What is limiting low-temperature atomic layer deposition of Al2O3? A vibrational sum-frequency generation study

The surface reactions during atomic layer deposition (ALD) of Al2O3 from Al(CH3)3 and H2O have been studied with broadband sum-frequency generation to reveal what is limiting the growth at low temperatures. The –CH3 surface coverage was measured for temperatures between 100 and 300 °C and the absolute reaction cross sections, describing the reaction kinetics, were determined for both half-cycles. It was found that –CH3 groups persisted on the surface after saturation of the H2O half-cycle. From a direct correlation with the growth per cycle, it was established that the reduced reactivity of H2O towards –CH3 is the dominant factor limiting the ALD process at low temperatures.