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

Diffusion behaviour of aluminium in silicon at temperatures up to T = 900 d egrees C was investigated by nuclear reaction analysis (NRA). Previously pu blished results predict diffusion coefficients ranging from 3 x 10(-15) to 1.3 x 10(-13) cm(2) s(-1) at T = 900 degrees C. In a first series aluminium films were vapour deposited onto Si(1 0 0) substrates, followed by isochro nal annealing. The diffusion coefficient was found to be less than 10(-15) cm(2) s(-1) at 900 degrees C. In a secund series Si(1 0 0) and Si(1 1 1) sa mples were implanted at room temperature and at 250 degrees C with a fluenc e of 5 x 10(16) Al+ cm(-2). For the samples implanted at 250 degrees C and subsequently annealed at 900 degrees 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 im planted samples. Channeling analyses revealed extensive radiation damage in the latter samples, which was still present after annealing for 1 h at 900 degrees C. In contrast to this, the samples implanted at 250 degrees C wer e virtually defect-free. From this it is concluded that the high values obs erved for the room-temperature implants are due to defect-assisted diffusio n. (C) 2000 Elsevier Science B.V. All rights reserved.