Group III impurities – Si interstitials interaction caused by ion irradiation L. Romano * , A.M. Piro, R. De Bastiani, M.G. Grimaldi, E. Rimini MATIS-INFM and Dipartimento di Fisica e Astronomia, Universita ` di Catania, Via S. Sofia 64, 95123 Catania, Italy Available online 25 October 2005 Abstract The off-lattice displacement of substitutional impurities (B, Ga) in Si caused by irradiation with energetic light ion beams has been investigated. Samples have been prepared by solid phase epitaxy (SPE) of pre-amorphized Si subsequently implanted with B and Ga at a concentration of about 1 · 10 20 at/cm 3 confined in a 300 nm thick surface region. The off-lattice displacement of the impurities was induced at room temperature (RT) by irradiation with high energy (>600 keV) light ion beams (H, He) and detected by the channelling technique along different axes, using the 11 B(p,a) 8 Be reaction and standard RBS, for B and Ga, respectively. The normalized channelling yield v of the impurity signal increases with the ion fluence, indicating a progressive off-lattice displacement of the dopant during irra- diation, until it saturates at v F < 1 suggesting a non-random displacement of the dopant. Although the precise value of v F depends on the channelling direction and dopant species, the off-lattice displacement rate, deduced from the v versus interstitial fluence curve, only depends on the excess of Si self-interstitials (Si I ) generated by the irradiating beam through a parameter r that can be interpreted as an effective cross-section for the impurity–Si I interaction. Ó 2005 Elsevier B.V. All rights reserved. PACS: 61.80.Jh; 61.72.Dd; 66.30.Jt Keywords: B; Ga; Si; Self-interstitial; Ion channelling; TED 1. Introduction Obtaining and maintaining a good electrical activation and precise control of dopant concentration profiles of dopant in Si are crucial keys in fabricating high level, long time duration Si based devices. It is well known that tran- sient enhanced diffusion (TED) of dopant in Si during implantation and annealing causes the spreading of the doping profile and poses a real limitation for the formation of shallow junctions in submicron device structures. Many recent investigations [1] have shown that dopant–defect interactions during post-implant thermal processing are dominated by the net-excess defects induced by implanta- tion. On this basis, the interaction between impurities and point defects in Si, such as vacancy or self-interstitial, constitutes a charming issue in fundamental research as well as a strategic challenge for technological reasons, since it determines the dopant diffusion, its electrical activation and clustering [2–5]. Dopant diffusion in silicon is mediated by native point defects [6]. Substitutional dopant atoms migrate in silicon by pairing with either a Si self-interstitial I or a vacancy V, respectively, as follows: A+I ! AI; A+V ! AV, where AI is a dopant interstitial pair and AV is a dopant vacancy pair. It has been demonstrated that substitutional group III impurities diffuse prevalently by an interstitial (cy) mechanism [6,7] and deviations from the equilibrium diffusion coefficient have been correlated to the excess of Si I . Many researchers studied non-equilibrium dopant diffu- sion to gain information on the interaction of impurity with point defects: in these cases diffusion was promoted 0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.08.190 * Corresponding author. Tel.: +39 0953785289; fax: +39 0953785231. E-mail address: lucia.romano@ct.infn.it (L. Romano). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 242 (2006) 646–649 NIM B Beam Interactions with Materials & Atoms