Varying implant dose rate for defect reduction in laser thermal processing

In this article we report the role of excess interstitials in the end-of-range region in transient enhanced diffusion of boron during annealing of laser-processed samples. The results show that although the amorphous layer in preamorphized silicon can be completely annealed by laser irradiation, the end-of-range damages were not sufficiently annealed. The end-of-range region contains a supersaturation of interstitial defects that enhance the diffusion of boron during a post-laser processing anneal. It is found that the transient enhanced diffusion is significantly suppressed when the melt depth is extended beyond the amorphous layer such that the interstitial dose in the region adjacent to the laser-melted layer is minimized. In this way, the abruptness of laser-processed ultrashallow junctions can be maintained upon further annealing at moderately high temperatures. Cross-sectional transmission electron microscopy shows that a virtually defect-free regrown layer is obtained by overmelting beyond the amorphous layer into the substrate.

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

Lindsay

Pawlak

Stolk

et al. 2002

MRS Proc.

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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.

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Varying implant dose rate for defect reduction in laser thermal processing

Cited by 3 publications

References 10 publications

Status and open problems in modeling of as-implanted damage in silicon

Status and open problems in modeling of as-implanted damage in silicon

Control of transient enhanced diffusion of boron after laser thermal processing of preamorphized silicon

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

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