Proximity gettering of platinum in silicon following implantation with alpha particles at low doses

Platinum has been diffused into epitaxial n-type silicon at 600, 650, and 700°C for 30 min following implantation with 3.3 MeV alpha particles. The doses employed were between 1×1011 and 1×1014 He+ cm−2. Thereafter the samples were characterised using DLTS (deep level transient spectroscopy). The samples diffused at 700°C show only the deep level at 0.23 eV below the conduction band that is attributed to substitutional platinum. DLTS profiling reveals a decoration of the region of maximal damage by the platinum for lower doses while for higher ones the platinum concentration is observed to decrease or vanish in this region. In addition, other deep levels may appear (so-called K-lines). As the implantation dose increases, so does the platinum concentration following diffusion at 700°C at the shallow end of the DLTS working region. It is shown that by controlling the amount of implantation induced defects and the diffusion temperature one can steer the amount of platinum that arrives in the region of maximal damage. The stability of the defect decoration has also been studied by varying the diffusion times at 700°C from 10 to 50 min. For diffusion times longer than 30 min a reduction in the maximum platinum concentration is observed. It is assumed that the platinum diffuses further into the bulk.