Comprehensive Study on Advanced Chip on Wafer Hybrid Bonding with Copper/Polyimide Systems

We have studied the hybrid bonding process with a copper (Cu)/polyimide (PI) system by optimizing aqueous acid treatment, height control of Cu protrusion, and temporary/permanent bonding conditions for practical use. The study found that the treatment with an aqueous solution of citric or ascorbic acid and 80 nm-protrusion contributed to the improvement in the bonding yield of Cu electrodes. The suitable temperature and pressure of the permanent bonding were determined at 250 °C and 5 MPa, and the mechanically tough junctions for both Cu-Cu and PI-PI interface were successfully achieved with relatively low resistance.