Wafer bonding became during past decade an important technology for MEMS manufacturing and waferlevel 3D integration applications. The increased complexity of the MEMS devices brings new challenges to the processing techniques. In MEMS manufacturing wafer bonding can be used for integration of the electronic components (e.g. CMOS circuitries) with the mechanical (e.g. resonators) or optical components (e.g. waveguides, mirrors) in a single, wafer-level process step. However, wafer bonding with CMOS wafers brings additional challenges due to very strict requirements in terms of process temperature and contamination. These challenges were identified and wafer bonding process solutions will be presented illustrated with examples.

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Metal layers can be used as bonding layers at wafer-level in MEMS manufacturing processes for device assembly as well as just for electrical integration of different levels. One has to distinguish between two main types of processes: metal diffusion bonding and bonding with formation of an interface eutectic alloy layer or an intermetallic compound. The different process principles determine also the applications area for each. From electrical interconnections to wafer-level packaging (with emphasis on vacuum packaging) metal wafer bonding is a very important technology in MEMS manufacturing processes.

Wafer level bonding is an important technology for the manufacturing of numerous microelectromechanical systems. In this work the aluminum thermo-compression wafer bonding is characterized. The effects and significance of various bond process parameters and surface treatment methods are reported on the final bond interfaces integrity and strength. Experimental variables include the bonding temperature, bonding time, and bonding atmosphere (forming gas and inert gas). Bonded wafer samples were investigated with scanning acoustic microscopy, scanning electron microscopy, and four point bending test. Interfacial adhesion energy and bond quality were found to be positively correlated with bonding temperature. A bonding temperature of 500 ºC or greater is necessary to obtain bond strengths of 8-10 J/m 2 .

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 lm 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.