Optimized Nitridation of Al_2O_3 Interlayers for Atomic-Layer-Deposited HfO_2 Gate Dielectric Films

摘要

HfO_2/Al_2O_3 gate dielectric thin-film stacks were atomic-layer-deposited on HF-cleaned Si wafers. The 2.3 nm thick Al_2O_3 interlayer was treated under an NH_3 atmosphere at 790 deg C for 40 s with and without rf plasma prior to a 4 nm thick HfO_2 film deposition. Plasma nitridation increased Al_2O_3 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 HfO_2 /Al_2O_3 stack. The thermal stability of the capacitance density and flatband behavior were also improved by thermal nitridation of the interlayer. Furthermore, nitridation of the Al_2O_3 interlayer greatly reduced the interface trap density of the samples.