Influence of Diffusive Penetration of Small Molecules/Atoms into Vacuum Cavity Sealed by Silicon Migration

Silicon Migration Seal (SMS) is applied to wafer-level vacuum packaging of MEMS, where submicron release holes are closed by silicon reflow in hydrogen at high temperature (>1000°C). In this study, to investigate the mechanism of the pressure increase, the gas permeability coefficient of the SMSed package was investigated using hydrogen at various temperatures. As a result, the permeability coefficient is found to follow Arrhenius equation. Also, it is about 5 times as large as a literature value for quartz glass at 150°C. This finding indicates that the primary pathway for gas permeation is through Si/Si0<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> direct bonding interfaces.