A study on bonding pad structure and layout for Fine pitch hybrid bonding

Hybrid bonding technology is required for high density I/O in the 3D package structure to overcome the limitations of thermos compression bonding. Compared to bump bonding with micro solder, hybrid bonding can achieve fine pitch bonding and have excellent SI/PI characteristics. One of the key technologies of hybrid bonding is pad processing which is optimized for the bonding environment. We should consider Cu expansion at anneal temperature and bonding area between pads because the expansion of Cu pad is proportional to temperature and pad volume. [1]However, annealing temperature is determined depending on the thermal properties of the device. Hence, it is important to adjust pad dishing so that connectivity can be secured at annealing temperature. The initial pad design including pad dishing should be determined by expecting thermal expansion at process condition. The amount of Cu extrusion at annealing can be adjusted with an appropriate pad size, or by changing bonding shape. Therefore, design rule for fine pad pitch is required based on the relationship between Cu pad surface area and height.In this study, we evaluate various factors of layout for fine pitch hybrid bonding. Bonding quality was investigated according to the surface topology and misalignment of bonding pad. The effect of bonding area was studied by using misalignment via chain that changed up to 0-95%. Through the experiment, we can define specific design rule showing high yield for fine pitch hybrid bonding.