Secondary Ion Mass Spectrometry (SIMS)

  • qualitative trace analysis of all elements (including isotope separation, depth resolution some nm) by  mass separation of secondary ions emitted while ion bombardment of solid surfaces
  • excitation with (scanned) medium energy ion beams: oxygen (low matrix effect) or noble gas  ions (Ar), Cs+ ions (usable for negatively charged secondary ions)
  • analysis of emitted ions by a mass spectrometer (quadrupol-, magnetic, time-of-flight-), ion detection with ion counting using open electron multipliers
  • depth resolution in the nm-range limited by effects of ion-solid interaction: ions come only from the topmost atomic layer but atomic mixing depending on ion energy
  • sputter depth profiling with multiple measurement while continous ion sputtering: scanning the ion beam and using an "electronic gate" for crater rim effects
  • high dynamic range (>  6 decades)
  • Analytical features:
    • spectral analysis of all elements in the periodic system, including hydrogen
    • profiling analysis up to some µm depth
    • oxygen gas floating possible for higher intensities

     

detection limits: in the ppm-range depending on element and materials composition
correctness: standardless not better than factor 10, standardization necessary, standard material with low concentrations by ion implantation
sample requirements: - low vapour pressure<br>- flat surface<br>- sufficient electrical conductivity
application fields: - diffusion phenomena<br>- surface reactions and interface layers<br>- corrosion problems<br>- inclusions-, segregation-, element trace element distributions
materials: - semiconductors (dopant distribution, diffusion, trace impurities)<br>- thin film systems (interdiffusion, interface reactions)<br>- metals (trace analysis, grain boundaries, inclusions)<br>- amorphous materials<br>- compound materials (metal/metal, metal/ceramics, ...)

Examples

Diffusion profiles of Si into amorphous FeNbBCu after thermal treatment.
SIMS depth profile of a Cr/CoSm/Cr/SiN structure at 3.5 keV. A concentration fluctuation (CoSm) is visible, but no diffusion of Si or O is observed.