Analysis of Sulfuric Acid Using a Single Set of Operating Conditions with HR-ICP-MS

Importance of the Topic

Continual scaling in integrated circuit production demands ultra low levels of trace metals in process chemicals. Concentrated sulfuric acid is a critical wafer cleaning reagent that must be monitored for metallic impurities to prevent device contamination. High precision elemental analysis of high purity acids is essential to ensure quality control in semiconductor fabrication.

Study Objectives and Overview

The application note demonstrates single operating conditions for high resolution ICP-MS analysis of trace metals in 9.8 % m/m sulfuric acid. Goals include meeting detection limits and recoveries defined by SEMI Tier C guidelines and evaluating the performance of the Thermo Scientific ELEMENT 2 high resolution sector field ICP-MS for multi-element analysis in aggressive, high matrix samples.

Methodology and Instrumentation

• Sample Preparation: 1:10 dilution of concentrated H2SO4 in ultra-pure water to minimize handling and contamination risk.
• Instrument: Thermo Scientific ELEMENT 2 high resolution ICP-MS based on magnetic sector field technology.
• Sample Introduction System: Self-aspirating PFA μFlow nebulizer, Peltier-cooled PFA spray chamber at 0 °C, platinum injector, and platinum-tipped cones for inertness and long-term stability.
• Operating Conditions: Single set of hot plasma parameters with rapid switching between low (LR=300), medium (MR=4000), and high (HR=10000) mass resolution to eliminate interferences without collision/reaction gases.

Key Results and Discussion

• Detection Limits: Sub-pg·g⁻¹ to a few pg·g⁻¹ limits achieved for 21 elements in 9.8 % H2SO4.
• Background Equivalent Concentrations: All BEC values were below the SEMI Tier C threshold of 100 pg·g⁻¹ in concentrated acid, with most under 10 pg·g⁻¹.
• Interference Removal: High resolution effectively resolved sulfur-based polyatomic interferences (e.g. SN on Ti, SO₂ on Zn) at HR=10000.
• Spike Recoveries: At a 5 pg·g⁻¹ spike level, recoveries ranged from 86 % to 105 % across all elements with RSDs below 10 %, satisfying SEMI criteria.
• Sensitivity and Stability: Sensitivity exceeded 2×10⁶ cps per ng·g⁻¹ for mid-mass elements and off-peak noise remained under 0.2 cps, supporting reliable sub-pg·g⁻¹ quantification.

Benefits and Practical Applications

• Simplified sample handling with only dilution reduces contamination risk and increases throughput.
• Single plasma condition for multi-element analysis streamlines method development and daily operation.
• High resolution sector field ICP-MS provides robust 24/7 production monitoring and quality control of semiconductor process chemicals.

Future Trends and Potential Applications

Ongoing advances in sector field ICP-MS, including automated resolution switching and enhanced plasma control, are expected to further lower detection limits and extend application to other corrosive and high matrix process chemicals. Integration with automated sample preparation will boost throughput in high volume semiconductor and advanced materials laboratories.

Conclusion

The Thermo Scientific ELEMENT 2 HR-ICP-MS, operated under a single set of plasma parameters, delivers the sensitivity, selectivity, and stability required to analyze trace metals in high purity sulfuric acid at SEMI Tier C levels. This streamlined approach enhances routine quality control and contamination prevention in semiconductor manufacturing.