Metal diffusion and chemical processes of mono and bi-layer thin films

The physics and chemistry of Sn etching in EUVL must be understood to ensure that etching is complete. Electronegativity is a useful predictor for hydrogen etching of Sn from metal surfaces. Sn can be completely etched from transition metals with electronegativity values that are lower than or equal to Sn. We observed incomplete Sn etching when Sn was deposited onto materials with an electronegativity value higher than that of Sn.
To investigate metal oxide formation in Sn removal, metallic and oxidized Sc thin films were studied. Tin can be fully etched from both, metallic and oxidized Sc. Sc2O3 significantly slows the etch rate, due to electrons being trapped at defect sites in the Sc2O3 layer. This effect is strengthened when Sc metal is present below the Sc2O3, due to the built-in electric field spanning the oxide, generated by the difference in work function between Sc and Sn.
Catalytic dissociation of CO2 on Ru single crystal surface was studied as a precursor for hydrogen control studies. Our results show that CO2 adsorption on a Ru(0001) surface results in partial dissociation, with CO2 and CO present on the surface. The dissociation of CO2 is irreversible and starts already at 85 K. By annealing the surface at 120 K, the rate of CO2 dissociation was increased and that the CO restructures to a weaker bond between the surface and CO. CO and H may react to form water and volatile hydrocarbons. This may then reduce the hydrogen concentration at the surface.
Scandium oxide (Sc2O3) is a possible candidate for high-k dielectric applications. In this thesis, metal diffusion was studied to test if Sc2O3 layers acts as a diffusion barrier. Properties of Sc2O3 were tested using a MIM structure, consisting of Ru, Sc2O3, and Sn. We observed complete Sn etching thin layers of Sc2O3. Already 0.71 nm Sc2O3 forms a closed oxide layer that prevents the diffusion of Sn through to the Ru layer. The Sn etching time depends on the Sc2O3 barrier thickness and increased with increasing Sc2O3 thickness. This is explained by the formation of a MIM junction between the Ru, Sc2O3 and Sn.