Nucleation and adhesion of ALD copper on cobalt adhesion layers and tungsten nitride diffusion barriers

Atomic layer deposition (ALD) was used to make conformal diffusion barrier layers of WN, adhesion layers of Co, and seed layers of Cu. Transmission electron microscopy and atomic force microscopy were used to study the nucleation of these layers. WN and Co nucleated uniformly as continuous layers. Cu nucleated as discontinuous islands on SiO2, Si3N4, and WN, but as a continuous, nanocrystalline layer on Co/WN. Electrical continuity was found for Cu/Co layers with a thickness under 2 nm. Extremely strong adhesion (> 31 J/m(2)) was measured for the Cu/Co/WN/SiO2 structure, more than five times higher than the Cu/Ta/TaNx/SiO2 structures currently used for interconnects. (c) 2005 The Electrochemical Society.