Evaluation of Dielectric Reliability of Ultrathin HfSiOxNy in Metal-Gate Capacitors

Abstract

We have studied the electrical and breakdown characteristics of 5 nm-thick HfSiO x N y (Hf/(Hf + Si) =∼0.43, nitrogen content = 4.5-17.8 at.%) in Al-gate and NiSi-gate capacitors. For Al-gate capacitors, the flat-band shift due to positive fixed charges increases with the nitrogen content in the dielectric layer. In contrast, for NiSi-gate capacitors, the flat band is almost independent of the nitrogen content, which is presumably controlled by the quality of the interface between NiSi and the dielectric layer. The leakage current markedly increases with nitrogen content. Correspondingly, although the time-to-soft breakdown, t SBD , gradually decreases with increasing nitrogen content, the charge-to-soft breakdown, Q SBD , increases with the nitrogen content. For Al-gate capacitors, the Weibull slope of time-dependent dielectric breakdown (TDDB) under constant voltage stress (CVS) remains constant at ∼2 for a nitrogen content of up to 12.5 at.% and then decreases to unity at 17.8 at.%. This must be a condition critical to the formation of the percolation path for breakdown. In contrast, for NiSi gate capacitors, a Weibull slope smaller than unity was obtained, suggesting that structural inhomogeneity, involving defect generation, is introduced during the NiSi gate fabrication, but this negative impact is reduced with nitrogen incorporation.