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Unformatted text preview: Effect of near-interfacial nitrogen on the oxidation behavior of ultrathin silicon oxynitrides H. C. Lu, E. P. Gusev, T. Gustafsson, and E. Garfunkel a) Departments of Physics and Chemistry, and Laboratory for Surface Modification, Rutgers University, Piscataway, New Jersey 08855 ~ Received 17 December 1996; accepted for publication 23 January 1997 ! Medium energy ion scattering has been used to study the role of nitrogen in the thermal oxidation kinetics of ultrathin silicon oxynitrides. Oxynitride films with different amounts of nitrogen near the SiO x N y /Si interface and pure ~ control ! SiO 2 /Si films were reoxidized in dry 18 O 2 under equivalent conditions. The spatial distribution of 18 O incorporated into the films was analyzed by high-resolution depth profiling methods. Analogous to the pure SiO 2 case, we observed two distinct regions where oxygen incorporation into the oxynitride films occurs: at/near the interface and near the outer oxide surface. The ~ near ! interface oxide growth reaction is found to be significantly retarded by the presence of near-interfacial nitrogen ~ with a higher degree of the retardation for higher concentrations of nitrogen ! . The presence of nitrogen near the interface does not affect the surface exchange reaction. © 1997 American Institute of Physics. @ S0021-8979 ~ 97 ! 05409-1 # INTRODUCTION There is a growing interest in ultrathin ( , 5 nm) silicon oxynitride films (SiO x N y ) for applications as gate dielectrics in next-generation ultra-large-scale integration ~ ULSI ! devices. 1–12 Oxynitride films have improved electrical prop- erties, such as reliability, hot-electron immunity, interface traps, and breakdown strength, and a suppression of boron penetration with respect to conventional (SiO 2 ) oxides. These beneficial effects have been attributed to the presence of a small amount of nitrogen ~ typically on the order of 5 3 10 14 cm 2 2 ) at/near the SiO x N y /Si interface. 1–11 It is known that near-interfacial nitrogen retards the ki- netics of further oxidation of silicon ~ in O 2 , N 2 O, and NO ! . 13,14 However, neither the mechanism of this retardation nor, generally speaking, the mechanism of ~ re ! oxidation of thin oxynitrided films is well understood. Experiments with isotopic substitution of reactive gases @ labeled, for example, by 18 O ~ Refs. 15–17 ! or 15 N ~ Ref. 18 ! atoms # have proven to be powerful in tracing the oxidation reaction and further un- derstanding these mechanisms. Isotopic ( 18 O 2 ) oxidation of ‘‘pure’’ (Si 16 O 2 ) oxides and subsequent analysis of the pro- files of the two isotopes in the film by ion scattering 17,19–21 or nuclear reaction 15,22,23 techniques demonstrated that the tra- ditional model of silicon oxidation, the Deal–Grove model, 24 was insufficient in the limit of ultrathin films. It was shown that, in addition to a classical Deal–Grove-like reaction be- tween diffusing oxygen with the silicon substrate ~ which oc- curs at/near the SiO...
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