Depth Profiling of Defects in He Implanted $SiO_2$

Thin layer of $SiO_2$ thermally grown on p-type Si was implanted with $He^+$ ions at 30 keV with a dose of $5×10^{15}$ ions/$cm^2$. $SiO_2//Si$ samples were depth profiled by Doppler broadening positron annihilation spectroscopy to identify induced defects in the silicon oxide, at the interface and in the Si substrate. In one sample the silicon dioxide layer was removed by etching after implantation. It is shown that removing the silicon dioxide layer some more information about defects into the substrate can be found.