Optimizing Cu-Cu Bonding Strength in Nanotwinned Cu Films Through Plasma-Induced Surface Roughening

Cu-Cu bonding is crucial in 3D IC advanced packaging due to its excellent electrical conductivity and thermal stability. This study explores the effect of plasma-induced surface roughening on the bonding strength of highly <111>-oriented NT-Cu films. Cu thin films were treated with argon plasma for 2, 4, and 8 min at 100 W to increase their surface roughness and surface energy. Shear tests and FIB analysis showed enhanced bonding strength, peaking with 8-min Ar plasma exposure. SEM confirmed a transition from mixed-mode to ductile fracture with increased roughness. These results suggest that controlled plasma treatment improves Cu-Cu bonding by promoting atomic diffusion and stress gradients, making it suitable for microelectronic packaging.