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

Charge-to-breakdown (Qbd) 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 Qbd is examined, as well as the relationship between Qbd and oxide thickness. Using oxides ranging from 45 to 80 A, two Qbd measurement methods are employed: constant current stress (CCS) and an exponential current ramp (ECR). A variety of current densities (for the constant current stress) and step durations (for the exponential current ramp) are studied. It is shown that not only does Qbd depend on oxide thickness, but that Qbd depends strongly on the measurement conditions, and that, depending on the test conditions, Qbd can increase or decrease as the oxide thickness decreases. It is also shown that there is a strong agreement between the Qbd measured with a constant current stress and the Qbd measured with an exponential current ramp. Finally, an algorithm is proposed for transforming the Qbd distribution obtained from a series of exponential current ramps into the Qbd and/or t BD domains of constant current stressing. © 1999 Elsevier Science Ltd. All rights reserved.