The composition of oxides grown on PbInAu films by rf oxidation

Abstract

Oxides grown on PbInAu alloys using a combined thermal and rf oxidation process have been examined with x-ray photoemission spectroscopy (XPS or ESCA) and ellipsometry. The oxides were prepared on alloy films deposited at 300 K containing 13 and 26 at. % In in the PbIn phase and on fine-grain alloy films deposited at 95 K containing 13 at. % In. Following an in situ thermal oxidation at 75 °C, the films were rf-plasma oxidized while mounted on an electrode coated with either In or photoresist. The XPS spectra showed that both lead oxide and indium oxide were present, in agreement with previous findings that the bulk of such oxides consists of a layer of In2O3 overlying a layer of PbO. The binding energy of the Pb 4f peak from the oxide was shifted by 0.9–1 eV from the metal peak, a shift characteristic of PbO. Analysis of the XPS intensities based on a layered structure indicated that oxides on the films deposited at 300 K consisted of about 2.7 nm of In2O3 on top of 1.6 nm of PbO. Oxides on the fine-grained alloy were composed of about 4.3 nm of In2O3 and only about 0.4 nm of PbO. The ellipsometric determination of the total thickness agreed with the XPS thickness. The increased amount of In2O3 on the fine-grained film is attributed to the increased availability of In during oxidation as a result of enhanced diffusion through the grain boundaries of the metal film.