Extreme ultraviolet reflectometry for structural and optical characterization of thin films and layer systems

Abstract

The aim of this work is to explore the capabilities of extreme ultraviolet reflectometry (EUVR) as a metrology method for determination of layer parameters (such as thickness, density, roughness, chemical composition) in application to industry-relevant high-k semiconductor films. As a short-wavelength photon-in/photon-out technique, spectral EUVR allows for non-destructive characterization of layer systems at the sub-nanometer scale. A special focus of the study is put on the near-edge spectral region, considering the advantage of high chemical contrast that it provides. Adding the angular dimension to the analyzed reflectivity dataset places additional constraints on the layer model, improving quality of the structural reconstruction and opening a possibility of the complex refractive index determination. A modification of a laboratory polychromatic EUVR setup that enables multi-angle (2°-15°) spectrally broadband (9.5-17 nm) grazing incidence reflectance measurements is presented. The capabilities of the tool are initially tested on a set of thin (1-9 nm) HfO2 films on Si substrates. Further studies are performed on a non-uniform sample contamination layer in spatially resolved reflectivity mapping mode, showing the potential of the technique for local characterization of surfaces. The presence of amorphous Al2O3 in the contamination layer is confirmed by the near-edge fine structure analysis. In addition, spatial resolution extendibility study is performed. With minor alterations to the sample illumination scheme, an EUV spot size of 25 x 30 μm (FWHM) is experimentally achieved. Another major topic of the present thesis is optical and structural characterization of LaLuO3 (LLO) films, a promising high- candidate for future MOSFET technology. EUV reflectivity is experimentally obtained for amorphous, orthorhombic, cubic and hexagonal LLO modifications in the range of 70-200 eV (6.2-17.7 nm)at 5°, 12° and 20° angle of incidence using synchrotron radiation. Previously unreported La absorption edge features are observed. After extending the angular range of the measurement to 2°-50°, the optical constants of amorphous and orthorhombic LLO films are determined, along with the corresponding layer structure parameters. From the near-edge optical constant analysis, La:Lu stoichiometry ratio and the film density are derived. Compared to X-ray reflectance, EUVR method shows a higher sensitivity to sample contamination, substrate oxidation and strain effects. Correlation analysis of the fit parameters for the EUVR and XRR results indicates that both methods allow for precise determination of the layer structure, also highlighting a superior chemical contrast of the EUVR measurements. In attempt to optimize the EUVR data acquisition process, it is found that angle-resolved approach presents the greatest potential for the EUVR method, allowing for in-depth probing and more precise reconstruction of layer structures. The measurement wavelength in this case may be selected to provide the best chemical contrast, according to the studied material