Adhesive wafer bonding with photosensitive polymers for MEMS fabrication

Adhesive wafer bonding is a technique that uses an intermediate layer (typically a polymer) for bonding two substrates. The main advantages of using this approach are: low temperature processing (maximum temperatures lower than 400°C), surface planarization and tolerance to particles contamination (the intermediate layer can incorporate particles with the diameter in the layer thickness range). The main bonding layers properties required by a large field of applications/designs can be summarized as: isotropic dielectric constants, good thermal stability, low Young’s modulus, and good adhesion to different substrates. This paper reports on wafer-to-wafer adhesive bonding using SINR^TM polymer materials. Substrate coating process as well as wafer bonding process parameters optimization was studied. Statistical analysis methods were used to show repeatability and reliability of coating processes. Features of as low as 15 μm size were successfully resolved by photolithography and bonded. An unique megasonic-enhanced development process of the patterned film using low cost solvent was established and proven to exceed standard development method performance.