Short-duration rapid-thermal-annealing processing of tantalum oxide thin films

Abstract

The effect of the rapid thermal annealing (RTA) processing time on the electrical properties of reactively sputtered tantalum oxide (Ta2O5) films that was deposited onto Pt/SiO2/ n-Si substrates, which resulted in the formation of a metal-insulator-metal (MIM) planar capacitor structure, was studied, The Ta2O5 MIM capacitors were subjected to different RTA processing times (30 s to 30 min) at temperatures in the range of 600 degrees-800 degrees C in an ambient oxygen-gas atmosphere. A very-short-duration RTA process at a temperature of 800 degrees C in oxygen gas for 30 s crystallized the films, decreased the leakage current density (to 10(-10) A/cm(2) at a stress field of 100 kV/cm), increased the dielectric constant (to 52), and resulted in the most-reliable time-dependent dielectric-breakdown characteristics. The decrease in leakage current density was attributed to the reduction of oxygen vacancies and the suppression of silicon diffusion from the SiO2/n-Si substrate into the Ta2O5 grain and the grain boundary, because of the shorter-duration annealing, Increasing the annealing time to >30 s increased the leakage current density. The annealing duration of the RTA process was more crucial in regard to obtaining optimum dielectric properties and low leakage current densities. Time-dependent dielectric-breakdown characteristics indicated that Ta2O5 MIM film capacitors that were subjected to an RTA process at a temperature of 800 degrees C for 30 s in oxygen gas can survive a stress field of 1.5 MV/cm for 10 years. The electrical and dielectric measurements in the MIM configuration showed that Ta2O5 is a good dielectric material and is suitable for use in future dynamic random-access memories.