Modeling Dopant Diffusion in SiGe and SiGeC alloys
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B9.4.1/C9.4.1
Modeling Dopant Diffusion in SiGe and SiGeC alloys Ardechir Pakfar1,2, Philippe Holliger2, Alain Poncet3, Cyril Fellous1, Didier Dutartre1, Thierry Schwartzmann1 and Hervé Jaouen1. 1 STMicroelectronics, 850 rue Jean Monnet F-38926 Crolles cedex, France. 2 CEA-DRT-LETI/DTS, 17 rue des Martyrs, F-38054 Grenoble cedex 09, France. 3 LPM - INSA de Lyon, 20 av. Albert Einstein, F-69621 Villeurbanne cedex, France. ABSTRACT A unified diffusion model is developed, valid for all usual substitutional atoms in SiGe and strained SiGeC layers, in accordance with all published experimental data and predicting the enhancement of Arsenic diffusion in SiGe and SiGeC strained layers. Using a new SIMS methodology, the study of As intrinsic diffusion in SiGe and SiGeC layers is performed, at low concentration and under equilibrium annealing conditions. Arsenic diffusivity in fully-strained SiGe and SiGeC layers on Si substrates was successfully compared to the unified diffusion model. INTRODUCTION The different devices of conventional Si technology show improved electrical characteristics when Si/SiGe(C) layers are combined to form pertinent heterostructures using the wide range of induced physical properties: Band Gap change, reduced boron diffusivity or strain effect on carrier mobility. But, the optimal use of SiGe and SiGeC alloys in Si-based applications will be possible only if the influence of Ge and C atoms on the diffusion behavior of substitutional atoms is correctly taken into account. To reach this goal, the precise understanding of dopant diffusion and the consecutive control of the dopant profiles is a major challenge that our phenomenological diffusion model addresses. In order to be predictive in SiGe(C) alloys, the diffusion model should be settled on physical hypothesis. Moreover, this study will also lead us to a better understanding of the diffusion mechanisms in pure Silicon. A unified diffusion model is formulated, considering the change of point defects concentrations with the Ge and C content of SiGe and SiGeC layers. Then the model parameters are calibrated on reliable experimental Boron, Phosphorus, Antimony and Germanium diffusion data from literature. And finally, its application on Arsenic diffusion predicts an important acceleration of As diffusivity with increasing Ge and C content of SiGe and SiGeC strained layers. Using a new SIMS methodology, the diffusion of As in in situ-doped SiGe and SiGeC epitaxies at low concentration and under equilibrium annealing conditions is studied for the first time, and is successfully compared to our simulations.
B9.4.2/C9.4.2
THEORY The major part of the published diffusion models are limited to the diffusion of boron in strained SiGe and SiGeC layers [2], well adapted for the challenging applications of heterojunction bipolar transistors (HBT’s) but can not be extended to relaxed SiGe layers or to any other substitutional atom. For Ge and C contents respectively lower than x=0.50 and y=0.02, Si1-x-yGexCy are purely covalent alloys having the same diamo
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