3 - Packaging related technologies

Anodic bonding is a wafer to glass bonding technique, which involves bonding a silicon wafer to a glass wafer at an elevated temperature, using the assistance of electrostatic field. The bonding mechanism is an electrochemical process. At elevated temperatures mobility of the sodium ions present in the glass substrate is fairly high, ad the presence of an electrical field causes them to migrate to the negatively charged cathode at the back of the glass wafer. As the Na+ ions migrate toward the cathode, they leave behind permanently bound negative ions. This negative ions form a depletion region adjacent to the silicon surface. As a result of this electric field, the glass wafer and the silicon wafer are pulled into a contact with each other. At the same time, the extremely high electric field transports oxygen from the glass to the silicon-glass interface. Here the oxidation of silicon takes place, and the thin layer of SiO₂ that is formed creates a bond between the silicon and glass wafer.