AVS 53rd International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS1-WeM

Paper PS1-WeM10
Scattering Dynamics of Fluorinated Ions on Surfaces of Relevance to Plasma Etching

Wednesday, November 15, 2006, 11:00 am, Room 2009

Session: Plasma-Surface Interactions II
Presenter: M.J. Gordon, LTM/CNRS, France
Authors: M.J. Gordon, LTM/CNRS, France
X. Qin, California Institute of Technology
J. Mace, California Institute of Technology
K.P. Giapis, California Institute of Technology
Correspondent: Click to Email
Fluorocarbon plasmas are extensively used for SC, dielectric, and metal etching; in particular, F-based etching of Si has been studied for many years. However, little is known about specific interactions (kinematics/charge exchange/reaction dynamics) of F-containing ions at collision energies relevant to plasma processing (0.1-1 keV). This talk will focus on experiments involving mass-filtered ions (F+, CFx+) with tunable energy (50-1000 eV) and high flux scattered off a variety of surfaces. Beam studies were carried out in an ICP-based accelerator system with simultaneous energy/mass analysis of products leaving the target. We first highlight two new effects in the F+-Si/Al systems: electronic excitation during the hard collision to form inelastic F+/F2+ and stimulated desorption of hyperthermal (10-20 eV) F+ (HT-F+). Inelastic losses and F2+ were attributed to the formation of doubly-excited autoionizing states of F and F+ (analogous to Ne) in the hard collision. HT-F+ is thought to originate from core-hole charge transfer involving a surface-bound F atom. These two effects are potentially important for profile evolution because F+ scattering becomes inelastic at low collision energies (300/500 eV for Al/Si) and desorbing HT-F+ may enhance the reactivity at surfaces not accessible to plasma ions. In the second part of the talk, collision kinematics of CFx+ ions off Si and metals will be discussed. Velocity analysis of scattered fragments suggests that neutralization induced dissociation of the projectile occurs before the hard collision (CF3+ is neutralized on approach and dissociates to form CF or CF2). The resulting CF/CF2 fragments then scatter elastically off the surface to form a hot positive ion, which dissociates to F+C or F+CF, with both fragments leaving at similar velocities. This reaction scheme was seen to depend on both the incident energy and target material. Implications of these findings for plasma etching and profile evolution will be discussed.