Determination of ultratrace elements in semiconductor grade nitric acid using the Thermo Scientific iCAP TQs ICP-MS

Importance of the Topic

The purity of chemicals used in semiconductor fabrication directly impacts device yield and performance. Ultratrace elemental impurities in high-purity nitric acid can lead to wafer surface contamination, reducing production efficiency. Monitoring and controlling contaminants at sub-ng·L⁻¹ levels is therefore critical for quality assurance in semiconductor manufacturing.

Objectives and Study Overview

This study demonstrates a robust method for quantifying ultratrace elements in semiconductor-grade HNO₃ using a triple-quadrupole ICP-MS (iCAP TQs). Key aims include:

• Evaluating hot vs. cold plasma modes for interference suppression.
• Assessing single-quad and triple-quad configurations for sensitivity and detection limits.
• Establishing reliable switching between analysis modes within a single run.

Methodology and Instrumentation

Sample Preparation:

• All bottles and labware pre-cleaned with ultrapure water and dried in a laminar flow hood.
• 2% (v/v) semiconductor-grade HNO₃ used for blanks, rinses, and matrix.
• Multielement standards (10 – 100 ng·L⁻¹) prepared gravimetrically from certified stock.

Instrument Configuration:

• Thermo Scientific iCAP TQs ICP-MS with dry fore-vacuum pump for clean-room compatibility.
• Sample introduction: quartz cyclonic spray chamber (2.7 °C), PFA microflow nebulizer (100 µL·min⁻¹), sapphire-injector torch.
• Pt sampler and skimmer cones, cold plasma extraction lens.

Analysis Modes:

• Single Quadrupole: hot plasma (CH-SQ-N/A), cold plasma (CL-SQ-N/A), hot+He KED (CH-SQ-KED).
• Triple Quadrupole: cold plasma with H₂/He (CL-TQ-H₂), cold plasma with NH₃ (CL-TQ-NH₃), hot plasma with O₂ mass shift (CH-TQ-O₂).

Main Results and Discussion

Mass Shift vs. KED:

• 51V analysis: CH-TQ-O₂ mode shifted V⁺ to VO⁺, eliminating ClO⁺ interferences. Compared to He KED, the mass shift mode delivered ~5× lower background equivalent concentrations (BEC) and improved detection limits.
• 40Ca analysis: CL-TQ-H₂ on-mass mode removed 40Ar⁺ interferences more effectively than cold-NH₃ single-quad, achieving sub-ng·L⁻¹ detection limits.

Detection Limits:
Using ten replicate blank measurements, BEC and LOD for 44 elements were determined. All analytes achieved sub-ng·L⁻¹ limits, demonstrating the method’s suitability for semiconductor-grade acid analysis.

Benefits and Practical Applications of the Method

This approach offers:

• Flexible switching between hot/cold plasma and single/triple quadrupole modes.
• Superior interference removal with mass shift and collision/reaction cell technologies.
• High throughput and ease of use via automated mode selection in Qtegra ISDS software.

Applications include incoming reagent QC, process control, and contamination tracking in semiconductor fabs.

Future Trends and Potential Applications

Emerging developments may include:

• Integration with automated sample handling for continuous monitoring.
• Advanced chemometric tools for real-time drift correction and data analytics.
• Expansion to other high-purity reagents and complex matrices in microelectronics and biotechnology.

Conclusion

The Thermo Scientific iCAP TQs ICP-MS demonstrates exceptional flexibility and sensitivity for ultratrace elemental analysis in semiconductor-grade HNO₃. By combining cold plasma operation, collision/reaction cell strategies and triple quadrupole mass shift techniques, the method achieves sub-ng·L⁻¹ detection limits across a broad elemental range while maintaining high throughput and reproducibility.