Low-temperature direct copper-to-copper bonding enabled by creep on highly (111)-oriented Cu surfaces.

We achieve low-temperature Cu-to-Cu direct bonding using highly (111)-orientated Cu films. The bonding temperature can be lowered to 200°C at a stress of 114psi for 30min at 10−3 torr. The temperature is lower than the reflow temperature of 250°C for Pb-free solders. Our breakthrough is based on the finding that the Cu (111) surface diffusivity is the fastest among all the planes of Cu and the bonding process can occur through surface diffusion creep on the (111) surfaces. [ABSTRACT FROM AUTHOR]