How to Design a Corrosion-Resistant Exhaust System for a Semiconductor Fab

Article Summary

Semiconductor fabs use acids, alkaline chemicals, solvents and specialty gases that can create highly corrosive exhaust streams. A reliable exhaust system must safely capture and transport those contaminants while maintaining stable airflow, protecting equipment and supporting continuous production.

Effective semiconductor exhaust system design requires more than selecting a corrosion-resistant fan or duct material. Engineers must evaluate exhaust chemistry, stream segregation, pressure drop, condensation, drainage, wet scrubbing, monitoring, maintenance access and future fab expansion as parts of one connected system.

Why Semiconductor Fabs Need Corrosion-Resistant Exhaust Systems

Wafer cleaning, etching, deposition, stripping and chemical handling can generate acid gases, alkaline gases, chemical mists and other hazardous emissions. These contaminants can attack metal surfaces, seals, joints, fan components and ductwork when the equipment is not compatible with the operating environment.

The consequences extend beyond premature equipment replacement. Corrosion can create leaks, restrict airflow, reduce structural integrity and increase the risk of unexpected shutdowns. In a facility where process tools depend on stable exhaust around the clock, a small failure can disrupt a much larger production area.

That is why semiconductor exhaust system design should address both chemical resistance and long-term operating reliability.

Identify and Segregate Semiconductor Exhaust Streams

The first design step is identifying what each process produces and determining which streams can be safely combined.

Acid Exhaust Systems

Acid exhaust may contain hydrogen fluoride, hydrogen chloride, nitric acid vapors, sulfur-containing compounds or acidic mists. These streams require materials and treatment equipment selected for the specific chemistry and concentration.

Alkaline Exhaust Systems

Ammonia and other alkaline contaminants can require different scrubbing chemistry from acid gases. Combining alkaline and acidic streams without careful evaluation may create salts, deposits or reactions within the ductwork.

VOC and Solvent Exhaust Systems

Solvent and VOC exhaust may require treatment technologies other than wet scrubbing. These streams should be evaluated according to flammability, concentration, condensation risk and applicable emission requirements.

Toxic and Specialty Gas Exhaust Systems

Specialty gases may require dedicated point-of-use treatment, separate routing or additional safeguards before entering a facility exhaust system.

Why Incompatible Exhaust Streams Should Remain Separate

Exhaust segregation helps prevent reactions, solids formation, condensation and unexpected corrosion. Systems should be grouped according to chemistry and treatment needs, not merely according to physical proximity within the fab.

Characterize the Exhaust Before Selecting Equipment

Material and equipment choices should follow a complete assessment of actual operating conditions.

Identify Chemical Species and Peak Concentrations

Engineers should document normal and peak contaminant concentrations, possible chemical combinations and the effects of process changes. The highest credible load may occur when multiple tools operate simultaneously or during cleaning and maintenance cycles.

Document Airflow, Temperature, Humidity and Condensation Risk

Temperature and humidity influence corrosion, condensation and gas behavior. A stream that remains gaseous near the tool may condense as it travels through cooler ductwork.

The design should also account for minimum, average and peak airflow rather than relying on one nominal value.

Account for Process Changes and Peak Tool Loads

Fab exhaust requirements evolve as process recipes change and new tools are installed. Capacity planning should include reasonable future loads so the system does not become undersized shortly after commissioning.

Select Corrosion-Resistant Materials for the Exhaust Chemistry

No material is universally resistant to every semiconductor exhaust stream. Selection should consider chemical species, concentration, temperature, moisture, mechanical loading and fire-performance requirements.

FRP Exhaust Fans and Ductwork

Fiberglass reinforced plastic is commonly considered for corrosive exhaust because resin and reinforcement systems can be tailored to the application. CECO’s corrosion-resistant centrifugal exhaust fans use FRP materials and vinyl ester resin systems for harsh operating conditions.

Likewise, corrosion-resistant FRP exhaust ductwork can provide resin-rich interior surfaces, structural reinforcement and UV-stabilized, fire-retardant exteriors.

Thermoplastics and Other Corrosion-Resistant Materials

Polypropylene, PVC and other thermoplastics may also be suitable for certain exhaust conditions. The best choice depends on temperature, chemical resistance, structural needs, code requirements and installation environment.

Resin Selection, UV Exposure and Fire-Retardant Requirements

The label “FRP” alone is not enough. The resin system must be compatible with the contaminants, and outdoor components may need protection against ultraviolet exposure. Exterior fire-retardant requirements should also be considered during specification.

Protect Joints, Flanges, Seals and Other Failure Points

Corrosion often begins at transitions, penetrations, joints, flanges and poorly drained areas. These details should receive the same chemical-compatibility review as the main duct or fan housing.

Size Semiconductor Exhaust Fans for Airflow and Pressure Drop

The fan must maintain the required capture and transport airflow across the full operating range.

Calculate Total Exhaust System Resistance

System resistance includes losses through hoods, duct runs, elbows, dampers, scrubber packing, mist eliminators and stacks. Dirty or wet operating conditions may create more resistance than clean startup conditions.

Account for Scrubbers, Mist Eliminators, Dampers and Stacks

A fan selected without the downstream treatment equipment may be unable to maintain the required airflow once the full system is connected. Fan and scrubber selection should therefore occur together.

Maintain Stable Capture Airflow at Process Tools

Insufficient airflow can allow contaminants to escape at the source. Excessive airflow can increase energy use, system pressure and treatment equipment size. Controls should maintain the intended balance as tools cycle on and off.

Control Fan Vibration Near Sensitive Manufacturing Equipment

Semiconductor processes can be sensitive to vibration. Fan location, foundation design, balance, isolation and duct connections should limit vibration transmission into production areas.

Design Corrosion-Resistant Exhaust Ductwork

Ductwork must move contaminants safely while limiting leakage, deposits and liquid accumulation.

Select Duct Size and Velocity for Reliable Contaminant Transport

Duct velocity should support contaminant transport without creating excessive pressure loss or noise. Mist and particulate-containing streams may require different design considerations than dry gas streams.

Prevent Condensation and Chemical Accumulation

Temperature changes can cause vapors to condense inside the duct. Insulation, routing, material selection and operating temperature should be evaluated where condensation is possible.

Include Drainage for Low Points and Liquid Carryover

Low points should not become uncontrolled collection areas. Where liquid accumulation is possible, the system may need drains, slopes and compatible collection provisions.

Minimize Leakage and Pressure Loss

Excessive fittings, abrupt transitions and poorly designed connections increase pressure loss and create potential leak points. A more direct layout can improve both efficiency and reliability.

Provide Inspection and Maintenance Access

Access points should allow teams to inspect joints, drains, deposits and internal surfaces. Equipment that cannot be inspected is more likely to develop unnoticed problems.

Integrate Wet Scrubbers Into the Semiconductor Exhaust System

Acidic and alkaline exhaust may require wet scrubbing before discharge.

When Acid and Alkaline Exhaust Requires Wet Scrubbing

Packed bed wet scrubber systems increase contact between exhaust gas and a scrubbing liquid, supporting absorption and chemical neutralization of soluble contaminants. Ionizing wet scrubbers can also be applied when the exhaust stream requires acid-gas control together with fine-particle or aerosol removal.

Coordinate Scrubber Pressure Drop With Fan Selection

Packing depth, mist eliminators and internal components add resistance. The exhaust fan must accommodate those losses while maintaining stable capture at connected tools.

Control Mist Carryover After the Scrubber

Mist eliminators reduce liquid droplets leaving the scrubber. Effective droplet control helps protect downstream ductwork, fans and stacks from chemical carryover and deposits.

Manage Chemical Dosing, Recirculation and Blowdown

Scrubber performance depends on recirculation flow, pH, liquid distribution and chemical dosing. Facilities also need a plan for blowdown and wastewater generated by the treatment process.

Improve Semiconductor Exhaust System Reliability

Reliability planning should reflect the production consequences of system downtime.

Build in Fan, Pump and Control Redundancy

Critical applications may require redundant pumps, fans, blowers or controls. CECO’s semiconductor exhaust system case study incorporated redundant recirculation pumps and blowers into a complete horizontal wet scrubber package designed for a restricted footprint. Verantis semiconductor case studies also show how wet-scrubber configurations can vary by fab requirement: one application treated ammonia exhaust sources independently before combining them with acid exhaust, while another used 24 scrubber systems in a central air abatement system (CAAS) treating approximately 600,000 CFM.

Monitor Airflow, Pressure, Vibration and Scrubber Performance

Monitoring can identify rising resistance, airflow loss, fan vibration, liquid-distribution problems or declining scrubber performance before they become larger failures.

Plan Preventive Maintenance Around Continuous Fab Operations

Maintenance access, spare parts and service procedures should be considered during design. Waiting until equipment fails can make even a routine repair disruptive.

Design for Future Process Tools and Fab Expansion

Available fan capacity, duct routing, treatment capacity and controls should be reviewed before new tools are connected. Expansion should not compromise capture performance elsewhere in the network.

Common Semiconductor Exhaust System Design Mistakes

Frequent mistakes include selecting materials based only on the primary contaminant, combining incompatible streams, underestimating pressure drop and ignoring condensation or drainage.

Other problems result from limited inspection access, insufficient redundancy and failure to reserve capacity for future tools. A reliable system depends on corrosion-resistant air pollution control equipment working as an integrated network rather than as isolated components.

Design the Complete Exhaust System for Corrosion Resistance and Uptime

A corrosion-resistant semiconductor exhaust system must align chemistry, airflow, materials, fan performance, duct routing, drainage, wet scrubbing, monitoring and maintenance. To evaluate a new system, expansion or retrofit, contact CECO for professional guidance and assistance with semiconductor exhaust handling and air pollution control.

Frequently Asked Questions