An atomistic picture on build-up and degradation reactions in area-selective atomic layer deposition with a small molecule inhibitor

We investigate the blocking layer formation of the trimethoxypropylsilane small molecule inhibi-tor (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 essential to obtain 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 which 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 neither inert against common aluminum precursors nor the co-reactant water as our comprehensive analysis of the var-ious 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’ and the newly found ‘reactivity reduction’ effects. For trimethylaluminum (TMA) an additional favorable SMI layer decomposi-tion mechanism is found compared to the bulkier triethylaluminum (TEA) which could explain the lower selectivity of TMA found experimentally. Our computational work offers some princi-ples and ideas for future experiments to improve selectivity in AS-ALD processes.