Investigation of abnormally high growth-per-cycle in atomic layer deposition of Al2O3 using trimethylaluminum and water

Atomic layer deposition (ALD) has the excellent advantage of precisely controlling the thickness of thin films at the atomic scale owing to the self-limiting chemisorption of precursors, but its low growth-per-cycle (GPC) is a weakness in applications requiring thick films. Under the saturation process conditions for the self-limiting growth behavior in Al2O3 ALD using trimethylaluminum (TMA) and H2O, the GPC values are limited to approximately 1–1.2 Å/cycle in the temperature range of 80–250 °C. However, in the practical use of the Al2O3 ALD, abnormally high GPC often occurs, which is generally regarded as the failure to control saturation conditions such as insufficient water purge. Based on comparisons of the normal ALD processes and various modified ALD processes with abnormally high GPC, we report that the unusually high GPC in the Al2O3 ALD is not only caused by the residual H2O but also due to the dimeric nature of TMA. Dimeric aggregate fragments of TMA and dimethylaluminum hydroxide were identified by quadrupole mass spectrometry during TMA exposure and Ar purge steps. This observation supports the dimeric interaction of TMA with the residual H2O.