Inherently Selective Water-Free Deposition of Titanium Dioxide on the Nanoscale: Implications for Nanoscale Patterning

Water-free inherent selective deposition of TiO2 on Si and SiO2 in preference to SiCOH has been studied via atomic layer deposition (ALD) and pulsed chemical vapor deposition (CVD). SiCOH is a nonreactive low-k dielectric material, consisting of highly porous alkylated SiO2. Water-free deposition was studied to protect SiCOH and increase selectivity. The titanium precursor used in all studies was Ti(OiPr)4 [titanium(IV) isopropoxide] and contains four oxygen atoms enabling it to form TiO2 through single-precursor CVD. At 250 °C substrate temperature, selective water-free ALD of TiO2 using Ti(OiPr)4 and either acetic acid (AcOH) or formic acid (HCO2H) as a second precursor was studied. By both ALD processes, around 2 nm of TiO2 was deposited on Si and SiO2 without any deposition on SiCOH. The TiO2 ALD films had a root-mean-square roughness of 2–3 Å. In situ X-ray photoelectron spectroscopy showed that Ti(OiPr)4 + AcOH ALD occurred via ligand exchange between −OiPr and AcO–. ALD with formic acid, which is a 10× stronger proton donor than acetic acid, displayed similar selectivity but with a 10× higher growth rate than ALD with acetic acid. Single-precursor pulsed CVD with Ti(OiPr)4 was also studied at 250 and 295 °C substrate temperatures. At 250 °C, TiO2 growth on all substrates was minuscule (<1 nm for 400 pulses). Single-precursor pulsed CVD (2000 pulses) at 295 °C displayed the highest selectivity among all processes studied: 16.9 and 40.1 nm TiO2 molecules were deposited on Si and SiO2, respectively, while less than a monolayer of TiO2 was deposited on SiCOH. The pulsed CVD at 295 °C showed ∼20 nm of selective TiO2 deposition on nanoscale patterned samples. It is expected that the selective TiO2 CVD can be applicable in the nanoscale patterning process in metal-oxide-semiconductor field-effect transistor fabrication.