Quantitation and Characterization of Copper Plating Bath Additives by Liquid Chromatography with Charged Aerosol Detection

Significance of the Topic

Copper electroplating is a cornerstone in industries ranging from consumer cookware to advanced microelectronics. Precise control of bath chemistry—particularly the levels of accelerator, suppressor and leveller additives—is essential to ensure uniform deposit thickness, smooth surfaces and reliable performance. Traditional techniques such as cyclic voltammetric stripping are time-consuming and can lack accuracy. The development of rapid, sensitive and robust high-performance liquid chromatography (HPLC) workflows with specialized detection modes addresses these challenges and supports quality control and research in plating bath formulation.

Study Objectives and Overview

This work aimed to establish two complementary HPLC methods for simultaneous quantitation of three key additives in acid copper plating baths:

• An electrochemical detection (ECD) method for accelerator and leveller quantitation.
• A charged aerosol detection (CAD) method for accelerator and suppressor quantitation.

Both approaches were integrated on a dual-LC platform to maximize throughput and enable shared sample preparation. Calibration, precision, recovery and sensitivity were evaluated for representative commercial bath formulations and spiked samples.

Methodology and Used Instrumentation

Sample Preparation:

• Neutralization of plating bath aliquots to pH 5–6.
• Standard solutions prepared at 300% nominal concentration (NC) and serially diluted for calibration.
• Spike-recovery experiments at 50% spike levels.

Liquid Chromatography:

• System: Thermo Scientific UltiMate 3000 x2 Dual LC configured in parallel.
• Columns: C18 reversed-phase (Accucore C18 2.6 μm and Acclaim 120 C18 5 μm, 4.6×150 mm).
• Mobile phases: aqueous perchlorate/acetic acid buffers, methanol, acetonitrile mixtures optimized per method.
• Gradient and flow rates tailored to resolve the three additives in under 16–22 minutes per run.

Detection Modes:

• Electrochemical Detector: Dionex Coulochem III ECD with dual coulometric electrodes (+650 mV and +900 mV) for selective oxidation of accelerator and leveller.
• Charged Aerosol Detector: Dionex Corona ultra RS CAD for universal mass-based detection of nonvolatile species at nanogram sensitivity, employing a power function fit for linear calibration.

Key Results and Discussion

Calibration and Precision:

• Linear correlation coefficients (R2) exceeded 0.994 for all analytes in both detection modes.
• Peak area precision (RSD) was <3% for accelerator and supressor, and 5–18% for leveller at low concentration levels.

Sensitivity and Limits:

• ECD method LOQ/LOD for accelerator: 1%/0.3% NC; leveller: 20%/7% NC.
• CAD method LOQ/LOD for accelerator: 0.6%/0.2% NC; suppressor: 1.5%/0.5% NC.

Recovery and Sample Analysis:

• Spike recoveries: 99–103% for accelerator, 95–100% for suppressor, and ~70% for leveller (confirmed by standard addition).
• Overlay of new vs. used bath chromatograms revealed up to seven-fold depletion of high-molecular-weight suppressor fractions and a 2.5× change in accelerator levels after bath operation, indicating additive consumption and degradation patterns.

Benefits and Practical Applications

• Rapid turnaround: full analysis in under 22 minutes per sample, suitable for high-throughput QA/QC laboratories.
• High sensitivity for trace additive monitoring without reliance on UV-active chromophores.
• Flexibility to adapt to varied bath chemistries by adjusting gradients and detection parameters.
• Detailed insight into additive degradation and bath aging, supporting optimized replenishment schedules.

Future Trends and Applications

Emerging needs in microelectronics and advanced surface finishes will drive further refinements in multi-detector HPLC platforms. Potential developments include:

• Integration with high-resolution mass spectrometry to identify unknown degradation products.
• Miniaturized or on-line sampling systems for real-time bath monitoring.
• Advanced chemometric algorithms for multivariate pattern recognition of complex bath formulations.

Conclusion

The combined use of electrochemical and charged aerosol detection on a dual-LC system provides a powerful, robust and versatile solution for comprehensive quantitation of copper plating bath additives. Methods exhibit excellent linearity, precision, sensitivity and recovery, and deliver actionable data on additive consumption and degradation to support industrial process control.

References

• Hong, K. J. “Copper Plating Additive Analysis by CVS in Korean Physical Society,” 43(2), 2003, pp. 286–289.
• Thermo Fisher Scientific. “Determination of Additives and Byproducts in an Acid Copper Plating Bath by Liquid Chromatography,” Application Note 139, 2002.
• Pavlov, M., Shalyt, E., Bratin, P. “A New Generation of CVS Monitors Cu Damascene Plating Baths,” Electro IQ, Vol. 46, Issue 3.