Analysis of High-k Dielectric Thin Films with Time-of-Flight Medium Energy Backscattering
Geil, Robert Druhan
Time-of-flight medium backscattering (TOF-MEBS) is a powerful analytical technique for characterizing high-k dielectric thin films and their interface with Si. The amount of information that can be obtained from backscattering experiments can be maximized by carefully choosing a detailed thin film model for simulations and by implementing an experimental configuration that optimizes depth resolution. This thesis presents four main studies. In the first study a thin film model for simulating backscattering spectra is developed and used to extract interfacial information from thin dielectric films. A sufficient film model was found to consist of three layers: 1) dielectric material 2) interfacial silicate and 3) substrate. In the next study, the influence of multiple scattering and surface roughness on the shape of backscattering spectra was evaluated by generating spectra using Monte Carlo simulations. For TOF-MEBS analysis of thin (~50 Å) ZrO2 films on Si, multiple scattering and surface roughness were found to have a negligible influence on the shape of a backscattering spectrum. The third study presents calculations and measurements of the energy and depth resolution of the TOF-MEBS system, and the experimental configuration for optimizing depth resolution was determined. For the analysis of thin films (~50 Å), the depth resolution of the TOF-MEBS system can be improved by operating at a beam energy around 150 keV and by using a glancing tilt angle (~54°). However, if the angle is too glancing, multiple scattering and surface roughness can significantly degrade depth resolution and distort the shape of the backscattering spectrum. ZrO2 films deposited on H-terminated Si and native Si oxide surfaces were characterized with TOF-MEBS for the final study. The deposition surface was found to significantly affect the physical and chemical properties of MOCVD ZrO2 films and their interface with Si. ZrO2 films deposited on H-terminated Si are low in density and susceptible to the formation of an interfacial layer of a Zr-silicate. ZrO2 films deposited on native Si oxide surfaces results in dense films that are less susceptible to interfacial layer formation, although some silicate formation is likely.