HfO2/Al2O3 gate dielectric thin-film stacks were atomic-layer-deposited on HF-cleaned Si wafers. The 2.3 nm thick Al2O3 interlayer was treated under an NH3 atmosphere at 790 degreesC for 40 s with and without rf plasma prior to a 4 nm thick HfO2 film deposition. Plasma nitridation increased Al2O3 interlayer thickness by 0.9 nm and decreased overall capacitance, whereas thermal nitridation did not, and overall capacitance was the same as that of a nontreated HfO2/Al2O3 stack. The thermal stability of the capacitance density and flatband behavior were also improved by thermal nitridation of the interlayer. Furthermore, nitridation of the Al2O3 interlayer greatly reduced the interface trap density of the samples. (C) 2004 The Electrochemical Society.