Reaction mechanisms of α,ω-bifunctional molecules toward atomic layer deposition versus molecular layer deposition

Abstract

Atomic layer deposition (ALD) and molecular layer deposition (MLD) are key techniques used to fabricate high-quality thin films. Organic α,ω-bifunctional precursors often exhibit different growth behaviors depending on the functional groups as well as the chain length of the molecular backbone, so that some organic precursors produce thin films of organic-inorganic hybrid materials, while others may deposit purely inorganic thin films without incorporation of the hydrocarbon moiety. In this study, we investigated the surface reaction mechanisms of α,ω-bifunctional molecules (X(CH2)nX, n = 2, 3, 4, 5, 6, and X = OH, SH, NH2) with diethylzinc toward MLD and ALD using density functional theory (DFT) calculations. It was found that the length of the aliphatic alkyl chain and the terminal functional groups of bifunctional organic precursors significantly influences their reactivity, resulting in the possibility toward removal or incorporation of the organic moiety in the product. Bifunctional reactants with longer alkyl backbones (n > 4) showed higher reactivity for removal of the hydrocarbon chain, facilitated by a ω-2 hydrogen transfer reaction. Furthermore, a reactivity trend of SH > OH > NH2 for removal of the hydrocarbon chains was observed. Our study provides in-depth theoretical insights into the adsorption reaction mechanisms occurring when bifunctional molecules are employed as organic reactants in ALD and MLD processes.