Growth of Tantalum(V) Oxide Films by Atomic Layer Deposition Using the Highly Thermally Stable Precursor Ta(NtBu)(iPrNC(Me)NiPr)2(NMe2)

The atomic layer deposition (ALD) growth of Ta2O5 films was demonstrated using Ta(NtBu)-(iPrNC(Me)NiPr)2(NMe2) and water with substrate temperatures between 225 and 400 °C. At 325 °C, self-limited growth was demonstrated with Ta(NtBu)(iPrNC(Me)NiPr)2(NMe2) and water pulse lengths of ≥0.5 s. An ALD window was observed between 275 and 350 °C, with a growth rate of 0.28 Å/cycle. The growth rates were 0.33 and 0.37 Å/cycle at 250 and 225 °C, respectively. At 375 and 400 °C the growth rate increased slightly to 0.31 Å/cycle, and precursor thermal decomposition may contribute to growth at these temperatures. In a series of films deposited at 325 °C, the film thickness increased linearly with the number of deposition cycles. X-ray photoelectron spectroscopy of films deposited at 300 and 350 °C revealed stoichiometric Ta2O5 with carbon and nitrogen levels below the detection limits. The films were amorphous as deposited, but annealing at 700 °C in dry air resulted in crystallization of hexagonal δ-Ta2O5. Atomic force microscopy found root-mean-square surface roughnesses of 0.6−0.7 nm for 45 nm thick films deposited at 300 and 350 °C. The index of refraction of films grown at 325 °C was determined to be 2.12−2.16 at 633 nm using ellipsometry.