Electrical characteristics and TDDB breakdown mechanism of N2-RTA-treated Hf-based high-κ gate dielectrics

This study investigates the effects of rapid thermal annealing (RTA) in nitrogen ambient on HfO2 and HfSiOx gate dielectrics, including their electrical characteristics, film properties, TDDB reliability and breakdown mechanism. The optimal temperature for N2 RTA treatment is also investigated. The positive oxide trap charges (oxygen vacancies) in HfO2 and HfSiOx dielectric films can be reduced by the thermal annealing, but as the annealing temperature increased, many positive oxide trap charges (oxygen vacancies) with shallow or deep trap energy level will be formed in the grain boundaries, degrading the electrical characteristics, and changing the breakdown mechanism. We believe that variation in the number of positive oxide trap charges (oxygen vacancies) with shallow or deep trap energy levels is the main cause of the CV shift and difference in the breakdown behaviors between HfO2 and HfSiOx dielectrics. With respect to CV characteristics and TDDB reliability, the optimal temperature for N2 RTA treatment is in the range 500–600 °C and 800–900 °C, respectively.