Void evolution in silicon under inert and dry oxidizing ambient annealing and the role of a Si1−xGex epilayer cap

Voids were formed in silicon (Si) and silicon germanium/silicon (Si1−xGex/Si) samples containing 5% or 9% Ge (at. %) by 30 keV, 5 × 1016 cm−2 helium (He+) implantation followed by annealing in nitrogen (N2) or dry oxygen (O2) atmospheres in the temperature range 960–1110 °C. Si1−xGex thicknesses were 60 nm and 20 nm for 5% and 9% Ge, respectively. He+ implantation energy was set such that in Si1−xGex/Si samples voids were formed inside the Si substrate. An increase in annealing temperature resulted in an increase in the average void diameter and decrease in the average void density. Due to the presence of implantation damage and the relatively high temperature anneals, Ge diffusion occurs, which results in a stress gradient in the sample that interacts with the void layer. The presence of Ge also results in weaker Si-Ge bonds (compared to Si-Si bonds). This leads to an increase in the rate of cavity migration providing a likely explanation for the increase in the average void diameter and decrease in the average void density in Si1−xGex/Si samples when compared to the similarly prepared Si samples. No impact on the void evolution process was observed as a result of changing the anneal atmosphere from N2 to dry O2.