Carbon Diffusion and Clustering in SiGeC Layers Under Thermal Oxidation
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Carbon Diffusion and Clustering in SiGeC Layers Under Thermal Oxidation D. De Salvador1, E. Napolitani1, A. Coati1, M. Berti1, A.V. Drigo1, M. Carroll2, J.C. Sturm2, J. Stangl3, G. Bauer3, L. Lazzarini4 1 Dept. of Physics, University of Padova and INFM, Padova, ITALY 2 Dept. of Electrical Engineering, Princeton University, Princeton, USA 3 Inst. For Semiconductor Physics, J. Kepler University of Linz, Linz, AUSTRIA 4 CNR-MASPEC, Parma, ITALY ABSTRACT In this work we investigated the diffusion and clustering of supersaturated substitutional carbon 200nm thick SiGeC layers buried under a silicon cap layer of 40nm. The samples were annealed in inert (N2) or oxidizing (O2) ambient at 850°C for times ranging from 2 to 10 hours. The silicon self-interstitial (I) flux coming from the surface under oxidation enhances the C diffusion with respect to the N2 annealed samples. In the early stages of the oxidation process, carbon escape by diffusion across the layer/cap interface dominates. This phenomenon saturates after an initial period (2-4h) which depends on the C concentration. This saturation is due to the formation and growth of C containing precipitates which are promoted by the I injection and act as a sink for mobile C atoms. The competition between clustering and diffusion is discussed for two different C concentrations. INTRODUCTION In the last years strong efforts have been devoted to the investigation of the structural properties of SiGeC alloy, due to its potential use as a Si-based material with band-gap [1] and lattice parameter [2] tailoring properties. Recently, the role of C in Si and SiGe alloys as a Si self-interstitial (I) trap was evidenced by the reduction of Boron diffusion [3] and by the suppression of both B transient enhanced diffusion (TED) and B oxidation enhanced diffusion (OED) [4,5]. This pushed up a renewed interest in the use of SiGeC layers to control the diffusion of dopants in silicon devices. Therefore, understanding the behavior of C in SiGeC/Si heterostructures under I supersaturation is of crucial importance. It is known that C diffusion is strongly enhanced by I supersaturation [6], as the silicon self-interstitials promote the formation of mobile C interstitial atoms via the kick-out or Frank-Turnbull mechanisms. Recently, a C-diffusion enhancement by interstitials injection was observed also in SiGeC alloys with high C concentration, above 1020 cm-3 [7]. Nevertheless, even in the absence of an external I injection (i.e. after inert thermal annealing), it has been reported the tendency of C to precipitate and to form β-SiC clusters [8]. All these facts suggest that the control of the C behavior in Si-based materials under thermal treatments is challenging for technological applications. In this work we report on the diffusion and clustering behavior of C in buried SiGeC layers under supersaturated I non-equilibrium conditions, induced by thermal oxidation of the silicon cap. We’ll describe the presence of a complex competitive mechanism between C diffusion and C accumulation in clust
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