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In this letter, a room-temperature multideposition multiannealing (MDMA) technique in ultraviolet ozone (UVO) ambient is applied to metal-gated (TiN) ALD HfO2 gate dielectric. Compared to the conventional rapid thermal annealing, the nMOSFETs with UVO MDMA show superior properties, in terms of enhanced channel electron mobility, improved immunity to biased temperature instability, and reduced gate dielectric relaxation current. This is explained by the reduction of bulk oxide trap and interface trap density because of healing of oxygen vacancies (Vo) after UVO MDMA annealing. The novel room-temperature UVO annealing is thus proposed to be a promising technique to enhance the gate stack integrity in a gate-last integration scheme.