Suppression of Phosphorous Out-Diffusion in PH3 Plasma Immersion Ion-Implanted Germanium Epilayer Grown on Silicon (100) Substrate through SiOx Capping Layer

The PH3 plasma immersion ion implantation (PIII) process was used to introduce phosphorus (P) atoms in a germanium (Ge) film epitaxially grown on a silicon (Si) (100) substrate. A SiOx capping layer was formed on the implanted Ge epilayer, followed by activation annealing at 500-800 degrees C under flowing N-2 atmosphere. The out-diffusion behavior of the implanted P atoms in the SiOx-capped Ge epilayer was investigated as a function of activation annealing temperature and was compared with the out-diffusion behavior of an uncapped Ge epilayer. The PIII process introduced damage near the Ge surface with the formation of a thin amorphous Ge layer whose thickness was comparable to the projected range calculated from simulation. Irrespective of the SiOx capping layer, the sheet resistance decreased with increasing annealing temperature, which could be attributed in part to the recovery of the implantation damage and to dopant activation. The SiOx capping layer was effective in suppressing the out-diffusion of implanted P atoms into the Ge epilayer, resulting in insignificant dopant loss during activation annealing. This allows that the SiOx-capped samples showed lower sheet resistance than the uncapped ones over the whole temperature range. The increase in annealing temperature resulted in reducing the number of implantation-induced defects and misfit dislocation of the Ge epilayer grown on Si, leading to improved structural properties. Furthermore, annealing at 800 degrees C facilitated softening and reflow of the implanted Ge epilayer, which could be responsible for the remarkable improvement of surface roughening caused by the PIII process.