The influence of decoupling capacitor on the discharge behavior of fully silcided power-clamped device under HBM ESD event

In this paper, a new electrostatic-charge discharge (ESD) phenomenon is found. It occurs at the power pad during the human-body model (HBM) zapping event. We call this new ESD phenomenon as the charged capacitor model (CCM). Unlike the IO pad under the HBM event, the power pad under the HBM zapping event doesn't behave the same with IO pad if it is in parallel with a large decoupling capacitor. Before the power-clamped device (Pdev) turns on, the charges will flow from the HBM discharge head to the decoupling capacitor below the power line. After the Pdev turns on, the decoupling capacitor will discharge its stored charges to give the additional stress current to the Pdev. Compared to the HBM event, the rising time of the CCM is much shorter since the decoupling capacitor is connected to the Pdev by a metal bus line. Under such short rising time pulse, only few regions of the device can be turned on to discharge the charges, resulting in the HBM failure threshold voltage of the power pad much smaller than the desired voltage level.