Surface analysis study of the oxidation of organotin films deposited by ArF excimer laser chemical vapor deposition

ArF excimer laser photolysis of gas phase tetramethyltin was used to deposit thin organotin films on Si. In situ Auger electron spectroscopy and x-ray photoelectron spectroscopy (XPS) film analysis, showed the presence of C and Sn, which, according to C 1s and Sn 3d_5/2 peak deconvolution, were organized in highly branched polymeric chains likely containing H as well. The film was oxidized at room temperature by exposure to controlled quantities of O₂ up to 5.4×10¹²L. Sn 3d_5/2, C 1s, and O 1s XPS peaks monitoring allowed us to follow the sequence of the oxidative reactions. It resulted that oxygen attacks first the Sn–H and Sn–C sites leading to the elimination of H₂O and C containing volatile compounds, which determines a rearrangement of the cleaved bonds and an overall decrease of the measured C content. After this fast phase, oxygen is inserted in the Sn–Sn and Sn–C bonds, with formation of Sn–O–Sn, Sn–O–C, and Sn–C–O species. At the highest oxygen doses the dominating SnO₂ component shows that almost all available Sn bonds are oxidized to Sn⁴⁺. However, either core level or valence-band spectroscopy demonstrated that below the near-surface layer the tin oxide phase remains substoichiometric, as if the SnO₂ at the surface behaves as a passivating agent toward further oxidation. © 1997 America- - n Vacuum Society.