Tantalum nitride films grown by inorganic low temperature thermal chemical vapor deposition - Diffusion barrier properties in copper metallization

Key findings are presented from a systematic study which evaluated the performance of chemical vapor deposited (CVD) nitrogen-rich tantalum nitride (TaNx,x similar to 1.8) films as a diffusion barrier in copper (Cu) based metallization schemes. For this purpose, 3800 Angstrom thick Cu films were grown by physical vapor deposition (PVD) on 550 Angstrom thick TaNx films which were deposited by low temperature (<425 degrees C) thermal CVD (TCVD) using tantalum pentabromide (TaBr5), ammonia, and hydrogen as coreactants. The resulting stacks were annealed in argon ambient at 450, 500, 550, and 650 degrees C for 30 min each, along with similar PVD Cu/PVD TaNx bilayers of identical thickness. Both types of pre- and postannealed stacks were characterized by X-ray photoelectron spectroscopy Auger electron spectroscopy, Rutherford backscattering spectrometry, nuclear reaction, analysis for hydrogen profiling, X-ray diffraction, stack sheet resistance measurements, and Secco chemical treatment and etch-pit observation by scanning electron microscopy. The resulting findings showed that the PVD TaNx films provided an excellent barrier against Cu diffusion throughout the annealing window investigated. Alternatively, the TCVD TaNx films exhibited similar stability up to 550 degrees C. Barrier failure occurred, however, at temperatures between 550 and 600 degrees C, as revealed by the formation of etch pits after Secco etch treatment. The failure of the TCVD TaNx films could not be attributed to bromine incorporation, given that residual bromine (similar to 0.5 atom %) in the TCVD TaNx films was highly stable against thermal diffusion in the temperature window investigated. Instead, the higher thermal stability of the PVD TaNx was attributed to differences in film microstructure and crystalline phase, or the location of excess nitrogen within the fdm matrix. (C) 1999 The Electrochemical Society. S0013-4651(98)04-001-4. All rights reserved.