Impact of time dependent dielectric breakdown and stress-induced leakage current on the reliability of high dielectric constant (Ba,Sr)TiO/sub 3/ thin-film capacitors for Gbit-scale DRAMs

摘要

Time dependent dielectric breakdown (TDDB) and stress-induced leakage current (SILC) are investigated for the reliability of (Ba,Sr)TiO/sub 3/ (BST) thin films. Both time to breakdown (T/sub BD/) versus electric field (E) and T/sub BD/ versus 1/E plots show universal straight lines, independent of the film thickness, and predict lifetimes longer than 10 y at +1 V for 50 nm BST films with an SiO/sub 2/ equivalent thickness of 0.70 nm. SILC is observed at +1 V after electrical stress of BST films; nevertheless, 10 y reliable operation for Gbit-scale DRAMs is predicted in spite of charge loss by SILC. Lower (Ba+Sr)/Ti ratio is found to be strongly beneficial for low leakage, low SILC, long TBD, and therefore greater long-term reliability. This suggests a worthwhile tradeoff against the dielectric constant, which peaks at a (Ba+Sr)/Ti ratio of 1.05.