Low Weibull slope of breakdown distributions in high-k layers

The reliability of various Al/sub 2/O/sub 3/, ZrO/sub 2/ and Al/sub 2/O/sub 3//ZrO/sub 2/ double layers with a physical oxide thickness from 3 nm to 15 nm and TiN gate electrodes was studied by measuring time-to-breakdown using gate injection and constant voltage stress. The extracted Weibull slope /spl beta/ of the breakdown distribution is found to be below 2 and shows no obvious thickness dependence. These findings deviate from previous results on intrinsic breakdown in SiO/sub 2/, where a strong thickness dependence was explained by the percolation model. Although promising performance on devices with high-k layers as dielectric can be obtained, it is argued that gate oxide reliability is likely limited by extrinsic factors.