Precise control of multilayered structures of Nb–O–N thin films by the use of reactive gas pulsing process in DC magnetron sputtering

Multilayered niobium oxynitride films were deposited onto (100) Si using DC magnetron sputtering with a reactive gas pulsing process. The argon and nitrogen flows were kept constant during sputtering of a pure niobium target and the oxygen flow was pulsed during deposition. Pulse durations of T = 10, 40 and 100 s and duty cycles α = tON / T of 0.3, 0.6 and 0.9 were chosen (tON = injection time of high oxygen flow). A mounting triangle was used as the pulse shape for the oxygen injection. During thin film deposition the cathode voltage, Ucath, the O2 and N2 partial pressures, p(O2) and p(N2), were recorded. A delay of both parameters (Ucath, p(O2)) was observed after each pulse, for the return to the values during tOFF = T − tON (off-time of oxygen injection with high flow). High resolution scanning electron microscopy revealed a multilayered structure for coatings deposited with T = 40 and 100 s. Transmission electron microscopy was used to verify that also the coatings with T = 10 s possess a multilayered structure with a period of λ = 10 nm. Despite this low period small crystallites (< 7 nm) were present in these layers. The indentation hardness and the Youngs modulus were in the range of 8.3–16.5 GPa and 154–180 GPa, respectively.