Understanding of carbon/fluorine Co-implant effect on boron-doped junction formed during soak annealing

Abstract

The formation of highly activated ultrashallow junctions is one of the main challenges for the forthcoming generation of complementary metal oxide semiconductor (CMOS) devices. Co-implantation of impurities such as carbon (C) or fluorine (F) is an attractive technique. However, junction optimization can only be achieved with a complete understanding of the underlying physical mechanisms. In this paper, the effect of CF co-implant on boron (B)-doped preamorphized silicon during the soak annealing is extensively studied. CF atoms are located in the middle range between the B BF2 concentration profiles and the end-of-range (EOR) defect band, with the aim of reducing the interactions of dopants with the interstitials released from EOR region. Isochronal annealing study is performed to investigate the impact of CF codoping on the dopant de/reactivation behavior. It is shown that transient enhanced diffusion can be reduced by both co-implant schemes. The B-doped junction formed with the C co-implant is relatively stable and dopant deactivation is inhibited, while it is presumed that F atoms form B-F complexes, which reduces the B activation level. A physical insight on the dopant-defect interactions associated with CF co-implant is established through the combination of diffusion and activation studies during soak annealing. © 2007 The Electrochemical Society.