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

Abstract

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(O i Pr)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(O i Pr)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(O i Pr)4 + AcOH ALD occurred via ligand exchange between −O i Pr 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(O i Pr)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.

Selective Pulsed Chemical Vapor Deposition of Water-Free TiO2/Al2O3 and HfO2/Al2O3 Nanolaminates on Si and SiO2 in Preference to SiCOH

“…28 A monolayer thickness of TiO 2 sublayer requires approximately 30 pulses of Ti(O i Pr) 4 (0.009 nm/pulse was calculated based on the single precursor TiO 2 pulsed CVD shown in Figure S3). 17 Consequently, the initial supercycle was composed of 30 pulses of Ti(O i Pr) 4 followed by 1 pulse of TMA 300 °C.…”

“…). 17,18 It is hypothesized that the (OH − ) groups in the intermediate react with weaker bonding H−Si and OH−SiO 2 sites inducing chemisorption followed by a continuous growth. Even with TMA being introduced later, there are still enough H−Si or OH−SiO 2 reactive sites to nucleate and maintain the growth.…”

“…18 Around 17 and 40 nm TiO 2 were selectively deposited on Si and SiO 2 in preference to SiCOH (≤0.5 nm) with a selectivity of 34 on the Si surface. 17 Pulsed water-free Hf(O t Bu) 4 CVD proceeds by a similar mechanism and deposited 1.8 and 5 nm of HfO 2 on Si and SiO 2 in preference to SiCOH (0.13 nm) with a selectivity of 14 on Si versus SiCOH. 18 Note, the selectivity was greater for SiO 2 versus Si but was quantified for Si versus SiCOH since the thickness was more accurately measured by ellipsometry on Si.…”

“…In our earlier works, selective water-free single precursor TiO 2 and HfO 2 pulsed CVD deposition on Si, SiO 2 , and SiCOH was studied. , SiCOH is an unreactive surface but requires a water-free process to avoid hydroxylation which can result in both loss of selectivity and substrate oxidation.…”

“…Optimization of the pulsed single precursor CVD process (substrate time and pulse lengths) increases selectivity and prevents gas-phase reaction and uncontrollable growth rate . Around 17 and 40 nm TiO 2 were selectively deposited on Si and SiO 2 in preference to SiCOH (≤0.5 nm) with a selectivity of 34 on the Si surface . Pulsed water-free Hf­(O t Bu) 4 CVD proceeds by a similar mechanism and deposited 1.8 and 5 nm of HfO 2 on Si and SiO 2 in preference to SiCOH (0.13 nm) with a selectivity of 14 on Si versus SiCOH .…”