Optimisation of Junctions formed by Solid Phase Epitaxial Regrowth for sub-70nm CMOS

Abstract

For the 70nm CMOS node, it is anticipated that conventional implantation and spike annealing approaches, even with pre-amorphisation and co-implantation, are unlikely to provide pMOS junctions consistent with the ITRS requirements. Here the junction performance is limited by equilibrium solid solubility.As laser annealing and in-situ doping techniques currently have unsolved integration problems, there is a renewed interest in using solid phase epitaxial regrowth (SPER) to form ultra-shallow metastable junctions. Such junctions have the potential to have an active dopant profile similar to the as-implanted profile. This offers above equilibrium solid solubility and abrupt profiles compatible with 70nm and even 45nm nodes. However there are concerns about residual defects, deactivation, diffusion and uniformity.In this paper we show how the Ge, F and B implant and SPER anneal can be optimised for abrupt, uniform and highly activated B junctions. There is latitude for higher doses and energies than conventional implants, however results show that this may lead to clustering causing enhanced deactivation and reduced mobility. We give attention to the probing issues involved in characterising partially annealed junctions.With this approach, p-type junctions having a sheet resistance of 265 ohms/sq and depth of 22nm are realised which are compatible with 70nm and potentially 45nm CMOS nodes.

Leakage optimization of ultra-shallow junctions formed by solid phase epitaxial regrowth

“…[2][3][4][5][6][7] The drawbacks of this method are mainly related to the relative high density of residual defects at the end-of-range ͑EOR͒ region and limited thermal budget for post-anneal processing. The main advantages are the above-equilibrium activation of dopants, minimal diffusion, good control over junction depth, and compatibility with high-K and metal gate thermal budget requirements.…”

Metastable boron active concentrations in Si using flash assisted solid phase epitaxy

“…Though not widely recognized, the extremely shallow junctions that are the focus of study in research groups often have a considerable amount of leakage current to the substrate due a variety of reasons such as probe penetration to the substrate, 11 band to band tunneling, 12 and end of range (EOR) damage left after the anneal. Irrespective of the mechanism, the leakage current to the substrate provides an alternative path for the current to flow resulting in erroneous, low sheet resistance readings.…”

Implants of ClusterBoron® and ClusterCarbon^TM materials for USJ applications - a study with various anneal techniques

“…In general, low energy boron implants followed by rapid thermal anneals suffer from low levels of dopant activation limited by the equilibrium solid solubility of boron in Si. Coimplants of F or C along with dopant implants are a alternate route to obtaining reduced dopant diffusion and/or higher activation along with more abrupt junctions [3][4][5][6]. Carbon is found to reduce boron diffusion more efficiently than fluorine.…”