Formation and characterization of low resistivity sub-100 nm copper films deposited by electroless on SAM

Thin Cu films of microelectronic quality and low electrical resistivity were created by electroless deposition (ELD) onto SiO2 surface modified first with self-assembled monolayer (SAM) of 3-aminopropyltrimethoxysilane (APTMS) and activated then by 5 nm gold nano-particles (AuNPs). The presence of highly oriented amino-terminated SAM was revealed by XPS and ToF-SIMS analyses. The Cu films were deposited in boron- and phosphorous-free tartrate/formaldehyde electrolyte. Controlling the deposition rate via the solution pH permitted a minimum value in resistivity ρ. XPS depth profile revealed that diffusion of Cu into SiO2 modified by APTMS did not take place after annealing at 220 deg. C, 4 h. Moreover, annealing resulted in the drop of electrical resistivity to ρ = 4 ± 0.4 μΩ cm for the films with the thickness of 35-100 nm. This value of ρ is several times smaller than those reported in literature for sub-100 nm Cu films deposited by electroless on different SAMs. It is speculated that nano-scale porosity and corrugated structure observed by HRTEM and AFM in the ELD Cu films contribute to the resistivity. The obtained results demonstrate a viable route for formation of low resistivity, sub-100 nm Cu films on dielectrics for microelectronic application.