CVD of tantalum oxide dielectric thin films for nanoscale device applications

A metallorganic chemical vapor deposition (MOCVD) process has been developed for the growth of Ta2O5 films from the reaction of tantalum penta-ethoxide [Ta(OEt)5] and oxygen in a 200 mm wafer tool platform. An optimized process was identified by performing a systematic study of the reaction-rate-limiting steps as a function of substrate temperature, Ta(OEt)5 partial pressure, and O2 partial pressure. Subsequent chemical and microstructural analyses showed that as-deposited Ta2O5 films were stoichiometric, amorphous, pure, and exhibited a smooth surface morphology. Carbon contamination was below the detection limits of the analytical techniques employed (<1 atom %). Typical as-deposited film dielectric constant and leakage current density were measured to be 27 and 2.0 × 10-9 A/cm2 (at 1 V), respectively. Annealing at 650°C for 30 min in O2 decreased both the dielectric constant and leakage current, while a similar anneal in Ar resulted in increased dielectric constant and associated decrease in leakage current. It was determined that Schottky emission was the dominant leakage current conduction mechanism in the MOCVD Ta2O5 films.