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SiOCH low-k dielectrics introduction in copper interconnects associated to the critical dimensions reduction in sub 45 nm technology nodes is a challenge for reliability engineers. Circuit wear-out linked to low-k dielectric breakdown is now becoming a major concern. With the reduction of the line to line spacing, the control of the copper line topology is becoming a first order parameter governing the low-k dielectric reliability. Improving the low-k reliability requires to discriminate each topological effect and quantify its impact on the lifetime at product level. This paper demonstrates the importance of the copper line shape, of the line edge roughness (LER) and of the median line to line spacing variation within the wafer on the low-k dielectrics reliability. Moreover, simple analytical models are described to quantify each effect on the Time-Dependant Dielectric Breakdown (TDDB) and particularly on the final product lifetime. Some advices are given to avoid erroneous lifetime projection.