We evaluate the dielectric reliability performance of 21 nm pitch interconnects integrated in a dense low-k and using a barrierless Ru fill scheme. We show our line-to-line and tip-to-tip TDDB pass 10 years of lifetime at 0.75 V for technology relevant line lengths and number of tips, respectively. Intrinsic dielectric breakdown without metal drift is demonstrated using BTS-TVS measurements. We also investigate the impact of dielectric scaling towards lower dimensions using planar capacitor structures. We observe an increasing field acceleration factor with decreasing thickness possibly suggesting different, slower, degradation mechanisms being present in the thinner dielectrics leading towards more reliability margin for scaled interconnects.