Determination of trace elements in ultrapure semiconductor grade sulfuric acid using the Agilent 8900 ICP-QQQ in MS/MS mode

Importance of the Topic

In semiconductor fabrication, the presence of trace metallic contaminants in process chemicals such as sulfuric acid can critically impair device yield, functionality, and reliability. During wafer cleaning steps, especially after ion implantation, ultra-pure sulfuric acid mixed with hydrogen peroxide (piranha solution) removes organic residues from silicon surfaces. Monitoring and controlling metal impurities at sub-parts-per-trillion (ppt) levels is essential to avoid particle or ionic contamination and ensure high-performance semiconductor devices.

Study Objectives and Overview

This work demonstrates a robust analytical protocol for quantifying 42 trace elements, including challenging analytes like titanium, vanadium, and zinc, in semiconductor-grade sulfuric acid. Using the Agilent 8900 triple quadrupole ICP-MS (ICP-QQQ) in MS/MS mode, the study aims to overcome sulfur-based polyatomic interferences and achieve reliable sub-ppt detection limits and accurate quantification suitable for routine quality control of high-purity chemicals.

Methodology and Instrumentation

Sample Preparation:

• Semi-conductor-grade 98% H2SO4 was diluted ten-fold with ultrapure water in pre-cleaned PFA containers.
• Quantification employed the method of standard additions (MSA) using certified multi-element standards.

Used Instrumentation

• Agilent 8900 ICP-QQQ with MS/MS capability (semiconductor configuration).
• Quartz torch (2.5 mm i.d. injector), quartz spray chamber, PFA concentric nebulizer, platinum-tipped interface cones.
• ORS4 octopole reaction cell between two quadrupoles; both quadrupoles set as unit mass filters.
• Cell gases evaluated: O2 (for mass-shift oxide formation), NH3 (for ammonia cluster reactions), H2 and He (for interference reduction and collision mode).
• Axial acceleration technology enabled higher transmission of slow-moving reaction product ions.

Main Results and Discussion

• Optimization of cell gas conditions (O2, NH3, O2+H2, He) and plasma mode (normal vs. cool plasma) achieved efficient removal of sulfur-based interferences for elements such as Ti, V, Cr, Zn, Ge, As, P, and Si.
• O2 mass-shift mode enabled detection of AsO+ (m/z 91), SeO+ (m/z 94), and SiO+ (m/z 44) with low background equivalent concentrations.
• NH3 mass-shift mode and axial acceleration allowed measurement of major Ti isotopes as Ti(NH3)n+ clusters, eliminating SO+ interference and enhancing sensitivity by a factor of five.
• Addition of H2 to O2 cell gas improved phosphorus sensitivity by 1.5× when detecting PO+ at m/z 47.
• Calibration curves showed excellent linearity (R > 0.9995) across all elements; detection limits ranged from sub-ppt to tens of ppt (Si ~44 ppt, P ~2.8 ppt, Zn ~1.5 ppt).
• Spike recoveries for 20 ng/L additions demonstrated recoveries between 95% and 107% with relative standard deviations below 4.5%, confirming method accuracy and precision.

Benefits and Practical Applications

The optimized ICP-QQQ MS/MS method provides:

• Sub-ppt sensitivity for a broad suite of elements in high-sulfur matrices.
• Reliable suppression of polyatomic interferences without complex sample pre-treatment.
• Robust routine analysis capability for semiconductor-grade reagents, ensuring process chemical purity and yield consistency.

Future Trends and Applications

Advancements in reaction cell chemistries, novel cell gases, and further improvements in ion transmission technologies are expected to push detection limits even lower and expand the range of analytes that can be accurately quantified in aggressive or complex matrices. Integration with autonomous sample handling and real-time process monitoring will enhance in-line quality control for next-generation semiconductor manufacturing.

Conclusion

The Agilent 8900 ICP-QQQ in MS/MS mode offers a powerful solution for ultra-trace elemental analysis in semiconductor-grade sulfuric acid. By applying tailored reaction cell conditions and axial acceleration, the method achieves sub-ppb to sub-ppt detection limits, accurate quantification, and robust interference removal. This approach is well suited for routine QA/QC of high-purity process chemicals in the semiconductor industry.

Reference

• Agilent 8800 Triple Quadrupole ICP-MS: Understanding oxygen reaction mode in ICP-MS/MS (Agilent publication 5991-1708EN, 2012)
• J. Takahashi, Determination of challenging elements in ultrapure semiconductor grade sulfuric acid by Triple Quadrupole ICP-MS (Agilent publication 5991-2819EN, 2015)