We have attempted to study the nature of Copper (Cu)-electrode surfaces formed from two distinct Cu-electroplating baths with different additives. The phase-shift data obtained from the intermittent-contact atomic force microscopy analysis revealed the following that the soft Cuelectrode with higher tensile strength formed from modified Cu-electroplating possesses more reactive surface than the harder Cu-electrode formed from conventional Cu-electroplating. Thus, we inferred that this soft nature of Cu grains is also important for successful $\mathbf{Cu}-\mathbf{SiO}_{2}$ hybrid bonding, and it does play a vital role in realizing the seamless Cu-Cu interface in the Cu $\mu$ -joints formed by Cu-SiO2 hybrid bonding.