Failure physics of ultra-thin SiO<inf>2</inf>gate oxides near their scaling limit

The present status and near future perspectives for ultra-thin SiO2gate oxide films are examined. With the ultimate physical thickness limit of 1 nm on the near horizon, leakage current and reliability issues are discussed. Our choice is to highlight the physics of the involved phenomena because we are convinced that a detailed knowledge of the involved physics is required for any accurate reliability forecasting exercise. The hypothesis of equilibrium conditions in the modelling of tunnel injection through ultra-thin oxide films is discussed. The present knowledge of the physics of degradation and breakdown is briefly reviewed, with particular emphasis on the open problems. The idea that the wear-out is a fluency- and energy-driven process is defended. The problem of monitoring the degradation of the oxide is addressed. The limitations of using indirect electrical monitors are presented and a method based on the analysis of statistical breakdown data is discussed. The status of the different breakdown modes (soft and hard) is considered. In this regard, it is concluded that the study of the mechanisms that control the severity of the breakdown events is one of the priorities in the field of ultra-thin oxide reliability. Finally, some attention is paid to the local probe techniques required for the atomic-scale characterization of the oxide properties.