HOT-CARRIER RELIABILITY LIFETIMES AS PREDICTED BY BERKELEYS MODEL

Hot-carrier effects pose a significant reliability problem in modern M OS processes. An accurate method of predicting hot-carrier lifetimes i s essential for the development of fine-geometry MOS technology. A hot -carrier degradation model developed by C. Hu et al. at the University of Berkeley is widely used to predict device lifetimes at given opera ting conditions from the results of accelerated tests. This paper demo nstrates a new method of performing hot-carrier stress measurements wh ich satisfies the key demand of this model. This method involves adjus ting device drain voltage in order to maintain a constant ratio of sub strate to drain currents. This method is employed to show that the Ber keley model makes a minimum lifetime prediction which is about an orde r of magnitude too short at accelerated stress conditions. This casts doubt on the suitability of the Berkeley model for use in circuit reli ability simulation and for use in setting industrial reliability bench marks. A new understanding of the importance of the gate-source voltag e during hot-carrier reliability characterization using the Berkeley m odel is also discussed.