Nucleation and Adhesion of ALD Copper on Cobalt Adhesion Layers and Tungsten Nitride Diffusion Barriers

摘要

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 SiO_2, Si_3N_4, 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/SiO_2 structure, more than five times higher than the Cu/Ta/TaN_x/SiO_2 structures currently used for interconnects.