Characterization of semiconductor materials by X-ray scattering

Cost reduction is the driving force in semiconductor industry which leads to a permanent downscaling of semiconductor structures. For the year 2003, the National Technology Roadmap for Semiconductors outlines the minimum lateral feature size of metal oxide silicon (MOS) transistors to be 100 nm only. As a consequence, there is an urgent need for non-contact, non-destructive characterization tools which allow to determine the real structure of semiconductors on the nm-scale of interest. X-ray reflectivity, X-ray diffraction, and high resolution X-ray diffraction are among the most promising characterization methods. Xray reflectivity allows to determine real structure parameters of layer stacks such as surface and interface roughness, layer density, and thicknesses of crystalline as well as amorphous thin layers down to 1 nm. Selected examples include ultra-thin gate oxides on Si substrates and hard-coatings acting as diffusion barriers. X-ray diffraction is widely used for the phase analysis and the determination of the chemical composition of partially crystalline structures, Here, X-ray diffraction is applied to measure the strain of microsized passivated metallizations and the orientation of crystal lattices in thin polycrystalline films. High resolution X-ray diffraction reveals the perfection of crystal lattices of thin epitaxial layers. It allows to measure the lattice mismatch and the degree of relaxation of thin layers on substrates as well as the chemical composition of alloys. High resolution X-ray diffraction is demonstrated on a SiGe layer structure, and the results are refined by applying X-ray reflectivity.