Influence of low thermal budget pre-anneals on the high temperature redistribution of low energy boron implants in silic
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Influence of low thermal budget pre-anneals on the high temperature redistribution of low energy boron implants in silicon F. Boucard1,2,3, M. Schott2, D. Mathiot2, P. Rivallin3, P. Holliger3, E. Guichard1 1 SILVACO France, 8, Avenue de vignate, F-38610 GIERES, France 2 PHASE/CNRS,23 rue du Loess, BP 20, F-67037 STRASBOURG Cedex 2, France 3 LETI, CEA GRENOBLE, 17 avenue des martyrs, F-38054 GRENOBLE Cedex 9, France
ABSTRACT It is now well established that the transient enhanced diffusion (TED) of ion implanted boron in silicon limits the formation of the ultra-shallow junctions required for the extreme deep submicron devices. It is also known that this TED is linked to the fate (elimination and agglomeration) of ion implantation related excess self-interstitials. Thus it can be expected that the final high temperature redistribution is at least partly governed by the effective initial point defect distribution at the onset of the high temperature plateau. In this contribution we present the experimental evidence that low thermal pre-anneals, by affecting the initial self-interstitials distribution, affects boron redistribution during a subsequent high temperature anneal. Samples implanted with high dose boron at 3 keV were first annealed at 700°C for various durations. These samples, as well as reference samples without the pre-anneal, were then RTA annealed at various high temperatures around 1000°C. The resulting B profiles were measured by SIMS. It is found that the pre-annealed samples exhibits a clear reduction of the TED as compared with the reference ones.
INTRODUCTION Ion implantation is the common technique to introduce impurities into silicon for doping advanced silicon devices in microelectronics. This technique induces a huge over-saturation of point defects in the Si crystal which leads to an anomalous broadening of the dopant profile during the high temperature activation anneal. This phenomenon, known as transient enhanced diffusion (TED) of dopant, is very noticeable for boron, the diffusion of which in Si is mainly mediated by self-interstitials silicon atoms. In fact, the implantation related initial over-saturation of self-interstitials leads to the nucleation and growth, upon annealing, of a collection of various self-interstitial clusters with the eventual formation of extended defects such as {113} defects or dislocation loops [1-3]. These various defects maintain in their vicinity a self-interstitial supersaturation depending on their exact shape and size [4]. Thus the overall boron TED is governed by the evolution and the annihilation / growth kinetics of the point and extended defects present in the material. On the other hand, it is well known for a long time that silicon self-interstitials can easily diffuse in silicon, even at room temperature. The purpose of this work is to test if it is possible to take advantage of this fact to modify the initial configuration and distribution of self-interstitial silicon atoms using low thermal budget pre-anneals, with the hope of reducing the subse
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