Gate oxide protection and ggNMOSTs in 65 nm

Unexpected functional failures were found in the core of an IC, processed in a 65 nm technology with 1.8 nm gate oxide after MM testing, although a comprehensive rail-based protection scheme was applied. Failure analysis was performed including Obirch, backside de-processing, and SEM analysis to locate the failure in the gate oxide of several core NMOS transistors. Careful TLP measurements on NMOSTs with 1.8 nm oxides yields a mean BVox = 6.06 V and standard deviation of 0.18 V, after correction for MM test conditions. Comparison with a mean Vt1 = 5.35 V and a standard deviation of 0.15 V for ggNMOSTs shows that the tails of the BVox and Vt1 distributions overlap. This implies that connecting a gate to a drain diffusion does not guarantee adequate protection for a 1.8 nm gate oxide in a 65 nm technology.