NEW INSIGHTS IN Hf BASED HIGH-k GATE DIELECTRICS IN MOSFETs

摘要

I.Two different traps (fast and slow) in HfO_2 gate dielectric areidentified. For the slow traps, the negative U (-U) property of trap isproposed and confirmed by the first principle calculation. Each trap cantrap two electrons or two holes and lower the trap energy due to a largelattice relaxation. The observed experimental result of reduction in slowcomponent of bias temperature instability (BTI) degradation with anincrease in stress frequency can be simulated with excellent agreement,based on the concept of -U. A fast BTI component is also observed. Thefast dynamic BTI degradation is increased with an increase in stressfrequency. It is due to the existence of fast traps and can be simulated bythe conventional trapping/de-trapping equations. The fast trap is astandard conventional trap. II.Mixing Ta and La into HfO_2 to form HfTaO and HfLaO gate dielectrichave been studied systematically. Comparing to the HfO_2gate dielectric,the HMO and HfLaO have the advantages of much higher crystallizationtemperature, much lower charge trapping as well as the BTI degradation,and increased channel mobility. In addition, variation of La concentrationin HfLaO/TaN or HfLaO/HfN gate stack can effectively tune the metalwork function continuously from mid gap to 4eV. Possible physicalexplanation for these interesting properties are discussed.