Suppression of phosphorous out-diffusion in PH₃ plasma immersion ion-implanted germanium epilayer grown on silicon (100) substrate through SiO_X 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 SiO_X capping layer was formed on the implanted Ge epilayer, followed by activation annealing at 500800° C under flowing N2 atmosphere. The out-diffusion behavior of the implanted P atoms in the SiO_X-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 SiO_X 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 SiO_X 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 SiO_X-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°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.