Helium ion-induced stoichiometry modification in hydrogenated silicon oxide films

The stoichiometry of amorphous hydrogenated silicon oxide films, grown in a dual-plasma system, has been investigated using elastic recoil detection (ERD), Rutherford backscattering, and infrared transmission. During ERD measurement of H profiles, using a 4He2+ beam of 3.0 MeV, ion-induced depletion of hydrogen atoms was observed, homogeneous over the 1 μm film thickness. Si-rich films (with H essentially bonded as Si–H) and nearly stoichiometric films (with H only bonded in Si–OH configurations) have been compared. The depletion is more pronounced in nearly stoichiometric oxides, whereas the apparent cross sections (≊1–2 nm2) are similar for both types of films. These observations are discussed in terms of an electron excitation process, with a subsequent chemical reconstruction via electron-hole recombination.