Evaluation of Dielectric Reliability of Ultrathin HfSiO_xN_y in Metal Gate Capacitors(Session 9A Silicon Devices VI,AWAD2006)

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We have studied electrical and breakdown characteristics of 5nm-thick HfSiO_xN_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 is increased with nitrogen content in the dielectric layer. But in contrast, for NiSi-gate capacitors, the flat band is almost unchanged with the nitrogen content, which is presumably controlled by the quality of the interface between NiSi and the dielectric layer. The leakage current is markedly increased with an increase in the nitrogen content. Correspondingly, although the time to soft-breakdown, t_<SBD>, is gradually decreased with increasing nitrogen content, the charge to soft-breakdown, Q_<SBD>, is increased with the nitrogen content. For Al-gate capacitors, the Weibull slope of TDDB (time-dependent dielectric breakdown) under constant voltage stress (CVS) remains constant 〜2 in the nitrogen content up to 12.5at.% and then decreased down to unity at 17.8at.%. It must be a condition critical to the formation of the percolation path for breakdown. In contrast, for NiSi gate capacitors, the Weibull slope smaller that unity was obtained, suggesting that structural inhomogeneity involving in defect generation is introduced during the NiSi gate fabrication but such a negative impact is reduced with nitrogen incorporation.
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2006-06-26