Quantitative depth profiling of SiOxNy layers on Si

Depth profiling of ultra-thin SiOxNy gate dielectrics calls for a precise and reproducible SIMS measurement protocol and quantification scheme to give accurate N- and O-concentrations and film thickness. We apply 500 eV Ar+ oblique-incidence primary ions to minimize transient effects and Si2M+/Si2+ (M=N, O) secondary ion intensity ratios for concentration depth profiles. Determination of N- and O-concentrations at different compositions is established by linear interpolation between sensitivities, as measured in the pure materials (i.e. Si, SiO2, Si3N4). Integral amounts of N and O thus obtained are in excellent agreement with high-resolution RBS. Apparently, sensitivities are surprisingly well constant (within a factor 2) over almost the full range of compositions. Crater depths below 10 nm are easily measured using optical profilometry, taking into account the different optical properties of transparent SiOxNy films and difference in erosion rates between Si, SiO2, Si3N4. The film thickness thus obtained is in good agreement with ellipsometry.