APWC: Analysis of Organic Solvent Samples by Automatic Standard Addition Method using ASAS-ICP-MS/MS

Significance of the Topic

Ensuring the purity of organic solvents at ultra-trace levels is critical for semiconductor manufacturing quality and yield. Impurities in isopropyl alcohol (IPA) can compromise wafer cleaning processes and introduce defects. Regulatory standards such as SEMI C41-0705 set maximum contaminant limits below 100 ppt for each metal, demanding highly sensitive and reliable analytical methods.

Objectives and Study Overview

This study aimed to develop and demonstrate an automated workflow for the quantification of trace metal impurities in high-purity IPA. The goals were:

• To implement a Method of Standard Addition (MSA) using an Automated Standard Addition System (ASAS).
• To couple ASAS with a triple-quadrupole ICP-MS (Agilent 8900) for interference-free detection.
• To achieve detection limits and background equivalent concentrations (BECs) meeting or exceeding SEMI specifications.

Methodology and Instrumentation

Sample Preparation and Automated Standard Addition

• Matrix: Electronic-grade IPA stabilized with 1 % ultrapure HNO₃.
• Stock Standard: 1 mg/L multi-element solution diluted in IPA.
• Automatic Preparation: ASAS system measures sample uptake via dual flow sensors and injects accurately calculated volumes of standard to spike samples at desired ppt levels.

ICP-MS/MS Configuration

• Instrument: Agilent 8900 in Semiconductor configuration.
• Sample Introduction: Self-aspiration via glass coaxial nebulizer and Peltier-cooled quartz spray chamber.
• Interface: Quartz torch with platinum-tipped cones.
• Gas Cell Modes: NH₃, O₂+He and H₂ gases used in the collision/reaction cell to remove polyatomic interferences.

Results and Discussion

Trace Element Performance

• Forty-eight elements were measured with detection limits (DLs) in the 0.005–1.6 ng/L range and BECs from 0.002 to 6.4 ng/L.
• All SEMI-specified elements achieved sub-ppt to low-ppt quantification levels.

Interference Removal

• Magnesium (²⁴Mg⁺) interference from ¹²C¹²C⁺ was eliminated using warm plasma with NH₃ cell gas, yielding a DL of 0.020 ppt and BEC of 0.082 ppt.
• Aluminum and chromium interferences were successfully suppressed under similar cell-gas conditions, with linear calibration and high recoveries.
• Phosphorus determination in He+O₂ mode achieved a DL of 2.6 ppt and BEC of 43 ppt, demonstrating reliable performance for non-metal analytes.

Benefits and Practical Applications

Automation Advantages

• Reduces manual handling and contamination risk during ultra-trace analysis.
• Ensures consistent standard addition and improves reproducibility regardless of operator skill.

Industrial Impact

• Meets or surpasses SEMI C41-0705 requirements for high-purity IPA.
• Supports quality control in semiconductor fabs and chemical manufacturing.

Future Trends and Opportunities

Advancements in in-line monitoring, miniaturized autosamplers and machine-learning-driven data analysis promise further improvements in speed and robustness. Integration of fully automated workflows with plant control systems could enable real-time impurity tracking. Expanding the approach to other critical solvents and emerging materials will broaden its industrial application.

Conclusion

The combination of ASAS-based automatic standard addition with ICP-MS/MS allows robust, interference-free quantification of ultra-trace metals in organic solvents. The high degree of automation and sub-ppt performance simplify semiconductor chemical analysis and support compliance with stringent industry standards.

References

1. SEMI C41-0705, Specifications and Guidelines for 2-Propanol, 2005.
2. J. Takahashi and K. Mizobuchi, Asia Pacific Winter Conference on Plasma Spectroscopy, 2008.
3. K. Mizobuchi, N. Yamada and M. Yukinari, The Japan Society for Analytical Chemistry, Touronkai, 2014.
4. K. Mizobuchi, N. Yamada and M. Yukinari, The Japan Society for Analytical Chemistry, Nenkai, 2017.