Crystal Structure, Microstructure and Mechanical Properties of NbN Coatings Deposited by Asymmetric Bipolar Pulsed DC Sputtering

Abstract

Single phase niobium nitride (NbN) coatings were deposited using asymmetric bipolar pulsed dc sputtering by varying pulse frequency and duty cycle of pulsed plasmas. Crystal structure, microstructure, morphology and mechanical properties were examined using XRD, FE-SEM, AFM and nanoindentation. Upon increasing pulse frequencies and decreasing duty cycles, the coating morphology was changed from a pyramidal-shaped columnar structure to a round-shaped dense structure with finer grains. Asymmetric bipolar pulsed dc sputtered NbN coatings deposited at pulse frequency of 25 ㎑ is characterized by higher hardness up to 17.4 ㎬, elastic modulus up to 193.9 ㎬, residual compressive stress and a smaller grain size down to 27.5 ㎚ compared with dc sputtered NbN coatings at pulse frequency of 0 ㎑. The results suggest that the asymmetric bipolar pulsed dc sputtering technique is very beneficial to reactive deposition of transition-metal nitrides such as NbN coatings.