Plasma doping for the fabrication of ultra-shallow junctions

Pulsed plasma doping (P2LAD) is an alternate doping technique for the formation of ultra-shallow junctions in silicon wafers. In the P2LAD technique, a pulsed negative voltage applied to the silicon substrate creates a plasma containing the desired dopant species and also accelerates the positive dopant ions from the plasma toward the substrate, where they are implanted. BF3 plasmas have been used to form p+–n junctions, while AsH3 and PH3 plasmas have been used for the formation of n+–p junctions. This paper will review the characteristics of ultra-shallow junctions formed by P2LAD. As-implanted and annealed profiles have been obtained by secondary ion mass spectrometry and compared with analogous profiles produced by B+, BF2+ and As+ ion implantation. Good sheet resistance uniformity, charging performance, structural quality, and photoresist integrity have been observed. In addition, junctions have been made which offer trade-offs between sheet resistance and junction depth that are better than those achieved with beamline implants. Finally, sub-0.2 μm pMOSFET devices have been fabricated with P2LAD and exhibit device characteristics that are similar to or better than beamline-implanted ones.