625-baumvol-prb-1999-1492 - Isotopic substitution of Si...

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Unformatted text preview: Isotopic substitution of Si during thermal growth of ultrathin silicon-oxide films on Si „ 111 … in O 2 I. J. R. Baumvol and C. Krug Instituto de Fı´sica, UFRGS, 91509-900, Porto Alegre, Brazil F. C. Stedile Instituto de Quı´mica, UFRGS, 91509-900, Porto Alegre, Brazil F. Gorris and W. H. Schulte Institut fu ¨r Experimentalphysik III, Ruhr-Universita ¨t Bochum, D-44780 Bochum, Germany ~ Received 31 March 1999 ! The transport of Si atoms during thermal growth of silicon-oxide films on silicon in dry O 2 was investigated by isotopic substitution of Si. The experiment consisted of depositing a 7.6-nm-thick epitaxial layer of 29 Si on a Si ~ 111 ! substrate and determining the 29 Si profiles, with subnanometric depth resolution, before and after oxidation in 50 mbar of dry O 2 at 1000 °C for 60 min. The results constitute an experimental confirmation of a widely held belief that Si does not diffuse through the growing oxide to react with oxygen at the gas/oxide interface, leaving O 2 as the only mobile species. @ S0163-1829 ~ 99 ! 10127-9 # There is a renewed and increasing interest in modeling the initial stages of thermal growth of silicon oxide films on Si in dry O 2 , 1 the most common material used as a gate dielectric in Si-based metal-oxide-semiconductor ~ MOS ! structures. As microelectronic device dimensions shrink below 0.25 m m, these oxide films are forced to scale down to thicknesses of 5 nm and less. Reliability of highly integrated Si devices is critically dependent on the characteristics of the gate oxide film, such as thickness uniformity, defect density, dielectric strength, etc. as well as on those of the oxide/Si interface, such as roughness, electronic states density, etc. 2–4 The elec- tronic structure and properties of ultrathin films of silicon oxide thermally grown on Si, and of the oxide/Si interface have been intensively studied, in strict synergism with the development of the semiconductor industry. 5 The knowledge of film growth kinetics, however, has not made any signifi- cant scientific progress since the early model of Deal and Grove, 6 which assumes that growth is promoted by intersti- tial diffusion of the oxidant species, the O 2 molecule, in steady-state regime, and reaction with Si at an abrupt oxide/Si interface. This model, and more specifically the re- sulting linear-parabolic growth law, is known to agree with the observed growth kinetics in dry O 2 only for films thicker than 20 nm, 6–8 well above the range of interest for present and future microelectronics applications. Improvements on modeling oxide growth below 20 nm are therefore highly desirable. A wealth of O isotopic substi- tution experiments 9–11 performed in oxides with thicknesses well below 20 nm support the ‘‘reactive layer’’ model....
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This note was uploaded on 12/10/2009 for the course IF PFIS1200 taught by Professor Antonio during the Spring '09 term at Universidade Federal do Rio de Janeiro.

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625-baumvol-prb-1999-1492 - Isotopic substitution of Si...

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