Whole Air Canister Sampling and Preconcentration GC-MS Analysis for pptv Levels of Trimethylsilanol in Semiconductor Cleanroom Air

Importance of the Topic

The presence of trace levels of trimethylsilanol (TMS) in semiconductor cleanroom air can lead to irreversible optics haze on photolithography tools, causing significant yield loss and equipment damage. Accurate monitoring of TMS at parts-per-trillion (pptv) levels is therefore critical for maintaining product quality and reducing operational costs.

Study Objectives and Overview

This study aims to develop and validate a whole-air canister sampling technique combined with preconcentration gas chromatography–mass spectrometry (GC-MS) for reliable measurement of TMS in cleanroom air at pptv levels. The method addresses limitations of solvent, bag, and solid-sorbent based sampling by enabling rapid grab sampling, extended sampling durations, and multiple analyses from a single canister.

Methodology and Preconcentration GC-MS Analysis

Field samples were collected in electropolished or silica-lined canisters cleaned and conditioned under humidified nitrogen. A Nutech 8900DS preconcentrator with three cryogenic traps removed interferents and focused analytes, delivering 400 mL of sample spiked with 100 mL of TO-14A internal standard to an Agilent 6890 GC coupled to a 5973 MS. Selected ion monitoring targeted m/z 75 (quantifier) and qualifier ions 45, 47, and 59. Calibration involved a seven-point curve from 0.95 to 95 pptv, using dynamically diluted primary standards.

Used Instrumentation

• Nutech 8900DS preconcentrator with Siltek® beads, Tenax® GR trap, and proprietary cryofocus trap.
• Agilent 6890 gas chromatograph with 5973 mass spectrometer detector (EI, 70 eV).
• Electropolished TO-Can® and silica-lined SilcoCan® air sampling canisters.
• TO-14A internal standard/tuning mix (bromochloromethane, 1,4-difluorobenzene, chlorobenzene-d5, 4-bromofluorobenzene).

Main Results and Discussion

• Analytical blanks averaged 0.06 pptv (below detection limit), yielding an ADL of 0.09 pptv.
• Calibration showed excellent linearity (RRF RSD 9.8%) from 1 to 100 pptv.
• Recovery/accuracy was 93% ±10% at 76.6 pg on-column.
• Method detection limit (MDL) was 0.12 pptv (0.48 ng/m3); practical quantitation limit (PQL) set at 0.60 pptv.
• Precision at 9.51 pptv was 6.8% RSD.
• TMS remained stable (84% recovery) after four days at 45% RH in electropolished canisters; stability declines after three days under extreme humidity or in silica-lined vessels.

Benefits and Practical Applications

The method enables near-instant (~10 s) grab sampling and multi-sample analysis from a single canister, simplifying logistics and improving throughput. Its low PQL and high precision meet semiconductor industry requirements for trace TMS control, supporting preventive maintenance of optics and reducing downtime.

Future Trends and Applications

Potential advancements include integration of automated canister handling, real-time monitoring platforms, expansion to other volatile siloxanes, and development of tailored canister coatings or inline filters to further improve stability and reduce background.

Conclusion

A robust whole-air canister sampling and preconcentration GC-MS method was developed for trace-level TMS analysis in cleanroom air. Performance metrics—low blanks, excellent linearity, high recovery, sub-pptv detection, and multi-day stability—demonstrate suitability for semiconductor process monitoring.

References

1. Grümping R, Mikolajczak D, Hirner AV. Determination of trimethylsilanol in the environment by LT-GC/ICP-OES and GC-MS. Fresenius J Anal Chem. 1998;361:133.
2. Lee JH, Jia C, Kim YD, Kim HH, Pham TT, Choi YS, Seo YU, Lee IW. An optimized adsorbent sampling combined with thermal desorption GC-MS method for trimethylsilanol in industrial environments. Int J Anal Chem. 2012;2012:690356.
3. Schweigkofler M, Niessner R. Determination of siloxanes and VOC in landfill gas and sewage gas by canister sampling and GC-MS/AES analysis. Environ Sci Technol. 1999;33:3680.
4. Glindemann D, Morgenstern P, Wennrich R, Stottmeister U, Bergmann A. Toxic oxide deposits from the combustion of landfill gas and biogas. Environ Sci Pollut Res. 1996;3:75.
5. Seguin K, Dallas A, Weineck G. Breakthrough chemical analysis of HMDS reveals a solution for the prevention of lens hazing. Semicond Filtration Tech Note. 2008;CFTN-1SC.
6. Seguin K, Dallas AJ, Weineck G. Rationalizing the mechanism of HMDS degradation in air and effective control of the reaction byproducts. Proc SPIE. 2008;6922:30.
7. Piechota G, Hagmann M, Buczkowski R. Removal and determination of trimethylsilanol from landfill gas. Bioresour Technol. 2012;103:16.
8. Oshita K, Ishihara Y, Takaoka M, Takeda N, Matsumoto T, Morisawa S, Kitayama A. Behaviour and adsorptive removal of siloxanes in sewage sludge biogas. Water Sci Technol. 2010;61:2003.
9. Ajhar M, Wens B, Stollenwerk KH, Spalding G, Yüce S, Melin T. Suitability of Tedlar gas sampling bags for siloxane quantification in landfill gas. Talanta. 2010;82:92.
10. Narros A, Del Peso MI, Mele G, Vinot M, Fernández E, Rodríguez ME. Determination of siloxanes in landfill gas by adsorption on Tenax tubes and TD-GC-MS. In: Sardinia 2009; CISA; 2009.
11. Huppmann R, Lohoff HW, Schroder HF. Cyclic siloxanes in the biological wastewater treatment process—determination, quantification and elimination. Fresenius J Anal Chem. 1996;354:66.
12. U.S. EPA. Compendium Method TO-15: Determination of VOCs in air in canisters by GC-MS. 1999.
13. Smith AL. The analytical chemistry of silicones. Wiley; 1991.
14. Atkinson R. Kinetics of gas-phase reactions of organosilicon compounds with OH and NO3 radicals and ozone. Environ Sci Technol. 1991;25(5):863.
15. Hsieh CC, Horng SH, Liao PN. Stability of trace-level VOCs stored in canisters and Tedlar bags. Aerosol Air Qual Res. 2003;3:17.