Counterdoped very shallow p+/n junctions obtained by B and Sb implantation and codiffusion in Si

Abstract

In this article we investigate the B and Sb codiffusion upon postimplantation annealing in order to fabricate very shallow p+/n junctions (≤70 nm), suitable for a complementary metal-oxide-semiconductor technology with a channel length of 0.18 μm. The junctions are prepared by implanting Sb and subsequently BF2, at a higher dose, in an n-type Si substrate. The preamorphization with Sb avoids the B channeling and increases the n-type doping in the junction region, thus confining the depth of the p layer. Furthermore, both the transient enhanced diffusion, being the B implanted in a preamorphized layer, and the standard diffusion, due to the pairing between donors and acceptors, are strongly reduced. This procedure allows us to obtain very shallow junctions even after annealings with relatively high thermal budget, like 800°C/8 h or 900°C/1 h, or 950°C/10 min or 1000°C/60 s. We verified that dopant diffusion is strongly affected by a direct donor-acceptor interaction, and that good prediction of the experimental results can only be obtained using a simulation code which takes into account the formation of neutral, near immobile, Sb-B pairs. © 1998 American Institute of Physics.