DC-SQUIDs fabricated by electron beam direct writing

An Electron Beam MicroFabricator (EBMF) has been used to write directly on a silicon wafer to obtain many equal chips containing dc-SQUIDs and superconducting test circuitry. We developed a complete lift-off technique on an electronic resist for all the seven needed layers of the process. The first layer, consisting of Au-Pd alloy, is used as resistor and for patterning the markers required to align the various layers. The calibration on such markers avoid the stitching problem due to the large chip dimensions (6.30×6.30 mm) as compared with the maximum range of the electron beam deflection. The direct writing permits alignment between the various layers better than 1um in any chip. The first test on the developed devices shows high reliability and flexibility of the overall process.