Handbook of Silicon Based MEMS Materials and Technologies

31.3. Low-Temperature Direct Bonding of Silicon

Direct wafer bonding of silicon wafers is a robust and simple method to fuse two wafers together, but it is not suitable for every application. A low-temperature bonding process may be needed if the wafers are pre-processed, contain temperature-sensitive materials or components, or have different thermal expansion coefficients. The most common methods used for low-temperature hydrophilic direct wafer bonding are based on plasma. In these methods the wafer surface or surfaces is/are activated with a short plasma treatment prior to the wafer contacting. Numerous plasma processes have been reported for bond strengthening. The most often reported plasma gases are argon, nitrogen and oxygen. Sometimes ...