Challenges for structural stability of ultra-low- k-based interconnects

Severe mechanical loads during multilevel metallization manufacturing, such as repeated thermal cycles and chemical–mechanical planarization processes, can induce high stresses in interconnect structures. It is shown that such stresses in ultra-low- k-based interconnect structures can experience relaxation either through interfacial adhesion failure or through the compliance of the porous dielectrics. Adhesion quality can be improved by careful interface engineering aimed at enhancing both the fundamental and the practical work of adhesion. However, the low stiffness of porous ultra-low- k films limits the range of loads in which mechanical responses remain elastic. Moreover, such films can show a time-dependent response (creep). Therefore, stresses in device fabrication and operation need to be kept under control to ensure structural stability.