Plasma-enhanced atomic layer deposition of Ir thin films for copper adhesion layer

The crystallinity of a Cu seed layer and its adhesion to a 3 nm-thick TaN diffusion barrier metal were improved by introducing a 3 nm-thick Ir adhesion layer prepared by plasma-enhanced atomic layer deposition (PEALD) using an alternating supply of (ethylcyclopentadienyl)(1,5-cyclooctadien) iridium [Ir(EtCp)(COD)] and NH3 plasma at 290 °C. The properties of the Ir adhesion layer were carefully compared with those of a Ru adhesion layer. The surface roughness of the Cu layer deposited on the 3 nm-thick Ir adhesion layer improved significantly compared with the 3 nm-thick Ru adhesion layer. Furthermore, the preferential orientation of Cu (111) on the Ir layer was more enhanced than that on the Ru layer due to the low lattice misfit. Consequently, a 10 nm-thick continuous Cu film with root-mean-squared (RMS) surface roughness of 0.7 nm was successfully prepared on a 3 nm-thick Ir film. Also, the 3 nm-thick Ir layer was found to be sufficient as a Cu adhesion layer.