Computational Investigation of Electronic and Steric Effects in Surface Reactions of Metalorganic Precursors on Functionalized Silicon Surfaces

Steric and electronic effects play a profound role in determining the mechanisms of surface reactions. In the case of reactions of metalorganic precursors on solid prefunctionalized surfaces, the contribution of these effects has to be considered both for the incoming metalorganic precursor molecule and for the functionalized surface itself. This study uses density functional theory calculations with simple cluster models to investigate the technologically important reactions of tetrakis(dimethylamido)titanium (TDMAT) and trimethylaluminum (TMA) with silicon surfaces functionalized with preadsorbed amines. This approach provides an opportunity to compare the contribution of electronic effects in the process of transamination for TDMAT and in the process of aluminum deposition followed by methane desorption for TMA. Bulky dimethylamido substituents of TDMAT are shown to suppress the electronic effects of the surface-bound amines unless the very open surface-bound structures of −NH 2 and −NHF are compared. At the same time, the relatively open structure of TMA allows for a comparison unobscured by the ligands of a precursor. A comparison within a number of substituted amines bound to the silicon surface is performed and electronic differences are explained by following the properties of the surface hydrogen needed for eliminating a substituent ligand during the deposition step.