Dissociative Ion Yields on Metal Surfaces Bombarded with Low-Energy Fluorocarbon Ions

Fluorocarbon ions ( CF+ 3, CF+ 2 and CF+) are mass-selected from a CF4 plasma and irradiated onto aluminum surfaces at energies up to 140 eV, to investigate the surface processes relevant to reactive ion etching. The irradiation of a CF+ x beam (x=1-3) at impact energies higher than 50-100 eV yields the smaller fragment species CF+ y (y<x) on the surface, in addition to the reflected species (y=x). The energy distribution function of each ion species scattered from the surfaces has been measured for the first time; most of the ions have kinetic energies lower than 10 eV while some reflected species have energies comparable to the incidence energy. In contrast to the previous results of hydrocarbon ions ( CH+ x ), the low-energy incidence (<50 eV) of fluorocarbon ions gives a low scatter of ions from the surface, except for the case of CF+ 3 incidence. The possible mechanisms of dissociation of fluorocarbon ions as a result of ion-surface interactions are discussed.