Influence of He implantation conditions on strain relaxation and threading dislocation density in Si_0.8Ge_0.2 virtual substrates

Abstract

The strain relaxation and threading dislocation density of He-implanted and annealed SiQe/Si heterostructures have been studied. For He doses above a threshold of 8×1015 cm-2, the degree of strain relaxation depends primarily on the SiGe layer thickness; a similar degree of strain relaxation is obtained when the He dose and energy are varied over a relatively wide range. In contrast, the threading dislocation density is strongly influenced by the implantation depth. There is a strong correlation between the parameter He(SiGe), the He dose in the SiGe layer calculated from He profiles simulated using the program Stopping and Range of Ions in Matter (SRIM), and the threading dislocation density. We find that to achieve a low threading dislocation density, <5×107 cm-2, He(SiGe) must be less than 1015 cm-2. The strain relaxation mechanism is also discussed.