10 µm fine pitch Cu/Sn micro-bumps for 3-D super-chip stack

Abstract

We develop novel micro-bumping technology to realize small size, fine pitch and uniform height Cu/Sn bumps. Electroplated-evaporation bumping (EEB) technology, which is a combination of Cu electroplating and Sn evaporation, is developed to achieve uniform height of Cu/Sn bumps. We develop CMOS compatible dry etching processes for removing sputtered Cu/Ta layers to achieve small size and fine pitch Cu/Sn bump. 5 mum square and 10 mum pitch Cu/Sn micro-bumps are successfully fabricated for the first time. Bump height variation is 5 mum plusmn3 % (95%, 2sigma), which is uniform compared to electroplated Cu/Sn bumps. We evaluate micro-joining characteristics of Cu/Sn micro-bumps. Good I-V characteristics are measured from the daisy chain consisting of 1500 bumps with 10 mum square and 20 mum pitch. Resistance of Cu/Sn bump is 35 mOmega/bump, which is very low value compared to electroplated Cu/Sn bumps.