Synthesis of tantalum pentoxide films by pulsed laser deposition: material characterization and scale-up

Abstract

Tantalum oxide (TaO x ) films were grown on silicon substrates using the pulsed laser deposition (PLD) technique. The beam of a KrF excimer laser was used to ablate Ta 2O 5 targets in an oxygen background gas. The composition, structure, and optical properties of the films were investigated as functions of the O 2 pressure (1–40 mTorr) and substrate temperature (150–800°C). Stoichiometric Ta 2O 5 films were obtained, with indices of refraction higher than 2.15 and extinction coefficients less than 10 −4. Amorphous-like coatings were produced at deposition temperatures of 150, 250 and 400°C. At 650°C, a transition towards a polycrystalline structure was observed for O 2 pressures higher than 1 mTorr. This transition involved β-Ta 2O 5 and an unidentified structure. At 800°C and an O 2 pressure higher than 20 mTorr, β-Ta 2O 5 was the predominant phase. An investigation of the TaO x /silicon interface revealed the presence of an ultra-thin Ta-rich silicon oxide interlayer (∼2 nm) and a shallow Ta-rich silicon layer (<2 nm) at the silicon substrate surface. Within the processing window that led to stoichiometric Ta 2O 5, films were deposited on 75 mm diameter silicon wafers. The coatings were found to be uniform over the entire area in terms of thickness, composition, structure, and optical properties.