Cross characterization of ultrathin interlayers in HfO2 high-k stacks by angle resolved x-ray photoelectron spectroscopy, medium energy ion scattering, and grazing incidence extreme ultraviolet reflectometry
In order to miniaturize metal oxide semiconductor field effect transistors even further and improve their performance, channel lengths and gate dielectric thicknesses must be decreased. Traditionally deployed SiO2 dielectrics face the difficulty of excessive leakage current and must be replaced by alternative (high-k) materials with larger dielectric permitivitties and smaller equivalent oxide thicknesses. A current focus of the industry is studying thin films of HfO2 because they are a main candidate for the next generation of gate dielectrics. Measuring the depth profiles of the constituents of these layered systems is instructive in that it provides information about the thicknesses of the layers and the degree of intermixing between them. Here we demonstrate the use of a novel characterization technique, grazing incidence extreme ultraviolet reflectometry (GIXUVR), which utilizes short wavelength radiation from non-synchrotron sources to measure the depth profile of such thin-film structures. Depth profiles of samples from the same wafers were also measured using angle resolved x-ray photoelectron spectroscopy, medium energy ion scattering, and synchrotron GIXUVR. These measurements show the compatibility and complementarity of the results. The benefits of GIXUVR are the short measuring time (on the order of milliseconds to seconds), as well as high thickness, density, and material sensitivity due to a very efficient interaction of extreme ultraviolet light with matter.