Bumpless Interconnect of Ultrafine Cu Electrodes by Surface Activated Bonding (SAB) Method

摘要

In this study, an ultrafine bumpless interconnect was realized by applying the surface activated bonding (SAB) method to the room-temperature direct bonding of Cu electrode, and its electrical performance was verified. Also, a thin flash memory chip and a Si interposer were interconnected with the bumpless structure to demonstrate its applicability to practical devices. We used the combination of the damascene process and RIE (reactive ion beam etching) process to fabricate bumpless electrodes with a diameter of 3 μm, pitch of 10 μm, and height of 60 nm, and bonded them with a highly accurate SAB flip chip bonder. One hundred thousand fabricated bumpless electrodes were successfully interconnected, and we showed that the contact resistance could be less than 1 mΩ with high thermal reliability at the interface. Also, we developed a fabrication process of bumpless electrodes that has a polyimide insulation layer by the combination of oxygen plasma ashing and CMP (chemical mechanical polishing), and applied it to the interconnection between a 0.1-mm-thick flash memory chip and an interposer with the same thickness. The bonded memory chip was assembled into a compact flash (CF) memory card module, and the entire memory region was successfully verified.