Pt s -O i Complex Formation in Platinum Diffused Silicon
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Pts-Oi Complex Formation in Platinum Diffused Silicon Wilfried Vervisch1,2,3, Laurent Ventura1, Bernard Pichaud2, Gérard Ducreux3 and André Lhorte3 1 LMP, Université de Tours, 16 rue P. et M. Curie, BP 7155, 37071 Tours cedex 2, France, 2 TECSEN, UMR 6122 CNRS, Université Aix-Marseille III, 13397 Marseille Cedex 20, France 3 STMicroelectronics, 16 rue P. et M. Curie, BP 7155, 37071 Tours cedex 2, France ABSTRACT When platinum is diffused at temperatures higher than 900°C in Cz or FZ low doped n-type silicon samples, which are then cooled slowly in the range [1-10]°C/min, a p-type doping leading to the formation of a pn junction can be observed by spreading resistance measurement. The lower the cooling rate, the deeper the junction is. This junction disappears after a second thermal treatment finishing with a quenching step. A platinum related complex formation is considered to explain this reversible doping behaviour. Different possible interactions between platinum and other impurities such as dopant atoms, intrinsic point defects, and common residual impurities (C, Oi, transition metallic atoms) are studied here. Experimental results from Pt diffusion processes in different qualities of silicon wafers, and simulation results, lead to the conclusion that the platinum related p-type doping effect is due to the formation of a Pts-Oi complex.
INTRODUCTION Platinum introduces deep energy levels into the silicon band gap that are usually used into the technology of power semiconductor devices to control carrier lifetime. The identification of substitutional platinum related deep energy levels is well established [1-10], with an acceptor level at 0.23 eV from the conduction band and a donor level at 0.32 eV from the valence band. Other additional levels have been also reported such as the mid-gap level [2-5,9,10,11] near 0.52 eV from the conduction band, and three other acceptor states at Ev+0.3 eV [11], Ev+0.36 eV [4] and Ev+[0.40-0.43] eV [5,6,7,8,12]. Sachse et al [11] have suggested that the mid-gap level and the acceptor states at Ev+0.3 eV, could be attributed to a platinum-hydrogen complex. The other acceptor states were not identified but were reported as being at the origin of n-type to p-type doping conversions [4,5,6,7,8,12]. Kwon et al. have also reported such n-type to p-type doping conversion in low doped silicon when platinum is diffused at temperatures higher than 1000°C, but they have focused their work on the mid-gap level which was suggested to be attributed to a platinum complex with oxygen [2]. More recently, we have shown that the concentration of the acceptor state, located near 0.42eV from the valence band, depended on the cooling, finishing the platinum diffusion step [12]. This p-type doping leads to the formation of a pn structure, with a junction which will be all the deeper as the cooling step will be slower. Moreover, the higher the diffusion temperature, the deeper the junction is. On the contrary, no junction is observed after a quenching step. This behavior has suggested the form
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