Anomalous thermal oxidation of gadolinium thin films deposited on silicon by high pressure sputtering

Abstract

Thin gadolinium metallic layers were deposited by high-pressure sputtering in pure Ar atmosphere. Subsequently, in situ thermal oxidation was performed at temperatures ranging from 150 to 750 ${}^{\circ }$C. At an oxidation temperature of 500 ${}^{\circ }$C the films show a transition from monoclinic structure to a mixture of monoclinic and cubic. Regrowth of interfacial SiO${}_x$ is observed as temperature is increased, up to 1.6 nm for 750 ${}^{\circ }$C. This temperature yields the lowest interface trap density, 4e10 eV${}^{-1}$ cm${}^{-2}$, but the effective permittivity of the resulting dielectric is only 7.4. The reason of this low value is found on the oxidation mechanism, which yields a surface with located bumps. These bumps increase the average thickness, thus reducing the capacitance and therefore the calculated permittivity.

22 pages, 7 figures, 1 table