Decomposition Kinetics of Tetraethoxysilane on SiO 2
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DECOMPOSITION KINETICS OF TETRAETHOXYSILANE ON SiO 2
BRADLEY G. TODD, JOHN B. HUDSON- AND PETER K-C. WU' *IBM corporation, Hopewell Junction, NY 12533 "'Materials Engineering Department, Rensselaer Polytechnic Institute, Troy, NY 12180
ABSTRACT The decomposition of tetraethoxysilane (TEOS) on a thermally grown SiO 2 surface has been studied using molecular beam scattering, with mass spectrometric detection and time of flight techniques. Decomposition was characterized over a range of temperatures from ambient to 1100 K using a mass spectrometer having a line of sight to the sample surface. Time of flight measurements were used to characterize parent and product species and to determine surface residence time. The initial step in the decomposition process at low temperatures is the loss of one ethoxy ligand to produce triethoxysilane, ethylene and possibly water as gas phase products. At temperatures above 850K there is a change in the rate limiting process and an abrupt increase in the decomposition probability. Observed kinetics are explained in terms of an adsorbed molecular precursor mechanism. INTRODUCTION The formation of thin insulating films of SiO 2 by chemical vapor deposition (CVD) from the precursor tetraethoxysilane (TEOS) is a common process in microelectronic fabrication technology. Thermal decomposition of TEOS in the 760 °C range, and plasma assisted deposition from TEOS - ozone mixtures in the 400 °C range are used to deposit blanket layers of SiO 2 with good conformality and physical properties. Because of its practical importance, the surface chemistry of TEOS on silicon and on SiO 2 surfaces has been the subject of several previous studies, using a range of standard surface science techniques. Tedder et a]. [1,2] have studied the adsorption and decomposition of TEOS on SiO 2 using infrared spectroscopy and thermal desorption spectroscopy. Results of this work indicated the formation of various ethoxy species on the sample surface, and the desorption of primarily ethylene. Recently there have also been a number of studies aimed at modelling the SiO 2 deposition process, aimed at determining the optimum conditions for trench filling by TEOS decomposition. These studies have involved attempts to fit the observed trench filling behavior to a model in which parameters such as the unit collision decomposition probability of the TEOS molecule, and the possible production of reactive intermediates or site blocking by products formed in the collision process have been treated as adjustable parameters (3,4). The chief limitations on the measurements reported to date are the lack of any data at the surface temperatures used in practical TEOS deposition systems, and the lack of information on the reaction probability of TEOS or its primary reaction products at various temperatures and under conditions resembling those used in practical deposition systems. In the work reported here, we report preliminary results of a study of the interaction of TEOS with clean SiO 2 surfaces, under conditions where the onl
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