Abstract
Flat band voltage ( V FB) roll-off in long channel devices at thin equivalent oxide thickness (EOT) is studied on SiO 2/nitrided-HfSiO stacks. V FB increases when SiO 2 interfacial layer thickness decreases, and charges pumping (CP) frequency sweep analysis shows higher trap density near Si/SiO 2 interface. Based on this observation, an atomic diffusion model is introduced. Higher concentration of nitrogen atom in the HfSiO(N) layer diffuses to the Si/SiO 2 interface through the SiO 2 layer in thinner SiO 2 device, and accumulates near Si/SiO 2 interface which can introduce higher density of interfacial traps. Lifetime extracted from negative bias temperature instability (NBTI), and mobility are also degraded in thinner SiO 2 devices due to the higher interfacial trap density. The V FB roll-off can be improved by lowering nitrogen concentration in the HfSiO(N) layer from optimizing plasma nitridation pressure, decreasing post deposition anneal temperature, or using defect absorbing layer on the high-k oxide.
Published Version
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