Plasma Treatment Mechanism in Si–SiO2 Direct Wafer Bonding

Abstract

We investigated the mechanism of plasma treatment in enhancing Si–SiO2 bonding strengths. In particular, two of the most dominant arguments, hydrophilicity and water diffusivity, were experimentally examined. Although Si–SiO2 bonding is often described as hydrophilic due to its fundamental mechanism, the results here show that changes in hydrophilicity do not have a linear relation with bonding strength. Instead, plasma treatment on SiO2 surfaces shows a greater effect on the bonding strengths than that on Si surfaces, indicating that water diffusivity plays a crucial role in wafer bonding. In certain circumstances, Si surface treatment in fact deteriorates the bonding strength, which is attributed to the removal of native oxide from the Si wafer.