Synchrotron measurement of the effect of dielectric porosity and air gaps on the stress in advanced Cu/Low-k interconnects

The stress of Cu interconnects embedded in advanced ultra-low-k (ULK) dielectrics was studied for different porosities. Interconnects formed a high porosity material result in a lower stress due to relaxation in the plane. This effect is less significant for narrow lines, where in-plane relaxation is reduced by the dense narrow spacing. The stress in isolated lines was found to be independent of dielectric porosity. We also studied air gap structures, showing the lowest stress. This work will be useful when interpreting reliability failure mechanisms and calibrating finite element models to predict stress in devices of future technology nodes.