For the past several years, there have been debates that backend IMD-TDDB Sqrt(E) lifetime model is too conservative and has become the constraint for BEOL technology scaling. In this study, it is demonstrated that low bias TDDB model could be varied from conservative E to aggressive Power-Law or 1/E model, depending on the material characteristics of extreme low-k (ELK), etch stop layer (ESL), and the process conditions. Based on J-V, I-t and defect generation rate analysis, Sqrt(E) model is adequate for high-bias TDDB; however, hydrogen release, initiated by low-bias with extremely low current conduction for film with better process, explained the TDDB lifetime performance improvement that better fits with the Power-Law lifetime model. The voltage acceleration factor from hydrogen release theory is consistent with that of TDDB data. Based on various clustering factors under wide range of TDDB stress voltages combined with the ELK chemical bonding analysis, we proposed an inhomogeneous percolation model which is an important factor in prolonging the TTF at medium or low bias contributes to more aggressive Power-Law or 1/E lifetime models.
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