Gold damascene interconnect technology for millimeter-wave photonics on silicon

Thick-gold-multilevel damascene-interconnect technology makes it possible to fabricate >10-µm-feature ultrahighspeed devices on Si. Adding H2O2 to a conventional KIO3-based slurry triples the removal rate of gold in chemical mechanical polishing (CMP). A ratio of H2O2 to slurry of ~1:1 is found to be the optimum for obtaining the highest gold removal rate. X-ray photoelectron spectroscopy (XPS) analyses show that gold is oxidized in spite of its chemical stability when the removal rate is high. The gold is oxidized due to the reduction of iodine at the optimum H 2O2 mixture ratio. This CMP of gold enabled us to make a thick (>10 µm) gold-multilevel damascene-interconnection structure for the first time. Integration of full-wafer wafer-bonded uni-traveling carrier photodiodes (UTC-PDs) with the gold multilevel interconnections as coplanar waveguides (CPWs) on a Si wafer has been achieved using this gold-CMP process.