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 m in width and was accelerated with longer chemical-mechanical polishing ͑CMP͒ 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 ͑SCC͒. 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.

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A scintillation counter telescope of aperture 0.47 m2 sr and incorporating layers of crossed neon flash tubes has been used to search for relativistic ei3 and 2e/3 quarks in the near-vertical cosmic radiation at sea level. Events were selected where the scintillator pulse heights were as expected for quarks and the corresponding flash tube records were studied.No events satisfied all the rigorous acceptance criteria and only upper limits can be given for the quark flux. These are, at the 90% confidence limits: < 1.15 x l 0 -l 0 c m -2 s -I s r -l for relativistic e/3 quarks and < 8.0 x c m -z s-I s r -l for relativistic 2e/3 quarks.

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