We investigated the mechanisms of thermal reoxidation in dry O2 of silicon oxynitride films prepared by processing Si~100! wafers in a rapid thermal furnace in a pure nitrous oxide ~N2O! 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 15N2 16O were 8-nm thick, with a small amount of nitrogen localized near the interfacial region. Under reoxidation in dry 18O2 , the thickness of the dielectric film increased while a pronounced isotopic exchange took place between the 18O from the gas and the 16O from the film, as well as a significant loss of 15N. This is in contrast with the reoxidation in dry O2 of pure SiO2 films, where the oxygen exchange is rather small as compared to that observed in the present case

Baumvol, Israel Jacob Rabin

Ganem, Jean-Jacques

Rigo, Serge

Stedile, Fernanda Chiarello

Trimaille, Isabelle

Lume 5.8

Dry oxidation mechanisms of thin dielectric films formed under N2O using isotopictracing methodsJ.‐J. Ganem, S. Rigo, I. Trimaille, I. J. R. Baumvol, and F. C. Stedile  Citation: Applied Physics Letters 68, 2366 (1996); doi: 10.1063/1.116135 View online: http://dx.doi.org/10.1063/1.116135 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/68/17?ver=pdfcov Published by the AIP Publishing  Articles you may be interested in Nitrogen transport during rapid thermal growth of silicon oxynitride films in N2O Appl. Phys. Lett. 69, 2385 (1996); 10.1063/1.117645  Evaluation of depth profile of defects in ultrathin Si film on buried SiO2 formed by implanted oxygen Appl. Phys. Lett. 69, 1367 (1996); 10.1063/1.117438  Hydrogen determination in Si‐rich oxide thin films J. Appl. Phys. 80, 109 (1996); 10.1063/1.362766  Growth and characterization of anodic oxides on Si(100) formed in 0.1 M hydrochloric acid J. Appl. Phys. 79, 8761 (1996); 10.1063/1.362502  The effect of thermal processing on polycrystalline silicon/SiO2/6H–SiC metal‐oxide‐semiconductor devices Appl. Phys. Lett. 68, 2231 (1996); 10.1063/1.115868    Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP:  143.54.44.137 On: Wed, 04 May 201620:15:42Dry oxidation mechanisms of thin dielectric films formed under N 2Ousing isotopic tracing methodsJ.-J. Ganem,a) S. Rigo, and I. TrimailleGroupe de Physique des Solides, URA 17 - CNRS, Universite´s Paris 6 et 7, 75251 Paris cedex 05, FranceI. J. R. Baumvol and F. C. StedileInstituto 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 O2 of silicon oxynitride filmsprepared by processing Si~100! wafers in a rapid thermal furnace in a pure nitrous oxide~N2O!ambient, using isotopic tracing of oxygen and nitrogen. Standard nuclear reaction analyses for themeasurement of the total amounts of the different isotopes, and very narrow resonant nuclearreactions for high resolution~1 nm! depth profiling of these elements were used. The siliconoxynitride films grown in pure15N216O were 8-nm thick, with a small amount of nitrogen localizednear the interfacial region. Under reoxidation in dry18O2, the thickness of the dielectric filmincreased while a pronounced isotopic exchange took place between the18O from the gas and the16O from the film, as well as a significant loss of15N. This is in contrast with the reoxidation in dryO2 of pure SiO2 films, where the oxygen exchange is rather small as compared to that observed inthe 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 andless. Various methods have been used to produce these di-electric films, the most promising ones being the thermalgrowth of a silicon oxynitride film on silicon in a nitrousoxide ~N2O! environment.1,2 Although atomic transport pro-cesses are fundamental for the understanding of the growthmechanisms, so far only a few studies have considered thisaspect.3–5 In this letter we report on the atomic transportmechanisms during thermal reoxidation6 of oxynitride filmspreviously grown on Si~001! under N2O, using isotopic trac-ing experiments of nitrogen and oxygen.Pure N2O (.99.998 %! enriched in15N ~99% labelledgas! was used for the oxynitridation of the silicon, and dry99 % 18O enriched oxygen gas (18O2) was used for thermalreoxidation. The treatment temperature was fixed at 1090°C for both oxynitridation and reoxidation. Oxynitridationunder15N2O was performed in a rapid thermal furnace at apressure of 103 Pa during 180 s treatment time, and reoxida-tions were performed under 104 Pa of dry18O2 for times of20 min, 40 min and 120 min in a classical resistance heatedfurnace. The thicknesses of the oxynitride films after thethermal treatments were 8.2 nm before reoxidation and 15.8nm, 20.5 nm and 31.8 nm after reoxidation times of 20 min,40 min and 120 min, respectively. A 15 nm-thick controloxide was also grown at 1050°C by subsequent oxidations in104 Pa of dry16O2 gas for 450 s and in dry18O2 for 150 s.The total amounts of nitrogen15N, 16O, and18O weredetermined through nuclear reactions analyses~NRA! usingthe cross section plateaus of the reactions15N~p,ag)12C at1000 keV,16O~d,p0)17O at 810 keV and18O~p,a0)15N at 730keV.7 The total amount of the different isotopes were deter-mined by comparison with standards having uncertaintiesless than 2%. The thicknesses of the films can be given inSiO2 equivalent: 1015 oxygen atoms.cm22 corresponds to0.226 nm, assuming a density of the silicon oxide of 2.21g/cm3. For atomic depth profiling (15N and 18O!, we usednuclear narrow resonant reaction analysis and the SPACESsimulation program.8,9 In the present work we used the nar-row resonance (G 5 100 eV! at 152 keV of the18O~p,a)15N nuclear reaction for the18O depth profiling,9 and thenarrow resonance (G 5 120 eV! at 429 keV of the15N~p,ag)12C nuclear reaction for the15N depth profiling.7 In bothcases the samples were tilted at 65° with the respect to nor-mal incidence in order to increase the depth resolution to 1nm near the surface.Figure 1 presents the excitation curves of the nuclearreaction18O~p,a0)15N near the narrow resonance (G 5 100eV! at Ep 5 152 keV, for the control oxide~Fig. 1 top! andfor the oxynitride ~Fig. 1 bottom! films. In the insets, thelocal concentrations of18O, namely18O/18O116O, as a func-tion of depth (18O depth profile! corresponding to the simu-lation of the experimental data are shown.8,9 The double lo-cation of the18O in Fig. 1 ~top! ~near the surface and at theinterface! is consistent with :~i! The oxidizing species aredissolved into interstitial positions and diffuse into the silicanetwork without reacting with the bulk; they react with Si atthe SiO2 /Si interface to form the new oxide. This is in agree-ment with the Deal and Grove theory;5 ~ii ! An exchangemechanism takes place between the oxygen from the gas andthe oxygen from the silica network due to local defectspresent near the surface of the SiO2 film.10,11 This phenom-enon is independent of the first mechanism described in~i!.The mechanism~i! is responsible for a pure Si18O2 film lo-calized at the oxide/silicon interface with a sharp transitionbetween Si16O2 and Si18O2. The mechanism~ii ! leads to afixation of 18O near the external surface and the18O depthprofile which correspond to it is erfc-like.10,11In Fig. 1 ~bottom! the shape of the profile is different,being the concentration of18O atoms different from zero ina!Electronic mail: ganem@gps.jussieu.fr2366 Appl. Phys. Lett. 68 (17), 22 April 1996 0003-6951/96/68(17)/2366/3/$10.00 © 1996 American Institute of Physics Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP:  143.54.44.137 On: Wed, 04 May 201620:15:42the bulk of the film. The NRA show that the reoxidation ofthe oxynitride in 18O2 is accompanied by an important ex-change phenomenon between the18O atoms from the gas andthe16O atoms from the oxynitride network. This exchange ismuch more effective compared to that observed in the caseof dry reoxidation of pure SiO2.10,11Approximately 29% ofthe oxygen atoms are exchanged during the first 20 min ofreoxidation; as the reoxidation time increases, this phenom-enon is enhanced to reach approximately 67% for 120 min ofreoxidation time. Furthermore, the amount of16O lost byexchange is proportional to the square root of the reoxidationtime, which indicates that this phenomenon is probably gov-erned by a diffusion process. Figure 2 displays the evolutionof the 18O depth profile with reoxidation time. As the filmgrows, the18O surface peak becomes wider due to the dif-fusing defects in the oxynitride film. Oxygen vacancy or in-terstitial defects could explain those profiles. But an anneal-ing at high temperature in vacuum or in non-reactiveatmosphere, did not show any modification in the18O ornitrogen depth profiles.12 This indicates that the defect re-sponsible for the exchange phenomenon is more likely inter-sticialcy. Otherwise, the presence of18O at the oxynitride/Siinterface, with a local concentration equal to the labelling ofthe gas~99%!, indicates that an oxidation within the frame-work of the Deal and Grove model still occurs in parallelwith the exchange phenomenon. However, the sharp transi-tion between the16O-rich region and the18O-rich region ex-isting in the case of the oxide is not observable after reoxi-dation in 18O2of the oxynitride, a fact that can be attributedto the significant overall diffusion of defects into the bulk ofthe oxynitride, leading to a16O/18O mixture in the film.The nitrogen distribution after the thermal treatment in15N216O is shown in Fig. 3. The nitrogen is fixed near theoxynitride/Si interface and less than 0.1% of nitrogen~N/N1O! has been detected near the surface region, in agree-ment with previous observations.13–15 As the reoxidation in18O2 proceeds, the distribution of nitrogen becomes wider, aloss of nitrogen is observed and the position of the maximumconcentration of15N shifts towards the surface as shown inFig. 4. The broadening of the peak, and the loss of nitrogenFIG. 1. Excitation curves of the nuclear reaction18O~p,a)15N near the reso-nance at 152 keV from„top… the control oxide grown at 1050°C in 104Pa ofdry 16O2 for 450 s subsquently reoxidized in18O2 in the same conditions butfor 150 s, and„bottom… a sample oxynitrided in 103 Pa of N2O at 1090 °Cfor 180 s and subsquently reoxidized in 104 Pa of dry18O2during 20 min at1090 °C. The related local concentration depth profiles of18O, namely@18O# 5 18O/(18O1 16O!, extracted from the experimental data are shown inthe insets.FIG. 2. Concentration depth profiles of18O in films grown in 103 Pa of15N2O at 1090 °C for 180 s and subsequently reoxidized in 104 Pa of dry18O2at 1090 °C for 20 min, 40 min, and 120 min.FIG. 3. Excitation curve of the nuclear reaction15N~p,ag)12C near theresonance at 429 keV (G5100 eV! from a silicon oxynitride obtained bythermal annealing under 103 Pa of pure15N216O at 1090 °C for 180 s. Therelated local concentration depth profile of15N, namely@15N# 5 N/~N1O!extracted from the experimental data is shown in the inset.FIG. 4. Concentration depth profiles of15N in a film grown in 103 Pa of15N2O at 1090 °C for 180 s, and in samples subsequently reoxidized in 104 Pa of dry18O2at 1090 °C for 40 min and 120 min. The arrows indicate theposition of the oxynitride/Si interface for the different samples.2367Appl. Phys. Lett., Vol. 68, No. 17, 22 April 1996 Ganem et al. Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP:  143.54.44.137 On: Wed, 04 May 201620:15:42are also proportional to the square root of the reoxidationtime, most probably due to defect diffusion in the film. Forthe same reasons developed for the18O diffusion, the migra-tion of nitrogen atoms is also probably due to interstitialdefects. However the shift of the distribution towards thesurface cannot be explained by a simple diffusion of N at-oms. Let us consider the samples reoxidized for 40 min and120 min; in the first one, the new position of theoxynitride/Si interface is far enough from the nitrogen atomsto allow us to neglect its effect on the N diffusion during theadditional 80 min of reoxidation necessary to form the sec-ond sample. If the outside surface would be permeable, thenafter a certain diffusion time, mathematically the position ofthe maximum concentration of nitrogen should move deeperinto the film. On the contrary, if we assume now that thesurface is like a reflecting wall, the maximum concentrationshould shift towards the surface. But after 120 min of reoxi-dation, the experimentally observed shift of N towards thesample surface is too large to be correlated to the broadeningof the nitrogen distribution; in this case one cannot explainthe transport mechanisms by a standard diffusion process. Toaccount for this phenomenon, we must consider a drift of thenitrogen in the direction of the sample surface during thermalreoxidation. The origin of this drift is not clearly identified,but should be due to a concentration gradient of defects.By simulating the evolution of the nitrogen and oxygenprofiles with the reoxidation time, we have extracted the ef-fective diffusion coefficients for nitrogenDN , as well as itsdrift velocity, VdN, and the effective diffusion coefficient foroxygen,DO. For both species, we made the hypothesis thatthey diffuse in a semi-infinite medium. We found 10218cm2s21,DN,2310218 cm2s21, 10217 cm2s21,DO,3310217 cm2s21, andVdN 131022 nm min21 . These diffu-sion coefficients show that the oxygen atoms diffuse fasterthan the nitrogen atoms. But the magnitudes ofDN andDOare too close to conclude that the defect responsible for themigration of nitrogen is different from that responsible forthe diffusion of oxygen. In a recent study, based on electronparamagnetic resonance~EPR! measurements on oxyni-trides, the authors established that the nature of nitrogen andoxygen defects are different.16In summary, we have studied the mechanisms of thermalreoxidation of silicon oxynitride films using isotopic tracingexperiments with18O and15N as tracers.15N depth profilerevealing that after the thermal treatment under nitrous oxidethe nitrogen is localized near the oxynitride/Si interface in arather small concentration~N/N1O.2%!. During reoxida-tion, we observed that the oxygen atoms react at the interfaceto form new silicon oxide layers, near the surface, and in thebulk of the oxynitride film a significant exchange phenom-enon takes place between the oxygen from the gas and theoxygen in the film. The nitrogen atoms diffuse in the filmand drift to the sample surface. A significant loss of nitrogenis also found. Most probably, the defects responsible for themigration of nitrogen and oxygen atoms are interstitialcies.No evidence has been found for equivalent defects linkedwith nitrogen and oxygen. To explain the nitrogen behaviorduring reoxidation, we propose the existence of a concentra-tion gradient of defects which favours the migration of nitro-gen atoms towards the surface.1L. K. Han, G. W. Yoon, J. Kim, J. Yan, and D. L. Kwong, IEEE ElectronDevice Lett.16, 348 ~1995!.2H. Wang, W. Ting, D. L. Kwong, and J. Lee, Appl. Phys. Lett.57, 1010~1990!.3S. Dimitrijef, D. Sweatman, and H. B. Harrison, Appl. Phys. Lett.62,1539 ~1993!.4W. Ting, H. Hwang, J. Lee, and D. L. Kwong, J. Appl. Phys.70, 1072~1991!.5B. E. Deal and A. S. Grove, J. Appl. Phys.36, 3770~1965!.6M. L. Green, D. Brasen, K. W. Evans-Lutterodt, L. C. Feldman, K.Krisch, W. Lennard, H.-T. Tang, L. Manchanda, and M.-T. Tang, Appl.Phys. Lett.65, 848 ~1994!.7I. J. Baumvol, F. C. Stedile, J. J. Ganem, S. Rigo, and I. Trimaille, J.Electrochem. Soc.142, 1205~1995!.8I. Vickridge and G. Amsel, Nucl. Instrum. Methods B45, 6 ~1990!.9G. Battistig, G. Amsel, E. d’Artemare, and I. Vickridge, Nucl. Instrum.Methods B61, 369 ~1991!.10S. Rigo, inThe Physics and the Chemistry of SiO2 and the Si-SiO2 Inter-face,edited by C. R. Helms and B. E. Deal~Plenum, New York, 1988!,Vol. 1, p. 75.11I. Trimaille, S. I. Raider, J. J. Ganem, S. Rigo, and N. A. Penebre12E. C. Carr, K. A. Ellis, and R. A. Buhrman, Appl. Phys. Lett.66, 1492~1995!.13F. H. P. M. Habraken and A. E. T. Kuiper, Mater. Sci. Eng.12, 123~1994!.14H. T. Tang, W. N. Lennard, M. Zinke-Allmang, I. V. Mitchell, L. C.FeldmanM. L. Green, and D. Brasen, Appl. Phys. Lett.64, 3473~1994!.15A. E. Kuiper, H. G. Pomp, P. M. Asveld, W. Arnoldbik, and F. H. M.Habraken, Appl. Phys. Lett.61, 1031~1992!.16E. H. Poindexter and W. L. Warren, J. Electrochem. Soc.142, 2508~1995!.2368 Appl. Phys. Lett., Vol. 68, No. 17, 22 April 1996 Ganem et al. Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP:  143.54.44.137 On: Wed, 04 May 201620:15:42

Applied Physics Letters

English

Dry oxidation mechanisms of thin dielectric films formed under n/sub 2/o using isotopic tracing methods

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Merlú  : revista de Radio Zamora: 1976

Universidade Federal do Rio Grande do Sul

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Merlú : revista de Radio Zamora: 1976

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Lume 5.8

Biblioteca Virtual de Prensa Histórica (Virtual Library of Historical Newspapers)

Universidade Federal do Rio Grande do Sul