved significantly [20][21][22]. Using this improved discharge model, we showed that the singlet metastable molecular states have a significant influence on the electron heating mechanism in the capacitively-coupled oxygen discharge [21][22][23][24] as well as the ion energy distribution [25]. We demonstrated that, when operating at low pressure (10 mTorr), the electron heating is mainly located within the plasma bulk (the electronegative core), while, when operating at higher pressures (50-500 mTorr), the electron heating appears almost solely within the sheath regions [22,23].…”

Electron power absorption dynamics in a low pressure radio frequency driven capacitively coupled discharge in oxygen

“…The secondary electron emission due to the electron impact on the electrodes has been neglected here as in all our previous works on the oxygen discharge. Through recent PIC/MCC simulations of a capacitively coupled oxygen discharge it has been demonstrated that the singlet metastable molecular states have a significant influence on the electron power absorption mechanism [13][14][15][16] as well as the ion energy distribution [38]. At low (high) pressure and high (low) electronegativity, i.e.…”

“…In recent years the oxygen reaction set in the oopd1 code has been improved significantly [12][13][14]. The oopd1 code has been applied to explore the electron power absorption in the capacitively coupled oxygen discharge while varying the various external parameters and operating conditions such as discharge pressure [14][15][16], driving voltage amplitude [17], driving frequency [18], the secondary electron emission [14,19], the surface quenching of the metastable states [20] and the electrode gap distance [21].…”