Boron diffusion across silicon–silicon germanium boundaries

Abstract

Most boron diffusion studies in Si–Ge have been made in regions of uniform germanium content. In this paper diffusion is observed from a boron-doped epitaxial silicon layer across surrounding Si–Ge layers. Pileup of boron in the Si–Ge layers shows that the activity coefficient for boron in Si–Ge is lower than that for pure silicon. A simple pairing model for Si–B interaction fitted the pileup quite well, with the same equilibrium constant applying to both Si0.9Ge0.1 and Si0.97Ge0.03 layers. The effect of this was simply to immobilize a significant fraction of the boron while retaining its acceptor qualities, the ratio of immobile boron to normal substitutional boron being proportional to the germanium content. Quasielectric field effects at the Si–SiGe interface have a strong effect on the results obtained.

The Lattice Kinetic Monte Carlo Simulation of Boron Diffusion in SiGe

“…Hitherto, it has been proposed that boron diffusion could be retarded in compressive strained Si 1-x Ge x alloys [8]- [12]. Boron diffusivity in strained as well as relaxed Si 1-x Ge x alloys largely decreased at Ge content up to 40% but increased again at high Ge levels were also reported [13]- [15]. Bang et al showed the boron diffusion reduced in Si 1-x Ge x alloy by DFT calculation and they pointed out that the retarded B diffusion could be attributed to the following reasons: 1) the presence of Ge increases the migration energy of a Si self-interstitial defect then reduces the numbers of Si self-interstitials available for B diffusion; and 2) increases the migration energy of the B interstitial [16].…”

Interaction of ion-implantation-induced interstitials in B-doped SiGe

“…When annealing at a furnace temperatures of 750 1C, boron diffusion decreases with increasing Ge content [9] presenting preferential Ge-B bonding as reasoning for retardation of B diffusion in SiGe [9][10][11]. Point defect injection from annealing ambient experiments in Si-rich SiGe suggests that B diffusion remains interstitially mediated [12,13] with fractional interstitialcy constants comparable to that of pure Si [14].…”

Boron Diffusion in Strained and Strain-Relaxed SiGe

“…Boron diffusivity under this circumstance has been modeled in [3,4] with a diffusivity retardation that is an exponential function of the strain. Alternatively, it is claimed that the retardation is from Ge-B pairing instead [5,6]. A quantitative assessment of the respective contribution from mechanical strain and Ge doping is therefore necessary for accurate boron modeling in SiGe.…”