Determination of ultratrace elements in semiconductor grade TMAH developer

Importance of the Topic

Semiconductor manufacturing demands extremely pure chemicals to avoid device defects. Tetramethyl ammonium hydroxide (TMAH) is widely used as a developer in lithography and metal contamination at pg/g levels can critically affect yield and performance. High-accuracy ultratrace analysis of TMAH is therefore essential for quality control in semiconductor fabs.

Objectives and Overview of the Study

This study evaluates the performance of a high-resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) under hot and cold plasma modes for direct quantification of 15 trace metals in 0.3 N TMAH. It aims to identify matrix-induced polyatomic interferences and establish detection limits ranging from 0.1 to 9 pg/g.

Methodology and Instrumentation

The instrument setup included a PFA concentric nebulizer, PFA spray chamber and a quartz torch with sapphire injector. Sample introduction and data acquisition were automated, allowing controlled switching between hot plasma (forward power 1030 W, gas flow 0.94 L/min), cold plasma (forward power 725 W, gas flow 1.00 L/min) and resolution modes (low resolution R≈300, medium resolution R=4000). Calibration was performed by standard additions (10–200 pg/g) in TMAH with 500 pg/g rhodium as internal standard.

Main Results and Discussion

The HR-ICP-MS achieved sensitivities in TMAH equivalent to dilute nitric acid (>1000 cps per pg/g In) and dark noise <0.2 cps. Polyatomic interferences from argon-based species and matrix-derived carbon, nitrogen and oxygen compounds required medium resolution for ten elements. Cold plasma reduced ArO interferences but introduced new species, reinforcing the need for resolution switching. Detection limits were 0.1 pg/g for Li and 9 pg/g for Cu. Direct analysis without sample preparation enabled high throughput with accurate quantification.

Benefits and Practical Applications of the Method

• Routine, unattended analysis of ultratrace metals in TMAH
• Sub-pg/g detection limits fulfill stringent semiconductor quality control requirements
• Automated switching between plasma modes and resolutions ensures interference-free results in a single run

Future Trends and Potential Applications

Advances in ICP-MS technology may allow even lower detection limits and simplified workflows through real-time interference correction. Integration with inline monitoring systems could provide continuous quality control in semiconductor fabs. The methodology could extend to other high-purity chemicals used in microelectronics and bioanalytical applications.

Conclusion

High-resolution ICP-MS with hot/cold plasma switching offers reliable, direct analysis of ultratrace metals in semiconductor-grade TMAH. The approach addresses matrix interferences through dynamic resolution control, enabling detection limits as low as 0.1 pg/g. This method supports stringent quality control in semiconductor manufacturing.

Reference

• Wills JD, Hinrichs J. Determination of ultratrace elements in semiconductor grade TMAH developer. Thermo Fisher Scientific Application Note 30072, 2018.