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Nanostructuration of Cr/Si layers induced by ion beam mixing 1

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L. Luneville , L. Largeau , C. Deranlot , N. Moncoffre , Y. Serruys , F. Ott6, G. Baldinozzi , 8 D. Simeone 1 DEN/DANS/DM2S/SERMA/LLPR/LRC-CARMEN, CEA Saclay, 91191 Gif-sur-Yvette, France 2 LPN-UPR20/CNRS, Route de Nozay, 91460 Marcoussis, France 3 Unité Mixte de Physique CNRS/Thales, 1 Avenue Augustin Fresnel, 91767 Palaiseau, France 4 IPNL-IN2P3, 69622 Villeurbanne, France 5 DEN/DANS/DMN/SRMP, CEA Saclay, 91191 Gif-sur-Yvette, France 6 DSM/IRAMIS/LLB, CEA Saclay, 91191 Gif-sur-Yvette, France 7 CNRS-SPMS/UMR 8580/ LRC CARMEN Ecole Centrale Paris, 92295 Châtenay-Malabry, France 8 DEN/DANS/DMN/SRMA/LA2M/LRC-CARMEN, CEA Saclay, 91191 Gif-sur-Yvette, France

ABSTRACT This work clearly demonstrates that the X Ray Reflectometry technique (XRR), extensively used to assess the quality of microelectronic devices can be a useful tool to study the first stages of ion beam mixing. This technique allows measuring the evolution of the Si concentration profile in irradiated Cr/Si layers. From the analysis of the XRR profiles, it clearly appears that the Si profile cannot be described by a simple error function. INTRODUCTION Thin films play a dominant role in modern technology instigating a great deal of research interest from the perspective of basic science. Extensive work has been carried out on thin transition metal films (Fe, Co, Cr, ...) on Si wafers to understand the formation mechanism of various silicide compounds by thermally induced reaction at the Si/Metal interface[1-3]. In this context, ion beam mixing has an advantage; the ballistic nature of ion beam mixing at low temperature makes possible to mix two distinct elements even in an immiscible system [4]. Although ion beam mixing allows overcoming the equilibrium phase diagram, physical mechanisms responsible for the mixing are far from being clearly understood. Despite conventional methods to obtain information on ion beam mixing include Rutherford Backscattering Spectrometry (RBS), secondary ion mass spectrometry and Auger electron spectrometry with ion etching, these techniques are not able to probe nanometric layers. By contrast, the X-Ray Reflectometry (XRR) technique is well known as a characterization tool for studying stratified media like semi conductor super lattices [5] and Langmuir Blodgett films. In XRR, the intensity of an X-ray beam is specularly reflected on the sample. Due to high precision diffractometers, this technique offers advantages including high spatial sensitivity at the nanometric scale, high penetration and non destructive capability. At low incidence angles, XRR measurements are sensitive to modulation profiles of electronic density and absorption coefficient in a layered structure. The main feature of this technique remains the fact that the resolution in depth does not depend on the material but only on the detector resolution. On the

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other hand, many models, based on the Parrat [6] formalism, are now available to simulate XRR diagrams over a large angu