Failure Analysis of Wire Bonding on Strain Gauge Contact Pads using FIB, SEM and Elemental Mapping

Stacks consisting of titanium, platinum, and gold layers constitute a popular metallization system for the bond pads of semiconductor chips. Wire bonding on such layer stacks at different temperatures has extensively been investigated in the past. However, reliable information on the bondability of this metallization system after a high-temperature sintering process is still missing. When performing wire bonding after pressure sintering at, e.g., 875 °C, bonding failures may occur that have to be identified and analyzed. In the present study, focused ion beam (FIB), scanning electron microscopy (SEM), and elemental mapping are utilized to characterize the root cause of failure. As probable root cause, infusion of metallization layers is found which causes an agglomerate formation at the interface of approximately 2 micron height difference on strain gauge contact pads and possibly an inhomogeneous mixing of layers as a consequence of the high-temperature sintering process. Potential treatment to tackle this agglomeration with the removal of above mentioned height difference during the process of contact pad structuring and alternative electrical interconnect methodologies are hereby suggested in this paper.