Low-temperature thermal and plasma-enhanced atomic layer deposition of metal oxide thin films

Abstract

Atomic layer deposition (ALD) is a method for thin film fabrication with atomic level precision. This thesis focuses on low-temperature thermal and plasma- enhanced ALD and presents results on thin film growth by these techniques with examples of common ALD materials: Al2O3, ZnO and TiO2. As an example of limitations of the thermal ALD the nucleation and growth of Al2O3 and ZnO films on different grades of poly(methyl methacrylate) (PMMA) are presented, showing that the initiation of the growth is strongly dependent on both the deposited material and the substrate. A potential application of the ALD ZnO films in polymer surface functionalization is demonstrated by changing in the surface wettability by means of UV-illumination. To overcome the nucleation delay in thermal ALD, room-temperature PEALD of ZnO films was demonstrated. It is shown that the growth and properties of the films depend on the PEALD reactor configuration and the plasma conditions therein. The plasma species interactions shown to be beneficial to the film growth were observed to damage the polymer substrates, the severeness depending on the polymer material. The last part of this thesis describes plasma mode transitions in capacitively- and inductively-coupled plasmas, that are typically used in PEALD processing. In addition to the mode transition induced changes in the plasma parameters, the contribution of the different plasma species to the growth and properties of ZnO and TiO2 films are demonstrated and discussed.