Overview
ISO 17331:2004 - Surface chemical analysis - Chemical methods for the collection of elements from the surface of silicon‑wafer working reference materials and their determination by total‑reflection X‑ray fluorescence (TXRF) spectroscopy - defines standardized chemical procedures to collect and quantify iron (Fe) and nickel (Ni) from silicon‑wafer working reference materials. The standard covers two collection techniques - vapour‑phase decomposition (VPD) and direct acid droplet decomposition (DADD) - and specifies conditions for subsequent determination primarily by TXRF, with GF‑AAS or ICP‑MS allowed as alternatives.
Key topics and requirements
- Scope & sensitivity: Applies to Fe and Ni atomic surface densities from 6 × 10^9 to 5 × 10^11 atoms/cm², targeting ultra‑low metal contamination relevant to semiconductor manufacturing.
- Collection methods: Detailed procedures for VPD and DADD to reproducibly transfer surface metals into measurable residues.
- Calibration & standards:
- Preparation of calibration specimens and calibration curves using defined calibration solutions.
- Use of an internal standard (vanadium or scandium) to normalize TXRF signal variation.
- Reagents & purity:
- Requirements for ultra‑pure water and acids (HF, H2O2, HNO3) with specified concentration ranges and impurity ceilings (pg/ml levels).
- Safety warnings and handling procedures for hazardous reagents (notably hydrofluoric acid).
- Apparatus, specimen prep & environment:
- Cleanroom considerations and specimen handling consistent with ISO 14644‑1.
- Instructions on scanning (rolling microdroplets) to cover wafer surface uniformly.
- Quality & reporting:
- Guidance on precision (repeatability/reproducibility) and the required test report content.
- Results supported by inter‑laboratory validation data.
Applications and users
ISO 17331:2004 is directly applicable to:
- Semiconductor process, metrology and contamination control laboratories performing surface chemical analysis on silicon wafers.
- Producers and users of working reference materials for TXRF calibration.
- Analytical labs using TXRF, GF‑AAS or ICP‑MS for trace metal surface contamination measurement.
- Quality assurance, materials characterization, and equipment manufacturers needing standardized procedures for low‑level Fe/Ni determination.
Practical benefits include improved comparability of ultra‑trace surface contamination data, validated calibration workflows, and documented safety/practice for handling ultra‑pure reagents and HF.
Related standards
Keywords: ISO 17331:2004, TXRF, silicon wafer, vapour‑phase decomposition, direct acid droplet decomposition, surface chemical analysis, iron nickel, working reference materials, semiconductor contamination.