Investigation of Metal Interconnect for Wafer-Level and Sealable Miniaturized MEMS Encapsulation

Different combinations of metal thin films were investigated as metal interconnect for miniaturized microelectromechanical system (MEMS) encapsulation with stable electrical properties and sealing capability. The candidates of metal as the adhesion layer include Cr, Ti, and Ta. Metals Pt and Pd are the selection for the diffusion barrier layer. Comparison results of adhesion tests, stress measurements, and aging tests show that the interconnect of Ti-Pd-Au has the best stability in MEMS devices. After the screening process, the analyses of scanning acoustic tomography (SAT), scanning electron microscope (SEM), and pull test verify that the symmetric and ultrathin Ti-Pd-Au structure can be bonded well for the sealing process. Furthermore, the plasma treatment was conducted to reduce the thermal budget of encapsulation. The reliability tests present the bonding scheme with plasma treatment can withstand rapid temperature variation and high moisture for a long duration. All the results show that the interconnect of Ti-Pd-Au simultaneously used in the sealable encapsulation has a great potential for advanced miniaturized MEMS packaging.