Determination of ultratrace elements in photoresist solvents using the Thermo Scientific iCAP TQs ICP-MS

Importance of the Topic

Propylene glycol methyl ether acetate (PGMEA) and N-methyl-2-pyrrolidone (NMP) are key solvents in semiconductor photoresist formulations, coming into direct contact with wafer surfaces. Ultralow levels of metal impurities at ng·L⁻¹ concentrations can cause defects in submicron structures, making sensitive and interference-free trace metal analysis essential for quality control in microelectronics manufacturing.

Objectives and Study Overview

This study demonstrates a direct analytical approach for quantifying ultratrace metal concentrations in semiconductor-grade PGMEA and NMP without laborious sample preparation. It highlights the use of cold plasma and triple quadrupole ICP-MS (ICP-TQ) technologies on the Thermo Scientific iCAP TQs system to minimize background equivalent concentrations (BEC) and lower detection limits (LOD). The method supports seamless switching between hot/cold plasma and single/triple quadrupole modes in a single measurement run.

Methodology and Instrumentation

Sample Preparation:

• Standards: Semiconductor-grade PGMEA used as matrix for 200, 400 and 1000 ng·L⁻¹ multielement spikes.
• Vessels: Precleaned PFA bottles rinsed with ultrapure water in a laminar hood.
• Recovery Tests: 100 ng·L⁻¹ spikes to assess accuracy.

Instrument Configuration:

• ICP-MS System: Thermo Scientific iCAP TQs ICP-MS, operated in SQ-KED (He), SQ-CP-NH₃ (cold plasma, NH₃), and TQ-O₂ (triple quadrupole, O₂) modes.
• Sample Introduction: 100 µL·min⁻¹ PFA concentric nebulizer, quartz cyclonic spray chamber at –10 °C, pure O₂ addition (30 mL·min⁻¹) to prevent carbon buildup.
• Interface: Platinum-tipped sampler and skimmer cones; 1.0 mm I.D. quartz injector; cold plasma extraction lens.
• Autosampler: Teledyne CETAC ASX-112FR.
• Operating Parameters: Forward power of 540 W (cold) to 1550 W (hot), nebulizer gas 0.68–1.17 L·min⁻¹, CRC gases (He, NH₃, O₂) optimized per mode.

Main Results and Discussion

The method achieved LODs in the sub-ng·L⁻¹ to low ng·L⁻¹ range for twenty-one elements in both PGMEA and NMP. Spike recoveries ranged from 88 % to 111 %, demonstrating accuracy. Cold plasma suppressed carbon and argon species, while triple quadrupole mass shift mode (e.g., As⁺→AsO⁺) eliminated polyatomic interferences. Calibration curves for Mg, Ti, As and Ag in PGMEA showed excellent linearity from 100 to 1000 ng·L⁻¹ under common settings, confirming sensitivity and robustness.

Benefits and Practical Applications

• Direct, minimal-prep analysis of volatile organic solvents at ultratrace levels.
• Flexible mode switching (hot/cold plasma, single/triple quadrupole) in a single run.
• One standardized method for both PGMEA and NMP simplifies workflow and boosts laboratory throughput.
• Reliable quantification supports semiconductor QC and failure prevention in device fabrication.

Future Trends and Potential Applications

Advances may include integration of automated mode selection to further streamline analyses, exploration of alternative reaction gases for enhanced interference removal, extension to other high-carbon or high-volatility matrices, and real-time process monitoring in semiconductor fabs through inline ICP-MS platforms.

Conclusion

The Thermo Scientific iCAP TQs ICP-MS, combining cold plasma, kinetic energy discrimination and triple quadrupole modes, delivers sensitive, interference-free multielement analysis of PGMEA and NMP at ng·L⁻¹ levels. Its methodological flexibility and consistent performance make it an ideal tool for rigorous quality control of photoresist solvents in semiconductor manufacturing.