Modeling of inductively coupled plasma SF₆/O₂/Ar plasma discharge: Effect of O₂ on the plasma kinetic properties

A global model has been developed for low-pressure, inductively coupled plasma (ICP) SF₆/O₂/Ar mixtures. This model is based on a set of mass balance equations for all the considered species, coupled with the discharge power balance equation and the charge neutrality condition. The present study is an extension of the kinetic global model previously developed for SF₆/Ar ICP plasma discharges [Lallement et al., Plasma Sources Sci. Technol. 18, 025001 (2009)]. It is focused on the study of the impact of the O₂ addition to the SF₆/Ar gas mixture on the plasma kinetic properties. The simulation results show that the electron density increases with the %O₂, which is due to the decrease of the plasma electronegativity, while the electron temperature is almost constant in our pressure range. The density evolutions of atomic fluorine and oxygen versus %O₂ have been analyzed. Those atomic radicals play an important role in the silicon etching process. The atomic fluorine density increases from 0 up to 40% O₂ where it reaches a maximum. This is due to the enhancement of the SF₆ dissociation processes and the production of fluorine through the reactions between SF_x and O. This trend is experimentally confirmed. On the other hand, the simulation results show that O(3p) is the preponderant atomic oxygen. Its density increases with %O₂ until reaching a maximum at almost 40% O₂. Over this value, its diminution with O₂% can be justified by the high increase in the loss frequency of O(3p) by electronic impact in comparison to its production frequency by electronic impact with O₂.