Determination of ultratrace elements in semiconductor grade Isopropyl Alcohol using the Thermo Scientific iCAP RQ ICP-MS

Importance of Ultrapure IPA in Semiconductor Manufacturing

Isopropyl alcohol (IPA) plays a critical role in semiconductor wafer cleaning due to its solvent properties and direct contact with sensitive surfaces. Any trace metal contamination at ultratrace levels (ng·L⁻¹) can compromise device performance and yield. High-precision elemental analysis of IPA is therefore essential to maintain quality control in semiconductor production.

Objectives and Study Overview

This application note presents a direct ICP-MS approach for determining ultratrace metal concentrations in semiconductor-grade IPA using cold plasma on the Thermo Scientific iCAP RQ ICP-MS. Key goals include:

• Quantifying 26 trace elements at ng·L⁻¹ levels.
• Reducing background equivalent concentrations (BEC) and detection limits (LoD) via cold plasma.
• Demonstrating rapid mode switching between hot and cold plasma to optimize throughput.

Methodology and Instrumentation

Sample Preparation and Calibration

• All blanks, standards, and samples prepared in precleaned PFA bottles, rinsed and dried in a laminar flow hood.
• Calibration standards at 20, 50, 100, and 200 ng·L⁻¹ in IPA gravimetrically spiked from multielement stock solutions.
• Recovery assessed by spiking IPA with 100 ng·L⁻¹ of analytes.

ICP-MS Configuration

• Instrument: Thermo Scientific iCAP RQ ICP-MS with dynamic frequency RF generator.
• Ion optics: 90° interface to remove neutrals and enhance sensitivity.
• Sample introduction: 100 μL·min⁻¹ self-aspirating PFA microflow nebulizer and peltier-cooled quartz spray chamber at –10 °C.
• Oxygen addition (50 mL·min⁻¹) to mitigate carbon buildup.
• Quartz injector (1.0 mm I.D.) and platinum-tipped cones for enhanced robustness.
• Operating conditions: Hot plasma at 1,350 W, cold plasma at 800 W; nebulizer gas flow 0.7 L·min⁻¹ (hot) and 1.0 L·min⁻¹ (cold); dwell time 100 ms per peak, 10 sweeps.

Main Results and Discussion

Direct analysis of IPA was completed in under 5 minutes, including uptake, measurement, washout, and plasma mode switching. Cold plasma effectively suppressed argon and carbon-based polyatomic interferences, especially for low ionization potential elements (Li, Na, Mg, K, Ca, Cr, Fe), enabling sub-ng·L⁻¹ LoDs. For instance, the interference at m/z 24 (12C2) affecting Mg was eliminated under cold plasma, yielding BEC of 0.78 ng·L⁻¹ and LoD of 0.54 ng·L⁻¹. Recovery for a 100 ng·L⁻¹ spike ranged from 86 % to 118 % across all 26 elements, demonstrating accuracy and precision. The dynamic frequency RF generator ensured stable signals during rapid transitions between plasma modes, supporting high throughput and extended measurement periods.

Benefits and Practical Applications

By applying cold plasma on the iCAP RQ ICP-MS, laboratories can:

• Achieve ultratrace detection limits required for semiconductor-grade solvents.
• Avoid laborious sample digestion or dilution steps, reducing contamination risk.
• Switch seamlessly between hot and cold plasma to tailor conditions per element.
• Maintain high sample throughput with reliable performance on organic matrices.

Future Trends and Opportunities

Emerging semiconductor applications demand even lower trace metal specifications. Future developments may include:

• Further optimization of plasma conditions for high-carbon organic solvents.
• Advanced collision/reaction cell chemistries to extend interference removal capabilities.
• Integration with automated sample handling for fully unattended ultratrace analysis.
• Machine learning algorithms for real-time signal correction and quality assurance.

Conclusion

The Thermo Scientific iCAP RQ ICP-MS with cold plasma technology provides a rapid, sensitive, and interference-free method for ultratrace element determination in semiconductor-grade IPA. The approach meets industry requirements for detection limits and reproducibility, while minimizing sample preparation and maximizing throughput.

Reference

Vincent T., Wu V., Wills J.D., Rottmann L. Application Note 43147, Thermo Fisher Scientific, 2017.