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Considering percolation path growth in low-k dielectric TDDB measurements

The failure time of low-k dielectrics during TDDB measurements consists of the time of percolation path formation and the time of percolation path growth. However, during conventional high voltage TDDB tests, percolation path growth is artificially enhanced due to local overstress. By both using a dedicated test vehicle, so-called p-caps, and damascene samples and by using controlled experiments, with a combined constant current and constant voltage stress approach, we focus on the understanding of the percolation path growth characteristics and on the quantification of the percolation path growth time. It is shown that the path growth time is not influenced by the original defect density in the low-k dielectrics and is only little impacted by temperature and dielectric thickness. The percolation path growth time passes 10 years at operating conditions in all the tested samples. We show that, in certain specific situations, this time can serve as an extra reliability margin for low-k dielectric TDDB. However, this margin might be reduced when multiple percolation paths grow at the same time.