  We present results of a fabrication-process development for the lithographic
pattern transfer into the sub-100nm range by combining electron-beam
lithography and reactive dry etching to obtain high quality niobium-based
light-sensitive superconducting devices. To achieve this spatial resolution, we
systematically investigated the stability of the positive organic etching masks
ZEP 520A and PMMA 950k in different properly operated fluoride based plasma
discharges. The chemically more robust ZEP 520A was used for defining the
nanoscaled superconductors during the dry plasma etching. Our etching recipe is
appropriate for a precisely controlled removal of a number of transition
metals, their nitrides and a number of lithographic resists. Our process
yielded lightsensitive superconducting devices made from NbN with smallest
planar lateral dimensions of about 50nm with a critical temperature Tc(0) of
about 13K , which is close to the transition temperature of the unstructured
thin film. Our ultra-narrow current paths are able to permanently carry
bias-currents up to 60% of the theoretical de-pairing current-limit.
