In-situ observation of grain boundary formation and strain gradient evolution during thermal fatigue of Cu grains within Cu interconnects

Interconnect copper lines represent a key component of microelectronic devices, which undergo severe thermal fatigue damage, resulting in a microstructural refinement and degradation of electrical parameters. The aim is to perform an in-situ characterization of crystal mosaicity and strain gradients across individual Cu grains located at surfaces and within interiors of Cu interconnects during cyclic heating. Using dark field X-ray microscopy at the ID06 beamline, the evolution of crystals' orientation across the grains and the formation of strain concentrations as well as grain boundaries will be characterized. For this purpose, a dedicated experimental setup including a power supply, a function generator and custom heating MEMS with Cu lines will be used. The pioneering experiment will provide a correlation between the sub-micron strain gradients, strain concentrations within individual Cu grains, as well as stepwise sub-grain formation as a function of the applied thermal cycles.