Development of high reliability $6\ \mu\mathrm{m}$-pitch Cu-Cu connections using over-400mm2-large Chip on Wafer bonding process

We developed high-reliability
$6\ \mu\mathrm{m}$
-pitch Cu-Cu connections by using over-400mm
²
-large chip-on-wafer (CoW) bonding process for the first time. This work was realized by optimizing the pretreatment and bonding process to achieve void-free CoW bonding even for large chips (over 400mm
²
). We obtained good yields in a long daisy chain of
$6\ \mu\mathrm{m}$
-pitch Cu-Cu connections and high reliabilities in stress-induced voiding and electromigration test. The yield and reliability of the CoW bonding structure were also shown to be equivalent to the proven WoW bonding structure. Cross-sectional images of the CoW bonding interface show that the copper pads are well aligned, the copper grains are recrystallized across the interface.