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In this brief, we report on how controllable process parameters such as metal-gate physical thickness and interfacial-layer-formation method affect the electrical and structural properties of TiN/HfO2/SiO2 gate stacks. We found evidence that Hf is diffusing into chemically formed SiO2 interfacial layers during device processing. The latter is not seen when SiO2 is formed thermally. We show that the interfacial layer is thinner when the physical thickness of TiN is reduced from 7 to 3 nm, resulting in electrically thinner gate stacks by 2 Aring. An electrical thickness in inversion as low as 11.4 Aring with gate-leakage-current density equal to 3.5 A/cm2 at 1 V was obtained for spike-annealed thin TiN/HfO2 stacks on chemically grown interfaces. Hf-rich chemical interfacial oxides do not degrade device performance. A small reduction in transconductance is only seen for physically thinner interfacial layers.
Date of Publication: July 2009