Investigation of Wet Pretreatment to Improve Cu-Cu Bonding for Hybrid Bonding Applications

The main development challenge of low temperature hybrid bonding technology is the oxidation of Cu surface. The schemes to achieve the high-quality surface condition of Cu before bonding is urgently demanded. In this study, four acid solutions, including sulfuric acid (H2SO4), hydrochloric acid (HCl), acetic acid (CH3COOH) and citric acid (C6H8O7), were chosen as wet pretreatment approaches to remove Cu oxides based on the respective chemical reactions. To investigate the influence of these acid solutions on bonding surface, different acid immersion times are examined and the XPS analysis is conducted to check the surface component composition. Next, thermal compression bonding (TCB) is conducted after the Cu oxide removal process, followed by various analyses, including SAT analysis to validate bonding results, FIB and SEM analyses to inspect bonding interface, and pull test to measure bonding strength. The results of analyses verify the ability of different wet pretreatment to improve Cu-Cu bonding.