Due to the constantly decreasing dimensions of electronic devices, the conventional dielectric material in transistors and capacitors, SiO2, has to be replaced by a material with higher dielectric constant. Some of the most promising candidates are tantalum oxide,Ta2O5, zirconium oxide, ZrO2 and hafnium oxide, HfO2.
This thesis describes new chemical vapour deposition (CVD) and atomic layer deposition (ALD) processes for deposition of Ta2O5, ZrO2 and HfO2 using the metal iodides as starting materials. The layer-by-layer growth in ALD was also studied in real time with a quartz crystal microbalance (QCM) to examine the process characteristics and to find suitable parameters for film deposition.
All the processes presented here produced high-purity films at low deposition temperatures. It was also found that films deposited on Pt substrates generally crystallise at lower temperature, or with lower thickness, than on silicon and single-crystalline oxide substrates. Films grown on MgO(001) and α-Al2O3(001) substrates were strongly textured or epitaxial. For example, monoclinic HfO2 deposited on MgO(001) were epitaxial for deposition temperatures of 400-500 C in ALD and 500-600 C in CVD. Electrical characterisation showed that the crystallinity of the films had a strong effect on the dielectric constant, except in cases of very thin films, where the dielectric constant was more dependent on layer thickness.