Sub-ppb detection limits for hydride gas contaminants using GC-ICP-QQQ

Importance of the Topic

Trace hydride gases such as phosphine, arsine, germane, hydrogen sulfide, carbonyl sulfide and silane are critical impurities in high-purity process gases used in the semiconductor and petrochemical industries. Even at sub-part-per-billion levels, these contaminants can degrade catalyst performance in polymer production and alter the electrical properties of semiconductor devices.

Study Objectives and Overview

This application note describes the development of a gas chromatography triple quadrupole inductively coupled plasma mass spectrometry (GC-ICP-QQQ) method using the Agilent 8800 system to achieve detection limits in the low parts-per-trillion range. The study compares this approach with conventional GC-ICP-MS on an Agilent 7900 platform and evaluates its ability to quantify multiple hydride-forming elements in a single analysis.

Methodology and Instrumentation

The analytical setup couples an Agilent 7890 GC equipped with a 100 m × 0.53 mm × 5 µm DB-1 column to an Agilent 8800 ICP-QQQ via a GC-ICP interface. An octopole reaction system (ORS3) cell enables MS/MS mass filtering (Q1) and collision/reaction chemistry (Q2). Oxygen reaction gas was used for measurement of phosphorus, arsenic, germanium and sulfur in mass-shift mode, while hydrogen cell gas enabled interference-free on-mass detection of silicon. GC parameters included isothermal run at ambient temperature, 4 psig column exit pressure, helium carrier at 20 psig, and dynamic dilution of microliter-level gas standards.

Results and Discussion

Single-element analysis of phosphine yielded a signal-to-noise ratio of 96.9 at 0.42 ppb, corresponding to a calculated detection limit of ~8.7 ppt (S/N method) and 19 ppt (standard deviation method). Multi-element calibration for PH3, GeH4 and AsH3 achieved linearity (R²=1.000) over 4–18 ppb, with detection limits of 12 ppt for phosphorus, 3.9 ppt for germanium and 1.3 ppt for arsenic. Hydrogen sulfide and carbonyl sulfide were quantified via SO+ at m/z 48, attaining detection limits near 0.1 ppb. Silane analysis at m/z 28 (on-mass with H2 cell gas) delivered limits around 0.14–0.20 ppb. Compared to conventional GC-ICP-MS, GC-ICP-QQQ improved detection limits by a factor of 5–10 for silane, phosphine, H2S and COS.

Benefits and Practical Applications

• Sub-ppt sensitivity enhances quality control for high-purity gas suppliers and semiconductor fabs.
• MS/MS mass filtering and reaction cell chemistry minimize polyatomic interferences.
• Simultaneous multi-element analysis streamlines workflow and reduces sample consumption.

Future Trends and Applications

Further reduction of detection limits may be achieved by exploring alternative stationary phases to minimize column bleed and by optimizing reaction gas chemistries. Real-time, on-line monitoring of process gases and miniaturized GC-ICP-QQQ systems could support continuous quality assurance in semiconductor manufacturing and petrochemical operations.

Conclusion

The Agilent 8800 GC-ICP-QQQ method demonstrates robust and interference-free analysis of hydride-forming contaminants at sub-ppb and ppt levels. Compared with single-quadrupole ICP-MS, this approach offers significantly lower backgrounds and higher sensitivity, meeting the stringent requirements of advanced industrial applications.

References

Geiger W.; Soffey E.; Wilbur S.; Scanlon C. Sub-ppb detection limits for hydride gas contaminants using GC-ICP-QQQ. Agilent Technologies Application Note 5991-5849EN, 2015.