Post-etch residue removal is an important cleaning step in semiconductor fabrication. After plasma etching, polymeric and other residues can remain on the wafer surface and must be removed before subsequent manufacturing steps. The performance of the cleaning process depends not only on the cleaning chemistry itself but also on maintaining the correct chemical composition. Inline refractometry provides continuous real-time information about changes in EKC® cleaning chemistry directly in the process.
Why Is EKC® Composition Important for Post-Etch Residue Removal?
EKC® cleaning chemistries are used in post-etch cleaning processes to remove residual polymers and other unwanted material from wafer surfaces. The water content of the EKC® solution must remain within its specified operating range. Excessive water content can increase the risk of corrosion, while insufficient water content can reduce the effectiveness of polymer removal. Reliable monitoring of the EKC®/water composition is therefore important for maintaining stable cleaning conditions, protecting wafer surfaces, and supporting consistent process results.
How Does Post-Etch Residue Removal Work?
During plasma etching, material is selectively removed from the wafer to create the required semiconductor structures. The interaction between plasma species, photoresist, and wafer materials can result in residues remaining on the wafer after the etching step.
These residues must be removed before subsequent processing because remaining contamination can interfere with downstream manufacturing steps and affect wafer quality. In a typical post-etch cleaning process, the wafer is exposed to a chemical cleaning solution designed to dissolve or remove the remaining residues. Spray solvent tools can use EKC® chemistry for this purpose.
Depending on the process configuration, the cleaning solution can be collected and returned to a tank after processing, creating a recirculating chemical system. Within this recirculation loop, the composition of the chemistry can change over time. Water can evaporate during operation, chemicals can be replenished or replaced, and process-related changes can alter the composition of the solution.
Why Does Accurate EKC® Concentration Monitoring Matter?
The EKC®/water ratio influences the performance of the post-etch cleaning process. Maintaining the required composition is therefore essential for achieving reproducible residue removal.
Both insufficient and excessive water content can be problematic. If the water content becomes too high, the risk of corrosion can increase. If the water content becomes too low, the cleaning chemistry may no longer provide the required polymer-removal performance.
Changes in composition can occur through evaporation, replenishment, chemical replacement, process carryover, or other changes within the recirculation system. Periodic manual sampling can identify these deviations, but only at individual points in time. Continuous inline measurement provides process operators with immediate information about changes in the cleaning solution while the process is operating.
How Does Refractive Index Measurement Monitor EKC® Composition?
The refractive index provides a parameter for characterizing the composition of liquid chemical mixtures. When the ratio between EKC® chemical and water changes, the optical properties of the solution change accordingly. Once an application-specific relationship between refractive index, temperature, and chemical composition has been established, refractometric measurement can be used to continuously monitor changes in the EKC®/water ratio. Unlike periodic laboratory sampling, an inline process refractometer measures directly in the circulating chemical stream. Refractive-index measurement can therefore be integrated as a Process Analytical Technology parameter for continuous semiconductor process monitoring.
How Is EKC® Chemistry Monitored During Operation?
Manual laboratory measurements can be used to periodically verify the condition of the cleaning chemistry. However, semiconductor manufacturing processes operate continuously or in repeated production cycles, and changes in chemical composition may occur between individual sampling intervals. Inline measurement provides continuous information between individual samples by measuring the refractive index directly in the EKC® circulation loop. Operators can therefore identify concentration changes as they occur instead of waiting for the next manual sample.
Continuous EKC® monitoring can provide:
- Real-time monitoring of cleaning chemistry composition
- Immediate detection of changes in water content
- Detection of unexpected concentration drift
- Verification of defined upper and lower process limits
- Reduced dependence on manual sampling
- Early indication of chemical composition deviations
- Improved transparency of the post-etch cleaning process
- Integration into automated process monitoring and control systems
The measurement signal can be transmitted to a PLC or higher-level process control system. This allows the condition of the EKC® chemistry to be monitored together with other relevant process parameters and provides continuous information about the cleaning process.
What Are the Benefits of Continuous EKC® Concentration Monitoring?
Continuous refractometric monitoring provides important advantages for post-etch residue removal processes. By measuring the cleaning chemistry directly in the process, changes in the EKC®/water composition can be detected immediately rather than only during periodic laboratory analysis.
The main benefits include:
- Continuous, real-time monitoring of EKC® cleaning chemistry
- Immediate detection of changes in water content
- Early detection of concentration drift
- Reliable monitoring of defined upper and lower process limits
- Support for consistent polymer and post-etch residue removal
- Reduced dependence on manual sampling and laboratory analysis
- Improved process transparency and chemical control
- Support for controlled chemical replenishment and bath management
- Integration of chemical monitoring into automated process control
- Earlier identification of deviations before they can affect subsequent process steps
- Support for stable and reproducible post-etch cleaning conditions
Continuous measurement therefore turns chemical composition from a periodically checked laboratory parameter into a continuously available process parameter. This can help operators maintain the cleaning chemistry within its specified process window and respond more quickly to changes in the recirculating solution.
