Hermetic sealing of MEMS including lateral feedthroughs and room-temperature anodic bonding

Abstract

This paper reports on a method for hermetic sensor housing including lateral feedthroughs and room-temperature anodic bonding. The planarisation of the lateral feedthroughs, essential for the purpose of hermetic sealing, is realised by means of an etch-back process of (PE)CVD silicon dioxide combined with an additional spin-on glass (SOG) layer. The quality of the planarisation technique with regard to the main process variables is evaluated by FIB and tactile measurements. It is proven that 3D surfaces, represented here by the wiring and feedthrough layer, can be planarised almost completely. The applied bonding process features thin-films of a highly ionic conductive glass, enabling anodic bonding at unique conditions (room temperature and low applied voltages in order of 100 V). The general applicability of the packaging method is demonstrated with a setup of encapsulated, commercially available thermoelectric radiation sensors, which are used for the verification of the hermeticity of the setup as well.