Test resist lift-off followed by CMP for removing residual SiO₂ wings

Test an alternative chemical-mechanical polishing process for Nb/Al-AlOₓ/Nb cross-type Josephson junctions in which the photoresist is lifted off before polishing and the remaining SiO₂ wings are subsequently removed by CMP.

Background

The reported fabrication process deposits SiO₂ while retaining the photoresist mask and then uses chemical-mechanical polishing (CMP) to planarise the trilayer structures. Retaining the photoresist avoids residual SiO₂ wings and enables reliable electrical contact between the top trilayer electrode and the subsequent Nb wiring layer. The paper nevertheless identifies an alternative, untested process sequence in which the resist would first be removed and the residual SiO₂ wings would then be polished away.

Determining whether this alternative sequence can achieve adequate planarisation and insulation while preserving junction quality and yield is relevant to optimizing fabrication of wafer-scale cross-type Josephson tunnel junctions.