Elemental and Particle Analysis of N-Methyl-2-Pyrrolidone (NMP) by ICP-MS/MS

Significance of the Topic

The demand for ever finer line widths in semiconductor manufacturing drives stringent control of both dissolved and particulate inorganic impurities in process chemicals. N-Methyl-2-pyrrolidone (NMP) is widely used in wafer cleaning and resist removal steps, where trace metal and nanoparticle contaminants can degrade device yields and reliability. Advanced analytical methods capable of quantifying sub-ppt levels of dissolved elements and characterizing metal nanoparticles (NPs) are therefore essential for quality control in fabs and chemical supply chains.

Study Objectives and Overview

This study evaluates the performance of the Agilent 8900 triple quadrupole ICP-MS (ICP-QQQ) for comprehensive elemental and NP analysis in two grades of NMP: an electronic (EL) grade and a new supreme pure (SP) grade. The objectives were to quantify 54 dissolved elements by standard addition and to detect and size 14 metal NPs using single-particle ICP-MS (spICP-MS) in a single automated workflow, demonstrating compliance with SEMI C33-0213 specifications.

Methodology and Instrumentation

• Sample Preparation
    • Direct analysis without acidification or dilution for both grades.
    • Standard addition calibration for 54 dissolved elements using certified multi-element and single-element standards.
    • spICP-MS mode for 14 NP-forming elements with 0.1 ms integration time.
• Instrumentation
    • Agilent 8900 ICP-QQQ with MFN-100 nebulizer, quartz spray chamber, Cu/Pt cones, and 1.5 mm injector torch.
    • Option gas: 20 % O₂ in Ar to minimize organic matrix build-up.
    • Cell gases: NH₃, H₂, He, O₂ in multitune MS/MS modes for interference removal.
• Nanoparticle Calibration
    • Nebulization efficiency determined using 200 nm SiO₂ NP RM (19.6 %).
    • Validation of spICP-MS size and mass accuracy with 25 nm Fe₃O₄ NPs (measured mass 40 ag vs theoretical 42 ag).

Main Results and Discussion

The method achieved low background equivalent concentrations (BECs) well below SEMI grade-3 limits for all 54 elements. SP grade NMP exhibited significantly lower dissolved metal levels than EL grade, confirming enhanced purity. Carbon-based polyatomic interferences on Mg, Al, P, and Cr were effectively removed using optimized cell-gas and mass-shift modes. spICP-MS data revealed that EL grade NMP contained higher counts and larger sizes of Fe, Cr, Ni, Mn, and Cu NPs, with total Fe NP concentration of 2.7 ng/L compared to 69 pg/L in SP grade. Size distributions indicated predominantly 20–30 nm particles in the EL sample, whereas SP grade showed far fewer and smaller particles overall.

Benefits and Practical Applications

• Unified analysis of dissolved and particulate impurities in a single run enhances throughput and reduces sample handling.
• Sub-ppt detection limits and comprehensive interference removal meet or exceed SEMI specifications for high-purity NMP.
• Multi-element NP characterization supports root-cause identification of contamination sources from equipment or supply systems.
• Flexible method accommodates an unlimited number of elements, facilitating extension to new semiconductor chemicals and matrices.

Future Trends and Potential Uses

As device geometries continue to shrink, tolerance for both soluble metals and metallic nanoparticles will tighten further. Integration of ICP-QQQ methods into inline or at-line monitoring, coupled with automated data analysis, can provide real-time contamination control. Expanding the technique to include nonmetallic impurities, organometallic species, and isotopic tracing will enhance process understanding. The combination of spICP-MS with complementary imaging and surface analysis methods promises a more complete characterization of nano-contaminants in advanced process chemicals.

Conclusion

The Agilent 8900 ICP-QQQ, leveraging multitune ICP-MS/MS and spICP-MS modes, delivers a robust, sensitive, and fully automated platform for simultaneous determination of 54 dissolved elements and 14 elemental nanoparticles in NMP. The method clearly distinguishes impurity profiles of EL and SP grades, ensures compliance with SEMI C33-0213, and provides actionable data for contamination control in semiconductor fabrication.

References

1. Agilent Technologies. Measuring Inorganic Impurities in Semiconductor Manufacturing; Pub. 5991-9495EN.
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4. SEMI C33-0213: Specifications for N-Methyl-2-Pyrrolidone.
5. SEMI F104: Particle Test Method Guide for Ultrapure Water and Liquid Chemical Systems.
6. FUJIFILM Wako Pure Chemical Corporation. High-purity Solvent and Acid.
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