Observations were made of defects following 1.7MeV Si+ through-implantation of SiO2 films which were thermally grown onto Si(100) substrates. The films were irradiated to fluences of 1012, 1013 or 1014/cm2, and were analyzed by using a variable-energy positron beam. An enhanced depth resolution was achieved by repeated chemical etching. It was found that the positron annihilation S-parameter was reduced in the implanted oxide due to a reduction in the formation of positronium, and was increased in the Si substrate due to the creation of vacancy-type defects. The concentration of implantation-induced defects was found to be almost constant as a function of depth in the oxide film, thus indicating that both electronic and nuclear stopping of the implanted Si+ ions made a significant contribution to the production of positron-trapping defects. The maximum overlayer thickness which permitted the simultaneous detection of defects in the substrate was about 600nm.

Enhanced Depth Resolution in Positron Analysis of Ion Irradiated SiO2 Films. P.J.Simpson, M.Spooner, H.Xia, A.P.Knights: Journal of Applied Physics, 1999, 85[3], 1765-70