High-resolution depth profiling of ultrathin gate oxides using medium-energy ion scattering

Medium-energy ion scattering (MEIS) has been used to characterize the composition of ultrathin gate dielectrics. Examples covering investigations on silicon-oxides and oxynitrides as well as high-dielectric constant (high-K) films on silicon substrates are discussed, with special emphasis on understanding film growth. In the MEIS spectra obtained from ultrathin films, the signals from different oxygen and nitrogen isotopes are well separated. By analyzing samples that have undergone different thermal processing steps in gases of different isotopes, both growth mechanisms and also atomic exchange effects can therefore be monitored directly. For various high-K dielectric films, we found that oxygen-isotope exchange is significant even at temperatures below 500°C. This may point to a serious limitation for the application of such materials as gate dielectrics in semiconductor devices.