sims (secondary ion mass spectrometry)

SIMS (Secondary Ion Mass Spectrometry) provides depth profiles of elemental and isotopic composition by sputtering the sample surface and analyzing ejected secondary ions. **Principle**: Primary ion beam (Cs+, O2+, or Ga+) sputters sample surface. Ejected secondary ions analyzed by mass spectrometer. Composition measured as function of sputter depth. **Depth profiling**: Continuous sputtering progressively excavates crater. Composition measured at each depth level. Produces concentration vs depth plot. **Sensitivity**: Detection limits as low as 10^14 - 10^16 atoms/cm³ depending on element and matrix. Among the most sensitive analytical techniques. **Applications**: Dopant depth profiles (B, P, As concentrations vs depth), contamination analysis, thin film composition, interface characterization, diffusion studies. **Primary beams**: O2+ enhances positive secondary ion yield (good for electropositive elements - B, Al). Cs+ enhances negative ion yield (good for electronegative elements - C, O, F, As, P). **Mass spectrometers**: Magnetic sector (high mass resolution), quadrupole (faster, lower resolution), TOF-SIMS (surface analysis, imaging). **Dynamic SIMS**: Continuous sputtering for depth profiles. Primary use in semiconductor. **Static SIMS/TOF-SIMS**: Very low primary dose preserves surface. Surface composition and molecular identification. **Quantification**: Standards with known concentrations (implant dose standards) required for quantitative analysis. **Matrix effects**: Ion yield varies with matrix composition. Can complicate quantification at interfaces.