This study performs surface reduction treatments, including hydrogen plasma treatment and rapid thermal anneal (RTA) in hydrogen ambient, to reduce the nitrogen content in the surface layer of the TaNx ultrathin film deposited by plasma-enhanced atomic layer deposition (PE-ALD). A four-point bend delamination test and a pull-off tensile test are used to study the interfacial strength of the PE-ALD thin film with copper. According to X-ray photoelectron spectroscopy and Auger electron spectroscopy, a new chemical phase with a very small nitrogen content, possibly beta-TaNx, is formed on the PE-ALD TaNx thin film after the RTA treatment. The increase in the Ta/N atomic ratio in the RTA-treated TaNx thin film significantly improves the adhesion of the TaNx film with the sputter-deposited Cu layer. However, the hydrogen-plasma-treated TaNx thin film shows a slight decrease in nitrogen content but still demonstrates better adhesion with the Cu layer compared with the as-deposited one. While the Cu overlayer on the RTA-treated PE-ALD TaNx thin film can sustain the thermal anneal at 600 degrees C, the one on the as-deposited TaNx thin film exhibits voiding even at a temperature as low as 400 degrees C.