Direct Analysis of Photoresist and Related Solvents Using the Agilent 7500cs ICP-MS

Importance of the Topic

The rapid growth of semiconductor device complexity places stringent demands on the purity of process materials. Photoresists, critical for lithographic patterning, must be free of metallic impurities that can compromise device performance and yield. Ultralow detection of trace metals (often below 10 ppb) in high-carbon, high-viscosity matrices requires robust analytical approaches.

Objectives and Overview of the Study

This application note presents a streamlined method for direct analysis of positive photoresists and related organic solvents using the Agilent 7500cs ICP-MS equipped with the Octopole Reaction System (ORS). The study aims to simplify sample preparation by applying a single-step dilution in propylene glycol monomethyl ether (PGME) and to demonstrate that the ORS cell effectively removes polyatomic interferences, enabling accurate quantification of a full suite of metallic contaminants.

Methods and Instrumentation

Sample Preparation:

• Photoresist diluted 1:10 in PGME to yield a ~3 % resin solution.
• Solvent blank (PGME) purified in-house to minimize background impurities.

ICP-MS Configuration:

• Agilent 7500cs ICP-MS with ORS and organic solvent introduction kit.
• Quartz narrow-bore injector torch and cooled (–5 °C) spray chamber.
• Self-aspirating concentric nebulizer at 68 µL/min.
• Addition of 20 % O₂ in Ar (0.2 L/min) to prevent carbon deposition.

Tuning and Calibration:

• Helium and hydrogen cell gases optimized to reduce both matrix- and Ar-based polyatomic interferences.
• External matrix-matched calibration using spiked PGME and photoresist standards (0.5–2 ppb).
• No internal standards to avoid additional contamination.

Data Acquisition:

• I-AS autosampler with 0.3 mm capillary to minimize sample contamination.
• Integration times: 1 s per element (3 s for Ti), three replicates each.
• PGME rinse between samples to prevent drift from polymer deposition.

Main Results and Discussion

Detection Limits and Spike Recoveries:

• Detection limits for 35 elements ranged from sub-ppt to tens of ppt in the diluted photoresist (effective DL ≈ 0.001–0.2 ppb).
• 0.5 ppb spike recoveries averaged 87 %–104 % across all elements, including challenging analytes (B, Mg, Al, K, Ca, Ti, Cr, Fe, Zn).

Interference Removal:

• ORS in He mode effectively suppressed carbon- and solvent-derived interferences on Ti and Zn.
• Hydrogen mode minimized ArH and ArC interferences on K, Ca, and Fe.

Instrument Stability:

• Two-hour stability study showed RSD < 3 % for most elements in a spiked photoresist over 120 min.

Benefits and Practical Applications

This method offers significant advantages for semiconductor process control laboratories:

• Minimal sample preparation reduces time, hazard, and potential analyte loss.
• High sensitivity and interference removal enable monitoring of ultratrace metal levels (< 10 ppb) required by industry.
• Rapid throughput (~3.5 min per sample for 35 elements) with excellent precision and accuracy.

Future Trends and Potential Applications

As device geometries shrink and material purity requirements tighten, demand will grow for even lower detection limits and faster turnaround. Future developments may include:

• Enhanced reaction cell chemistries for targeted suppression of emerging matrix interferences.
• Automation of solvent purification and inline calibration to streamline workflows.
• Extension of direct-dilution ICP-MS methods to other high-matrix process chemicals (e.g., CMP slurries, developer solutions).

Conclusion

The Agilent 7500cs ICP-MS with ORS and specialized organic solvent introduction provides a robust, high-throughput solution for direct quantification of trace metals in photoresists. The protocol’s simplicity, combined with reliable interference removal and sub-ppb sensitivity, meets current and future needs of semiconductor manufacturing quality control.

Reference

• Takahashi J; Youno K. Direct Analysis of Photoresist and Related Solvents Using the Agilent 7500cs ICP-MS. Agilent Technologies Application Note 5989-0629EN, Feb 2004.