INVESTIGATION OF THE INFLUENCE OF RAMPED VOLTAGE STRESS ON INTRINSIC T(BD) OF MOS GATE OXIDES

This study investigates the influence of a pre-stressing ramped voltag e stress prior to a constant voltage stress on the time to breakdown. Constant voltage stress and combined ramped/constant voltage stress me asurements were performed on six MOS gate oxide thicknesses. The time to breakdown distributions were compared and an increase of the time t o breakdown for pre-stressed oxides was observed in some cases. A furt her analysis of the current-time characteristics gave conclusions abou t the trapping properties of the oxide. It was found that the initial positive charge build up in the oxide is an important indicator for de gradation which must be considered for highly accelerated reliability measurements on pre-stressed oxides. Since common understanding of oxi de breakdown and models for breakdown mechanisms cannot describe all o f the experimental results a qualitative model is proposed. (C) 1997 E lsevier Science Ltd.