Thermodynamic approach to the redistribution of boron and fluorine implanted at the interface of an SiO2/Si system

In microelectronics, during fabrication of ultrashallow p-n junctions boron is implanted in a silicon monocrystal, However, the subsequent rapid therm al annealing (RTA) causes anomalous fast diffusion (transient enhanced diff usion, TED) of the boron inwards in the crystal, hindering the formation of the desired ultrashallow junction. It was found that this accelerated diff usion can be overcome by applying a silica protective layer on top of the m onocrystal and implanting BF2+ instead of elementary boron, This work offers a thermodynamic explanation as to why the silica layer and the presence of fluorine slow down the TED of boron, The nature, direction and magnitude of the thermodynamic forces controlling the processes are ex amined by two methods of approach. First, the problem is treated as the seg regation-desegregation of boron at the interface, governed by excess surfac e Gibbs free energy of the components in the SiO2(B)-Si(B)-Si 'sandwich' st ructure. Second, the thermodynamic probability of solid-phase chemical inte ractions is considered and calculated by computer program. The effect of fl uorine is treated according to its reaction with the silicon interstitials, Copyright (C) 2000 John Whey & Sons, Ltd.