Study for Defect Minimization of Ag Nano Layer using Galvanic Displacement Deposition for Cu-Cu Hybrid Bonding

A uniform Ag layer with minimized defects was developed as a passivation layer using displacement deposition for low-temperature Cu–Cu hybrid bonding applications. Defect minimization during displacement deposition on the surface is crucial to ensure its effective application. To address this issue, an electrochemical monitoring technique based on open circuit potential (OCP) was introduced to measure potential variations during deposition, enabling the prediction of surface changes to Ag as well as the defect formation. These results were validated through scanning electron microscopy and atomic force microscopy analyses, demonstrating that OCP monitoring is an effective method for predicting plating defects. Additionally, polyvinylpyrrolidone (PVP) was introduced to regulate the nucleation and growth kinetics of Ag, thereby suppressing agglomeration and improving the uniformity of the deposited layer. The optimal uniformity was achieved at a concentration of 100 ppm PVP, resulting in the successful formation of an Ag layer 4 nm thick. Bonding experiments confirmed that Cu–Cu bonding was achieved at 140℃ under 1.7 MPa for 10 min using the Ag layer. Furthermore, cross-sectional analysis at 170℃ revealed that the sample with the Ag layer exhibited a larger bonded area and superior interfacial quality compared to that without the Ag layer.