Superconformal filling of 41 nm trenches with Cu electroless deposition on Au-activated self-assembled monolayer

In order to completely fill a 41 nm trench pattern with Cu using electroless deposition (ELD), we introduced a method of forming Au catalytic layer based on a self-assembled monolayer (SAM) of aminopropyltriethoxy silane molecules as a coupling agent. The nano-sized Au catalyst layer was deposited on Ta/SiO2/Si substrate through electrostatic interactions between the positively charged amine-SAM layer on the substrate and the negatively charged Au nanoparticles. The interspacing among Au nanoparticles was adjusted by controlling the pH in order to obtain a close-packed catalytic layer. The size of deposited Au nanoparticle catalyst was approximately 4 nm and uniform distribution was obtained at pH 6. After Au catalysts were formed on the amine-coated substrate at pH 6, the substrate soaked in electroless bath with polyethylene glycol as an inhibiting additive. Cross-section views showed that the Cu completely filled the pattern without voids or seams. The electrical resistivity of the electrolessly deposited Cu films with 41 nm thickness was determined to be 2.6 μΩ cm after the annealing process; a this resistivity is 1.4 times lower than recommended by the International Technology Roadmap for Semiconductors. Therefore, the SAM modified ELD is a promising method for filling a 41 nm trench pattern with Cu.