ISO 5618-2:2024

Overview

ISO 5618-2:2024 - "Fine ceramics (advanced ceramics, advanced technical ceramics) - Test method for GaN crystal surface defects - Part 2: Method for determining etch pit density" - defines a standardized laboratory method to determine etch pit density (EPD) on single-crystal GaN substrates and films. The method detects dislocations and processing-introduced surface defects exposed on the (0001)Ga polar face and is applicable to defects listed in ISO 5618-1 for:

• single-crystal GaN substrates;
• homoepitaxial GaN films on GaN substrates;
• heteroepitaxial GaN films on Al2O3, SiC, or Si substrates.

The standard applies where etch pit density is ≤ 7 × 10^7 cm−2.

Key topics and technical requirements

• Principle: etching accelerates material removal at dislocation sites, producing characteristic etch pits (inverted hexagonal pyramidal pits for threading dislocations; oval pits for basal plane dislocations).
• Sample preparation: pre-treatment, etching and washing procedures to form etch pits (general steps described without prescribing specific reagents or parameters).
• Imaging and microscopy: use of optical microscopy under defined observation conditions (objective lens selection, numerical aperture, image resolution / pixels per inch) to capture analyzable etch pit images.
• Measurement design: defined measurement area and measurement points for representative sampling; normative annexes provide verification procedures.
• Counting and calculation: explicit counting criteria for etch pits, method for calculating etch pit density (EPD), and calculation of coefficient of variation to assess measurement repeatability.
• Pit-size analysis: procedures to categorize inverted hexagonal pyramidal pits by size, construct histograms, and compute size-level percentages to support defect classification.
• Reporting and verification: required test report items and annexes for verification and classification reproducibility.

Practical applications

• Quality control and acceptance testing of GaN substrates and epitaxial films for:
  • LED, laser diode, and photonics device manufacturers;
  • GaN power device developers (high-voltage/high-current applications);
  • Semiconductor fabs performing process monitoring and failure analysis.
• R&D and materials characterization labs assessing dislocation densities, process-induced defectivity, and substrate/epilayer quality.
• Calibration and competency checks in testing laboratories aiming for ISO/IEC 17025 compliance.

Who should use this standard

• Material scientists, process engineers, metrology specialists, QC managers, and laboratory technicians involved in GaN substrate/film production, device fabrication, and reliability assessment.

Related standards

• ISO 5618-1 - Classification of GaN surface defects (normative reference)
• ISO 19606 - AFM test method for surface roughness of fine ceramic films
• ISO 21920-2:2021 - Surface texture terminology and parameters
• ISO/IEC 17025 - Laboratory competence and calibration requirements

ISO 5618-2:2024 provides a consistent, reproducible framework for etch pit density measurement, enabling better comparability of GaN surface-defect data across industry, research, and quality systems.