Overview
ISO/TR 15969:2021 provides practical guidelines for measuring sputtered depth in sputtered depth profiling used in surface chemical analysis. It covers methods applicable when ion bombardment removes material to produce depths typically from 1 nm to 500 µm, and describes how to convert sputtering time or ion dose into an accurate depth scale (sputter rate, e.g., nm/s). The report aims to improve comparability of depth profiles between instruments and to support industrial and research use of depth-profiling techniques.
Key topics
- Scope and definitions - Terms align with ISO vocabularies (ISO 18115‑1/2, ISO 22493, ISO 15932).
- Methods of sputtered depth determination:
- Crater depth measurement after profiling:
- Mechanical stylus profilometry: direct contact scans produce 1D/2D crater profiles; suitable when surface roughness is small relative to crater depth. Typical measurable range: ~10 nm to 100 µm. Calibration uses step-height standards; reported calibration uncertainty ~1% (for 1 µm gauge). Round‑robin uncertainties cited (e.g., ±1.3% for 2 µm craters).
- Optical interferometry: non‑contact method (Mireau/Michelson objectives) for smooth, flat samples (e.g., wafers, coatings). Applicable depths ~0.01 µm (10 nm) to 5 µm; uncertainties dominated by fringe counting and fractional fringe estimation (example: 325 nm ±9 nm).
- Comparison with layered samples (interfaces as markers): uses known layer thicknesses and interface positions to derive sputter depth from the 50% intensity point in profiles. Discusses systematic effects such as initial sputtering-rate changes and interface shifts caused by signal escape depth or atomic mixing (typical errors ~1–2 nm).
- Uncertainties and practical limitations - noise, surface roughness, swelling/oxidation, multi‑layer sputter rate variations, crater non-uniformity; need for multiple scans and appropriate reference materials.
Applications and users
ISO/TR 15969:2021 is directly relevant to:
- Surface analysis laboratories performing SIMS, AES, XPS depth profiling
- Semiconductor fabs and thin‑film/coatings manufacturers validating layer thickness and interfaces
- Instrument vendors and calibration labs establishing sputter rate and depth-scale traceability
- R&D groups in materials science requiring reliable depth quantification for layered structures
Practical benefits include improved depth-scale accuracy, better cross-instrument comparability, and guidance for choosing measurement methods and estimating uncertainties.
Related standards
Keywords: ISO/TR 15969:2021, surface chemical analysis, depth profiling, sputtered depth, sputter rate, crater depth measurement, stylus profilometry, optical interferometry, SIMS, XPS, AES.
