Hermeticity and diffusion investigation in polysilicon film encapsulation for microelectromechanical systems

The hermeticity and diffusion behavior of “epi-seal” encapsulation [R. N. Candler et al., J. Microelectromech. Syst. 15, 1446 (2006); B. Kim et al., Proceedings of the ASME 2007 InterPACK Conference (InterPACK’07), 33234 (2007)], an epitaxially deposited polysilicon film encapsulation for microelectromechanical systems (MEMSs), were investigated. MEMS resonators with pressure sensitive quality factor were fabricated inside episeal cavities. By measuring the quality factor and inferring cavity pressure, leakage through the encapsulation was studied as a continuation of previous hermeticity investigations [B. Kim et al., Proceedings of the 2004 ASME International Mechanical Engineering Congress and Exposition, IMECE, pp. 413–416 (2004)]. During long-term monitoring performed at 100 °C in a normal atmosphere, the encapsulated cavity pressure increased at a rate of 5–10 mTorr/yr, whereas no measurable pressure change could be detected in our previous room temperature measurement performed with identically des...