Abrupt breakdown in dielectric/metal gate stacks: a potential reliability limitation?

In downscaled poly-Si gate MOSFET devices reliability margin is gained by progressive wearout. When the poly-Si gate is replaced with a metal gate, the slow wearout phase observed in ultrathin SiON and HfSiON dielectrics with poly-Si gate disappears, and with it, the reliability margin. We demonstrate for several combinations of dielectric and gate materials that the large abrupt current increase (ΔI) as compared to poly-Si is not likely due to process issues, but is an intrinsic property of the dielectric/metal gate stack. The occurrence of large ΔI is a potential limitation for the reliability of metal gate devices.