Characterization of Sputtered Ta and TaN Films by Spectroscopic Ellipsometry

Spectroscopic ellipsometry is emerging as a routine tool for in-situ and ex-situ thin-film characterization in semiconductor manufacturing. For interconnects in ULSI circuits, diffusion barriers of below 10 nm thickness are required and precise thickness control of the deposited layers is indispensable. In this work, we studied single films of tantalum and two stoichiometrics of tantalum nitride as well as TaN/Ta film stacks both on bare and oxidized silicon. Spectroscopic ellipsometry from the UV to the NIR was applied to determine the optical properties of the films for subsequent modeling by a Lorentz-Drude approach. These models were successfully applied to TaN/Ta thin-film stacks where the values of the film thickness could be determined exactly. Moreover, it is shown that considerable differences in the optical properties arise from both film thickness and substrate