Inherent substrate-dependent growth initiation and selective-area atomic layer deposition of TiO₂ using “water-free” metal-halide/metal alkoxide reactants

Titanium dioxide atomic layer deposition (ALD) is shown to proceed selectively on oxidized surfaces with minimal deposition on hydrogen-terminated silicon using titanium tetrachloride (TiCl₄) and titanium tetra-isopropoxide [Ti(OCH(CH₃)₂)₄, TTIP] precursors. Ex situ x-ray photoelectron spectroscopy shows a more rapid ALD nucleation rate on both Si–OH and Si–H surfaces when water is the oxygen source. Eliminating water delays the oxidation of the hydrogen-terminated silicon, thereby impeding TiO₂ film growth. For deposition at 170 °C, the authors achieve ∼2 nm of TiO₂ on SiO₂ before substantial growth takes place on Si–H. On both Si–H and Si–OH, the surface reactions proceed during the first few TiCl₄/TTIP ALD exposure steps where the resulting products act to impede subsequent growth, especially on Si–H surfaces. Insight from this work helps expand understanding of “inherent” substrate selective ALD, where native differences in substrate surface reaction chemistry are used to promote desired selective-area growth.