The dielectric material dependence of stress and stress relaxation on the mechanism of stress-voiding of CU interconnects

The line width dependence of stress in damascene Cu was examined experimentally as well as with a numerical simulation. The measured hydrostatic stress was found to increase with increasing line width. The larger stress in an interconnect with large dimension is attributed to the larger grain size, which induces higher growth stress in addition to thermomechanical stress. A stress model based on microstructure was constructed and the contribution of the growth and thermal stress of the damascene lines were quantified using finite element analysis. It was found that the stress of the via is lower than that of wide lines when both the growth stress and thermal stress were considered. Therefore, the characteristic failure mode, i.e. voiding in a via neighboring a wide line, was successfully explained by our stress model.