Paper PS2-WeM12
Fragmentation Dynamics of Energetic Fluorinated Ions on Inert and Reactive Surfaces

Wednesday, October 17, 2007, 11:40 am, Room 607

Fluorinated ions with energies between 50-1000eV are important in plasma etching and deposition of materials used in the semiconductor industry. However, the scattering dynamics of molecular ions with surfaces are still not well understood in terms of fragmentation and energy transfer. We report results on the collision of mass-selected ions, such as SF⁺ and SiF⁺, with Si and Ag surfaces under UHV at impact energies relevant to plasma processing conditions (< 1 keV). Positive and negative products leaving the surface were analyzed in both mass and energy under high flux bombardment conditions (~monolayer/s) to compare with fragmentation of CF_x⁺. Results show that daughter ions leaving a relatively inert surface (Ag) are much more energetic (not SIMS-like) than those from a reactive surface like Si. Characteristic overlaps in the velocity spectrum of species leaving the target surface suggest that a pre-dissociated projectile scatters nearly elastically off a target atom and breaks apart after the hard collision step. For instance, several daughter ions (S⁺, F⁺, F^-, SF⁺) leave the surface at velocities much larger than expected for an elastic deflection of the molecular ion projectile. Product distributions (chemical identity and energy content) with respect to impact energy for a similar series of projectile ions (i.e., SF₃⁺, SiF₃⁺, CF₃⁺) will be compared to understand the dynamics of how molecular ions fragment upon impact. Detailed reaction channels that lead to the formation of scattered products and etching of the surface will be discussed.