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
β-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°C
, the one on the as-deposited
TaNx
thin film exhibits voiding even at a temperature as low as
400°C
.