Gas Phase Organic Functionalization of SiO₂ with Propanoyl Chloride

Abstract

The reaction mechanism of propanoyl chloride (C 2 H 5 COCl) with −SiOH-terminated SiO 2 films was studied using in situ surface infrared spectroscopy. We show that this surface functionalization reaction is temperature dependent. At 230 °C, C 2 H 5 COCl reacts with isolated surface −SiOH groups to form the expected ester linkage. Surprisingly, as the temperature is lowered to 70 °C, the ketone groups are transformed into the enol tautomer, but if the temperature is increased back to the starting exposure temperature of 230 °C, the ketone tautomer is not recovered, indicating that the enol form is thermally stable over a wide range of temperatures. Further, the enol form is directly formed after exposure of a SiO 2 surface to C 2 H 5 COCl at 70 °C. We speculate that the enol form, which is energetically unfavorable, is stabilized because of hydrogen bonding with adjacent enol groups or through hydrogen bonding with unreacted surface −SiOH groups. The surface coverage of hydrocarbon molecules is calculated as ∼6 × 10 12 cm −2 , assuming each reacted −SiOH group contributes to one hydrocarbon linkage on the surface. At a substrate temperature of 70 °C, the enol form is unreactive with H 2 O, and H 2 O molecules simply physisorb on the surface. At higher temperatures, H 2 O converts the ketone to the enol tautomer and reacts with Si−O−Si bridges, forming more −SiOH reactive sites. The overall hydrocarbon coverage on the surface can then be further increased through cycling H 2 O and C 2 H 5 COCl doses.

Selective Gas-Phase Functionalization of SiO2 and SiNx Surfaces with Hydrocarbons

“…As shown in Figure 3a, upon the exposure of a −SiOH-terminated SiO 2 surface to CAZ, a sharp decrease in absorbance is observed at ∼3750 cm −1 , which indicates the reaction of CAZ with the isolated −SiOH species on the surface. 8,41,53 Further, as observed in previous work, it also confirms that the isolated −SiOH species are the primary reactive sites on the plasma-deposited SiO 2 surface. 8 The low wavenumber tail indicates the reaction of CAZ with surface vicinal (weakly hydrogen bonded) -SiOH groups as well (see Figure S1).…”

“…We have previously shown that the ∼3650 cm −1 mode corresponds to the −SiOH groups that are embedded in the bulk, while the isolated −SiOH groups are the surface reactive sites. 8 Figure 2b shows the infrared absorbance spectrum of a typical plasma-deposited SiN x film on a bare ZnSe IRC. The reference spectrum was recorded immediately prior to the plasma strike; therefore, the spectrum contains contributions from both the bulk and surface vibrational modes.…”

“…13−17 In semiconductor device manufacturing, SiN x and SiO 2 are two of the most commonly used dielectric materials. 8,13,14,18 Thus, functionalizing SiO 2 over SiN x surfaces and vice versa is highly desired for area-selective atomic layer deposition (ALD). 19 In an ideal area-selective ALD process, a SAM would be chemically patterned onto the substrate via selective attachment to either a SiO 2 or a SiN x surface.…”

Surface reactions of aminosilane precursors during N2 plasma‐assisted atomic layer deposition of SiNx

“…The SiN x films were grown via ALD in the surface analysis chamber depicted in Figure a, which has been described in detail previously . Briefly, this chamber is equipped with an inductively coupled plasma source operated at 13.56 MHz, and an ATR‐FTIR spectroscopy setup that allows for the detection of surface species.…”

“…The SiN x films were grown via ALD in the surface analysis chamber depicted in Figure 1a, which has been described in detail previously. [21][22][23] Briefly, this chamber is equipped with an inductively coupled plasma source operated at 13.56 MHz, and an ATR-FTIR spectroscopy setup that allows for the detection of surface species. We used 1 × 10 × 50 mm trapezoidal ZnSe internal reflection crystals (IRCs) as substrates, which provide submonolayer sensitivity to surface adsorbates due to the~25 internal reflections on each face.…”