The authors investigated the etching of grooves in low-k in Cu technology. Correlation between the line edge roughness (LER) and the time-dependent dielectric breakdown (TDDB) reliability for 100 nm pitch Cu interconnects was investigated. They controlled LER by using various gases to etch multilayer photoresist. CF3I gas was found to reduce LER better than conventional gases such as CF4 and CHF3 because CF3I has higher etching selectivity of photoresist against spin-on glass film. The LER did not affect measures of electrical performance such as wiring resistance, capacitance, and leakage current, but did affect TDDB lifetime because, according to their simulation, the electric field was strongly enhanced at curvatures in the interconnects. The maximum electric field (Emax) was also determined to evaluate the effect of LER on TDDB lifetime. All their results show that CF3I etching is promising for creating reliable Cu interconnects with smaller pitches.