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

Significance of the Topic

Isopropyl alcohol (IPA) is widely used in semiconductor wafer processing as a solvent for cleaning surfaces. Ensuring ultratrace purity is essential because metal contaminants at ng·L-1 levels can cause defects and yield losses. Direct, contamination-free analysis of IPA for trace metals is critical for quality control in semiconductor manufacturing.

Objectives and Study Overview

This application note aimed to develop a robust ICP-MS method for measuring ultratrace metal impurities in semiconductor-grade IPA. It combined cold plasma and triple quadrupole ICP-MS technologies to minimize background equivalent concentrations (BECs) and achieve low detection limits (LODs) without extensive sample preparation. The study demonstrated flexible switching among hot/cold plasma and single/triple quadrupole modes within a single measurement run.

Methodology and Instrumentation

• Sample Preparation: Blanks, standards, and IPA samples were handled in precleaned PFA bottles under laminar flow. Calibration standards were prepared gravimetrically in the ng·L-1 range (10× for phosphorus) using semiconductor-grade IPA as blank matrix.
• Instrument Configuration: Thermo Scientific iCAP TQs ICP-MS with dedicated organic sample introduction including a 100 µL/min PFA microflow nebulizer, peltier-cooled (-10 °C) quartz spray chamber with O2 addition, 1.0 mm quartz injector, and platinum sampler/skimmer cones. Teledyne CETAC ASX-112FR autosampler presented samples.
• Operational Modes: Single quadrupole modes (Standard, KED, Cold plasma) and triple quadrupole modes (TQ-O2 and TQ-NH3 mass shift) were selected automatically via Reaction Finder in Qtegra ISDS software. Cold plasma (600 W) suppressed argon and carbon interferences; hot plasma (1450 W) was used for high-IP elements. CRC gases (O2, NH3, He) enabled specific mass shifts and collision filtering.
• Autotune: Instrument parameters such as nebulizer gas flow, extraction lens voltage, and CRC gas flows were optimized automatically for each mode to ensure consistent plasma conditions.

Key Results and Discussion

• Background Equivalent Concentrations (BECs) and Limits of Detection (LODs) for 35 elements in IPA were determined, showing BECs as low as 0.01 ng·L-1 (Li) and LODs down to 0.001 ng·L-1 (Cd).
• Triple Quadrupole O2 mass shift mode effectively removed polyatomic interferences at 31P by shifting to 47[PO]+, achieving low BEC and LOD for phosphorus.
• Calibrations for representative elements (Li, P, K, Ti, As, Zr, Ta) demonstrated excellent linearity and sensitivity in the ng·L-1 range.
• Oxygen addition to the spray chamber eliminated carbon deposits on the cones, stabilizing signals during direct analysis of the high-carbon IPA matrix.
• Seamless switching between analysis modes within a single run improved throughput and user productivity without manual reconfiguration.

Benefits and Practical Applications

• Direct analysis of IPA without sample digestion or dilution, reducing contamination risk and preparation time.
• Flexible mode switching tailors plasma conditions and interference removal to each element, optimizing sensitivity and accuracy.
• Automated Reaction Finder and autotune streamline method development and ensure reproducible performance.
• Applicability to routine quality control in semiconductor fabs, supporting ultratrace monitoring of cleaning solvents.

Future Trends and Applications

Continued development of ICP-MS technologies may include integration of additional reaction gases to target challenging interferences, further refinements in cold plasma interfaces, and coupling with cleanroom-compatible autosamplers. Expansion to other high-purity organic solvents and advanced data analytics (e.g., real-time QA/QC dashboards) will enhance process control and predictive maintenance in semiconductor manufacturing.

Conclusion

The Thermo Scientific iCAP TQs ICP-MS, combining cold plasma and triple quadrupole mass spectrometry, provides a powerful, flexible solution for ultratrace metal analysis in semiconductor-grade IPA. The method delivers low BECs and LODs, reliable operation across multiple modes, and streamlined workflows, supporting stringent purity requirements in semiconductor quality control.

References

No references were provided in the original text.