Mechanisms for CF2 radical generation and loss on surfaces in fluorocarbon plasmas

During fluorocarbon plasma etching, plasma-surface reactions result in the surface acting as either a source or sink for reactive species, thereby impacting the properties of the bulk plasma. For example, experiments have shown that surfaces in radio frequency (rf) capacitively coupled discharges can be either sources or sinks of CF2 depending on, among other properties, the sheath potential. The coupling of rf bulk and surface reactions, and their combined effects on the CF2 density, were investigated using an integrated plasma equipment and surface kinetics model. While CF2 sticking on surfaces led to its loss, CF2 can be generated from surfaces by energetic ion bombardment resulting in sputtering of polymeric films, or neutralization and dissociation of ions. The net effect of a surface for CF2 production depends on the relative rates of these loss and generation processes. A surface can transform from a net CF2 sink at low incident ion energies to a CF2 source at high ion energies because the CF2 yield by ion–surface interactions typically increases with increasing ion energy. The sensitivity of the model to probabilities of major surface reactions was also investigated.