In-situ strain measurement with metallic thin film sensors

With increasing importance of 3D packaging systems, more and more dies will be stacked on top of each other and connected using through silicon vias (TSVs) and solder bumps. In-situ stress measurements near these bump pads are important to help understand the evolution of die stresses associated with the packaging process. Unlike piezoresistive doped Si sensors that require high-temperature processing, metal-based sensors use low-temperature fabrication processes. The sensor fabrication uses standard cleanroom processes such as UV lithography and physical vapor deposition. In this paper, thin-film micro-scale metallic (Ni/Cr) resistors have been studied with different design dimensions including gauge width, film thickness, and spacing between the lines in the serpentine pattern. Silicon test strips with sensors have been subjected to four-point bend testing, and finite-element simulations have been carried out to mimic the four-point bend testing as well as to determine stress contours where the sensors are placed.