Assessment ofVacuumLifetime innL-Packages

Vacuumwaferbonding technology provides a number ofveryeffective techniques toproduce low-cost, hermetic sealed packages formicromachined sensorsandactuators. Besidetheprotection of the devicefrom outside environmental stresses, thepackage mustalsoprovide a cavity ambient compatible withthedevice performance and reliability. Thepaperreviews theshortcomings ofexisting fine leak tests toassessthestability ofthecavity atmosphere overlongtime. A new ultra-fine leaktestbasedon Q-factor monitoring was developed that hasthepotential tobeused forin-line critical leakratetesting on waferlevel before device singulation. Withtheexampleofa poly-silicon resonating microsensor, itisshownthatthetestissensitive enough topredict thecavity pressureforademanded device lifetime of15years.Theroleofan integrated thinfilm getter instabilizing thecavity vacuum andextending device lifetime isdiscussed.