Buckling suppression of SiGe islands on compliant substrates

Abstract

A cap layer was used to suppress buckling during the relaxation of compressively strained 30 nm Si0.7Ge0.3 islands on borophosphorosilicate glass. The lateral expansion and buckling of a bilayer structure made of SiGe and a cap layer were studied by both modeling and experiment. Both epitaxial silicon and amorphous silicon dioxide (SiO2) caps were investigated. Caps stiffen the islands to reduce buckling and accelerate the lateral relaxation, so that larger, flat, relaxed SiGe islands can be achieved. Using a 31 nm silicon cap, flat Si0.7Ge0.3 islands up to 200 μm×200μm were achieved. However, germanium diffusion in the SiGe/Si structure took place during relaxation anneals and lowered the germanium fraction of the final fully relaxed SiGe film. Silicon dioxide caps, which are not prone to germanium diffusion, allowed suppression of SiGe buckling without lowering the germanium percentage. Full relaxation of SiGe islands was achieved by a controlled multicycle silicon dioxide removal and anneal procedure. Large, fully relaxed, smooth SiGe islands obtained using cap layers indicate that this approach could be of potential use for electronic device applications.