DC reactive magnetron sputtered NbN thin films prepared with and without hollow cathode enhancement

A comparison was made between NbN thin films prepared with and without hollow cathode enhancement of DC reactive magnetron sputtering. The hollow cathode arc source is used in a triode configuration with the magnetron. This design allows sputtering to take place at pressures as low as 5×10^-4 torr and has been shown to improve process control in the sputtering of oxides from metal targets. These films were investigated for application in NbN Josephson junctions. Film deposition parameters have been related to growth rate, stoichiometry as measured by Auger electron spectroscopy (AES), transition temperature, growth texture as measured by X-ray diffraction (XRD,), and ellipsometric parameters. The relationships were investigated using factorial experimental design. An important pressure-power interaction which leaves T_c nearly invariant was observed. This interaction is explained in terms of the counteracting effects of ion bombardment. The maximum T_c´s achieved were 14.18 K and 14.75 K with and without the use of the hollow cathode, respectively. The data suggest that the effect of the hollow cathode is to increase ion bombardment of the substrate, at least when used with small magnetrons