AVS 52nd International Symposium
    Plasma Science and Technology Tuesday Sessions
       Session PS-TuM

Paper PS-TuM10
Scattering Dynamics of Energetic F@super +@ Ions on Si and Al Surfaces

Tuesday, November 1, 2005, 11:20 am, Room 304

Session: Plasma Surface Interactions I
Presenter: J. Mace, California Institute of Technology
Authors: J. Mace, California Institute of Technology
M.J. Gordon, California Institute of Technology
K.P. Giapis, California Institute of Technology
Correspondent: Click to Email
Fluorine is a significant component of many processing plasmas. Its reactions with surfaces have been extensively studied in the presence and/or absence of ion bombardment. Yet, little is known about the interaction of energetic F@super +@ ions with fluorinated semiconductor and metal surfaces, perhaps because of the difficulty in conducting well-defined experiments with F@super +@ beams. Using high flux (monolayers/sec) of F@super +@ extracted from an inductively-coupled plasma (ICP) source coupled to a mass-selective beamline accelerator, we have studied the scattering dynamics of 50-1000eV tunable F@super +@ ion beams with Si and Al surfaces. Energy and mass analysis of all scattered products was performed by a triply-differentially pumped electrostatic energy analyzer preceeding a quadrupole mass spectrometer capable of detecting single ions. We observed a transition from elastic to inelastic behavior at 500 and 300eV for Si and Al, respectively, where the directly scattered F@super +@ exits the surface with energy considerably lower than that predicted from binary collision theory due to quantum mechanical effects. At the threshold energy, we observed the onset of F@super ++@ production at considerably lower energy than F@super +@. The inelastic energy losses were attributed to formation of doubly-excited auto-ionizing states of F and F@super +@. In addition, we also saw in much greater yield low-energy (5-20eV) scattered F@super +@, believed to be generated via a stimulated desorption process involving charge transfer to the incident ion from an F atom bound to the surface, leaving the latter in a highly repulsive state. We have also monitored all scattered ionic products as a function of beam energy and identified SiF@super +@ as the dominant fluorinated species emitted from a Si surface, while SiF@sub 2@@super +@ was barely detectable. The implications of these findings for plasma etching and profile evolution will be discussed in the talk.