Increasing bonding strength of chips and substrates assembly by argon plasma

Abstract

The plasma surface activation was applied to the thermal-compression bonding of chips and substrates. An Ar gas was selected to perform the physical plasma treatment on the bonding surface of Au bumps and Cu electrodes. This plasma-activated technology was expected to remove the surface contaminants, and then to reduce the bonding barrier for chips and substrates assembly. The experimental results presented an effective improvement in the die-shear force performance of chips and substrates assembly using the Ar plasma activation. Increasing the die-shear force was attributed to remove the contaminants on the surface of Cu electrodes and Au bumps by the Ar plasma activation. After Au bumps and Cu electrodes were activated by Ar plasma, neither delamination nor crack is found at bonding interface between Au bumps and Cu electrodes for chips and substrates assembly. The die-shear forces were higher than the minimum required value stated in the JEDEC specifications for Cu electrodes and Au bumps with Ar plasma activated. As Cu electrodes with Ar plasma treating under various activated durations, the fracture mode of Au bumps separating from the surface of Cu electrodes transforms to that of Au bumps separating from the bond pads, indicating the bonding strength of Au bumps and Cu electrodes is higher than that of Au bumps and bond pads. A low contact angle was also determined on the surface of Cu electrodes after the Ar plasma activated, indicating a clean bonding surface was achieved. A clear atomic interdiffusion between Au bumps and Cu electrodes was observed for Au bumps and Cu electrodes with Ar plasma activated. The Ar plasma activation was an effective scheme to improve the bonding strength of chips and substrates assembly. Thus, the Ar plasma activation has great potential to be applied to chips and substrates assembly.