Low-temperature atomic layer deposition of TiO₂, Al₂O₃, and ZnO thin films

We studied low-temperature atomic layer deposition (LT-ALD) of TiO₂, Al₂O₃, and ZnO thin films at temperatures down to room temperature, mainly focusing on the growth characteristics and the film's properties. Here, two kinds of ALD deposition systems were introduced. Initially, for the thermal ALD (T-ALD) process using a commercial ALD system, a very long purging time of up to ~300 s was required to entirely evacuate the remaining H₂O vapors at room temperature due to the large volume and the complicated inner structure of the commercial ALD chamber. For the realization of LT-ALD with a short process time, a plasma-enhanced ALD (PE-ALD) process using O₂ plasma was employed, which enabled us to effectively remove the residual reactants at temperatures down to room temperature. As another method, we specifically designed a homemade ALD system with a small volume and a simple inner structure, thereby being able to use T-ALD to synthesize TiO₂, Al₂O₃, and ZnO thin films by using H₂O with very short H₂O purging times even at room temperature, which reveals that the chamber size and design are the critical factors enabling LT-ALD with a short process time. The LT-ALD processes produced highly-pure Al₂O₃, TiO₂, and ZnO films without any C and N impurities by complete elimination of ligands and exhibited excellent conformality in 3-dimensional nanoscale via holes.