IWLPC (Wafer-Level Packaging) Conference Proceedings

Reliability of TSV and Wafer-Level Bonding for a 3D Integrable SOI Based MEMS Application

Authors: Torleif André Tollefsen, Maaike M. Visser Taklo, Thor Bakke, Nicolas Lietaer, Per Dalsjø, and Jakob Gakkestad
Company: SINTEF ICT, Vestfold University College, and Norwegian Defence Research Establishment (FFI)
Date Published: 11/5/2012   Conference: IWLPC (Wafer-Level Packaging)

Abstract: The reliability of a 3D integrable miniaturized wafer-level encapsulated MEMS acceleration switch has been studied. The through silicon vias (TSV) and the benzocyclobutene (BCB) bonding process used for the encapsulation were examined regarding the survival of various environmental stress tests. Sample groups using different metallization schemes (NiCr or TiW as adhesion layer/ diffusion barrier for the Au metallization) and different parameters for the bonding (temperature and environment) were fabricated. Samples were exposed to low temperature storage (LTS) at -55 °C, high temperature storage (HTS) at +230 °C and thermal shock cycling (TSC) between -55 and 125 °C. Four-point resistance measurements of daisy chain structures, die shear tests, and cross-sectioning were done to characterize the TSVs and the bond properties associated with the different sample groups and tests.

The initial bond strength was high for all sample groups (above 24 MPa). LTS and TSC reduced the bond strength of NiCr/Au metallized samples (more than 50% after LTS), while it remained unchanged for TiW/Au metallized samples. Lowering the bonding temperature from 250 °C to 200 °C increased the bond strength by 10 to 20 %, assumedly due to less residual stress. The electrical resistance of the TSVs with NiCr/Au metallization increased after HTS, while it remained low both after HTS and TSC for the TiW/Au samples. The demonstrated TSV technology with TiW/Au metallization and encapsulation by BCB bonding proves to be well suited for 3D MEMS packaging for harsh environment applications.

Key Words: 

BCB, TSV, MEMS switch, harsh environment, wafer-level 3D integration.

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