Abstract
Hydrophilic direct wafer bonding involves two types of bonding voids: classical voids caused by contamination or surface topography, and edge voids resulting from the bonding wave dynamics. The adiabatic expansion of the bonding wave at the wafer edge can lead to condensation of humidity and the formation of small water droplets, resulting in bonding defects even without contamination. These defects persist even under dry gas conditions. Two methods are used to address this issue. The first is vacuum bonding (<0.1 mbar), and the second involves using gases with a negative Joule-Thomson coefficient, such as helium. Helium is preferred due to its low coefficient and cost-effectiveness. However, bonding under pure helium results in lower adhesion and adherence energy. In this study, humid helium, generated using a dedicated humidifier, is used to evaluate the adhesion energy and adherence of standard Si/SiO2 bonding.
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