Thermo-mechanical stress induced voiding in a tungsten-AlCu interconnect system

This paper presents a novel stressing technique for investigation of via quality and integrity in tungsten-AlCu interconnect systems. This stressing technique induces a new manifestation of the stress induced voiding failure mechanism for a tungsten-AlCu interconnect system. This voiding is caused by mechanical stress cycling at the tungsten-metal interface. This mechanical stress cycling results from the Joule heating induced by the AC current stress. Finite element analysis numerical simulations were performed, and the simulated mechanical stress results correlated well with physical failure analysis results. The interaction of these mechanical stresses with localized aberrations in interfacial quality causes the metal voiding to occur. It is demonstrated that use of cleaner ILD and metal etching techniques reduce the failure rate due to this mechanism