Modelling of the oxidation of Suspended Silicon Nanowires
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1144-LL18-06
Modelling of the oxidation of Suspended Silicon Nanowires P. F. Fazzini1-2, C. Bonafos1, A. Hubert3, J.-P. Colonna3, T. Ernst3, M. Respaud4, F. Gloux1 1
CEMES-CNRS - Université de Toulouse,29 rue J. Marvig, 31055, Toulouse, France
2
LAAS-CNRS - Université de Toulouse, 7 avenue du Colonel Roche, 31077, Toulouse, France
3
CEA-LETI, Minatec, 17 rue des martyrs, 38054 Grenoble Cedex 9, France.
4
LPCNO, INSA, Département de Physique, 135 avenue de Rangueil, 31077, Toulouse France
ABSTRACT The oxidation of suspended Si nanowires is studied under wet and dry conditions. The nanowire characteristics are extracted from Electron Microscopy images. In parallel, the Deal and Grove model is extended to cylindrical geometry. The used model also assumes that stress effects reduce the oxidation rate and predicts the retardation of oxide growth on curved surface, leading to a self-limited process. The model predictions show a good agreement with experiments.
INTRODUCTION Ultra-thin and narrow channels (below 10 nm) are ideal for OFF state leakage current (IOFF) control as future sub-22 nm Metal Oxide-Semiconductor (MOS) transistors [1]. Suspended nanowires (NWs) and multi-channels are currently being developed in order to increase the current density per surface unit [2]. The three dimensional (3D) multi-channel Gate-All-Around (GAA) process flow detailed in ref. [3] was used in this study to obtain 1-level suspended Si nanowires. First, 45 nm wide suspended silicon nanowires with near square cross-sections were obtained thanks to e-beam lithography and specific dry etching techniques [4, 5]. Due to optical and electronic lithography limitations, a specific oxidation process has been developed in order to reduce Si NW dimensions to values below 10 nm and to round off the nanowires for optimal IOFF reduction. The use of thermal oxidation to further reduce the diameter of NWs has already been reported [1, 5, 6] but there are only a few data concerning the oxidation kinetic process itself. The aim of this work is to study and model the thermal oxidation of Si NWs. The methodology and physical hypothesis are similar to what we reported for spherical nanocrystals (NCs) [7]. NW oxidation is examined as a function of the duration of thermal treatments performed at 950°C and 1100°C under respectively wet and dry conditions. The NW characteristics (size of the core and of its oxide envelope) have been extracted from Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) images. In addition, we have extended the
1D Deal and Grove model [8] to cylindrical geometry in order to properly reproduce the Si NW evolution under oxidation. Our model assumes that stress effects associated with non-uniform deformation of the oxide by viscous flow reduce the oxidation rate as observed by Kao et al [9]. This retardation effect increases when the NWs size decreases, leading to a self-limiting oxide growth. The model predictions show a good agreement with the experimental results. EXPERIMENTAL DETAILS Both wet
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