Titration of phosphoric, nitric, and acetic acid mixtures

Significance of the topic

Aluminum etching using a mixture of phosphoric, nitric, and acetic acids (PAN etchant) is critical in semiconductor manufacturing for precise patterning of aluminum interconnects. Reliable monitoring of acid composition ensures process consistency and etching efficiency.

Objectives and overview

This Application Note demonstrates a rapid thermometric titration method for sequential determination of all three acids in PAN etchant using a single automated titration sequence. The method aims to offer a faster and more convenient alternative to the SEMI C37 potentiometric standard.

Methodology and instrumentation

No sample pretreatment is needed beyond dilution with deionized water. The titration is performed on an OMNIS Professional Titrator equipped with a high-sensitivity digital dThermoprobe and automated dosing modules. Standardized sodium hydroxide is added until three distinct exothermic endpoints corresponding to neutralization of acetic, nitric, and phosphoric acids are detected.

Použitá instrumentace

• OMNIS Professional Titrator with magnetic rod stirrer
• dThermoprobe digital temperature sensor
• OMNIS Dosing Module for automated reagent delivery

Main results and discussion

The method delivers accurate quantification of each acid component within approximately 95 seconds per analysis. The thermometric titration curve clearly shows three exothermic peaks, enabling precise endpoint determination. Results demonstrate high reproducibility and agreement with known concentrations in simulated PAN etchants.

Benefits and practical use

• Rapid analysis suitable for high-throughput quality control
• No electrode maintenance or calibration required
• Fully automated workflow reduces operator intervention and error

Future trends and possibilities

Advancements may include integration of inline monitoring for real-time process control, expansion to etchants containing hydrofluoric acid, and application of AI algorithms for improved endpoint detection. Miniaturization of titration setups and broader applicability to other multiprotic acid mixtures are promising developments.

Conclusion

Thermometric titration provides a fast, accurate, and robust alternative for determination of phosphoric, nitric, and acetic acid in semiconductor etchants. Its automation capabilities and rapid turnaround make it valuable for modern etching process control.

References

1. Aluminum technology - Metallization - Semiconductor Technology from A to Z (Halbleiter.org). Accessed 2023-07-26.
2. SEMI C37 Specification for Phosphoric Etchants; SEMI: Milpitas, CA, USA, 2011.