Low temperature plasma-assisted chemical vapor deposition of tantalum nitride from tantalum pentabromide for copper metallization

Abstract

In this article, the authors report the development of a new low temperature plasma-assisted chemical vapor deposition (PACVD) process for the growth of low resistivity, cubic tantalum nitride (TaNx) for incorporation as a diffusion barrier/adhesion promoter in emerging ultralarge-scale integrated (ULSI) multilevel metallization (MLM) schemes. TaNx films were produced in a low density plasma using tantalum pentabromide, hydrogen, and nitrogen as coreactants. The films were grown at substrate temperatures of 350–450 °C, reactor working pressures of 0.9–1.6 Torr, hydrogen flow rates between 250 and 1500 sccm, nitrogen flow rates of 100–600 sccm, and plasma power ranging from 10 to 60 W, corresponding to a power density of 0.06–0.33 W/cm2. The films were subsequently characterized by Auger electron spectroscopy, Rutherford backscattering spectrometry, x-ray diffraction, atomic force microscopy, four-point resistivity probe, and cross-sectional scanning electron microscopy. These studies indicated that the TaNx films produced were stoichiometric and carbon and oxygen free, contained bromine concentrations below 3 at. %, and exhibited resistivities as low as 150 μΩ cm. The conformality was higher than 95% in the nominally 0.3 μm, 4.5:1 aspect ratio structures. These results indicate that in the case of halide-based Ta chemistries, PACVD in a (N2+H2) plasma might be more viable than thermal CVD in a NH3 atmosphere for the deposition of TaNx for ULSI MLM applications.