Reliability of Ultra-Thin Gate Oxide Below 3 nm in the Direct Tunneling Regime

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Abstract
Cluster tool furnace technology was used to control the growth of extremely uniform ultra-thin 1.5 nm to 3 nm SiO2 layers on Si. The transition from Fowler-Nordheim tunneling to direct tunneling electron injection for sub-3-nm oxide poly-Si gate metal-oxide-silicon capacitor structures is described and the influence on the oxide reliability is discussed. It is shown that oxide breakdown can still occur at low voltages in the direct tunneling regime under the condition of electron injection from the poly-Si gate. Soft breakdown of these ultra-thin oxide layers, accompanied by the occurrence of complex fluctuations in the direct tunneling current, is demonstrated. Using this as the definition of sub-3-nm oxide breakdown, it is shown for the first time that the time to dielectric breakdown of the sub-3-nm gate oxide in the direct tunneling regime is determined by the electrical field strength in the oxide similarly to the case of the sub-3-nm dielectric breakdown in Fowler-Nordheim tunnel stressing.

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