Atomic transport across the interfaces during the formation of ultrathin silicon oxide/nitride/oxide films

Baumvol, Israel Jacob Rabin; Salgado, Tânia Denise Miskinis; Radtke, C.; Krug, Cristiano; Andrade, Jones de

doi:10.1063/1.122338

Applied Physics Letters

1998

DOI: 10.1063/1.122338

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Atomic transport across the interfaces during the formation of ultrathin silicon oxide/nitride/oxide films

Israel Jacob Rabin Baumvol

Tânia Denise Miskinis Salgado

C. Radtke

et al.

Abstract: The redistribution of O and N during the final, thermal oxidation in dry O2 step in the formation of ultrathin silicon oxide/nitride/oxide dielectric films (ONO) was investigated using isotopic tracing and depth profiling with nanometer resolution. The results show that the final oxidation step induces atomic transport of O and N species in the system, such that the formed ONO structures are not stacked layer structures, but rather a silicon oxynitride ultrathin film, having moderate concentrations of N in the… Show more

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“…In a previous work 19 we addressed the usefulness of isotopic substitution and depth profiling with nanometric resolution in the investigation of the atomic transport across the interfaces during the formation steps of ultrathin ONO structures. Those results already sug- Isotopic tracing was used to determine the distribution of O and N after the final fabrication step of ultrathin silicon oxide/nitride/ oxide (ONO) films, revealing how the processing parameters affect the characteristics of the resulting structure.…”

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“…Subsequently, a nitride layer (Si 3 15 N 4 ) was deposited by plasma enhanced chemical vapor deposition in a mixture of 15 N 2 and silane, leading to a bilayered ultrathin film structure Si 3 15 N 4 /SiO 2 /Si with abrupt interfaces, as described in Ref. 19. This starting structure underwent a second thermal oxidation step in a Joule-effect heated furnace, under 5 kPa of dry 18 O 2 (enriched to 97%).…”

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“…20 Figure 1 shows a particle spectrum obtained in the 16 O analysis of a typical sample. Next to the peak of interest, corresponding to 16 O(d,p 0 ) 17 O, one sees peaks from particles resulting from other nuclear reactions that occur simultaneously, including a close peak originated by the 18 O(d,p) 19 O reaction. The experimental arrangement is sketched in the inset of the figure.…”

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Effects of the Final Oxidation Step on N and O Distributions in Silicon Oxide/Nitride/Oxide Ultrathin Films

Salgado¹,

Radtke²,

Krug³

et al. 1999

J. Electrochem. Soc.

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Defect density and breakdown strength of single-layer thermal silicon oxides do not fulfill the requirements for dielectrics used in modern dynamic random access memory (DRAM) applications, 1-4 which require ultrathin dielectric films along with an increase of read/ write cycles and good charge retention capability. 5,6 Silicon oxidenitride-oxide (ONO) films constitute alternative dielectrics for nonconducting operation in DRAM cell capacitors, first reported by Watanabe et al. in 1984. 7 ONO structures exploit concomitantly the advantages of oxide and nitride films. 8 In ONO multilayer structures, the oxide in contact with the Si substrate (bottom oxide) provides device-quality electrical SiO 2 /Si interface. 6,9 The nitride layer increases the effective dielectric constant of the ONO sandwich 6 in such a way that a film twice as thick as SiO 2 -based dielectric shows equal capacitance, thus offering increased process reliability or, for comparable thickness, higher storage capacity. 10,11 Furthermore, the nitride layer acts as a diffusion barrier for boron transport from the doped poly-Si gate electrode toward the SiO 2 /Si interface. 8,12 The top oxide provides the electrical contact to the poly-Si gate electrode. 8,9 An ideal ONO structure could then provide 8 (i) low defect density, (ii) high effective dielectric constant, (iii) high electric breakdown strength, (iv) low current conduction, and (v) minimal B diffusion to the SiO 2 /Si interface. In order to achieve thinner dielectrics, as required for future DRAM applications, it is necessary to understand the properties of the ONO structure, something that cannot be achieved without precise knowledge of the composition through the film and how it is affected by the successive processing stages.Ultrathin ONO films are usually prepared 1,2,6,13,14 by thermal growth of a 2-5 nm thick SiO 2 film (bottom oxide) on Si substrates in dry oxygen. Subsequently a 5-10 nm thick Si 3 N 4 layer is deposited by a low pressure chemical vapor deposition (LPCVD) process. Finally, a thermal reoxidation is performed in wet or dry oxygen or, in order to form a top oxide without consuming any nitride, a LPCVD high temperature oxide can be deposited. Although this preparation route can be thought to produce a stacked ONO structure, it does not seem to do so, at least for ultrathin films. It was observed 6 that even very thin oxide layers of approximately 1 nm prevent electron-and hole-currents into the nitride very effectively. As this feature could not be explained by a simple model of a 1 nm oxide with sharp boundary between SiO 2 and Si 3 N 4 , it was assumed that thermal oxidation produced a graded transition between top oxide and nitride which removed Si 3 N 4 trap levels in the close vicinity of the Si 3 N 4 /SiO 2 interface. X-ray photoelectron spectroscopy (XPS) was used 15 to investigate the ONO structure obtained by the sequence: (i) thermal oxidation of Si at 900ЊC (90 Å bottom oxide), (ii) LPCVD nitride layer deposition (60-120 Å), and (iii) rapid thermal oxidation (...

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confidence: 99%

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confidence: 99%

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confidence: 99%

mentioning

confidence: 99%

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Effects of the Final Oxidation Step on N and O Distributions in Silicon Oxide/Nitride/Oxide Ultrathin Films

Salgado¹,

Radtke²,

Krug³

et al. 1999

J. Electrochem. Soc.

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“…Previous works 13,14 have reported N and O mobility during thermal oxynitridation in NO of thermally grown SiO 2 films on Si. They showed that during the NO process, besides incorporation of N near the SiO 2 / Si interface, there is also atomic exchange between oxygen from the gas phase ͑NO͒ and oxygen from the SiO 2 film.…”

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Sequential thermal treatments of SiC in NO and O2: Atomic transport and electrical characteristics

Soares

Baumvol

Hold

et al. 2007

Applied Physics Letters

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Articles you may be interested inThermal annealing effects on the structure and electrical properties of Al 2 O 3 gate dielectrics on fully depleted SiGe on insulator Sequential thermal oxidations and oxynitridations of SiC were performed using 18 O 2 and NO. The resulting films were characterized by x-ray photoelectron spectroscopy, ion beam analyses, and capacitance-voltage measurements. The best electrical characteristics were obtained from films directly grown in NO. A subsequent oxidation in O 2 degraded the interface due to negative flatband-voltage shift, removal of N, and formation of C compounds, while a further annealing in NO brought the flatband shift in the C-V curves to rather moderate figures. This shift is related to competitive processes taking place during dielectric film formation which are discussed.

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Atomic transport during growth of ultrathin dielectrics on silicon

Baumvol

1999

Surface Science Reports

148

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Atomic transport across the interfaces during the formation of ultrathin silicon oxide/nitride/oxide films

Cited by 4 publications

References 17 publications

Effects of the Final Oxidation Step on N and O Distributions in Silicon Oxide/Nitride/Oxide Ultrathin Films

Effects of the Final Oxidation Step on N and O Distributions in Silicon Oxide/Nitride/Oxide Ultrathin Films

Sequential thermal treatments of SiC in NO and O2: Atomic transport and electrical characteristics

Atomic transport during growth of ultrathin dielectrics on silicon

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