Determination of the Suppressor Additive in Acid Copper Plating Bath

Importance of the Topic

The quality of copper deposition in semiconductor manufacturing relies heavily on the precise control of suppressor additives in acid copper plating baths. These proprietary inhibitors modulate deposition kinetics and surface morphology. Accurate determination of individual suppressor concentrations ensures consistent plating performance, reduced defect rates, and optimized process yields.

Objectives and Study Overview

This study presents a liquid chromatography method coupled with evaporative light-scattering detection (ELSD) to quantify two proprietary suppressor additives in acid copper plating baths. The aim was to overcome limitations of cyclic voltammetric stripping, which cannot distinguish individual organic components, and to establish a reliable analytical procedure for routine quality control in plating operations.

Methodology and Instrumentation

A polymeric reversed-phase IonPac NS1 column was selected for its stability across pH 0–14 and inert PEEK fluid path to resist corrosive plating solutions. The eluent gradient ranged from 40% to 90% acetonitrile over 2–7 minutes at a constant flow of 1.0 mL/min. Samples (100 µL) of make-up bath spiked with suppressor standards were injected directly. ELSD parameters were optimized: evaporator temperature 80 °C, nebulizer temperature 75 °C, and nitrogen nebulizing gas at 1.0 L/min. Calibration curves were constructed over the recommended operating ranges for each suppressor additive.

Instrumentation Used

• Dionex DX-600 Liquid Chromatography System (GP50 pump, AS50 autosampler)
• IonPac NS1 Analytical column (4 x 250 mm, polymeric reversed-phase)
• Polymer Labs PL-ELS 1000 Evaporative Light Scattering Detector
• UCI-100 Universal Chromatography Interface
• PeakNet Chromatography Workstation, Version 6.0 or higher

Main Results and Discussion

• Enthone suppressor was fully resolved from the large copper sulfate/sulfuric acid matrix peak, eluting at 6 minutes. Calibration over 4–12 mL/L yielded r² = 0.9993.
• Shipley suppressor separated at 9 minutes under identical gradient conditions. Calibration over 20–25 mL/L produced r² = 0.9798.
• ELSD provided stable baselines (noise < 200 μV) and reproducible peak areas despite the nonchromophoric nature of suppressors.

Benefits and Practical Applications

• Enables direct quantification of individual suppressors in complex acidic matrices.
• PEEK-based fluid path prevents corrosion from high acidity and copper content.
• ELSD detection circumvents the need for UV-active labels, facilitating routine analysis of nonvolatile additives.
• Supports real-time process monitoring and quality assurance in semiconductor plating operations.

Future Trends and Applications

• Integration of mass spectrometric detection for structural confirmation of unknown plating additives and by-products.
• Development of miniaturized or inline LC-ELSD systems for continuous process control.
• Extension of method to other plating bath chemistries and novel organic additives.

Conclusion

The developed LC-ELSD method offers a robust, corrosion-resistant, and sensitive approach for quantifying proprietary suppressor additives in acid copper plating baths. High resolution, linear calibration, and simple sample preparation make it ideal for routine quality control and process optimization in semiconductor manufacturing.

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