Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5362392 | Applied Surface Science | 2008 | 7 Pages |
Abstract
The Ti-doped Ta2O5 thin films (<10Â nm) obtained by rf sputtering are studied with respect to their composition, dielectric and electrical properties. The incorporation of Ti is performed by two methods - a surface doping, where a thin Ti layer is deposited on the top of Ta2O5 and a bulk doping where the Ti layer is sandwiched between two layers of Ta2O5. The effect of the process parameters (the method and level of doping) on the elemental distribution in-depth of the films is investigated by the time of flight secondary ion mass spectroscopy (ToF-SIMS). The Ti and Ta2O5 are intermixed throughout the whole thickness but the layers are very inhomogeneous. Two sub-layers exist in all the samples - a near interfacial region which is a mixture of Ta-, Ti-, Si-oxides as well as TaSiO, and an upper Ti-doped Ta2O5 sub-layer. For both methods of doping, Ti tends to pile-up at the Si interface. The electrical characterisation is performed on capacitors with Al- and Ru-gate electrodes. The two types of MIS structures exhibit distinctly different electrical behavior: the Ru gate provides higher dielectric permittivity while the stacks with Al electrode are better in terms of leakage currents. The specific metal-dielectric reactions and metal-induced electrically active defects for each metal electrode/high-k dielectric stack define its particular electrical behavior. It is demonstrated that the Ti doping of Ta2O5 is a way of remarkable improvement of leakage characteristics (the current reduction with more than four orders of magnitude as compared with undoped Ta2O5) of Ru-gated capacitors which originates from Ti induced suppression of the oxygen vacancy related defects.
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Physical and Theoretical Chemistry
Authors
A. Paskaleva, M. Tapajna, E. Atanassova, K. Frohlich, A. Vincze, E. DobroÄka,