Method to evaluate the adhesion distribution on wafers

Direct wafer bonding plays an essential role in semiconductor manufacturing. Although several methods for evaluating wafer separation force are established, those for measuring the adhesion force a crucial factor determining the success of wafer-to-wafer direct bonding-are limited. In this study, we propose a novel approach to evaluate adhesion by combining wafer bonding experiments with test structures featuring cylindrical mesas and a bonding simulation incorporating the interactions between wafers and fluid. The proposed method excludes instrumental artifacts in scanning acoustic microscopy and provides a more accurate characterization. The adhesion energy obtained here is smaller than the separation energy and is in good agreement with values reported in previous literature. With the proposed method, it becomes possible to quantify adhesion distribution not limited to the wafer edge but extending to all areas encompassing the central region of the wafer.