Synchrotron radiation photoemission analysis of ArF laser deposited tin oxide

Abstract

The composition of films deposited by dissociating pure tetramethyltin (TMT) or TMT/O2 mixtures at 193 nm, was monitored by ‘‘in situ’’ Auger spectroscopy. The presence of C contamination, which was considerable in films obtained from the pure organometallic, was greatly reduced by the occurrence of oxidation and carbon-free films were achieved when the gas phase concentration of TMT was sufficiently small. The dependence of the O/Sn Auger electron spectroscopy peak-to-peak height ratio on the p(O2)/p(TMT) ratio in the precursor mixture showed a saturation for large concentration of oxygen. The surface properties of the tin oxide films were investigated by synchrotron radiation ultraviolet photoemission spectroscopy (UPS). To this aim samples were transferred to a synchrotron radiation facility, without any exposure to air and kept in dynamical high vacuum. The UPS demonstrated that the films were essentially made of SnO2: in fact the valence band exhibited the typical features of SnO2 and the analysis of the 4dSn core levels demonstrated that all metal atoms were oxidized, since no contribution to the peak shape due to metallic tin was found. A weak emission from the band gap region indicated the presence of oxygen vacancies.