Bumpless Interconnect of 6- $\mu$m-Pitch Cu Electrodes at Room Temperature

Bumpless interconnect of 6-mum-pitch Cu electrodes was realized at room temperature with the surface activated bonding (SAB) method. In this study, we propose a novel bumpless structure, where the electrodes and a surrounding Cu frame are fabricated with the same height to increase bond strength and demonstrate the feasibility of a sealing interconnection between Cu surfaces. The damascene process, assisted by the reactive ion beam etching (RIE), was used to fabricate the Cu structures. 923 521 electrodes placed inside the frame were arranged into a spiral chain to enable the detection of the positions with insufficient interconnection by electrical resistance measurements. Using the SAB conditions optimized with simple chemo-mechanical polishing (CMP)-Cu film samples, we found that 744 769 electrodes were successfully interconnected, except some specific lines near the frame, which might be due to sample preparation error rather than a bond defect. The mean contact resistance was below 0.08 Omega a sealing effect was achieved at the frame structure because there was little increase in the contact resistance in high temperature storage testing performed at 150degC for 1000 h, in ambient air.