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118-ganem-apl-1996-2366 - Dry oxidation mechanisms of thin...

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Dry oxidation mechanisms of thin dielectric films formed under N 2 O using isotopic tracing methods J.-J. Ganem, a) S. Rigo, and I. Trimaille Groupe de Physique des Solides, URA 17 - CNRS, Universite ´s Paris 6 et 7, 75251 Paris cedex 05, France I. J. R. Baumvol and F. C. Stedile Instituto de Fisica and Instituto de Quimica - UFRGS, Porto Alegre, RS 91540-000, Brazil ~ Received 18 December 1995; accepted for publication 20 February 1996 ! We investigated the mechanisms of thermal reoxidation in dry O 2 of silicon oxynitride films prepared by processing Si ~ 100 ! wafers in a rapid thermal furnace in a pure nitrous oxide ~ N 2 O ! ambient, using isotopic tracing of oxygen and nitrogen. Standard nuclear reaction analyses for the measurement of the total amounts of the different isotopes, and very narrow resonant nuclear reactions for high resolution ~ 1 nm ! depth profiling of these elements were used. The silicon oxynitride films grown in pure 15 N 2 16 O were 8-nm thick, with a small amount of nitrogen localized near the interfacial region. Under reoxidation in dry 18 O 2 , the thickness of the dielectric film increased while a pronounced isotopic exchange took place between the 18 O from the gas and the 16 O from the film, as well as a significant loss of 15 N. This is in contrast with the reoxidation in dry O 2 of pure SiO 2 films, where the oxygen exchange is rather small as compared to that observed in the present case. © 1996 American Institute of Physics. @ S0003-6951 ~ 96 ! 03717-8 # The developments in very large-scale integration ~ VLSI ! devices require reliable gate insulator materials with thick- nesses compatible with the scaling rules, namely 10 nm and less. Various methods have been used to produce these di- electric films, the most promising ones being the thermal growth of a silicon oxynitride film on silicon in a nitrous oxide ~ N 2 O ! environment. 1,2 Although atomic transport pro- cesses are fundamental for the understanding of the growth mechanisms, so far only a few studies have considered this aspect. 3–5 In this letter we report on the atomic transport mechanisms during thermal reoxidation 6 of oxynitride films previously grown on Si ~ 001 ! under N 2 O, using isotopic trac- ing experiments of nitrogen and oxygen. Pure N 2 O ( . 99.998 % ! enriched in 15 N ~ 99% labelled gas ! was used for the oxynitridation of the silicon, and dry 99 % 18 O enriched oxygen gas ( 18 O 2 ) was used for thermal reoxidation. The treatment temperature was fixed at 1090 °C for both oxynitridation and reoxidation. Oxynitridation under 15 N 2 O was performed in a rapid thermal furnace at a pressure of 10 3 Pa during 180 s treatment time, and reoxida- tions were performed under 10 4 Pa of dry 18 O 2 for times of 20 min, 40 min and 120 min in a classical resistance heated furnace. The thicknesses of the oxynitride films after the thermal treatments were 8.2 nm before reoxidation and 15.8 nm, 20.5 nm and 31.8 nm after reoxidation times of 20 min, 40 min and 120 min, respectively. A 15 nm-thick control oxide was also grown at 1050°C by subsequent oxidations in 10 4 Pa of dry 16 O 2 gas for 450 s and in dry 18 O 2 for 150 s.
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