Room temperature bonding of wafers using au films with various holding times in air

The bonding of two flat wafers using nanocrystalline Au films is a promising process to achieve wafer bonding at room temperature in air. In this study, we kept wafers in air after Au-film deposition on the wafer surfaces. Bonding was then performed after exposure time texp. Quartz glass wafers were bonded using Au films (3, 7, and 20 nm thick) with Ti underlayers. The bonding strength was assessed as a function of texp and film thickness. TEM images revealed that the recrystallization of Au atoms at the Au - Au bonded interface occurs at room temperature, even with texp =168 h (1 week). The bonding energy tended to decrease as the Au film thickness decreased, but the bonding energy was greater than the Au film surface energy (=1.63 J/m²) even with 3 nm Au films in the texp range up to 1 week, indicating that the bonding process is highly reliable.