Abstract
Bump-less copper (Cu) bonding is currently the most attractive approach for fine-pitch (<20 μm) 3D integration due to its compatibility with the wafer back-end-of-the-line (BEOL) fabrication process. In this study, themocompression bonding of bump-less Cu pads with a diameter of 4 μm and a pitch size of 10 μm was pursued, while chemical mechanical polishing (CMP)-processed Cu pads enclosed in SiO2 were employed with both protruded and recessed topographies. The effects of Cu topography (protruded or recessed) and bonding temperature on the electrical and microstructural properties of the die bonds as well as mechanical bonding strength were investigated. It was found that thermocompression bonding of CMP-processed Cu can be realized at shorter processing times, lower bonding temperatures, and pressures than standard electroplated Cu bonding. The bonding yield of the three configurations, i.e. protruded-protruded, protruded-recessed, and recessed-recessed Cu pads was also compared.
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