An Atomistic Picture of Buildup and Degradation Reactions in Area-Selective Atomic Layer Deposition with a Small Molecule Inhibitor

Abstract

We investigate the blocking layer formation of the trimethoxypropylsilane small molecule inhibitor (SMI), its blocking mechanisms, and all relevant blocking layer disintegration reactions on SiO₂ in the area-selective atomic layer deposition of Al₂O₃ with density functional theory-based methods. The choice of amorphous silica (a-SiO₂) surface models proves to be essential for obtaining the correct SMI chemistry. We demonstrate that complete blocking of reactive sites is possible here and deduce an upper SMI density limit of the resulting blocking layer that is limited by Pauli repulsion. The SMI adsorption process can nevertheless leave unreacted silanol groups, which could be remedied by using a second monodentate SMI. The SMI layer is inert against neither common aluminum precursors nor the co-reactant water as our comprehensive analysis of the various blocking layer disintegration reactions for different SMI layer densities shows. We report a new blocking mechanism of the SMI layer and propose to differentiate what is discussed as the “steric blocking” effect into the known “adsorption prevention” effect and the newly found “reactivity reduction” effect. For trimethylaluminum (TMA), an additional favorable SMI layer decomposition mechanism is found compared to that of the bulkier triethylaluminum (TEA), which could explain the lower selectivity of TMA found experimentally. Our computational work offers some principles and ideas for future experiments to improve selectivity in area-selective atomic layer deposition processes.