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13 November 2002 Nano-film assisted anodic bonding
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The paper reports on the development of low temperature silicon-to-glass anodic bonding for wafer level microelectromechanical systems (MEMS) packaging. A hydrogen-free amorphous silicon layer of about 40 nm thickness was deposited on the silicon substrate. The effects of bonding temperature and voltage on the bond integrity and strength were investigated. The bonding temperatures and voltages ranged from 200 to 300 °C and 200 to 1000 V, respectively. It is found that bubble-free interface can be achieved as long as the temperature is above 250 °C. Even at lower temperatures, the unbonded area can be less than 0.5% of the wafer area. The bubble size decreases with an increase in the bonding temperature. A similar effect was observed with the applied voltage. The bond strength obtained was typically 20 MPa or higher. In the destructive tests, fractures were found to occur mainly inside the glass wafer rather than at the interface. The interface was analysed with Raman spectroscopy and SIMS. The analyses showed that Si-O chemical bonds are formed at the interface. Higher bonding temperatures result in more oxygen migrating to the interface and reacting with Si to form Si-O bonds. Electrostatic attraction and chemical reaction are the two main mechanisms that generate the bonding between silicon and glass wafers.
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J. Wei, H. Xie, C. K. Wong, and L. C. Lee "Nano-film assisted anodic bonding", Proc. SPIE 4936, Nano- and Microtechnology: Materials, Processes, Packaging, and Systems, (13 November 2002);


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