Overview
ISO 23170:2022 defines a non-destructive, quantitative method for depth profiling nanoscale heavy metal oxide ultrathin films on silicon (Si) substrates using medium energy ion scattering (MEIS). The standard covers MEIS measurement principles, recommended experimental setup, spectrum simulation and fitting, and reporting practices for accurate surface chemical analysis of amorphous or polycrystalline thin films (typically <10 nm).
Key topics and technical requirements
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Technique and scope
- MEIS is specified for ultrathin heavy metal oxide films on Si; the document is targeted at amorphous or polycrystalline films (not crystalline films).
- Typical projectiles: H or He ions in the medium energy range (around 100–500 keV).
- MEIS provides near-atomic depth resolution for surface and interface composition analysis.
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Experimental controls and reporting
- Set and report all ion scattering conditions: ion energy, ion species, incidence angle, scattering angle, ion dose/current and analysis time, beam radius, and energy analyser type.
- Specimens should be flat; surface contamination >~1 nm should be cleaned prior to analysis.
- For ultrathin films around ~1 nm, report results as surface areal density rather than thickness for better reproducibility.
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Spectrum simulation and fitting
- Use validated simulation codes (examples referenced: PowerMeis, SIMNRA) incorporating binary scattering, electronic stopping, and ideally multiple scattering.
- Line shapes: start with Gaussian; use exponentially modified Gaussian for high-resolution systems when needed.
- Choose appropriate interatomic potentials (e.g., Molière) and straggling models.
- Fit measured spectra by adjusting layer thickness/composition and using chi-square or iterative matching.
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Electronic stopping power
- SRIM-derived stopping powers are acceptable for non-critical analyses but can have significant errors.
- For high-accuracy (consistency better than 10%), use measured or tabulated stopping powers from the IAEA stopping power database; fitting parameters and guidance are provided in the standard.
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Expected uncertainty
- When guidelines are followed, uncertainty can be below 10% for ultrathin films; additional calibration standards improve reliability.
Practical applications
- Semiconductor metrology: characterization of nm-scale gate oxides, interfaces, and contamination on Si.
- Thin-film and nanomaterials research: composition and depth profiling of heavy metal oxide coatings and core–shell nanoparticles.
- Quality assurance and process control in microelectronics and materials labs where non-destructive, high-resolution depth profiling is required.
- Instrument manufacturers and MEIS service labs implementing validated MEIS workflows.
Who should use this standard
- Surface analytical laboratories, semiconductor process engineers, materials scientists, metrology labs, and instrument vendors seeking standardized MEIS procedures for reproducible, quantitative depth profiling.
Related standards and resources
- Normative reference: ISO 18115 (Surface chemical analysis - Vocabulary).
- Other resources cited: PowerMeis and SIMNRA code sources, Casp line-shape tools, and the IAEA electronic stopping power database for improved accuracy.