Monocrystalline thin-film waferlevel encapsulation of microsystems using porous silicon

A new technology for thin-film MEMS encapsulation based on a monocrystalline silicon membrane and interfacial bonding is presented. The thickness of the membrane, used here, is 36 μm. It is produced on a dedicated wafer using a further development of the “Advanced Porous Silicon Membrane (APSM)” Process. The membrane wafer is attached on waferlevel to a MEMS wafer by glass-frit bonding. Before and during bonding the membrane is mechanically connected to its substrate by vertical anchors. Finally, the substrate is detached by cracking the anchors. Detaching the substrate is optimized by a variation of the lateral and the vertical anchor geometries. The new encapsulation technology enables a very low sensor height by a hermetically sealed monocrystalline MEMS-Cap while using well known technologies from mass production. Hence, a cost-efficient all-purpose thin-film encapsulation is presented. We demonstrate the new encapsulation technology by a capped absolute pressure sensor.