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

Selective functionalization of dielectric surfaces is required for area-selective atomic layer deposition and etching. We have identified precursors for the selective gas-phase functionalization of plasma-deposited SiO₂ and SiN_x surfaces with hydrocarbons. The corresponding reaction mechanism of the precursor molecules with the two surfaces was studied using in situ surface infrared spectroscopy. We show that at a substrate temperature of 70 °C, cyclic azasilanes preferentially react with an -OH-terminated SiO₂ surface over a -NH_x-terminated SiN_x surface with an attachment selectivity of ∼5.4, which is limited by the partial oxidation of the SiN_x surface. The cyclic azasilane undergoes a ring-opening reaction where the Si-N bond cleaves upon the reaction with surface -OH groups forming a Si-O-Si linkage. After ring opening, the backbone of the grafted hydrocarbon is terminated with a secondary amine, -NHCH₃, which can react with water to form an -OH-terminated surface and release CH₃NH₂ as the product. The surface coverage of the grafted cyclic azasilane is calculated as ∼3.3 × 10¹⁴ cm^-2, assuming that each reacted -OH group contributes to one hydrocarbon linkage. For selective attachment to SiN_x over SiO₂ surfaces, we determined the reaction selectivity of aldehydes. We demonstrate that aldehydes selectively attach to SiN_x over SiO₂ surfaces, and for the specific branched aliphatic aldehyde used in this work, almost no reaction was detected with the SiO₂ surface. A fraction of the aldehyde molecules reacts with surface -NH₂ groups to form an imine (Si-N═C) surface linker with H₂O released as the byproduct. The other fraction of the aldehydes also reacts with surface -NH₂ groups but do not undergo the water-elimination step and remains attached to the surface as an aminoalcohol (Si-NH-COH-). The surface coverage of the grafted aldehyde is calculated as ∼9.8 × 10¹⁴ cm^-2 using a known infrared absorbance cross-section for the -C(CH₃)₃ groups.