Empirical Interatomic Potential for Si-H Interactions
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An empirical Tersoff-type interatomic potential has been developed for describing Si-H interactions. The potential gives a reasonable fit to bond lengths, angles and energetics of silicon hydride molecules and hydrogen-terminated silicon surfaces. The frequencies of most vibrational modes are within 15% of the experimental and ab initio theory values. The potential is computationally efficient and suitable for molecular dynamics investigations of various processing treatments of hydrogen-terminated silicon surfaces.
The chemistry of hydrogen and silicon has received increased attention recently. Hydrogen is an important component in various VLSI processing steps such as chemical cleaning, chemical vapor deposition (CVD), reactive ion etching and lithography. Hydrogen is present in CVD growth precursors such as silane and disilane and plays an important role in the overall epitaxial growth mechanism. In low temperature chemical vapor deposition, hydrogen desorption has been shown to limit the growth rate [1]. Hydrogen in bulk silicon is known to passivate dopants and deep level defects. On the surface, hydrogen can terminate the dangling bonds and passivate the surface from oxidation over long periods of time. Hydrogen-termination of silicon prior to epitaxy in ultra-high vacuum has become increasingly popular due to the relatively low desorption temperature. Epitaxial silicon layers have been deposited on hydrogen-terminated silicon surfaces [2, 3, 4]. A low temperature Ar+ and He+ ion beam-induced (2 x 1) reconstruction from an initially dihydride-terminated Si(001) surface has also been observed [5]. Many of these processes occur on a time scale and crystal size scale which is beyond the scope of a first principles approach. We have developed an empirical Si-H potential for molecular dynamics simulations of the hydrogen-terminated silicon surfaces and various gas-surface interactions. Empirical expressions for the Si-H potential have been developed previously. These expressions were either not tested over a sufficiently wide range of configurations [6] or were restricted to a few gas phase species [7]. The chemistry of hydrogen and silicon has been studied both experimentally and theoretically [8]. The various silicon hydride compounds (SimHn species) have been characterized by their bond dissociation energies, bond lengths and angles and vibration frequencies. On the silicon surface, different hydrogen-induced reconstructions have been observed as a function of hydrogen coverage. In bulk silicon, the energies of various interstitial sites for both atomic and molecular hydrogen have been estimated using first principles techniques. Extended hydrogen defects called platelets have also been observed [9]. These different configurations serve as a database for the evaluation of the parameters in the chosen interatomic potential. In recent years, several interatomic potentials have been developed to model siliconsilicon interactions[10, 11]. The Si potential in Ref. [10] gives a good description of the 355 Mat. Res.
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