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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.

The selective etching characteristics of silicon, germanium, and SiGe subjected to a downstream H/CF/Ar plasma have been studied using a pair of in situ quartz crystal microbalances (QCMs) and X-ray photoelectron spectroscopy (XPS). At 50 °C and 760 mTorr, Si can be etched in preference to Ge and SiGe, with an essentially infinite Si/Ge etch-rate ratio (ERR), whereas for Si/SiGe, the ERR is infinite at 22 °C and 760 mTorr. XPS data showed that the selectivity is due to the differential suppression of etching by a ∼2 ML thick CHF layer formed by the H/CF/Ar plasma on Si, Ge, and SiGe. The data are consistent with the less exothermic reaction of fluorine radicals with Ge or SiGe being strongly suppressed by the CHF layer, whereas, on Si, the CHF layer is not sufficient to completely suppress etching. Replacing H with D in the feed gas resulted in an inverse kinetic isotope effect (IKIE) where the Si and SiGe etch rates were increased by ∼30 times with retention of significant etch selectivity. The use of D/CF/Ar instead of H/CF/Ar resulted in less total carbon deposition on Si and SiGe and gave less Ge enrichment of SiGe. These results are consistent with the selectivity being due to the differential suppression of etching by an angstrom-scale carbon layer.

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