Copper diffusion into silicon substrates through TaN and Ta/TaN multilayer barriers

A study of copper (Cu) diffusion into silicon substrates through Ta nitride (TaN) and tantalum (Ta/TaN) layers was investigated based on an experimental approach. TaNx and Ta/TaNx thin films were deposited by radiofrequency sputtering under argon (Ar) and Ar-nitrogen (N) plasma. The influence of the N-2 partial pressure on the microstructure and the electrical properties is reported. X-ray diffraction patterns showed that the increase of the N-2 partial pressure, from 2 to 10.7%, induces a change in the composition of the delta TaN phase, from TaN to TaN1.13, as well as an evolution of the dominant crystallographic orientation. This composition change is related to a drastic increase of the electrical resistivity over a N-2 partial pressure of 7.3%. The efficiency of TaN layers and Ta/TaN multilayer diffusion barriers was investigated after annealing at temperatures between 600 and 900 degrees C in vacuum. Secondary ion mass spectrometry profiles showed that Cu diffuses from the surface layer through the TaN barrier from 600 degrees C. Cu diffusion mechanisms are modified in the presence of a Ta sublayer.