Development of Polymer Base Hybrid Bonding Process

We have developed a hybrid bonding process that uses low-temperature curable polyimide to bond silicon chips with minimal damage. We designed a low elasticity photosensitive polyimide and a low-CTE polyimide for the hybrid bonding. As a result, we found that the elastic modulus at the temperature of bonding and the surface activation treatment affected the adhesiveness. It is thought that the plasma activation treatment increases the number of hydrophilic groups on the polyimide surface, and hydrogen bods are induced between the polyimide surfaces during low temperature bonding. Then, subsequent post annealing treatment causes a chemical reaction to bond polyimide surface. Furthermore, polishing conditions that could expose approximately 1-10nm of copper using CMP processes on a silicon wafer which formed Cu pad and polyimide. As a result, polyimide-polyimide and polyimide-Cu void free hybrid bonding processes are confirmed below 250°C.