Trace Elemental Analysis of Trichlorosilane by Agilent ICP-MS

Significance of the Topic

High purity trichlorosilane is a critical intermediate in the production of photovoltaic silicon wafers. Metallic impurities even at trace levels can reduce solar cell efficiency and impact yield. Sensitive and reliable analysis of these impurities in the TCS feedstock therefore plays a vital role in quality control and process optimization in the solar industry

Objectives and Scope of the Study

This study aimed to develop and validate a robust method for quantifying 33 trace elements in trichlorosilane using inductively coupled plasma mass spectrometry. Key goals included achieving sub-ppb detection limits, confirming method accuracy by spike recovery, and comparing impurity levels in different TCS sources

Methodology and Sample Preparation

Liquid TCS was hydrolyzed under an inert atmosphere to convert it into silicon dioxide and volatile byproducts. The SiO2 precipitate was dissolved in hydrofluoric acid and removed as SiF4 gas during gentle heating. The residual salts were evaporated to dryness and reconstituted in 0.4 percent hydrochloric acid prior to analysis. This procedure prevents Si deposition in the ICP-MS interface and avoids matrix effects

Used Instrumentation

• Agilent 7700s ICP-MS equipped with Octopole Reaction System
• PFA concentric nebulizer and PFA double-pass spray chamber
• Demountable torch with platinum injector
• Automated switching between cool plasma, no gas, and helium collision modes

Main Results and Discussion

The method achieved final-solution detection limits down to tenths of ppt and original-sample limits below 1 ppb for all analytes. Optimized helium collision mode enabled direct measurement of phosphorus at mass 31 with a detection limit of 0.1 ppb. Two commercial TCS samples were measured: one stored in glass showed minimal contamination while a second stored in stainless steel exhibited elevated Fe, Ni, and Cr. A 5 ppb multielement spike recovery test in TCS demonstrated recoveries between 80 and 120 percent, confirming method accuracy and negligible loss of volatile elements such as boron

Benefits and Practical Applications

This analytical approach allows photovoltaic silicon manufacturers to screen TCS intermediates for ultratrace metallic impurities before polysilicon production. Reliable impurity monitoring supports improved conversion efficiency, reduced waste, and enhanced process control

Future Trends and Applications

Further developments may include inline or online ICP-MS sampling of TCS, advanced reaction cell chemistries to extend interference removal, miniaturized or portable systems for field monitoring, and expanded analyte panels for other silicon-chemical intermediates

Conclusion

A validated sample preparation and ICP-MS method has been demonstrated for trace elemental analysis of trichlorosilane. The use of an ORS cell yielded excellent interference removal and low detection limits, while the preparation protocol ensured accurate quantification across a broad element range. This capability supports stringent quality control in photovoltaic silicon manufacturing

References

1. Ultratrace Analysis of Solar Photovoltaic Grade Bulk Silicon by ICP-MS Agilent Application Note 5989-9859EN October 2008