The role of spacer-bottom oxide on the hot carrier reliability in sub-halfmicron LDD nMOSFET with nitride spacer

We report a method to optimize the device lifetime of LDD nMOSFET under hot carrier degradation by controlling the thickness, T-ox of spacer-bottom ox ide when nitride spacer is employed. The device is fabricated with T-ox=3.0 , 4.5, and 6.8nm, for the gate length and oxide thickness of 0.3 mu m and 6 .5 nm, respectively The experimental results show enhanced device lifetime by orders of magnitude as T-ox decreases. The device simulation also reveal s the decrease in channel electric field as T-ox decreases due to the fring ing field effect. The poor interface condition of the nitride/oxide, howeve r, is known to exert a detrimental effect when T-ox is quite small. Employi ng the fitting parameter expressions developed earlier for the power law, t he condition for optimum reliability is obtained in terms of spacer-bottom oxide thickness. The process window for the device lifetime is presented, t he result of which is in accordance with the experimental data.