Monitoring quality parameters in standard cleaning baths

Significance of the topic

Chemical cleaning baths such as SC1 (ammonium hydroxide and hydrogen peroxide) and SC2 (hydrochloric acid and hydrogen peroxide) are essential for defect-free silicon wafer production. Real-time monitoring of these baths ensures optimal reagent concentrations, reduces defects, and improves overall yield in semiconductor manufacturing.

Objectives and study overview

This application note demonstrates inline near-infrared spectroscopy (NIRS) for simultaneous monitoring of NH4OH, H2O2, and HCl in SC1 and SC2 cleaning solutions. The goal is to maintain bath composition within tight specifications, minimize chemical consumption, and enhance process safety.

Methodology and Instrumentation

Process control is achieved using the NIRS XDS Process Analyzer – SingleFiber. A custom PFA flow cell clamps onto existing circulation loops, requiring no system modifications. Real-time spectra (800–1300 nm) are correlated with reference methods such as ion chromatography and titration to build robust calibration models.

Main Results and Discussion

Inline NIRS provided continuous concentration profiles of NH4OH and H2O2 in SC1, showing periodic reagent spiking to maintain setpoints. Similar monitoring of HCl and H2O2 in SC2 assured acid bath stability. The approach reduced chemical consumption by approximately 25%, as reagents were replenished only when necessary.

Benefits and Practical Applications

• Enhanced wafer yield and reduced defect density.
• Lower chemical usage and cost savings.
• Improved process reproducibility and throughput.
• Increased operator safety through reagent-free inline measurement.

Future Trends and Opportunities

Advanced inline spectroscopy may expand to additional etch and plating baths, integrate machine learning for predictive maintenance, and connect with Industry 4.0 platforms for comprehensive process analytics.

Conclusion

Inline NIRS analysis enables precise, real-time monitoring of semiconductor cleaning baths, offering significant savings, higher yield, and safer operations. The Metrohm NIRS XDS system with multipoint capability provides a flexible solution for modern wafer cleaning processes.

Reference

• AN-PAN-1012 Electroless Nickel Plating: Analysis of Nickel ion & Hypophosphite content.
• AN-PAN-1028 Monitoring Tetramethylammonium Hydroxide (TMAH) in Developer.
• AN-PAN-1054 Online monitoring of hydrogen peroxide during CMP process.