Localized silicon fusion and eutectic bonding for MEMS fabrication and packaging

Silicon fusion and eutectic bonding processes based on the technique of loc alized heating have been successfully demonstrated. Phosphorus-doped polysi licon and gold films are applied separately in the silicon-to-glass fusion bonding and siticon-to-gold eutectic bonding experiments. These films are p atterned as line-shape resistive heaters with widths of 5 or 7 mu m for the purpose of heating and bonding. In the experiments, silicon-to-glass fusio n bonding and silicon-to-gold eutectic bonding are successfully achieved at temperature above 1000 degrees C and 800 degrees C, respectively, by apply ing 1-MPa contact pressure. Both bonding processes can achieve bonding stre ngth comparable to the fracture toughness of bulk silicon in less than 5 mi n. Without using global heating furnaces, Localized bonding process is cond ucted in the common environment of room temperature and atmospheric pressur e. Although these processes are accomplished within a confined bonding regi on and under high temperature, the substrate temperature remains low. This new class of bonding scheme has potential applications for microelectromech anical systems fabrication and packaging that require low-temperature proce ssing at the wafer level, excellent bonding strength, and hermetic sealing characteristics.[467].