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This paper reports a hermetic MEMS package structure with silicon wafer as bonded cap at wafer-level scale. CMP followed by spraying chemical smoothing process is utilized to thin the N(100) silicon cap wafer to the thickness of 150 mum after wafer-level Cu/Sn isothermal solidification bonding. Method for the thinning process and parameters for Cu/Sn isothermal solidification bonding process are researched and optimized. TMAH etching is used to open trenches penetrating through the cap wafer and then Pb63Sn37 bumps redistribution and reflow are utilized to achieve the final I/O interconnection. Such approaches have the most important features of simplified fabrication process compatibility with most MEMS processes and low-cost. Fine-leak tests as well as gross-leak tests have been done on the packaged samples in order to characterize the hermeticity of the bonded wafers which indicating an excellent leak rate of around 1.9times10-9 atm cc/s. The shear strength of the packaged samples has been measured and average shear strength of 19.5 Mpa is achieved. Both results meet the demands of MIL-STD-883E.
Date of Conference: 10-13 Aug. 2009