The damage induced by damascene patterning to low permittivity dielectrics, even when limited to a region near the sidewalls, leads to a significant increase of the effective interline dielectric constant in narrow spaced interconnects. A figure of merit, the electrical equivalent sidewall damage, is suggested to estimate the extent of dielectric damage from interline capacitance measurements, enabling a prompt extrapolation of the impact of such damage on ultranarrow interline spacings. The application of this model to lines embedded in a microporous SiOC: H dielectric reveals the presence of an electrical equivalent sidewall damage of about 10 nm. (C) 2004 The Electrochemical Society.