Anomalously high alumina atomic layer deposition growth per cycle during trimethylaluminum under-dosing conditions

Under nominal conditions for this study, alumina atomic layer deposition (ALD) using trimethylaluminum and water as precursors was found to give a growth-per-cycle (gpc) of 1.1 A under saturating conditions. As either precursor dose is reduced, one expects to find a point where the gpc begins to drop from the self-saturating plateau to zero in a monotonically decreasing manner while thickness nonuniformity along the deposited film starts to increase. In this paper, the authors find anomalously high gpc values—more than twice our nominal value of 1.1 A—during the transition to precursor under-dosing as the trimethylaluminium dose is reduced while the water dose is held constant. Unlike previous studies documenting abnormally high alumina ALD gpc, the authors find that film thickness remains spatially uniform in this region, up to the point where precursor depletion becomes significant, resulting in films with severe spatial gradients in the direction of precursor flow. A simple reaction mechanism is postul...