Release of hydrogen gas from PECVD silicon nitride thin films in cavities of MEMS sensors

In this work we investigate the release of hydrogen gas from PECVD silicon nitride thin films in the cavities of MEMS based inertial sensors. Firstly, material characterization is conducted on two types of PECVD silicon nitride thin films to study the release of hydrogen gas with analytical methods. The release of hydrogen gas from these materials in encapsulated cavities of MEMS sensors, and its influence on the cavity pressure is also investigated experimentally with the help of functional microchips of MEMS based inertial sensors. Based on our findings and reports from other works, we propose steps by which change in the cavity pressure of the investigated microchip occurs over its different fabrication processes. We suggest that hydrogen gas is released form PECVD silicon nitride thin films at high temperatures during wafer bonding, which can then diffuse in cavities at low pressure over the lifetime of the sensor. • PECVD silicon nitride release hydrogen gas in cavities of MEMS sensors during fabrication • Two general mechanisms are chemical dissociation of bonded hydrogen to form molecular hydrogen, and diffusion molecular hydrogen. • Dissociation reactions occur during high temperature fabrication processes such as Al Ge wafer bonding. • At low temperatures, diffusion of hydrogen gas through silicon dioxide is the relevant mechanism.