Yield improvement for anodic bonding with suspending structure

Abstract

A method is presented to improve the yield of the anodic bonding process involving MEMS devices with suspended structures. In the proposed method, a metal layer is deposited and patterned on the Pyrex substrate in advance to form the electrode and connection wire simultaneously. The electrode which faces the suspended structure directly above, also acts as the bottom electrode for electrostatic actuation or capacitive sensing. The wire connected to the bottom electrode runs across the bonding area and electrically connects to the suspended structure outside the device area. As a result, the electric potential between the suspended silicon structure and the bottom electrode on the glass can be kept at zero during the anodic bonding process, thus preventing the suspended structure from being damaged by the extremely large electrostatic force. A novel photoresist filling step was also used to protect the bonding pads and cavity from being damaged by following process. Finally, a dicing process is used to separate the electrical connection between the suspended structure and bottom electrode for subsequent device operations.