Dielectric relaxation studies of ion diffusion into low-k dielectrics

High speed interconnects in advanced integrated circuits require ultra-low-k dielectrics to reduce the RC time constant. Reduction of the dielectric constant in these films is typically achieved via incorporation of nanopores in materials containing silicon, carbon, oxygen and hydrogen (SiCOH). Trap states build-up as dielectric breakdown is approached and increased leakage is observed. To understand the mechanism of breakdown we study nanoporous SiCOH films of k=2.4 to 2.7 primarily using dielectric relaxation. Dielectric films, in the thickness range of 40 nm, are incorporated into interwoven capacitor structures. To quantify dielectric relaxation in the pre-breakdown regime, capacitance and dielectric losses are determined as a function of frequency and temperature. Through these dielectric measurements, we have obtained activation energies in the range of 0.1-0.2 eV for humidified and annealed capacitors; and 0.9-1.2 eV for copper ion incursion into the dielectric. We also deduce a charge center density of 10$^{15}$/cm$^3$. Our measurements provide an estimate of the impurity content and changes in activation energy with annealing and other fabrication parameters.