QDR (Quick Dump Rinse) is 3–5 times faster than overflow rinse and reduces UPW consumption by 30%–50% based on industry empirical data. Its working principle relies on a large-bore bottom drain to rapidly lower the liquid level, and the flowing water scours the surface to wash away residues. Overflow rinse adopts gradual solution exchange via four-lip overflow weirs. It delivers a clear endpoint judgment but consumes longer cycle time and more ultrapure water. The optimal practice is combined application: deploy QDR immediately after the process to seize critical time for residue removal, and use overflow rinse as the final polishing step with resistivity as the endpoint criterion.

The core mechanism of QDR is rinsing during draining. All advantages of QDR originate from the instant opening of the large-bore bottom dump valve. When draining speed is sufficiently high, the falling liquid level itself strips the chemical boundary layer on wafer surfaces. Combined with top-side spray and nitrogen bubbling, one full exchange cycle can be finished within tens of seconds. If wafers stay immersed in chemical solution for an extra minute, residues will continuously etch the wafer surface. This effect is especially destructive for sensitive surfaces after DHF treatment. Key design points of QDR include the bore size and response speed of the bottom dump valve, uniform spray coverage, and anti-siphon protection during draining. Domestic manufacturers such as CSE Group have taken QDR as a standard bath configuration for batch wet cleaning systems.

The endpoint criterion for overflow rinse is resistivity. The pass standard for overflow rinse is that the resistivity of ultrapure water in the bath recovers close to the feedwater level. The theoretical limit of ultrapure water is 18.2 MΩ·cm at 25°C. In engineering applications, the widely accepted rinse endpoint is stable resistivity above 10 MΩ·cm. Reaching 15 MΩ·cm or higher is more conservative, while it is unnecessary to pursue the theoretical 18.2 MΩ·cm limit. Continued overflow after reaching the target value only wastes water. Overflow rinse works through continuous water feeding via four-lip overflow weirs. Ions and contaminants are carried out with overflow stream, and there is nearly no hydrodynamic impact. Therefore, it fits the final rinse after SC-2 and before drying. At this stage, wafer surfaces are highly clean and hydrophilic; turbulent flow and mechanical impact will increase the risks of particle re-deposition and watermarks.

Water consumption accounting must be calculated per cassette per process step. Three variables dominate the water balance: UPW consumption per cassette, exchange ratio, and wastewater discharge volume. According to industry benchmarks, a standard overflow rinse consumes 100–300 L of UPW per 25-wafer cassette, while QDR integrated with spray can reduce this volume to roughly one third. Given the production cost of UPW at tens of RMB per ton, the annual UPW cost of a multi-bath wet cleaning line can reach hundreds of thousands of RMB. Wastewater treatment is equally important. DHF-containing fluorine wastewater must be treated in dedicated fluorine removal systems before discharge. The water saved by QDR directly cuts the wastewater treatment load.

Comparison

• For rinse speed: QDR quick dump rinse is fast, with a single cycle completed within tens of seconds; overflow rinse is relatively slow, and one single bath cycle takes several minutes up to ten minutes.

• For UPW consumption: QDR quick dump rinse features low water consumption and can save 30%–50% ultrapure water compared with overflow rinse; overflow rinse consumes a large volume of UPW.

• For mechanical impact: QDR quick dump rinse brings mechanical impact generated by combined flow scouring and bubbling; overflow rinse produces almost no mechanical impact.

• For residue control: QDR quick dump rinse avoids continuous chemical erosion on substrates; overflow rinse supports quantifiable residue control via resistivity endpoint monitoring.

• For preferred application position: QDR quick dump rinse is suitable for use right after highly corrosive chemistries such as DHF; overflow rinse is mainly applied in the final rinse stage before drying.

FAQ

Q: What does QDR stand for? 

A: QDR stands for Quick Dump Rinse. It is a rinsing method that rapidly empties bath liquid through a large-bore bottom dump valve while spraying ultrapure water synchronously for solution exchange.

Q: Can QDR crack wafers? 

A: Properly designed QDR will not crack wafers. Cassettes and baffles guide the flow. The main risk is siphon effect when the liquid level crosses the cassette plane, which can be avoided by mature anti-siphon design.

Q: When is overflow rinse mandatory? 

A: Overflow rinse is required for the final rinse after SC-2 and right before drying. This stage needs low-disturbance solution exchange and resistivity endpoint confirmation.

Q: What resistivity value indicates sufficient rinsing? 

A: The industry standard criterion is stable resistivity above 10 MΩ·cm. A reading above 15 MΩ·cm is more reliable, and there is no need to chase the 18.2 MΩ·cm theoretical limit.

Q: Can QDR be followed by overflow rinse? 

A: Yes and highly recommended. This is the mainstream configuration: QDR removes bulk residues quickly, and overflow rinse polishes to guarantee the target resistivity.

Conclusion

The optimal combination of QDR and overflow rinse is to deploy QDR after DHF for time-sensitive residue removal, adopt overflow rinse after standard cleans to secure the rinse endpoint, and accept the process when resistivity stabilizes above 10 MΩ·cm. Water accounting is performed per cassette per process step. QDR reduces UPW consumption by 30%–50% and lowers fluorine-containing wastewater treatment load, which represents the optimal water balance solution for batch wet cleaning baths.