In semiconductor manufacturing, particles as small as 0.1 micron can cause fatal defects on a wafer, leading to yield loss, rework costs, and delayed shipments. Fabs producing chips at advanced nodes must therefore operate within cleanrooms rated ISO Class 1 to ISO Class 4 — among the most demanding cleanliness standards in industrial manufacturing.
1. ISO 14644 Cleanroom Classification for Semiconductor Fabs
The ISO 14644 standard defines cleanroom classes based on the maximum allowable concentration of airborne particles at specified sizes. Different process areas within a fab require different classes and corresponding filtration:
- ISO Class 1–2 (Lithography / EUV): the most stringent zones, requiring ULPA U17 filtration
- ISO Class 3–4 (Etching / Deposition / Wafer Handling): require ULPA U15 or U16 filtration
- ISO Class 5–6 (Assembly / ATE — Automated Test Equipment): require HEPA H14 filtration
- ISO Class 7–8 (Support areas / clean storage): require HEPA H13 filtration
2. ULPA vs. HEPA: When to Upgrade
Selecting between HEPA and ULPA filtration depends on the required efficiency at the Most Penetrating Particle Size (MPPS):
- HEPA H14: efficiency ≥99.995% at MPPS
- ULPA U15: efficiency ≥99.9995% at MPPS
- ULPA U16: efficiency ≥99.99995% at MPPS
- ULPA U17: efficiency ≥99.999995% at MPPS
ULPA filtration is recommended for sub-28nm process nodes, areas with direct wafer exposure, and ISO Class 1–4 zones requiring high-resolution particle inspection.
3. Fan Filter Units (FFU)
A Fan Filter Unit combines a centrifugal fan with a HEPA or ULPA filter in a single ceiling-mounted module, and is the core building block of semiconductor cleanroom ceilings.
- Ceiling coverage ratio typically ranges from 20% to 100%, depending on the required cleanliness class
- EC (electronically commutated) motors reduce energy consumption and allow variable airflow control
- Top-loading design allows filter replacement without halting production
- ISO Class 1–3 fabs commonly use 100% FFU ceiling coverage to achieve Unidirectional (Vertical) Laminar Flow
4. Airborne Molecular Contamination (AMC) Control
Beyond particles, semiconductor fabs must also control Airborne Molecular Contamination — gaseous chemical contaminants that can damage wafers even at trace concentrations. This is addressed with activated carbon and chemisorption media that remove acidic, basic, and organic molecular contaminants from the recirculated air.
5. Air Filtech Solutions
- ULPA U15/U17 filters (Camfil) with MPPS and scan-test certification
- EC motor Fan Filter Units with BMS/SCADA integration
- HEPA H14 Terminal Housing (Green Series) with 304 stainless steel frame
- Zeolite and activated carbon AMC filters
- Commissioning and particle count verification per ISO 14644-3
6. Featured Projects
- Samsung HCMC CE Complex (Ho Chi Minh City) — HEPA/ULPA filtration for the ISO Class 5 assembly area
- Hòa Lạc Hi-Tech Park (Hanoi) — FFU and ULPA filtration for an R&D cleanroom
- Intel Vietnam Factory (Bình Dương) — periodic HEPA filter replacement per OEM standard
Contact Air Filtech: 08 999 44 666 | info@airfiltech.vn
