Effects of O2 rapid thermal annealing on themicrostructural properties and reliability of RF-sputteredTa2O5 films

The microstructural properties and reliability of sputtered Ta₂O₅ films treated by various temperatures of rapid thermal annealing (RTA) in O₂ atmosphere have been systematically investigated. Analytical results revealed that whenever the RTA temperature was >650°C, the noncrystallinity of as-grown Ta₂O₅ film would be effectively improved from an amorphous phase to the β-Ta₂O₅ phase. Leakage current measurement indicated that leakage current decreases with increasing annealing temperature in a low RTA temperature range (⩽650°C) and, contrarily, increases with increasing annealing temperature in a high RTA temperature range (650 to 950°C). The former result was asserted in that reducing pinholes and oxygen vacancies played key factors. However, the latter result arose due to significant Si diffusion into the Ta₂O₅ film, causing a leaky transition layer distributed along the grain boundary to form the leakage path. Finally, the time-dependent dielectric-breakdown experiments revealed that 950°C O₂ RTA treated Ta₂ O₅ film possessed the superior crystallinity, creating less interfacial hole trap states at the junction of Ta₂O₅/Si and exhibiting the best long-term reliability