Quantitative Determination of the Mechanical Stresses in BEoL Films and Structures on Si Wafers with Sub-micron Spatial Resolution by fibDAC

Abstract

ABSTRACTThe fibDAC stress analysis method, a new tool for local stress measurement, has been applied to patterned BEoL structures after being validated at complete films by established industrial methods like wafer bow measurement. The new tool uses focused ion beam (FIB) to mill a narrow trench of down to 30 nm width into the surface of the structure under investigation to trigger stress relief in its vicinity. Capturing the corresponding deformation by high resolution SEM micrographs and local digital image correlation, the original stress can be determined by simulating the stress relief process by automated finite element analyses. Simultaneously, the extraction of key material parameters of the film like Young’s modulus and Poisson’s ratio is possible.The spatial resolution of the fibDAC stress analysis method is 1 μm and better. It has been demonstrated at arrays of BEoL interconnects. The magnitude of the local stresses inside the metal traces has been shown to be substantially different to those occurring in the dielectrics between the lines. Such a spatial resolution clearly outperforms all established industrial methods.