Advanced Functions of AHUs in Semiconductor Fabs
Multi-Stage Filtration
AHUs integrate HEPA/ULPA filters to achieve ISO Class 1-5 cleanroom standards, removing particles as small as 0.1–0.3 microns.
Chemical filtration (e.g., activated carbon) may be added to absorb airborne molecular contaminants (AMCs) like acids, dopants, or solvents.
Pressure Cascade Control
Maintains positive/negative pressure gradients between cleanroom zones to prevent cross-contamination.
Critical in photolithography and etching areas where airborne particles can ruin wafers.
Redundancy and Reliability
N+1 redundancy is common to ensure uninterrupted operation—a single AHU failure can cost millions in lost yield.
Backup systems (e.g., dual fans, emergency power) are critical for 24/7 fabs.
Recirculation vs. Once-Through Airflow
Recirculating AHUs (90–95% air reuse) save energy but require rigorous filtration.
Make-Up Air Units (MAUs) supply fresh, conditioned air to offset exhaust from tools (e.g., scrubbers, process chambers).
Energy Efficiency Innovations
Semiconductor fabs consume 2–4% of global industrial electricity, with HVAC accounting for ~30–50% of a fab’s energy use.
AHU optimizations include:
Variable Frequency Drives (VFDs): Adjust fan speeds based on real-time demand.
Heat Recovery Systems: Capture waste heat from process exhaust to pre-condition incoming air.
AI/ML-Based Control: Predictive algorithms optimize airflow, temperature, and humidity setpoints.
EC (Electronically Commutated) Fans: More efficient than traditional AC fans.
Challenges in AHU Design
Process Sensitivity: Advanced nodes (e.g., 3nm, GAAFETs) require tighter tolerances (e.g., ±0.1°C temp, ±1% RH).
Chemical Compatibility: AHUs must resist corrosion from aggressive chemicals (e.g., HF, NH₃).
Scalability: AHUs must adapt to fab expansions or process changes
Future Trends
Smart AHUs: IoT-enabled sensors monitor filter life, airflow, and energy use in real time.
Sustainable Designs: Heat pumps, liquid desiccant dehumidification, and renewable energy integration.
Modular AHUs: Pre-fabricated units for faster installation in new fabs .
