Daniel Franta, Ivan Ohlídal, David Nečas, František Vižďa, Ondřej Caha, Martin Hasoň, Pavel Pokorný

Optical characterization of HfO₂ thin films

Thin Solid Films 519 (2011) 6085-6091

Hafnia films prepared onto silicon wafers at three substrate temperatures of 40, 160 and 280 °C are optically characterized utilizing the multi-sample method. The characterization uses the combination of variable angle spectroscopic ellipsometry and spectroscopic reflectometry within the spectral region 1.24-6.5 eV (190-1000 nm). The structural model of the HfO₂ films includes boundary nanometric roughness, thickness non-uniformity and refractive index profile. Spectral dependences of the film optical constants are expressed using a recently developed parametrized joint density of states (PJDOS) model describing the dielectric response of both interband transitions and excitations of localized states below the band gap. It is shown that the observed weak absorption below the band gap does not correspond to the Urbach tail.

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