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

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 (D-it) of 3 x 10(11) cm(-2) eV(-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 1 nm with keeping low D-it by using plasma post-nitridation with an ultrathin Al2O3 interfacial layer between HfO2 and SiGe. (C) 2013 Elsevier B.V. All rights reserved.