A Novel Model for Boron Diffusion in SiGe Strained Layers Based on a Kinetics Driven Ge-B Pairing Mechanism
A new temperature dependant model for the Ge-B pairing mechanism has been established and implemented in a process simulator. The combination of both lattice strain effects and GeB clustering has been successfully applied to various anneals. The match with experimental SIMS profiles is excellent.
Boron diffusion across silicon–silicon germanium boundaries
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.
Measurement and modeling of boron diffusion in Si and strained Si1−xGex epitaxial layers during rapid thermal annealing
Boron concentration profiles in rapid thermally annealed Si and strained Si1−xGex in situ doped, epitaxial layers were measured using secondary‐ion‐mass spectroscopy. Comparison of the Si1−xGex samples to the Si samples after rapid thermal annealing revealed a retarded B diffusivity inside the strained Si1−xGex layers. A simple empirical expression for the B retardation, which depended linearly on the Ge concentration, was developed and incorporated into a diffusion model for dopants in heterostructures. This model accurately simulated the measured B concentration profiles over a wide range of Ge fractions (0%–10%), B peak concentrations (2×1018–3×1019cm−3), and rapid thermal annealing conditions (900–1025 °C for 20–30 s).