The electronic properties of thin film low-κ interlayer dielectric (ILD) and etch stop layers (ESL) are important issues in present day ULSI development. Low-κ ILD and ESLs with dielectric constants significantly less than those of SiO2 and SiN are utilized to reduce capacitance induced RC delays in ULSI circuits. Leakage currents, time dependent dielectric breakdown (TDDM) and stress induced leakage currents (SILC) are critical problems that are not yet well understood in ILD. A topic of current interest is ultraviolet light (UV curing) of low-k materials. We have made electron spin resonance (ESR) and current density versus voltage measurements on a moderately extensive set of dielectric/silicon structures involving materials of importance to low-k interconnect systems. Most of the dielectrics studied involve various compositions of SiOC:H. In addition we have also made measurements on other dielectrics including SiO2, SiCN:H and SiN:H.