Measurement and simulation of boron diffusion in strained Si1-xGex epitaxial layers

Boron and germanium concentration profiles in rapid thermal annealed and furnace annealed Si and strained Si_1-xGe_x in situ doped, epitaxial layers with both box-type and graded germanium (Ge) profiles were measured using secondary-ion-mass spectrometry (SIMS). A simple and accurate model that includes the modified strain, effect of trapping between B and Ge, the drift field due to bandgap narrowing, the intrinsic carrier concentration for Si_1ixGe_x for boron diffusion in Si_1-xGe _x, has been successfully implemented in simulation software. The model accurately simulates the measured boron as well as the Ge concentration profiles over a wide range of Ge fractions for box-type (0.06%, 0.2%, 4%, 10%, and 15%) and 15% for graded, and B peak concentrations for box-type (~3×10¹⁸ cm^-3 to 1×10¹⁹ cm^-3) and 1×10¹⁹ cm ^-3 for graded, and various thermal budgets including rapid thermal and furnace annealing conditions. A comparison of the Si_1-x Ge_x samples to the Si samples after both thermal anneals reveals a retarded B diffusivity inside the strained Si_1-x Ge_x layers. The Si_1-xGe_x heterostructure model simulated the B diffusion in Si/Si_1-xGe _x/Si heterostructures by incorporating both an enhanced B diffusivity and a Ge-dependent retardation. This retardation depends linear on the Ge concentration. Good agreement between the measured and simulated diffusion is obtained by including the model for strain and trapping effects