The change in leakage current in porous low-k interconnect dielectrics (LKDs) arising from time-dependent dielectric breakdown (TDDB) has been investigated. Using periodic measurements of temperature-dependent IV curves and photocurrent decay during voltage bias stress the apparent change in trap density and conduction mechanism in LKDs are investigated. A substantial change in the temperature-dependence of the current is observed, suggesting a move from a thermally excited conduction process to a tunnel-like or percolative process. This change is correlated with a large increase in trap density after long-term bias stress, consistent with a trap to trap tunneling interpretation. However, throughout the high-voltage bias stress, the leakage current continues to obey a √E field dependence. © 2012 IEEE.