Terminal ultrafiltration serves as the final physical barrier before ultrapure water is delivered from the UPW system to the wafer fabrication line. It retains particulate matter in water and eliminates micro-contamination during manufacturing processes. If the particle count of product water exceeds specifications, it will directly reduce wafer yield and lead to product scrap. This counts as a critical process abnormality that requires rapid root cause identification and closed-loop resolution.
The core troubleshooting logic lies in distinguishing the source of particles: 1) rupture or leakage of the ultrafiltration membrane itself; 2) secondary contamination from downstream pipelines and equipment. Below is a prioritized troubleshooting procedure ready for on-site implementation.
Section 1 Recheck Sampling and Instruments to Rule Out False Over-Limit Readings
Most transient particle over-limit incidents stem from non-standard sampling procedures or air bubble interference in instruments. Prioritize this recheck to avoid unnecessary troubleshooting work.
1.Standardize sampling operations to eliminate human-induced contamination
Flush the sampling port for 3–5 minutes to drain stagnant water. Replace with clean sampling bottles, conduct cross-sampling by different operators for comparison, and eliminate errors caused by human sampling contamination.
2.Verify the operating status of the online particle counter
Air bubbles in pipelines are the primary interference factor for particle counters. Inspect sample feed flow rate and pipeline tightness, vent air and stabilize pressure before retesting to confirm authentic data readings.
Section 2 Core Troubleshooting: Integrity Inspection of Ultrafiltration Membranes
After confirming genuine over-limit particle readings, priority shall be given to inspecting membrane modules. Typical faults include broken membrane fibers and seal leakage of membrane housings, which allow raw water to bypass directly and contaminate product water.
1.Isolation Troubleshooting for Individual Membrane Housings (Fastest Fault Localization)
For systems with multiple parallel membrane housings, adopt the one-by-one isolation method. If particle readings return to normal after cutting off a single housing, this module is confirmed defective.
2.Pressure Decay Test (Basic Detection for Broken Fibers)
Apply nitrogen pressure of 0.1 MPa to the product water side and maintain stable pressure during testing. Excessive pressure decay indicates cracked and leaking membrane fibers.
3.Bubble Point Integrity Test (Precise Verification)
The bubble point test verifies membrane pore retention accuracy. A measured bubble point pressure below standard value means the membrane module loses filtration capacity and requires immediate replacement.
Section 3 Source Tracing: Secondary System Contamination
If no abnormalities are found in membrane integrity, excessive particles mostly originate from upstream water quality fluctuations or secondary contamination in downstream pipelines and equipment.
1.Inspection of Ultrapure Water Storage Unit
Check the pressure stabilization status of the nitrogen-sealed water tank. Expired or damaged breather filters allow external dust to enter the water, triggering particle over-limit issues.
2.Troubleshooting of Polishing Mixed Bed Resin System
A broken screen on the polishing mixed bed resin trap will release resin fines, resulting in persistent particle excess and fouling of membrane modules.
3.Hidden Hazards in Circulation Pipelines and Valves
Welding slag and metal shavings left over from pipeline maintenance and welding, as well as debris shed from aging valve diaphragms and seals, constitute hidden particle contamination sources.
4.Inspection of TOC-UV Unit
Broken TOC-UV lamps or quartz sleeves generate glass fragments that continuously contaminate product water and cause abnormal particle levels.
Section 4 Review Operating Parameters and Operations
Most particle abnormalities and broken membrane fibers are caused by fluctuating working conditions and non-standard operations. Historical data and operation logs shall be reviewed for root cause analysis.
1.Check abrupt changes in feed water quality
Cross-reference particle data of upstream RO and ultrafiltration feed water recorded during the over-limit period to investigate surging upstream particle concentration and overloaded filtration load.
2.Troubleshoot water hammer impact and operational errors
Water hammer is the top human-induced cause of broken membrane fibers. Frequent pump start-stop cycles and rapid valve opening/closing create pipeline pressure surges that rupture membrane fibers, resulting in permanent leakage.
Summary of On-Site Rapid Troubleshooting
1.Eliminate false alarms: Standardize sampling operations and recheck instruments to rule out interference from air bubbles and sampling contamination.
2.Locate faulty membrane housing: Adopt single-housing isolation method to quickly identify defective ultrafiltration modules.
3.Verify membrane integrity: Conduct pressure decay test or bubble point test to confirm broken fibers, and replace membranes promptly.
4.Trace secondary contamination sources: Inspect hidden risks in water tanks, resin traps, circulating pipelines, valves and TOC-UV units.
Conclusion: Particle control at the ultrapure water terminal is critical to wafer yield. Standardized troubleshooting and rapid response can effectively mitigate the risk of micro-contamination during manufacturing processes.
