Bubbles and Cavities Induced by Rare Gas Implantation in Silicon Oxide
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Bubbles and cavities induced by rare gas implantation in silicon oxide E. Ntsoenzok1, H. Assaf1, M.O. Ruault2 1 CNRS-CERI, 3A, rue de la férollerie, 45071 Orléans, France 2 CSNSM, CNRS-IN2P3, Batiment 108-F-91405 Orsay, France
ABSTRACT In this pioneering study, we have extended noble-gas implant-induced cavity generation in Si and other semiconductors to a dielectric, viz., SiO2 by implanting a variety of inert gas species. It has been seen that helium and neon do not induce bubbles/cavities in SiO2, regardless of implantation parameters and nature of the sample. Krypton and xenon implantation however result in bubbles/cavities formation in the oxide layer. In the case of Xe a minimum threshold dose of about 1016 cm-2 is needed for their formation. Characterization by cross-section transmission electron microscopy (XTEM) and Rutherford backscattering spectrometry (RBS) showed that bubbles/cavities remain even after a 1100°C anneal, while Xe strongly desorbs out at that temperature. C-V measurements reveal that the effective dielectric constant K is reduced from 3.9 SiO2 for bulk SiO2 to < 2.6, thus making this technique very attractive for low-k applications in Si technology.
INTRODUCTION Bubbles and cavities induced by light ions (mainly hydrogen and helium) have been widely studied in metals [1,2] and semiconductors [3,4]. Their applications to semiconductor technology include the Smart-cut® wafer bonding technology [5] and gettering of metallic impurities in Si [6]. However, such work has not so far been extended to bubble formation in silicon oxide, a dielectric of supreme importance in Si very large scale integrated circuit (VLSI) technology. Low-K dielectrics for interconnects in IC devices constitute one of the potential applications of this modified SiO2. According to ITRS [7], the value of K must be lower than 2.5 by year 2007. Undoped SiO2 has a K of about 4 and cannot meet that requirement. The other low-K dielectric candidates being considered still need to be investigated fully for their overall compatibility with Si technology [8,9]. To create bubbles (especially by ion implantation), one needs gas atoms and vacancy complexes [10]. So it is necessary to consider (i) the behaviour of inert gases in SiO2 and (ii) the nature and the role of the defects created by irradiation. Schwickert et al [11] studied the evolution of implanted Xe in glasses and reported a faster exodiffusion with Xe dose. In another study, Wulf et al [12] found that in glasses a rare gas is usually surrounded by several oxygen atoms (its nearest neighbours). Guillot et al [13] reported that the solubility inert gases in glasses is size dependent, with He and Ne having much lower solubility than Ar, Kr and Xe. There is however a lack of data in the area of rare gas diffusivity in glasses. Extrapolation of results published by Boganov et al [14] show that at room temperature He is about 108 times more mobile in SiO2 than is Ar. Experimental results with He desorption spectroscopy [15] have also shown that He is much more mobi
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