3D MEMS high vacuum wafer level packaging

The main objective of this work has been to demonstrate the feasibility of combining hermetic high vacuum level MEMS packaging (vacuum target is below 10^-2 mbar) with 3D feed trough interconnections on 200 mm wafers. A vacuum Wafer Level Packaging (WLP) solution for MEMS will be presented. This solution is assessed on a test vehicle based on a MEMS resonator processed in a silicon wafer hermetically sealed to a glass wafer by an anodic bonding process. The resonator is used to characterize the vacuum inside the packaging by measuring the Quality factor of the resonator (Q factor). At first, a Through Glass Via (TGV) technology has been used. Thanks to this technology the MEMS can be electrically connected to the ASIC by wire bonding through the front side of the assembly. Then, a Through Silicon Via (TSV) solution has been developed through the backside of the assembly that makes possible to directly connect the MEMS to the PCB by flipchip bonding. Both technologies will be described in this paper. A specific measurement method of the Q factor through the glass has been developed using classical optical microscopy. This allows following the Q factor evolution during TSV process. The Q factor is also determined by electrical tests measurement at wafer level and chip level at the end of the process flow.