Monitoring quality parameters in standard cleaning baths

Importance of the Topic

Surface cleaning of silicon wafers is a critical step in semiconductor manufacturing. Any residual particles, organic films, or metal contaminants can degrade device performance and yield. Inline monitoring of standard cleaning baths (SC1 and SC2) ensures optimal chemical concentrations and process control, leading to higher throughput, lower defect rates, and improved profitability.

Objectives and Overview of the Study

This application note describes the real-time analysis of ammonium hydroxide, hydrogen peroxide, and hydrochloric acid concentrations in SC1 and SC2 cleaning baths using near-infrared spectroscopy (NIRS). The goals are to maintain bath composition within tight specifications, reduce chemical consumption, and simplify process monitoring without introducing additional reagents or manual sampling.

Methodology

Process streams are sampled through PFA tubing and directed to a custom flow cell clamped onto the existing circulation loop. A NIRS XDS Process Analyzer collects spectral data in the 800–1300 nm range. These spectra are correlated to primary reference methods (ion chromatography, titration) to build robust calibration models. Real-time concentration data are displayed and logged to maintain bath recirculation within target ranges.

Instrumentation Used

• NIRS XDS Process Analyzer – SingleFiber
• Low-dispersion single fiber optics (up to 100 m distance)
• Multiplexer option (up to nine sampling points)
• Custom PFA flow cell for clamp-on installation

Main Results and Discussion

Calibration models enabled simultaneous measurement of NH4OH and H2O2 in the SC1 bath and HCl and H2O2 in the SC2 bath with high precision. Inline analysis maintained chemical levels within tight limits, reducing reagent usage by approximately 25 %. Trend charts demonstrate rapid detection of concentration deviations and subsequent reagent spikes to restore setpoints. The system proved non-destructive, required minimal cleanroom footprint, and eliminated operator exposure to hazardous chemicals.

Benefits and Practical Applications

• Increased wafer yields through consistent bath control
• Reduced chemical consumption and operating costs
• Non-invasive, reagent-free analysis with no sample preparation
• Flexible installation outside the cleanroom or beneath wet benches
• Real-time monitoring enhances safety and process reliability

Future Trends and Opportunities

Future developments may include integration of advanced chemometric algorithms and machine learning for predictive bath maintenance, extension to additional process chemistries (etchants, plating solutions), and miniaturized fiber probes for tighter installation constraints. Multipoint monitoring and automated feedback loops will further streamline semiconductor wet processing.

Conclusion

Inline NIRS monitoring of SC1 and SC2 cleaning baths offers a rapid, accurate, and reagent-free solution for maintaining optimal bath chemistry. By leveraging real-time spectral analysis and robust calibration models, semiconductor manufacturers can improve yield, reduce costs, and enhance process safety with minimal cleanroom impact.

References

• 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