Influence of Ge concentration and compressive biaxial stress on interdiffusion in Si-rich SiGe alloy heterostructures

Abstract

The Si–Ge interdiffusivity in SiGe alloys grown epitaxially on Si (100) substrates was systematically measured for Ge concentrations between 0.075 and 0.192 over a temperature range of 770–870°C. For several alloy compositions, interdiffusion kinetics were compared between films with nominally identical Ge concentration profiles, but different degrees of misfit strain relaxation. X-ray diffraction measurements of the decay rate of small, periodic, modulations in composition superimposed onto the average background alloy fraction were used to determine interdiffusivity values. The interdiffusion rate was found to increase by about a factor of 2 over the concentration range studied. The measured activation enthalpy for interdiffusion decreased linearly with Ge concentration by 4.05±0.25eV∕unit Ge atomic fraction. The prefactor for interdiffusion was proportional to exp(−35XGe). Extrapolating these trends to a Ge fraction of zero yielded a prefactor and activation enthalpy consistent with accepted values for Si and Ge tracer diffusion in pure Si. Furthermore, it was found that changes in the compressive biaxial misfit strain during postgrowth annealing of these heterostructures yielded no detectable change in measured interdiffusion rates. These results were incorporated into an interdiffusion model that successfully predicted experimental results derived from a large composition-amplitude Si∕Si0.78Ge0.22 superlattice and from intermixing at the interfaces between Si capping layers and both Si0.9Ge0.1 and Si0.78Ge0.22 blanket films.