Impact of Al2O3 position on performances and reliability in high-k metal gated DRAM periphery transistors

The impact of the Al<sub>2</sub>O<sub>3</sub> position with respect to HfO<sub>2</sub> in the process flow, is investigated. It is shown that Al<sub>2</sub>O<sub>3</sub> incorporation in order to increase the pMOS threshold voltage, slightly degrades the mobility, slightly increases NBTI and increases the EOT with respect to the reference without Al<sub>2</sub>O<sub>3</sub> Moreover, the trap density profiles depend on the Al<sub>2</sub>O<sub>3</sub> position: higher in the interfacial layer when Al<sub>2</sub>O<sub>3</sub> is below and higher in the HfO<sub>2</sub> when Al<sub>2</sub>O<sub>3</sub> is above HfO<sub>2</sub>. Furthermore, Al<sub>2</sub>O<sub>3</sub> below HfO<sub>2</sub> shows higher gate leakage, reduced LF noise but marginal NBTI difference compared to AL<sub>2</sub>O<sub>3</sub> above HfO<sub>2</sub>.

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