Analysis of Trace Metal Impurities in High Purity Hydrochloric Acid Using ICP-QQQ

Significance of the Topic

The ultra-trace analysis of metal impurities in high-purity hydrochloric acid (HCl) is critical for semiconductor manufacturing. Cleaning solutions in the RCA process, especially the SC-2 step, must be free of ionic and metallic contaminants to prevent defects during high-temperature processing. Achieving sub-ppt detection in corrosive matrices remains a major analytical challenge.

Objectives and Study Overview

This application note evaluates the performance of an Agilent 8900 triple quadrupole ICP-MS (ICP-QQQ) for the direct determination of 50 elements in undiluted HCl (20–36%). Key goals include:

• Resolving polyatomic interferences arising from the chloride matrix.
• Demonstrating sub-ppt detection limits for SEMI-specified elements.
• Validating direct analysis without sample pretreatment.

Methodology and Instrumentation

An Agilent 8900 ICP-QQQ in semiconductor configuration was employed, featuring a PFA-100 nebulizer, Peltier-cooled spray chamber, quartz torch, Pt-tipped cones and s-lens optics. Self-aspiration mode minimized contamination. Multiple cell gases (He, H2, O2, NH3) and cool plasma mode were applied in MS/MS acquisition. Q1 mass filtering before the cell ensured precise precursor selection and controlled reaction chemistry. Calibration was performed by standard additions at 10–40 ppt and converted to external calibration curves for routine analysis. All work was conducted in a Class 10 000 clean room.

Main Results and Discussion

The ICP-QQQ achieved single-digit ppt detection limits for key elements in 20% HCl. Specific interference removal strategies included:

• Cool plasma with NH3 cell gas for 52Cr and 39K, yielding BECs of 0.12 ppt (Cr) and 0.17 ppt (K).
• NH3 MS/MS on-mass for 51V and mass-shift for 74Ge (as 74Ge·NH₃ cluster), providing DLs of 0.11 ppt (V) and 0.32 ppt (Ge).
• O2 MS/MS for As, measuring 75AsO⁺ at m/z 91 without 91Zr⁺ overlap, achieving a DL of 0.73 ppt.

An investigation of elevated As signals in the high-purity sample used a neutral gain scan to rule out ArClO⁺ interferences. Quantitative results for SEMI specification elements in 20% and 36% HCl confirmed contaminant levels well below the 100 ppt threshold.

Benefits and Practical Applications

Direct analysis of undiluted HCl simplifies workflow by eliminating matrix-removal steps that can introduce analyte loss or contamination. The superior interference control and sensitivity of ICP-QQQ support efficient QA/QC in semiconductor fabs, ensuring reagent integrity and process reliability.

Future Trends and Potential Applications

Advances in reaction cell gas chemistry and automated tuning protocols will further improve throughput and detection capability. Integration of triple-quad ICP-MS with inline process monitoring and coupling to separation techniques (e.g., LC-ICP-MS) could extend ultratrace analysis to other aggressive reagents and complex matrices in advanced manufacturing.

Conclusion

The Agilent 8900 ICP-QQQ delivers robust, interference-free analysis of trace metals in high-purity HCl at sub-ppt levels. Its flexible cell gas options, cool plasma performance and MS/MS capability enable direct measurement of SEMI-specified contaminants, outperforming conventional single-quad ICP-MS and supporting stringent semiconductor cleaning requirements.

References

1. SEMI C27-0708: Specifications and Guidelines for Hydrochloric Acid (2008)
2. Junichi Takahashi and Katsuo Mizobuchi, Use of Collision Reaction Cell under Cool Plasma Conditions in ICP-MS, 2008 Asia Pacific Winter Conference on Plasma Spectroscopy
3. Junichi Takahashi, Direct Analysis of Trace Metallic Impurities in High Purity Hydrochloric Acid by Agilent 7700s/7900 ICP-MS, Agilent Publication 5990-7354EN (2017)
4. Agilent Technologies, Handbook of ICP-QQQ Applications using the Agilent 8800 and 8900, 5991-2802EN (2017)