Enhanced depth resolution in positron analysis of ion irradiated SiO2 films

We report the observation of defects following 1.7 MeV Si+ through-implanta tion of SiO2 films thermally grown on Si(100) substrates. Films were irradi ated to fluences of 10(12), 10(13), and 10(14) ions/cm(2), and analyzed usi ng a variable energy positron beam. Enhanced depth resolution was achieved via iterative chemical etching and measurement, for the sample irradiated t o 10(12) Si+/cm(2), and for an unirradiated control sample. The positron an nihilation "S parameter" is reduced in the implanted SiO2, due to a reducti on in the formation of positronium (the atom-like positron-electron bound p air), and is increased in the Si substrate, due to the creation of vacancy- type defects. The concentration of implant-induced defects was found to be very nearly constant as a function of depth in the SiO2 film, indicating a significant contribution of both the electronic and nuclear stopping of the implanted Si+ ions to the production of positron-trapping defects. We find that the maximum overlayer thickness which allows simultaneous detection o f defects in the substrate (i.e., through-oxide probing of substrate defect s) is similar to 600 nm. (C) 1999 American Institute of Physics. [S0021-897 9(99)06103-4].