A new variation plot to examine the interfacial-dipole induced work-function variation in advanced high-k metal-gate CMOS devices

The interfacial dipole and bulk trap in HKMG stack have been found to be significant to the work function variation (σV_WF), in addition to the metal grains. In order to differentiate their effects on σV_WF, a new variation plot is proposed and the dipole and trap effects can be distinguished. Here, we propose a simple experimental method to separate the effects of MG/HK and HK/IL interfacial dipoles. In pMOSFET, HK/IL dipoles dominate HK induced variation; MG/HK dipoles are dominant in nMOSFET. However, in terms of the reliability test, after PBTI stress, HK bulk traps play a major role in the variation of nMOSFET, while after NBTI, HK/IL dipoles are strengthened by hydrogen bonds and still dominant in work function variation of pMOSFET. Design guideline is provided to deal with the passivation of high-k traps by nitrogen concentration and the improvement of variability in HKMG CMOS devices.