Precise slit-width control of niobium apertures for superconducting LEDs

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We introduce a novel three step procedure for precise niobium (Nb)-etching on the nm-scale, including the design of high contrast resist patterning and sacrifice layer formation under high radio frequency (RF) power. We present the results of precise slit fabrication using this technique and discuss its application for the production of superconducting devices, such as, superconductor-semiconductor-superconductor (S-Sm-S) Josephson junctions. For the reactive ion etching (RIE) of Nb we selected CF4 as etchant gas and a positive tone resist to form the etching mask. We found that the combination of resist usage and RIE process allows for etching of thicker Nb layers when utilizing the opposite dependence of the etching rate (ER) on the CF4 pressure in the case of Nb as compared to the resist. Precise slit-width control of 80 nm-thick and 200 nm-thick Nb apertures was performed with three kinds of ER control, for the resist, the Nb, and the underlying layer. S-Sm-S Josephson junctions were fabricated with lengths as small as 80 nm, which can be considered clean and short and thus exhibit critical currents as high as 50 μA. Moreover, possible further applications as for apertures of superconducting light emitting diodes (SC LEDs) are addressed.
2011-01-28