Investigation of phosphorus contamination in 49BF2+ implants

For the source drain doping, ⁴⁹BF₂⁺ implants may be used. Statistical follow-up of this process step on devices showed a 10% under dosing linked to a specific implanter. For investigating the origin of this issue, several physical (SIMS analysis, mass spectrum analysis) and electrical (sheet resistance measurements) characterizations have been performed. The results are presented in details in this paper and the analysis of these experiments demonstrates the capability of phosphorus to be a cross-contaminant of ⁴⁹BF₂⁺ implants. Experiments showed that for ⁴⁹BF₂⁺ implantations, ³¹P⁺ could be energetically coimplanted: ³¹P⁺ passes the mass resolution as a ⁵⁰PF molecule and afterwards is dissociated when the species is implanted. In conclusion, some recommendations are given for monitoring, solving and controlling this specific problem, which may significantly impact electrical characteristics of the devices.