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The electronic structure at the atomic scale of ultrathin gate oxides

Abstract

The narrowest feature on present-day integrated circuits is the gate oxide—the thin dielectric layer that forms the basis of field-effect device structures. Silicon dioxide is the dielectric of choice and, if present miniaturization trends continue, the projected oxide thickness by 2012 will be less than one nanometre, or about five silicon atoms across1. At least two of those five atoms will be at the silicon–oxide interfaces, and so will have very different electrical and optical properties from the desired bulk oxide, while constituting a significant fraction of the dielectric layer. Here we use electron-energy-loss spectroscopy in a scanning transmission electron microscope to measure the chemical composition and electronic structure, at the atomic scale, across gate oxides as thin as one nanometre. We are able to resolve the interfacial states that result from the spillover of the silicon conduction-band wavefunctions into the oxide. The spatial extent of these states places a fundamental limit of 0.7 nm (four silicon atoms across) on the thinnest usable silicon dioxide gate dielectric. And for present-day oxide growth techniques, interface roughness will raise this limit to 1.2 nm.

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Figure 1: The measured EELS O K edges of bulk a-SiO2 and for O atoms at an atomically smooth interface between [100]Si and native a-SiO2.
Figure 2: EELS spectra recorded point by point across a gate stack containing a thin gate oxide.
Figure 3: Oxygen bonding profiles from O K edge EELS.

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References

  1. Semiconductor Industry Association The National Technology Roadmap for Semiconductors 71–81 (>Sematech, Austi, 1997).

    Google Scholar 

  2. Timp, G. et al. in IEDM Technical Digest 615–618 (IEDM, San Francisco, 1998).

    Google Scholar 

  3. Cryot-Lackmann, F. Sur le calcul de la cohesion et de la tension superficielle des mataux de transition par une methode de liasions fortes. J. Phys. Chem. Solids 29, 1235–1243 (1968).

    Article  ADS  Google Scholar 

  4. Ourmazd, A., Taylor, D. W., Rentschler, J. A. & Bevk, J. Si to SiO2transformation: interfacial structure and mechanism. Phys. Rev. Lett. 59, 213–216 (1987).

    Article  ADS  CAS  Google Scholar 

  5. Himpsel, F., McFeely, F. R., Taleb-Ibrahimi, A., Yarmoff, J. A. & Hollinger, G. Microscopic structure of the SiO2/Si interface. Phys. Rev. B 38, 6084–6096 (1988).

    Article  ADS  CAS  Google Scholar 

  6. Grunthaner, F. J. & Grunthaner, P. J. Chemical and electronic structure of the Si/SiO2 interface. Mater. Sci. Rep. 1, 65–160 (1986).

    Article  CAS  Google Scholar 

  7. Pasquarello, A., Hybertsen, M. S. & Car, R. Theory of Si 2p core-level shifts at the Si(001)-SiO2 interface. Phys. Rev. B 53, 10942–10950 (1996).

    Article  ADS  CAS  Google Scholar 

  8. McFeely, F. R., Zhang, K. Z., Banaszak Holl, M. M., Lee, S. & Bender, J. E. An inquiry concerning the principles of the Si 2p core-level photoemission shift assignments at the Si/SiO2 interface. J. Vac. Sci. Technol. B 14, 2824–2830 (1996).

    Article  CAS  Google Scholar 

  9. Muller, D. A., Tzou, Y., Raj, R. & Silcox, J. Mapping sp2 and sp3 states of carbon at sub-nanometre spatial resolution. Nature 366, 725–727 (1993).

    Article  ADS  CAS  Google Scholar 

  10. Muller, D. A., Subramanian, S., Sass, S. L., Silcox, J. & Batson, P. E. Near atomic scale studies of electronic structure at grain boundaries in Ni3Al. Phys. Rev. Lett. 75, 4744–4747 (1995).

    Article  ADS  CAS  Google Scholar 

  11. Batson, P. E. Simultaneous STEM imaging and electron energy-loss spectroscopy with atomic column sensitivity. Nature 366, 727–728 (1993).

    Article  ADS  CAS  Google Scholar 

  12. Browning, N. D., Chisholm, M. M. & Pennycook, S. J. Atomic-resolution chemical analysis using a scanning transmission electron microscope. Nature 366, 143–146 (1993).

    Article  ADS  CAS  Google Scholar 

  13. Muller, D. A. & Silcox, J. Delocalization in inelastic scattering. Ultramicroscopy 59, 195–213 (1995).

    Article  CAS  Google Scholar 

  14. Egerton, R. F. Electron Energy Loss Spectroscopy in the Electron Microscope2nd edn (Plenum, New York, 1996).

    Book  Google Scholar 

  15. Colliex, C. & Jouffrey, B. Diffusion inelastique des electrons dans une solide par excitation de niveaus atomiques profonds. Phil. Mag. 25, 491–514 (1972).

    Article  ADS  CAS  Google Scholar 

  16. Müller, J. E. & Wilkins, J. Band-structure approach to the x-ray spectra of metals. Phys. Rev. B 29, 4331–4348 (1984).

    Article  ADS  Google Scholar 

  17. Muller, D. A. et al. Atomic scale observations of metal-induced gap states at {222} MgO/Cu interfaces. Phys. Rev. Lett. 80, 4741–4744 (1998).

    Article  ADS  CAS  Google Scholar 

  18. Brown, G. E. J, Waychunas, G. A., Stohr, J. & Sette, F. Near-edge structure of oxygen in inorganic oxides: effect of local geometry and cation type. J. Phys. 47, (Colloque C8) 685–689 (1986).

    Article  Google Scholar 

  19. Wallis, D., Gaskell, P. H. & Brydson, R. Oxygen K near-edge spectra of amorphous silicon suboxides. J.Microsc. 180, 307–312 (1993).

    Article  Google Scholar 

  20. Zangwill, A. Physics at Surfaces(Cambridge Univ. Press, New York, 1988).

    Book  Google Scholar 

Download references

Acknowledgements

We thank D. R. Hammann, M. S. Hybertsen, P. Rez, J. Neaton and B. Batlogg for discussions, and J. Silcox and M. Thomas for access to the Cornell Center for Materials Research STEM. Funding for the operation and acquisition of the STEM was provided by the NSF. Upgrades were founded by the US Air Force Office of Scientific Research. The X-ray diffraction was performed on X16B at the National Synchrotron Light Source.

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Muller, D., Sorsch, T., Moccio, S. et al. The electronic structure at the atomic scale of ultrathin gate oxides. Nature 399, 758–761 (1999). https://doi.org/10.1038/21602

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