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((OPr)-Pr-i)(4) [titanium(IV) isopropoxide] and contains four oxygen atoms enabling it to form TiO2 through single-precursor CVD. At 250 degrees 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 A. In situ X-ray photoelectron spectroscopy showed that Ti(OiPr)(4) + AcOH ALD occurred via ligand exchange between -(OPr)-Pr-i and AcO-. ALD with formic acid, which is a 10x stronger proton donor than acetic acid, displayed similar selectivity but with a 10x higher growth rate than ALD with acetic acid. Single-precursor pulsed CVD with Ti(OiPr) 4 was also studied at 250 and 295 degrees C substrate temperatures. At 250 degrees C, TiO2 growth on all substrates was minuscule (<1 nm for 400 pulses). Single-precursor pulsed CVD (2000 pulses) at 295 degrees 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 degrees C showed similar to 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.