Reliability characteristics of thin porous low-K silica-based interconnect dielectrics

The dielectric breakdown field (EBD) and the time-dependent-dielectric-breakdown (TDDB) of eight different low-K films with porosities between 3% (K=3.2) and 50% (K=1.8) and thicknesses between 15 and 60 nm were investigated using imec's planar capacitors (p-cap) test vehicle. EBD values decrease linearly with porosity to reach 6MV/cm at 50% porosity. The analogous Organo-Silicate Glass (OSG) films show a similar field acceleration factors independently of porosity. An OSG 2.0 film with 45% porosity and a periodic mesoporous organosilica (PMO) 1.8 film, both sealed with 12-nm OSG 3.0 sealing also showed the same field acceleration factor. On the other hand, the corresponding Weibull slopes vary and decrease linearly with porosity, which is in agreement with the percolation model. Also, the Weibull slopes decrease linearly with dielectric thickness. Extrapolating those data and analyzing the maximum allowed electrical fields to meet 10-years lifetime (EMAX), critical dielectric spacing are discussed as a function of porosity. It is shown that for 20-nm spacing remedial measures are required for porosities >30%.