Stability of Tantalum Nitride Film Influenced by Oxygen Substitution of Nitrogen

Abstract

Tantalum nitride (TaNx) thin films are widely used as reliable materials for high-precision chip resistors. However, oxidation is a serious issue that degrades the temperature coefficient of resistance (TCR) of TaNx thin films. In this study, TaNx films were deposited by magnetron sputtering at different nitrogen partial pressures, with the variation in the structural and electrical properties of these films as a function of exposure time studied in detail. X-ray diffraction shows that the texture of tantalum nitride evolves significantly with increasing N2 content. When the N2 content was 3%, the TaNx films were dominated by the Ta2N phase, which had the most stable structure and the lowest deviation of the TCR. The films prepared at other N2 contents were easily subjected to partial oxygen substitution of the nitrogen site, resulting in apparent degradation of TCR when exposed to the atmospheric environment. Isolated oxide islands are formed on the grain boundary owing to oxidation, which impedes electron transport through different grains. Finally, the thermal conductivity of the ideal film is also verified, which shows a stable value of 3.4 ±0.4 W·m-1K-1 irrespective of air exposure, as measured by the time-domain thermoreflectance.

Keywords: tantalum nitride, Magnetron sputtering, stability, TCR, thermal conductivity