Diffusion barrier properties of metallorganic chemical vapor deposited tantalum nitride films against Cu metallization

TaN_x films were deposited by chemical vapor deposition using a pentakis(diethylamido)tantalum (PDEAT) source with and without NH₃ at temperatures ranging from 300 to 375 °C. It was observed that both the resistivity and carbon content of the film drastically decreased upon the addition of NH₃. For example, the resistivity decreased from 60,000 to 12,000 μΩ cm, and the apparent carbon content obtained by Auger electron spectroscopy decreased from 30 to 1 atom % by the addition of 25 sccm NH₃. The grain size initially increased with the addition of 5 sccm NH₃ in the source gas, but then decreased as the NH₃ flow rate was increased to more than 10 sccm. As-deposited TaN_x film has a face-centered cubic structure irrespective of the amount of NH₃. The density of the film increased from about 5.1 to 7.2 g cm^-3 (bulk density of TaN: 16.3 g cm^-3). Barrier failure results identified by the etch-pit test showed that a 50 nm thickness of the TaN_x barrier deposited by a single source of PDEAT survived up to 500 °C after 1 h annealing. The TaN_x film deposited with 25 sccm NH₃ survived up to 550 °C after 1 h annealing. However, the step coverage of the films deposited with NH₃ is drastically decreased, from more than 80% (NH₃ = 0 sccm) to less than 10% (NH₃ = 25 sccm). Thus, while the addition of NH₃ significantly improves both the resistivity and carbon content in the film, it deteriorates the step coverage of the film.