Parallel angle resolved XPS investigations on 12 in. wafers for the study of W and WSix oxidation in air

Parallel angle resolved X-ray photoelectron spectroscopy (ARXPS) was used to study the oxidation of W and WSix thin films CVD-deposited on 12 in. silicon wafers. The thin films were exposed to air during defined periods of time. Immediately after layer deposition, the wafers were rapidly loaded in a vacuum carrier in order to measure various aspects of the oxidation kinetic by XPS. Angle resolved data were exploited to obtain accurate tungsten oxide thicknesses measurements and the results were compared with X-ray reflectometry (XRR). A precise in-depth evolution of the W oxidation kinetic, in term of oxidation velocity and bonding environment, was obtained. Non-destructive profiles of the first five nanometers of a WSix surface were extracted from Angle Resolved data. These profiles were compared to ToF-SIMS analysis, and we clearly show the presence of a stoichiometric silicon dioxide passive layer covering WSix silicide.