We use a global (volume averaged) model to study the dissociation processes and the presence of negative ions and metastable species in a low pressure high density O 2 /Ar discharge in the pressure range 1-100 mTorr. The electron density and the fractional dissociation of the oxygen molecule increases with increased argon content in the discharge. We relate this increase in fractional dissociation to an increase in the reaction rate for electron impact dissociation of the oxygen molecule which is due to the increased electron temperature with increased argon content in the discharge. The electron temperature increases due to higher ionization potential of argon than for molecular and atomic oxygen. We find the contribution of dissociation by quenching of the argon metastable Ar m by molecular oxygen (Penning dissociation) to the creation of atomic oxygen to be negligible. The negative oxygen ion O − is found to be the dominant negative ion in the discharge. Dissociative attachment of the oxygen molecule in the ground state O 2 (X 3 − g ) and in particular the metastable oxygen molecule O 2 (a 1 g ) are the dominating channels for creation of the negative oxygen ion O − .

A steady state global (volume averaged) model is developed for the chlorine discharge using a revised reaction set. Various calculated plasma parameters are compared with measurements found in the literature, showing a good overall agreement. The reaction rates for the various reactions are evaluated in the pressure range 1-100 mTorr. In particular, we explore the dissociation process as well as the creation and destruction of the negative ions Cl − . The discharge is highly dissociated throughout the pressure range explored, 1-100 mTorr, even when the absorbed power is low. The mechanism for Cl creation is complex. Although electron impact dissociation dominates with roughly 60-65% contribution, mutual neutralization of positive and negative ions and dissociative electron attachment are important contributors to the production of Cl atoms at high pressure. The electronegativity increases rapidly with decreasing dissociation fraction since the Cl − ions are created entirely by dissociative electron attachment, predominantly from Cl 2 (v = 0), but also up to 14% from Cl 2 (v > 0) at 100 mTorr. The negative ion Cl − is lost almost entirely through mutual neutralization with Cl + 2 at high pressure while Cl + has a significant contribution at low pressure.

A global (volume averaged) model is developed for a nitrogen discharge in the steady state for the pressure range 1-100 mTorr. The electron energy distribution function is allowed to vary from a Maxwellian to a Druyvesteyn distribution. Varying the electron energy distribution function from a Maxwellian-like to a Druyvesteyn-like influences mainly the density of excited species, ground state species being more important when the distribution is Druyvesteyn-like. We find that the nitrogen discharge is essentially atomic when the pressure is around 1 mTorr and is highly molecular when the pressure is 100 mTorr. The relative reaction rates for the creation and destruction of nitrogen atoms and atomic ions are explored over the pressure range of interest. The model calculations are compared with measurements found in the literature. There is excellent agreement between the model and the measurements for the electron and ion densities as well as the electron temperature. However, a large discrepancy between the model predictions and the measurements of the nitrogen atom density remains unexplained.

A steady state global (volume averaged) model is developed for a low pressure (1-100 mTorr) high density hydrogen discharge that is diluted with argon. The electron density increases, the dissociation fraction of hydrogen increases and the electron temperature decreases with increased argon dilution. We find that H + 3 is the dominant positive ion up to roughly 30% argon dilution at 10 mTorr, at which point Ar + becomes the dominant positive ion. The reaction rates for the creation and destruction of various species are explored versus the discharge pressure. In particular we explore the role of the vibrationally excited levels of the hydrogen molecule in the creation of the negative ion H − through dissociative attachment. The role of the ArH + ion in the discharge chemistry is discussed and we find that ArH + plays a significant role in the destruction of the H − ion. Furthermore, the creation and destruction of H + 3 and ArH + ions are explored. The electronegativity increases with increasing H 2 content and reaches a value of approximately unity in a pure H 2 discharge at 100 mTorr. The model is compared with measurements found in the literature and is found to be in agreement with measurements although certain discrepancies are pointed out and discussed.

A global (volume averaged) model is applied to a low pressure (1-100 mTorr) high density chlorine discharge that is diluted with oxygen. The influence of oxygen dilution on the particle densities and the electron temperature is explored. The electronegativity is found to increase strongly with increased pressure in a chlorine-rich mixture, whereas it is nearly pressure independent in an oxygen-rich mixture. The chlorine dissociation fraction increases with increased oxygen dilution, although the increase is neither pronounced nor sharp at low oxygen content. We explore the role of the ClO molecule in the discharge and confirm that the ClO molecule is mainly created through recombination of Cl and O atoms at the chamber wall, which in turn significantly increases the loss of Cl atoms in oxygen-rich mixtures. The most important loss process for ClO is electron impact dissociation in the plasma bulk. The molecular ion ClO + is almost entirely created by charge transfer for oxygen dilution below 67%, while electron impact ionization becomes the dominant creation process for ClO + at higher dilution.