Nonlocal reduced boron diffusivity in silicon below strained Si _1-xGe_x surfaces

The silicon (Si) surface can be the dominant source of self-interstitials for many annealing conditions. Incorporation of germanium (Ge) and strain into the surface may be expected to perturb the equilibrium point defect concentrations at the surface (i.e., the atomic steps at which the point defects are generated and annihilated) and consequently in the bulk Si. In this work, boron (B) diffusion marker layers were epitaxially grown in Si by rapid thermal chemical vapor deposition followed by either undoped Si, 45 nm of Si0.75 Ge0.25, or 5 nm of Si0.55 Ge0.45 leaving a surface with three different Ge contents. The B diffusivity (DB) below the Si1-x Gex surface layers was found to be as much as two times slower than that in the all-Si samples between 800 and 900 °C. The activation energy for the DB in the Si1-x Gex capped samples was also observed to increase to ∼4.1 eV. This work demonstrates that a Si1-x Gex surface can reduce the DB in the underlying Si during N2 annealing. Furthermore, this novel test structure helps separate the effects of strain and local Ge trapping on DB in Si1-x Gex.