Quantitative depth profiling of SiO xN y layers on Si

Abstract

Depth profiling of ultra-thin SiO x N y 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 Si 2M +/Si 2 + (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, SiO 2, Si 3N 4). 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 SiO x N y films and difference in erosion rates between Si, SiO 2, Si 3N 4. The film thickness thus obtained is in good agreement with ellipsometry.