Growth kinetics of chemically vapor deposited SiO 2 films from silane oxidation
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Growth kinetics of chemically vapor deposited SiO2 films from silane oxidation Fernando Ojeda, Alejandro Castro-Garc´ıa, Cristina G´omez-Aleixandre, and Jos´e Mar´ıa Albella Surface Science and Engineering Department, Materials Science Institute of Madrid (CSIC), Cantoblanco, 28049 Madrid, Spain (Received 21 May 1997; accepted 19 February 1998)
The growth kinetics of SiO2 thin films obtained by low-pressure chemical vapor deposition (CVD) from SiH4yO2yN2 gas mixtures has been determined at different temperatures and flow rates. The results show that the film growth is originated by some intermediate species (e.g., SiOx Hy ) produced in the gas phase. At low temperatures the deposition rate is limited by some homogeneous reaction with an apparent activation energy of 1.42 eV. Furthermore, the observation of critical limits when total pressure, oxygen/silane flow ratio, and temperature are decreased gives support to a branching-chain mechanism of deposition. Finally, we have observed that the deposition rate shows a hysteresis behavior when varying the temperature within the 300–400 ±C range, which has been attributed to the inhibition of silane oxidation by the Si –OH surface groups of the films grown on the reactor walls.
I. INTRODUCTION
Chemical vapor deposition (CVD) of SiO2 films from the silane/oxygen reaction is a widely implanted process in the manufacture of silicon-based, solid-state devices. This technique allows one to achieve reasonable deposition rates at low temperatures (typically between 200 ±C and 400 ±C) with no need of additional activation methods, i.e., plasmas or lasers, that complicate excessively the experimental system and may induce damages on sensitive devices. The low-temperature character of the silane oxidation makes it compatible with the more recent II-VI and III-V semiconductor-based technologies. This character, which is unusual in CVD processes where gas precursors of high vapor pressure are used, proceeds from the abundant formation of highly reactive-free radicals. In fact, there is little question that silane oxidation proceeds through a branchingchain process where the reaction of SiH3 species with oxygen molecules plays a crucial role. Some plausible routes for the SiH3yO2 reaction could be: HSiOOH 1 H, SiH2 O 1 OH, or SiH3 O 1 O. These SiOx Hy species are very reactive SiO2 intermediate precursors, and the hydrogen, hydroxyl, and oxygen radicals are the active chain carriers that lead to the production of new SiH3 species through the following reactions: SiH4 1 H SiH3 1 H2 SiH4 1 OH SiH3 1 H2 O SiH4 1 O SiH3 1 OH The heterogeneous and homogeneous quenching of the chain carriers, and even of the SiH3 species, determine the lower and upper critical limits of ignition. These schemes, though speculative, are consistent with the 2308
http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 8, Aug 1998
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observed reaction stoichiometry of SiH4yO2 explosions,1 ignition limits of silane oxidation,2 as w
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