Effects of Au Passivation Thickness on Improving Low-Temperature Cu-to-Cu Bonding Interface

With the continuous advancement of IT technology, the demand for multifunctional and high-performance semiconductor devices continues to rise. Therefore, there is significant interest in semiconductor packaging technology, and research on 3-D packaging technology is gaining prominence beyond traditional packaging methods. This study focuses on bonding in 3-D packaging technology, with particular emphasis on low-temperature Cu-to-Cu bonding using Au nanolayer. Au nanolayer was deposited on Cu surface with thicknesses of 5 and 12 nm, and bonding was conducted at 180 ° C. As a result of analysis of the bonding interface using transmission electron microscopy (TEM), the 5-nm Au sample showed more Au-Cu diffusion than the 12-nm Au sample, showing a bond close to a pure Cu-Cu bonding interface. Additionally, Cu oxide between Au and Cu hindered sufficient diffusion between the two metals, preventing the formation of an Au-Cu intermetallic compound (IMC). The average shear strength was measured as 21.85 MPa for Au 5 nm, 17.72 MPa for Au 12 nm, and 12.08 MPa for pure Cu-to-Cu interface.