Effects of dopant deposition on p+/n and n+/p shallow junctions formed by plasma immersion ion implantation

BF3 and AsH3 plasma immersion ion implantation (PIII) are used for formation of ultra-shallow p(+)/n and n(+)/p junctions. Both Pm processes are found to result in energetic ion implantation and dopant deposition on the wafer surface. Retained doses after implant and anneal were measured using nuclear reaction analysis (NRA), secondary ion mass spectroscopy (SIMS) and Rutherford back-scattering (RBS). Boron deposition from 2 kV BF3 Pm allows for higher retained doses and lower sheet resistance than possible with mass-analyzed 2 keV BF2+ implantation, for which the retained dose is sputter-limited. However, for the conditions used here, this lower resistance was also accompanied by a deeper junction depth, so that the benefit from lower resistance was lost. For arsenic implants, and for the conditions used in this work, PIII 2 kV AsH3 and mass-analyzed 2 keV As+ implantation produced a junction with similar sheet resistance and junction depth, whereas 10 kV AsH3 PIII produced a shallower, more abrupt junction than the mass-analyzed counterpart of similar sheet resistance.