On the initial growth of atomic layer deposited TiO2 films on silicon and copper surfaces

Atomic layer deposition (ALD) of TiO₂ using tetrakis(diethylamino)titanium precursor and H₂O was studied on silicon and copper surfaces in order to examine differences in nucleation. Both surfaces were patterned on the same substrate to assure identical deposition conditions. Spectral ellipsometry, X-ray photoelectron spectroscopy and surface profilometry were used to probe nucleation phenomena, growth rates, and surface morphology on both surfaces. The TiO₂ deposition on copper was found to exhibit a significant induction period of about 20-25 ALD cycles with no observable TiO₂ during the first 10-15 cycles on the copper side; in contrast, no such inhibited growth was observed in the TiO₂ deposition on silicon. This result opens up potential for selective ALD of TiO₂ films on silicon-based substrates patterned with a metal without the use of a mask, a self-assembled monolayer or soft lithography which is impractical for some nanoscale semiconductor fabrication processes. After film nucleation, the TiO₂ growth rate on both surfaces was found to be 0.10 nm/cycle.