Control of Silicon Quantum Dots nucleation and growth by CVD
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Control of Silicon Quantum Dots nucleation and growth by CVD F. Mazen1, T. Baron2, J. M. Hartmann3, M. N. Semeria3, G. Brémond1 1 LPM-INSA-Lyon , UMR 5511, 2 rue A. Einstein 69621 Villeurbanne, France. 2 LTM-CNRS, 17 avenue des Martyrs, 38054 Grenoble, France.3 CEA-DRT-LETI/DTS-CEA-GRE, 17 avenue des Martyrs, 38054 Grenoble, France. Abstract To be successfully integrated in nano-electronics devices, silicon quantum dots (Si-QDs) density, density uniformity, size and size dispersion must be controlled with a great precision. Nanometric size Si-QDs can be deposited on insulators by SiH4 CVD. Their formation includes two steps : nucleation and growth. We study the experimental parameters which influence each step in order to improve the control of the Si-QDs morphology. We show that the nucleation step is governed by the reactivity of the substrate with the Si precursors. On SiO2, OH groups are identified as nucleation sites. By controlling the OH density on the SiO2 surface, we can monitor the Si-QDs density on more than one decade for the same process conditions. Moreover, Si-QDs density as high as 1.5 1012 /cm² can be obtained. On the contrary, the growth step depends on process conditions. By modifying the gas phase composition, i.e by using SiH2Cl2 as Si precursor, we can grow the nuclei already formed during the nucleation step without formation of new Si-QDs. We discuss the advantages of this process to improve the control of the Si-QDs size and limit the size dispersion. Introduction : During the last few years, silicon quantum dots (Si-QDs) have been studied for nanoelectronics applications. Their unique physical properties, size confinement effect and coulomb blockade phenomena, make Si-QDs suitable for use in new silicon based devices like single electron transistor [1] or quantum dot floating gate memories [2]. For room temperature operation of such devices, nanometric size silicon dots (< 10 nm) are required. Chemical Vapor Deposition (CVD) is a good way to obtain Si-QDs for industrial applications because of its MOSFET technology compatibility. By controlling the early stages of the Si film growth, silicon crystallites of a nanometer size (5 nm) are obtained [3]. It has been shown that Si-QDs elaborated by SiH4 CVD exhibit coulomb blockade at room temperature [4] and can be integrated in memories [2][5]. Figure 1a shows the evolution of the Si-QDs density versus deposition time for fixed temperature and SiH4 partial pressure. It is typical of a volmer-Webber type growth mechanism : after an incubation time which is necessary to adsorbed precursor to form the first stable nuclei, their is a nucleation and growth step where the Si-QDs density and their mean size increase simultaneously until the saturation of the surface [6]. By consequence, to modify the size or the density of the Si-QDs, it’s necessary to change all the process parameters : P, T and deposition time. In this paper, we show that nucleation and growth of Si-QDs can be monitored separately. First we study the parameter which influence
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