Edge Water Penetration in Direct Bonding Interface

Abstract

A bonding interface between wafers usually exhibits a narrow gap due to the imperfect compression and matching of the facing wafer surface asperities. When hydrophilic bonding is considered, this gap can be partly filled with water originating from the adsorbed water before bonding or entering the gap from the surrounding atmosphere when bonded. The kinetics of water diffusion through the gap has been studied using two different techniques: X-ray reflectivity is able to monitor the interface density changes associated to the water front progression. The water intake is also revealed through defect creation upon annealing, creating a rim-like pattern whose extent also gives the water diffusion law. At room temperature, the kinetics observed by either techniques is consistent with Lucas-Washburn law for diffusion through a gap width smaller than 1nm. The distinction between adsorbed solid-like water and the additional water drawn in the assembly by capillarity will be discussed.