Hard and soft-breakdown characteristics of ultra-thin HfO/sub 2/ under dynamic and constant voltage stress

HfO/sub 2/ with EOT of 14 /spl Aring/ shows soft and hard breakdown behavior which consists of different Weibull distributions, area scaling factors, and acceleration factors. The thickness dependence of HfO/sub 2/ Weibull slope /spl beta/ indicates that the breakdown mechanism of HfO/sub 2/ is intrinsic. Similar to SiO/sub 2/, a steeper voltage acceleration factor of HfO/sub 2/ has been observed as thickness decreases. Unipolar AC voltage stress on MOS capacitors results in larger lifetime compared to constant voltage stress. This may be due to lower overall charge trapping as a result of short "on time" compared to the transition time and charge detrapping during the off period. The higher the frequency of the AC stress, the longer the time-to-breakdown.