A study of boron diffusion from selectively grown epitaxial silicon-germanium into silicon during rapid thermal annealing

Abstract

Boron diffusion from selectively grown epitaxial Si1-xGex into Si during rapid thermal annealing (RTA) was investigated. Selective epitaxial growth (SEG) of in-situ boron-doped strained Si1-xGex epitaxial layers with different Ge percentages were selectively grown by ultra high vacuum chemical molecular epitaxy (UHVCME). The results show that the boron diffusion depth from SEG Si1-xGex into n-type Si depends on boron concentration, Ge profile in the SEG area, and the size of the SEG area. Higher boron concentrations in SEG Si1-xGex film increases the boron diffusion depth. However, the diffusion depth can be reduced by increasing Ge composition in SEG Si1-xGex. It was also found that the samples with graded Ge profiles have higher diffusion depths than those with uniform profiles. In addition, the boron diffusion depth increases with the size of the SEG Si1-xGex area. The strain in SEG Si1-xGex, the chemical potential of Ge in SEG Si1-xGex and the dislocations induced in the SEG Si1-xGex layers are the main reasons for the phenomena observed.