Nucleation and adhesion of ultra-thin copper films on amino-terminated self-assembled monolayers

In this work, we report on the effect of amino-terminated self-assembled monolayers (SAMs) on the growth and adhesion of copper on a dielectric surface in ultra-high vacuum. The nucleation and adhesion of copper is studied for a range of self-assembled monolayers both with and without nitrogen containing terminal groups, and as a function chain length using X-ray photoelectron spectroscopy, dynamic water contact angle, sheet resistance, and adhesion testing measurements. In-situ X-ray photoelectron spectroscopy studies of ultra-thin copper films show that the presence of nitrogen significantly improves the nucleation of copper to the surface, particularly those coated with long chain SAMs. However, upon thermal annealing short chain amino-terminated SAMs retain much of the deposited copper while significant desorption occurs for longer chains. Results consistent with these observations are obtained during conventional tape test measurements to determine adhesion. As such, for CMOS interconnect applications which require copper trenches with a nano-scale cross section, short chain SAMs offer excellent nucleation and adhesion, as well as the potential to act as a pore-sealant for low-k materials, without impacting significantly on the cross-sectional area of the copper lines.