A new model for vacuum quality and lifetime prediction in hermetic vacuum bonded MEMS

Abstract

In many MEMS applications the level of vacuum is a key issue as it directly affects the quality of the device, in terms of response reliability. Due to the unavoidable desorption phenomena of gaseous species from the internal surfaces, the vacuum inside a MEMS, after bonding encapsulation, tends to be degraded, unless a proper getter solution is applied. The in situ getter film (PaGeWafer®) is recognised to be the most reliable way to get rid of degassed species, assuring uniform, high quality performances of the device throughout the lifetime. Moreover, post process vacuum quality control and reliability for hermetic bonding is extremely important for overall device reliability and process yield. In this paper we will discuss the main factors that are critical in the attainment of vacuum and will present a novel calculation model that enables the prediction of vacuum level after bonding, making also possible the estimate of the lifetime. Furthermore, a new analytical method based on the residual gas analyses (RGA) will be presented that gives the main characteristics of the materials. Modeling and simulation work support the process optimization and system design.