A novel two-step activation to control copper oxidation for small-pitch Cu/SiCN hybrid bonding

Hybrid bonding, one of the most promising three-dimensional (3D) integration technologies, faces significant challenges due to the rapid and uneven oxidation of Cu pads, especially at small interconnect pitch. In this work, we propose a two-step activation method combining formic acid (FA) treatment and atmospheric plasma (AP) treatment to mitigate the detrimental effects of Cu oxidation on bonding quality. The FA treatment removes the majority of the oxide layer through the corrosion of copper oxide, and the following AP significantly increases the hydroxyl density and hydrophilicity of dielectric materials while removing the remaining oxide layer. This two-step activation method enables precise regulation of the metal oxide layer and surface activity, leading to a void-free bonding interface with a bonding strength of 3.396 MPa for Cu/SiCN hybrid bonding at ~2 μ m interconnect pitch. This research provides a new idea for the surface treatment of heterogeneous materials in small-pitch hybrid bonding and will support the rapid development of 3D integration technology.