Problems of Wafer Level Packaging of Sensitive Elements for MEMS

Abstract

The key problems of technological processes used in the manufacture of sensitive elements (SE) of micromechanical accelerometers (MMA) of pendulum and compensation types with assembly and sealing at the level of plates are considered. A technology for the formation of dielectric stoppers has been proposed, which made it possible to increase the yield of suitable ones by eliminating the effect of "sticking" without affecting the output characteristics of MMA. It was found that such SE can withstand multiple impact overloads up to 700 g. The characteristics of the pendulum SE are given for the range of measured accelerations ±1 g and for the acceleration range ±10 g. It is shown that the silicon-over-cavity (SOC) technology used for the manufacture of compensating-type SE accelerometers is much more complicated than the pendulum-type SE technology, but has a better yield with high repeatability of characteristics. The main stages of SOC technology are shown: the stage of highly anisotropic vacuum-plasma etching of a thin silicon wafer; stage of anode bonding with a sealing glass cover; the stage of manufacturing hermetic contacts. Modes have been determined that make it possible to carry out highly anisotropic vacuum-plasma etching of the SE with etching walls that have a deviation from the vertical of only ±0.15 µm at a depth of 60 µm in grooves 4 µm wide, both for the pendulum and for the fixed part of the accelerometer. The SOC technology makes it possible to manufacture sensitive elements not only for MMA, but also for micromechanical gyroscopes. It is shown that SE accelerometers of compensation type can serve as micro-sized vacuum sensors when testing the efficiency of the getter coating in small-sized vacuum volumes.