Atomic layer deposition of tantalum oxide thin films from iodide precursor

Atomic layer deposition (ALD) of Ta2O5 films from evaporated TaI5 and H2O-H2O2 was investigated in the temperature range of 240-400 degreesC. It was shown that TaI5 as a novel ALD precursor is sufficiently stable for deposition of amorphous or polycrystalline films. According to XPS, the films were free from iodine residues. The refractive index of the films reached 2.24. The film formation mechanism depended on the substrate temperature. The growth rate decreased linearly,with substrate temperature. Real time monitoring of the growth process with a quartz crystal microbalance revealed the self-limiting nature of reactions between the film surface and precursors at substrate temperatures up to 325 degreesC. Etching of Ta2O5 in the TaI5 flow was observed at around 350 degreesC and higher temperatures. At 350 degreesC, the crystal growth was also initiated.