Ab Initio Calculations of the Reaction Mechanisms for Metal-Nitride Deposition from Organo-Metallic Precursors onto Functionalized Self-Assembled Monolayers
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- 作者：Mohit Haran ; James R. Engstrom ; and Paulette Clancy
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：January 25, 2006
- 年：2006
- 卷：128
- 期：3
- 页码：836 - 847
- 全文大小：537K
- 年卷期：v.128,no.3(January 25, 2006)
- ISSN：1520-5126
文摘
An atomistic mechanism has been derived for the initial stages of the adsorption reaction formetal-nitride atomic layer deposition (ALD) from alkylamido organometallic precursors of Ti and Zr onalkyltrichorosilane-based self-assembled monolayers (SAMs). The effect of altering the terminal functionalgroup on the SAM (including -OH, -NH2, -SH, and -NH(CH3)) has been investigated using the densityfunctional theory and the MP2 perturbation theory. Reactions on amine-terminated SAMs proceed throughthe formation of a dative-bond complex with an activation barrier of 16-20 kcal/mol. In contrast, thiol-terminated SAMs form weak hydrogen-bonded intermediates with activation barriers between 7 and 10kcal/mol. The deposition of Ti organometallic precursors on hydroxyl-terminated SAMs proceeds throughthe formation of stronger hydrogen-bonded complexes with barriers of 7 kcal/mol. Zr-based precursorsform dative-bonded adducts with near barrierless transitions. This variety allows us to select a kineticallyfavorable substrate for a chosen precursor. The predicted order of reactivity of differently terminated SAMsand the temperature dependence of the initial reaction probability have been confirmed for Ti-basedprecursors by recent experimental results.53 We predict that the replacement of methyl groups bytrifluoromethyl groups on the SAM backbone decreases the activation barrier for amine-terminated SAMsby 5 kcal/mol. This opens a route to alter the native reactivities of a given SAM termination, in this casemaking amine termination energetically viable. The surface distribution of SAM molecules has a strongeffect on the adsorption kinetics of Ti-based precursors. Unimolecular side decomposition reactions werefound to be kinetically competitive with adsorption at 400 K.