Measurement and Control of Copper Additives in Electroplating Baths by High-Performance Liquid Chromatography

Importance of the Topic

Electroplated copper films are essential in decorative finishes, industrial components and advanced semiconductor interconnects. Precise control of organic additives—suppressors, accelerators and levelers—in acid copper plating baths determines deposit uniformity, feature filling and overall reliability. Traditional cyclic voltammetric stripping (CVS) offers only qualitative, combined measurements and cannot distinguish individual additives or their degradation products, leading to limited process control and potential defect formation.

Study Objectives and Overview

This work presents two complementary high‐performance liquid chromatography (HPLC) methods that deliver quantitative, additive‐specific data:

• HPLC‐Charged Aerosol Detection (CAD) for suppressor and accelerator measurement.
• HPLC‐Electrochemical Detection (ECD) for accelerator and leveler quantitation.

By neutralizing the highly acidic bath and injecting one sample aliquot onto parallel HPLC streams, this approach overcomes CVS limitations and previously published HPLC challenges (column degradation, poor sensitivity).

Methodology and Instrumentation

Sample pretreatment involves raising bath pH to 2–4 with N,N-dimethylethanolamine. A Thermo Scientific UltiMate 3000 system runs dual gradients in parallel:

• HPLC‐CAD stream: Accucore C18 column, diethylamine‐acetate buffer and methanol/isopropanol gradient, Corona Veo RS detector.
• HPLC‐ECD stream: Acclaim RSLC PA2 column, perchlorate/perchloric acid mobile phase, UltiMate 3000 ECD3000RS cell at +650 mV (leveler) and +900 mV (accelerator).

Chromeleon CDS manages data acquisition. Standard curves (12.5–200 % nominal concentration) demonstrate linearity and low relative standard deviations.

Main Results and Discussion

Both HPLC methods achieved correlation coefficients ≥0.997 and precision better than 2.5 %RSD. Gage studies yielded SV/T values below 10 % for HPLC, compared with >40 % for CVS, confirming superior capability. HPLC‐CAD resolves suppressor degradants that accumulate during bath operation, enabling direct monitoring of bath breakdown products. Correlation plots with CVS show linear trends but higher intercepts for CVS due to cumulative electrochemical signals from both parent additives and their fragments.

Benefits and Practical Applications

• Accurate quantitation of each additive and its degradation products.
• Improved bath quality control reduces downtime and carbon treatment frequency.
• Enhanced deposition uniformity and defect reduction in semiconductor and decorative plating.

Future Trends and Opportunities

Integration of miniaturized UHPLC systems, coupling to mass spectrometry for structural elucidation, and real-time inline analysis promise further enhancements. Advanced data analytics and virtual metrology could enable predictive bath maintenance and adaptive process control.

Conclusion

The dual‐stream HPLC approach with CAD and ECD delivers fast, reliable, quantitative control of copper plating bath additives. It surpasses traditional CVS in speed, precision and specificity, supporting higher product quality, reduced operational costs and extended bath lifetimes.

References

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