Soft Breakdown of Ultra-Thin Gate Oxide Layers

The dielectric breakdown of ultra-thin 3 to 4 nm SiO2 layers used as a gate dielectric in poly-Si gate capacitors is investigated with tunnel current stressing. A soft breakdown phenomenon is demonstrated for these ultra-thin gate oxide layers that corresponds with an anomalous increase of the stress induced leakage current and the occurrence of fluctuations in the current. The occurrence of soft breakdown in these ultra-thin gate oxide layers however is difficult to detect during a standard high-field time dependent dielectric breakdown (TDDB) test.