Investigation of Ion-Neutral Collision Effects on Ion Velocity Distribution at Presheath/Sheath Edge in Argon-Oxygen Plasmas

Low-temperature plasmas using mixed gases have led to several phenomenological models and key plasma parameter-based analyses to interpret the plasma-surface interaction. In this study, we experimentally investigate the effect of ion-neutral collisions in argon-oxygen mixed plasma on the ion velocity distribution (IVD) at the presheath and sheath boundary. In mixed gases, heavy particle collisions such as quenching occur, thereby changing the properties of particle generation and, consequently, the incident properties on the surface. Under collisionless sheath conditions, the sheath potential determines the ion energy, and an incident angle distribution proportional to the ion temperature is formed. The ion velocity distribution at the presheath-sheath boundary was measured by laser induced fluorescence (LIF) technique while varying the Ar/O2 mixing ratio. The results showed that as the fraction of oxygen increases, the proportion of slow ions increases, leading to an increase in ion-neutral particle collisions. Further IVD analysis is currently underway. This provides information about the process plasma, especially incident ions in the etch profile, which can be utilized as domain knowledge for process analysis and control.