Low Contact Resistance and Low Temperature Hybrid Bonding with Polyimide and Highly <111>-oriented Nanotwinned Cu

Among the recent decades, the development of fine pitch hybrid bonding is eye-catching, since this kind of technology could realize high-speed signal transmission with high reliability due to the shrunk electrical joints and the surrounded dielectrics [1]. The polyimide (PI) possesses low Dk (~3.61 at IMHz), low Df (~0.037 at 1MHz), low curing temperature, simple process ability at low cost, excellent mechanical properties, high resistance and stability. It is considered as an excellent candidate to protect joints and enhance their bonding strength [2]. As for nanotwinned copper (NT-Cu), it is also a candidate for low-temperature Cu-Cu bonding. Highly <111>-oriented NT-Cu can be electroplated with good uniformity on Si wafers. With the high surface diffusivity and the low oxidation rate [3]–[4], the bonding can be achieved at lower temperature in the same time. The bonding temperature can be reduced to below 250 °C by using high surface diffusivity NT-Cu and low curing temperature PI which has low glass transition temperature (Tg), and increase the bonding strength simultaneously. As a result, PI is incorporated with highly <111>-oriented nanotwinned Cu (NT-Cu) to achieve the low contact resistance hybrid bonding (< 1.7 x 10– ⁸ Ω. cm2) with low bonding temperature (220 °C) in this study.