Study of the diffusion behaviour of aluminium in silicon up to 900°C by nuclear reaction analysis

Abstract

Diffusion behaviour of aluminium in silicon at temperatures up to T=900°C was investigated by nuclear reaction analysis (NRA). Previously published results predict diffusion coefficients ranging from 3×10 −15 to 1.3×10 −13 cm 2 s −1 at T=900°C. In a first series aluminium films were vapour deposited onto Si〈1 0 0〉 substrates, followed by isochronal annealing. The diffusion coefficient was found to be less than 10 −15 cm 2 s −1 at 900°C. In a second series Si〈1 0 0〉 and Si〈1 1 1〉 samples were implanted at room temperature and at 250°C with a fluence of 5×10 16 Al + cm −2. For the samples implanted at 250°C and subsequently annealed at 900°C, the diffusion coefficient was again found to be less than 10 −15 cm 2 s −1 , while diffusion coefficients of the order of 10 −13 cm 2 s −1 were observed for the room-temperature implanted samples. Channeling analyses revealed extensive radiation damage in the latter samples, which was still present after annealing for 1 h at 900°C. In contrast to this, the samples implanted at 250°C were virtually defect-free. From this it is concluded that the high values observed for the room-temperature implants are due to defect-assisted diffusion.