Superconducting Characteristics of NbN Films Deposited by Atomic Layer Deposition

A fabrication process for NbN films with a high transition temperature (T
_C
) of about 17 K was developed to realize NbN/AlN/NbN superconducting-tunnel-junction array particle detectors with a high operation temperature of >1 K and a high sensitivity by using atomic layer deposition (ALD). The source (precursor) of the NbN films was (tert -butylimido)bis(diethylamino)niobium [C
₁₆
H
₃₉
N
₄
Nb]. NbN films were deposited on M-plane sapphire wafers. A 50-nm-thick NbN film was deposited with a substrate temperature of about 570 K and exhibited a (T
_C
) of 12.35 K. To improve the superconducting properties of the NbN formed by ALD, a postdeposition rapid thermal annealing process was performed. The dependence of (T
_C
), the surface morphology, and the crystallinity of the film on thermal annealing temperatures was evaluated.