Measurement and simulation of boron diffusion in strained Si/sub 1-x/Ge/sub x/ epitaxial layers

Abstract

Boron and germanium concentration profiles in rapid thermal annealed and furnace annealed Si and strained Si/sub 1-x/Ge/sub 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/sub 1ix/Ge/sub x/ for boron diffusion in Si/sub 1-x/Ge/sub 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 (/spl sim/3/spl times/10/sup 18/ cm/sup -3/ to 1/spl times/10/sup 19/ cm/sup -3/) and 1/spl times/10/sup 19/ cm/sup -3/ for graded, and various thermal budgets including rapid thermal and furnace annealing conditions. A comparison of the Si/sub 1-x/Ge/sub x/ samples to the Si samples after both thermal anneals reveals a retarded B diffusivity inside the strained Si/sub 1-x/Ge/sub x/ layers. The Si/sub 1-x/Ge/sub x/ heterostructure model simulated the B diffusion in Si/Si/sub 1-x/Ge/sub 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.