Combined surface-activated bonding technique for low-temperature hydrophilic direct wafer bonding

Abstract

A combined surface-activated bonding technique is studied for surface activation and water management to improve the hydrophilic SiO2–SiO2 bonding quality. Prebonding treatment involving a Si-containing Ar beam bombardment and prebonding attach-detach is employed prior to wafer bonding in vacuum. The results of bonding strength measurement, Monte Carlo simulation, and surface analysis by Fourier transform infrared spectroscopy are reported. A mechanism is proposed to better understand the nature of the hydrophilic bonding at low temperatures of no more than 200 °C. We suggest that the Si-containing Ar beam modifies the SiO2 surfaces by Si enrichment to make them more reactive for OH adsorption, while the prebonding attach and detach facilitate a further increase in the number of OH and the removal of excess trapped H2O prior to bonding, respectively. As a consequence, SiO2–SiO2 bonding strength close to the Si bulk fracture energy can be achieved after low-temperature annealing.