Impact of plasma post-nitridation on HfO2/Al2O3/SiGe gate stacks toward EOT scaling

Abstract

Al2O3 interlayer with plasma post-nitridation can reduce Dit of HfO2/Al2O3/SiGe.Dit toward valance band is decreased by this method, compared with HfO2/SiGe MOS.There is an universal relationship between the Dit and ΔEOT by post-nitridation.0.28-nm Al2O3 with 150-W microwave plasma achieves Dit~1011cm-2eV-1, ΔEOT~0.3nm.With this method, we can achieve EOT scaling of HfO2/Al2O3/SiGe MOS with low Dit. Plasma post-nitridation for HfO2/Al2O3/SiGe gate stack has been investigated to achieve equivalent oxide thickness (EOT) scaling with keeping superior interfacial properties. Irradiation of nitrogen plasma to HfO2/SiGe gate stack cannot improve its interfacial property, while nitrogen plasma irradiation to Al2O3/SiGe gate stack prior to HfO2 deposition enables superior HfO2/Al2O3/SiGe gate stack. The thickness of Al2O3 interfacial layer between HfO2 and SiGe is crucial for achieving further EOT scaling; thus we have investigated the relationship between the Al2O3 thickness and the microwave power of nitrogen plasma for plasma post-nitridation to preserve superior interfacial properties even with a thin Al2O3 interfacial layer. It was found that plasma post-nitridation of 0.28-nm-thick Al2O3/SiGe exhibited interface trap density (Dit) of 3i?1011cm-2eV-1, which was comparable to that of 1-nm-thick Al2O3/SiGe gate stack when the microwave power of nitrogen plasma was reduced from 650W to 150W. Thus, EOT of HfO2/Al2O3/SiGe gate stack can be scaled down to less than 1nm with keeping low Dit by using plasma post-nitridation with an ultrathin Al2O3 interfacial layer between HfO2 and SiGe.