This thesis focuses on the study of physical and chemical processes occurring during growth and thermal oxidation of Ru and ZrO2 thin films. Acting as oxidation resistant capping materials to prevent oxidation of layers underneath, these films have several applications, i.e., in microelectronics such as gate dielectrics or memory devices, in photovoltaics, or in extreme ultraviolet lithography (EUVL) optics. High-sensitivity low-energy ion scattering (HS-LEIS) has been used in this thesis for in vacuo analysis of the initial growth stages of Ru and ZrO2 films on a-Si, SiN and SiO2 substrate layers, including an accurate determination of surface coverages and thicknesses required for closing the growing film. During ZrO2 growth, the oxygen concentration (high-O and low-O conditions) in the sputter gas was varied in order to study its effect on ZrO2 growth and its properties (e.g., stoichiometry, interaction with the underlying layer, mass density). The oxidation and/or oxygen diffusion behavior of Ru and ZrO2 films upon thermal annealing under atmospheric oxygen have been investigated. In the case of Ru, a detailed description of surface and sub-surface oxidation of Ru thin films has been presented, and a model for concurrent 2D and 3D ruthenium oxide growth has been proposed. It also was found that the 2D oxide did not grow as a single layer but a combination of two layers on top of each other, a low density RuOx (2<x≤3) layer on top of a near bulk density RuO2 layer. In situ XRR measurements during annealing have been used to determine diffusion rates and activation energies for oxygen diffusion through RuO2 thin films. Diffusion rates were found not to be constant, and to decrease with growing RuO2 thickness, while the activation energy increased. In the case of ZrO2, oxygen diffusion through low-O ZrO2 films on a-Si has been investigated by ex situ angular resolved X-ray photoelectron spectroscopy (AR-XPS) of thermally oxidized samples. For temperatures below 400°C, no additional oxidation of the underlying a-Si was observed. Based on this positive result, ZrO2 might be considered as a promising protective layer for applications where an a-Si film should be protected against oxidation.
|Award date||1 Mar 2017|
|Place of Publication||Enschede|
|Publication status||Published - 1 Mar 2017|