Zero-level packaging for (RF-)MEMS implementing TSVs and metal bonding

This paper presents a 0-level packaging technology for (RF-)MEMS implementing vertical feedthroughs or through-Si-via's (TSVs) and metal bonding. A thinned capping substrate (100μm thick) equipped with Cu-coated TSVs is bonded to a MEMS substrate. The vertical feedthroughs lead to a smaller footprint and make the package ready for 3D integration. The CuSn/Cu metal bonding provides a hermetic seal for the package. A full fabrication process for thinned Caps with “chamfered” shaped TSVs (70-120μm diameter) has been developed. Highly yielding TSVs (close to 100%) displaying a resistance of a single via of less than 10mQ have been obtained. The performance of traversing transmission lines (CPWs) patterned on the MEMS wafer (implemented in 1μm thick Cu and connected with the external terminals via the microbumps and the TSVs) has been measured. FEM based thermo-mechanical modelling is applied in order to evaluate the critical stress points and to estimate the Cap-to-MEMS die deflection under an external pressures.