Asymmetry hybrid bonding using Cu/Sn bonding with polyimide for 3D heterogeneous integration applications

In this work, hybrid bonding platform is successfully developed with solder bonding and photosensitive polyimide (PI) at 250 °C. Since solder may be affected by the curing process of polymer owing to its low melting point, an asymmetry hybrid bonding structure is proposed to overcome this issue. Metal and polymer can be well bonded simultaneously with wide integration flexibility through various ratios of polymer to metal. The mechanical strength of bonded structure is substantially improved with the better use of polymer filling in the extra areas between metal lines. The developed hybrid bonding structure shows excellent electrical characteristics and high wafer level uniformity. Furthermore, the bonded samples also show excellent reliability to endure temperature variation and humidity erosion after temperature cycling test and un-bias highly accelerated stress test. With the advantages of dielectric photosensitivity, excellent bonding qualities, high process flexibilities, strong mechanical strength, good electrical performance and high stability, the hybrid bonding structures have the outstanding potential to be used in future 3D heterogeneous applications.