Dresden 2011 – scientific programme

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DS: Fachverband Dünne Schichten

DS 21: High-k and Low-k Dielectrics (jointly with DF)

DS 21.3: Talk

Tuesday, March 15, 2011, 14:15–14:30, GER 38

Phase equilibria at Si-HfO₂ and Pt-HfO₂ interfaces from first principles thermodynamics — •Rampi Ramprasad¹ and Hong Zhu² — ¹University of Connecticut, Storrs, USA; Fritz-Haber-Institut der MPG, Berlin, Germany — ²University of Connecticut, Storrs, USA

In this work, two types of interfaces found in the emerging technologically important high-k MOSFETs have been studied. The phase diagrams of Si-HfO₂ and Pt-HfO₂ interfaces as a function of temperature and oxygen pressure have been determined using first principles thermodynamics (FPT), i.e., by combining conventional density functional theory results with thermodynamics [1]. The vibrational and configurational entropic contributions to the free energies of the condensed phases are explicitly included in this treatment. We demonstrate that the predictions of the FPT approach are in quantitative agreement with experiments for the classes of interfaces considered here. In particular, under UHV conditions, we show that FPT methods predict the correct Si-HfO₂ silica-like interface configurations. Likewise, we also show that an interfacial oxygen coverage of 0.5-1.0 monolayer is favored under UHV conditions at the Pt-HfO₂ interface before rapid oxidation of Pt may be expected (for higher oxygen pressures). These results have important implications both for the applicability of FPT methods for the considered classes of interfaces as well as for high-k dielectrics-based electronic devices in which such interfaces are expected.

[1] H. Zhu, C. Tang and R. Ramprasad, Phys. Rev. B, in print (2010).