Materials Engineering for Future Interconnects: “Catalyst-Free” Electroless Cu Deposition on Self-Assembled Monolayer Alternative Barriers

An alternative bottom-up Cu electroless deposition (ELD) method without other catalyst material activation is the focus of this paper. The process consists of reducing the Cu ions in a solution via standard reducing agents such as dimethylamine borane. The reaction pH and ionic strength values can be modulated to impart to the metallic Cu particle surface an opposite charge with respect to the deposition substrate functionalized by the 3-aminopropyltrimethoxysilane (APTS) self-assembled monolayer used as a diffusion barrier. At neutral pH, the negatively charged Cu particles are electrostatically attracted by the positively charged NH 2 groups, and they can form strong interfacial complexes if the required activation energy budget is supplied. A design of the experiment is carried out to optimize the critical deposition parameters such as temperature, time, Cu ion concentration, and pH. The formed ELD Cu nuclei positioned preferentially on the APTS layer, showing a wetting behavior that is accentuated upon anneal, leading to a decrease in surface roughness that corresponds to an increase in film closure. The observed debonding energy of the ELD Cu/APTS surface is ca. 2.2 J/m 2 before anneal, while it reaches ca. 4.5 and 8 J/m 2 after a 10 min anneal under forming gas at 300 and 450°C, respectively.