Failure physics of ultra-thin SiO2 gate oxides near their scalinglimit

Abstract

The present status and near future perspectives for ultra-thin SiO2 gate oxide films are examined. With the ultimate physical thicknesslimit of 1 nm on the near horizon, leakage current and reliability issues arediscussed. Our choice is to highlight the physics of the involved phenomenabecause we are convinced that a detailed knowledge of the involved physics isrequired for any accurate reliability forecasting exercise. The hypothesis ofequilibrium conditions in the modelling of tunnel injection through ultra-thinoxide films is discussed. The present knowledge of the physics of degradationand breakdown is briefly reviewed, with particular emphasis on the openproblems. The idea that the wear-out is a fluency- and energy-driven process isdefended. The problem of monitoring the degradation of the oxide is addressed.The limitations of using indirect electrical monitors are presented and amethod based on the analysis of statistical breakdown data is discussed. Thestatus of the different breakdown modes (soft and hard) is considered. In thisregard, it is concluded that the study of the mechanisms that control theseverity of the breakdown events is one of the priorities in the field ofultra-thin oxide reliability. Finally, some attention is paid to the localprobe techniques required for the atomic-scale characterization of the oxideproperties.