Non-destructive in situ test for anodic bonding

New test structures have been designed, fabricated and tested to monitor the quality of the anodic bonding between silicon and glass. The main advantage of the described test is that it is not destructive and allows the bond quality to be monitored in processed wafers. This test is very easy to implement in a chip or in a wafer because of its simplicity. Test structures consist of a matrix of circular and rectangular cavities defined by reactive ion etching (RIE) on the silicon wafer, with different sizes and depths. The bonding process and quality can be monitorized by the measurement of the size of the smallest bonded cavity and the distance between the bonded area and the cavity border. These structures give information about the level of electrostatic pressure that has been applied to pull together into intimate contact the surfaces of the two wafers. The higher the electrostatic pressure, the better the bond. We have applied these test structures to study the influence of the voltage and the temperature on the anodic bonding process. Results are in good agreement with finite-element method (FEM) simulations.