Porosity content dependence of TDDB lifetime and flat band voltage shift by Cu diffusion in porous spin-on low-k

The porosity dependence of Cu diffusion into the spin-on low-k dielectric having the same matrix with various porogen contents was studied using time dependent dielectric breakdown (TDDB) and capacitance voltage (C-V) measurements. Abrupt changes of the time to dielectric breakdown and the flat-band-voltage shift were observed when the porosity of the low-k was between 20% and 30%. Such a characteristic agrees with positronium annihilation lifetime spectroscopy (PALS) data, which indicates that the interconnectability of the pores abruptly increased for porosity between 20 and 30%. All the results suggest that the interconnection of pores in the low-k dramatically reduces the reliability of interconnects. The activation energy of Cu diffusion in the spin-on low-k dielectric without porosity was calculated to be 1.51 eV.