Surface Energy Characterization for Die-Level Cu Hybrid Bonding
The characteristics and quality of the bonding interface in hybrid bonding vary greatly depending on physical and chemical factors during the bonding process. Quantitative understanding and evaluation of the surface energy of the bond are essential to improve reliability. While destructive razor blade testing has been commonly used to quantify the surface energy and interface toughness in wafer-level bonding for years, there is currently no standard quantitative method for evaluating die-level direct bonding. In this study, the displacement control of single-beam cantilever (SBC) was specially developed as a new quantitative characterization method to evaluate the surface energy at the die level. For this characterization test, we first used a 10 × 10 mm2 die size with controlled bond surfaces, followed by a 6.3 × 10.3 mm2 Cu hybrid bonding sample with an array of Cu bond pad size of 6 μm in diameter and 12 μm pitch. The pre-bonding process (wafer protection, dicing, cleaning, and surface activation), and die-level bonding methods were evaluated using this new characterization method. Process optimization resulted in die-level bonding consistency with surface energy higher than 2.0 J/m2, and voids-free bonding.