Spherical silicon micromirrors bent by anodic bonding

Effect of Surface Cleaning Process on the Wafer Bonding of Silicon and Pyrex Glass

Anodic bonding is a reliable packaging method for MEMS devices, and the surface properties of the wafer directly affect the bonding efficiency. Therefore, the surface treatment of the wafer to be bonded is necessary. Herein, the effects of three different surface cleaning processes (degreasing, piranha solution and RCA solution) on the wafer surface were investigated by atomic force microscopy, scanning electron microscopy, infrared spectroscopy, and anodic bonding experiments. The analysis showed that during the anodic bonding of the RCA solution-cleaned wafer and Pyrex glass, the bonding interface was more closely attached, and the best surface properties were obtained. The anodic bonding experiments of the wafer and Pyrex glass showed that the bonding current increased with the applied voltage, and the bonding time decreased accordingly. This was most evident in the case of RCA cleaning. The SEM images showed that as the bonding voltage increased, the bonding interface became more uniform without obvious voids. Due to the influence of the strong electric field and temperature field, an irreversible chemical reaction occurred at the bonding interface, which formed a bonding layer that was key to successful bonding.