A new algorithm for transforming exponential current ramp breakdown distributions into constant current TDDB space, and the implications for gate oxide Q/sub BD/ measurement methods

Abstract

Charge-to-breakdown (Q/sub BD/) is one of the manufacturing parameters that is used as a measure of oxide quality. In this work, the influence of the measurement conditions on Q/sub BD/ is examined, as well as the relationship between Q/sub BD/ and oxide thickness. Using oxides ranging from 45 /spl Aring/ to 80 /spl Aring/, two Q/sub BD/ measurement methods are employed: constant current stress (CCS) and an exponential current ramp (ECR). A variety of current densities (for constant current stress) and step durations (for exponential current ramp) are studied. It is shown that not only does Q/sub BD/ depend on oxide thickness, but that Q/sub BD/ depends strongly on the measurement conditions, and that, depending on the test conditions, Q/sub BD/ can increase or decrease as the oxide thickness decreases. It is also shown that there is a strong agreement between the Q/sub BD/ measured with a constant current stress and the Q/sub BD/ measured with an exponential current ramp. Finally, an algorithm is proposed for transforming the Q/sub BD/ distribution obtained from a series of exponential current ramps into the Q/sub BD/ and/or t/sub BD/ domains of constant current stressing.