Demonstration of Low Temperature Cu-Cu Hybrid Bonding using A Novel Thin Polymer

Cu-Cu hybrid bonding is a key technology for continuous improvement of the performances of 3D and 2.5D stacked devices, and it will be used for wider application area including high bandwidth memory and heterogeneous integration on interposer. For the application of Cu-Cu hybrid bonding to these devices, a new die to wafer bonding process using a novel thin polymer is proposed to offer low thermal budget, stable bond strength even after long time storage, and robust bonding against voiding caused by particle entrapment. In this paper, it is shown that the novel polymer was permanently bondable after 150 °C baking, and the bonding property was maintained even after the cured polymer was stored for 3 months prior to bonding. By using the novel polymer, die to die Cu-Cu hybrid bonding was performed. Electrical connection of daisy chains with a total of 4,224 Cu-Cu contacts in the stacked die was obtained after thermal compression bonding at low temperature range from 160 °C to 200 °C. The stacked samples withstood reliability tests. Results for pressure-less Cu-Cu hybrid bonding and short time thermal compression bonding are also reported.