Galvanic displacement deposition of Ag using citric acid for Cu-to-Cu hybrid bonding

This study reports Ag deposition for hybrid bonding using galvanic displacement deposition. The galvanic displacement method enables selective deposition only on Cu without any additional process. To uniform Ag layer, citric acid was added. Citric acid suppresses the Cu dissolution and stabilize the Cu surface. The morphologies of Ag layer were observed by scanning electron microscopy (SEM). The deposited Ag atoms has a property of interdiffusion with Cu during bonding process because of the difference of activation energy. Depth-profiling X-ray photoelectron spectroscopy (XPS) shows the interdiffusion between Ag and Cu, and the bonding properties improve with Ag layer.