Gettering of diffused Au and of Cu and Ni contamination in silicon by cavities induced by high energy He implantation

Silicon samples were gold-diffused at different temperatures (870-950 degreesC) and implanted with He ions at 1.6 MeV and fluences ranging from 2 x 10(16) up to 10(17) cm(-2). The implantation induced defects observed by conventional and high resolution cross section electron microscopy were found to be essentially cavities 10 to 100 nm in size which are faceted mainly along {111}, but also along {110} and {100} planes. The cavities are located at the sample depth predicted by the transport range of ions in matter simulation. Secondary ion mass spectroscopy profiles exhibit a shouldered shape with a maximum at the projected range. They demonstrate that the cavities are very efficient sinks for Au atoms; the shoulder of the profile could be related to the presence of smaller cavities and dislocations in the vicinity of the projected range. Gold concentration in the cavity area was below the detection limit of the energy dispersive spectroscopy technique, but both Cu and Ni contamination gave rise to silicides and could be chemically analysed. Cu3Si precipitates have grown in cavities as already reported in the literature, while NiSi2 precipitates were observed for the first time in cavities.