The time dependent dielectric breakdown (TDDB) of four organo-silicate-glass (OSG) films with varying porosity (k=2.0, 2.5, 2.8 & 3.0) was investigated using metal-insulator-semiconductor (MIS) capacitors. Without any barrier, the dielectrics show lower TDDB-lifetimes under Cu ion drift conditions, where the OSG-2.8-film exhibits a better performance. Other results are that the damage caused by TaN/Ta barriers doesn't significantly change the TDDB performance and that the OSG-2.0-film showed excellent TDDB lifetimes.