Stress corrosion cracking of Cu interconnects during CMP with a Cu/porous low-k structure

Porous low-k materials are required in the construction of 45 nm node large-scale integrated devices. However, the extremely low Young's modulus values of these materials results in a high number of previously unreported defects. A porous low-k film stacked with a dense low-k film showed pronounced cracking in its Cu wiring, which was concentrated in isolated lines 0.18 mu m in width and was accelerated with longer chemical-mechanical polishing (CMP) times. Denser lines showed less cracking and the single structure of a dense low-k film showed no cracking. We hypothesized that this cracking might be categorized as stress corrosion cracking (SCC). Accordingly, we investigated the relation between stress and corrosion in certain kinds of slurry. We have also researched the effects on corrosion of temperature and various metals. In all of the slurry that we tested, tensile stress increased corrosion current in Cu samples. Furthermore, both finite element method analysis of stress during CMP and measurements of friction on the Cu/low-k surface by scanning probe microscopy indicated concentration of stress on low-k materials, especially at the edges of isolated wiring. Thus, we concluded that stress enhances corrosion during CMP and that there was a high possibility of SCC. (c) 2005 The Electrochemical Society. All rights reserved.