MEMS packaging reliability assessment: Residual Gas Analysis of gaseous species trapped inside MEMS cavities

Abstract The reliability of MEMS sensors or actuators such as accelerometers, gyroscopes, resonators, RF switches, microbolometers… is critically dependent on the vacuum level and on the nature of the gaseous species present inside the MEMS cavity (∼1 mm3 or less, usually in the 10−2–10−3 mbar vacuum range after sealing by Wafer Level Packaging process). Although a lot of methods have been explored, the Residual Gas Analysis (RGA) method – however destructive-reveals to be an interesting technique to determine the possible sources of gaseous species present in the MEMS cavity or outgassed by materials, in order to assess to which extent a given packaging technology is capable of maintaining the required environmental conditions all along the device lifetime. This paper introduces results recently achieved with two specifics RGA test benches developed at CEA–LETI (i) to analyze very small amounts of gases trapped inside MEMS cavities, and (ii) to assess the outgassing or pumping behavior of bulk or getter materials. These Ultra High Vacuum (UHV) RGA equipments operate with a residual background pressure level in the 10−10 mbar range and use Quadripolar Mass Spectrometers (QMS) for gas analysis. Experimental results confirm that the RGA technique is successfully used to identify the nature and proportions of gases outgassed by materials or trapped in cavities as small as 1 mm3 under a residual pressure lower than 10−2 mbar.