Surface Modification for PI-to-PI Direct Bonding

To achieve high-density 3D IC heterogeneous integration, the applications of new dielectric materials are very crucial. Due to excellent thermal stability, chemical resistance, mechanical and electrical properties, polyimide and its composites have been considered as dielectrics for 3D IC packaging. In this study, a novel surface modification technique was proposed to manipulate surface chemistry to achieve direct bonding between two polyimide surfaces at low temperature. This innovative integration technique offers advantages such as low processing temperature, low bonding load, short processing time, and high bonding performance. Two types of deep UV light sources, VUV (172 nm) and UVC (220 nm), were used. The increase in -OH groups on the surface and other hydrophilic groups after irradiation significantly improved bonding strength after annealing. Changes in surface roughness due to light exposure also mattered.