Pentalevel Resist Process for the Precise Fabrication of Small Area SIS Junctions

We have fabricated high quality M1/barrier/M2/Au superconducting insulating superconducting (SIS) junctions with Au over-layers using a new multilayer pentalevel resist process. The wafer/NFR/polyimide/SiO
₂
/Cr/imaging-resist pentalevel structure enables precise definition of submicron junction features in a self-aligned insulation process. This scheme, unlike our previous multilevel resists, affords precise definition of the final Nb layer from an initial etch of a thinner top Cr layer. The Cr layer, defined with chlorine based RIE, serves as an excellent mask for the subsequent fluorine and oxygen based RIE etches of the remaining pentalevel stack and M2 electrode. We present a detailed description of the pentalevel process and electrical characteristics of NbTiN SIS junctions fabricated with this new technique.