Low temperature Cu/SiO2 hybrid bonding via 〈1 1 1〉-oriented nanotwinned Cu with Ar plasma surface modification

Abstract

Argon (Ar) plasma surface modification and highly (111)-oriented nanotwinned copper (nt-Cu) were combined to lower the bonding temperature of Cu/SiO2 hybrid joints. The contact angle of water on SiO2 could be reduced from 22.6° to 3.3° after the plasma treatment. Benefiting from the high surface diffusivity of nt-Cu and great hydrophilicity of the plasma-assisted SiO2, the bonding temperature could be reduced to 150 ℃. However, such a plasma treatment caused the serious oxidation of the activated Cu in the ambient. To balance the activation and oxidation of the Cu films, Ar plasma power was tuned. X-ray photoelectron spectroscopy (XPS) was used to analyze the SiO2 surfaces. We found an increase (13.6% to 28.3%) in Si-OH and decreases in Si-O and C-O intensities after the plasma activation. Such decreases in Si-O and C-O intensities could be attributed to the removal of organic compounds. Shear tests were also conducted to characterize the bonding strength of the joints. An excellent bonding strength > 35 MPa was achieved after the post annealing and plasma treatment.