Low damage via formation with low resistance by NH3 thermal reduction for Cu/ultra low-k interconnects

In order to minimize plasma-damage on porous low-k films, a pre-clean treatment, NH3 thermal reduction, to remove CuOx thin layer from a via bottom before barrier metal deposition was investigated. A reduction rate of 3 nm/min for CuOx layer was obtained at 360 C degrees, and via resistance was reduced to 75% without any damage into porous low-k films such as increase of dielectric constant (k) and decrease in low-k film thickness, while conventional Ar or He/H2 plasma pre-clean treatments in severe damages into low-k-films.