Determination of Chloride in Acid Copper Plating Bath

Importance of the Topic

Chloride concentration in acid copper plating baths critically influences the morphology and adhesion of deposited copper layers on semiconductor wafers. Accurate monitoring of chloride levels ensures consistent deposition quality and prevents defects. Ion chromatography provides a rapid and precise alternative to traditional wet chemical methods for this application.

Objectives and Study Overview

This study aims to establish a reliable ion chromatography procedure using an IonPac AS15 column to quantify chloride in acid copper plating baths. The method emphasizes minimal sample preparation, high throughput, and robust performance in a complex matrix containing copper sulfate, sulfuric acid, hydrochloric acid, and proprietary additives.

Used Instrumentation

• Ion chromatography system with GP50 gradient pump and CD25 conductivity detector
• EG40 eluent generator with EGC-KOH cartridge
• IonPac AS15 analytical column (4 × 250 mm) with AG15 guard column
• ATC-1 trap column
• ASRS-ULTRA suppressor (4 mm)
• 25-µL PEEK sample loop and Rheodyne injector
• PeakNet chromatography workstation

Methodology

The copper plating bath is diluted 1:100 with Type I deionized water. A 25-µL injection is separated on the AS15 column using 30 mM potassium hydroxide eluent generated on-line at 1.2 mL per minute. Suppressed conductivity detection in recycle mode resolves chloride from excess sulfate. Standards are prepared by diluting a 1000 mg/L chloride stock to bracket sample concentrations. Anion trap and suppressor devices are regenerated with 2 M sodium hydroxide.

Main Results and Discussion

The method detection limit for chloride is 6 mg/L in the original bath (0.06 mg/L in a 25-µL injection). Typical chloride concentration measured in the acid copper bath is around 45 mg/L. Calibration over three levels with spiked samples yielded a coefficient of determination (r2) of 0.9983. Repeatability across 21 injections gave 47.2 ± 1.2 mg/L. The procedure demonstrated reliable quantification over more than 500 injections, although gradual retention time shifts may occur due to column fouling.

Benefits and Practical Applications

• Improved speed and accuracy compared to wet chemical titration
• Simple dilution and injection protocol suited for routine quality control
• High throughput with over 500 injections without loss of performance
• Effective separation of chloride from sulfate and other matrix components
• Automated eluent generation reduces reagent handling errors

Future Trends and Applications

Advances may include on-line column cleaning protocols, extended column lifetimes through improved stationary phases, integration with mass spectrometric detection for speciation analysis, and inline monitoring in production facilities. Development of green eluent systems and miniaturized IC modules could further enhance sustainability and field deployability.

Conclusion

The presented ion chromatography method offers a robust, accurate, and efficient approach for chloride determination in acid copper plating baths, supporting stringent quality control in semiconductor manufacturing. Its ease of use and reproducibility make it a valuable tool for analytical laboratories.

References

• Dionex Corporation Application Update 143 Determination of Chloride in Acid Copper Plating Bath 2001