Microstructure and stress characterization around TSV using in-situ PIT-in-SEM

Many studies have characterized the residual stress around TSV by using direct experimental measurement, finite element simulation, and microstructural analysis. The experimental approach is very useful in its speed and direct compatibility with processing, but cannot be used under all circumstances. Instrumented indentation testing, on the other hand, has many advantages: easy sample preparation and simple algorithms lead to a simple characterization of the micropartial stress between samples with the load difference at the same indentation depth. However, the current indentation method has the weak point that we cannot measure the residual stress when the stress-free state does not exist. Here we suggest a new algorithm to measure residual stress without knowledge of the stress-free state by analyzing the plastic pile-up mechanism around the contact area due to residual stress and using the invariant indentation properties obtained from the stressed state. We introduced this new algorithm into TSV-stress analysis to obtain the KOZ (keep out zone). In addition, we used in-situ SEM (scanning electron microscope) indentation to characterize more accurately the KOZ in the silicon around TSV, even in very minute areas.