Tag Archives: ESD-safe cleanroom ops

Techniques for Anti-Static Wipes in Class 100 Cleanrooms

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Class 100 cleanrooms (ISO Class 3)—critical for semiconductor, aerospace, and precision optics manufacturing—demand ultra-low particle counts (≤100 particles ≥0.5μm per cubic foot) and strict electrostatic discharge (ESD) control. Anti-static cleanroom wipes (static-dissipative: 10⁶–10¹⁰ Ω; conductive: 10³–10⁶ Ω) are indispensable here, but their effectiveness depends on tailored usage. Below are key application tips to maintain purity, prevent ESD damage, and optimize workflow.

1. Wipe Selection: Match to Cleanroom Task & ESD Sensitivity

Class 100 operations require wipes that balance anti-static performance, lint control, and solvent compatibility—avoid “one-size-fits-all” choices:
  • For Wafer/Optic Cleaning:

    Choose ultra-low-lint anti-static microfiber wipes (0.1μm fiber diameter) pre-wet with 99.9% electronic-grade IPA. Microfiber traps sub-micron particles (down to 0.1μm) without shedding, while the anti-static treatment keeps surface charge ≤50 V—critical for 3nm semiconductors or AR-coated lenses.

  • For Chamber/Equipment Maintenance:

    Opt for conductive anti-static polyester wipes (10³–10⁶ Ω) for high-ESD-risk tasks (e.g., CVD/PVD chamber cleaning). Conductive fibers rapidly channel static to ground, preventing discharges that damage sensitive tool electronics (e.g., sensor modules).

  • For Dry Dust Removal:

    Use dry anti-static cellulose-polyester blend wipes—the blend’s low-outgassing property avoids contaminating cleanroom air, and anti-static additives prevent dust from reattaching to surfaces (e.g., reticle pods).

  • Tip: Verify wipe certification (e.g., ISO 14644-1 Class 3, ANSI/ESD S20.20) via manufacturer docs—only certified wipes meet Class 100 purity/ESD standards.

2. Wipe Handling: Minimize Particle Generation & ESD Risks

Improper handling can introduce particles or static—follow these rules for Class 100 compliance:
  • Open Wipes in Mini-Environments:

    Retrieve wipes from sealed, Class 100-compatible packaging inside a laminar flow hood or glove box. Tear packaging slowly to avoid generating static (fast motions create charge buildup) and only remove one wipe at a time—exposing multiple wipes to cleanroom air increases particle contamination.

  • Hold Wipes by Edges Only:

    Grip anti-static wipes by their outer edges (not the cleaning surface) to avoid transferring skin oils or fibers. For small wipes (e.g., 2”x2” for reticle cleaning), use plastic-tipped tweezers (grounded to the cleanroom’s earth system) to handle them—eliminates direct contact and ESD transfer.

  • Fold for Multi-Use Coverage:

    Fold wipes into a 4-layer pad to create multiple “clean zones.” Use one layer per surface (e.g., one layer for a wafer chuck, a new layer for a sensor) —this reduces wipe usage by 30–40% and prevents cross-contamination between tasks. Avoid refolding soiled layers inward (traps particles).

3. Cleaning Techniques: Tailored to Class 100 Surfaces

Different surfaces in Class 100 cleanrooms require specific anti-static cleaning methods to preserve purity:
  • Wafer Chucks/Reticles:

    Wipe in slow, linear strokes (parallel to wafer/reticle edges) to avoid pushing particles into precision grooves. For chuck vacuum holes, use a folded wipe strip (1cm wide) and gently dab the opening—never insert the wipe into holes (risk of fiber ingestion).

  • Optical Tools (EUV Lenses, Laser Mirrors):

    Dab, don’t rub: Press the anti-static wipe lightly against the optical surface for 1–2 seconds to lift residue, then lift straight up. Rubbing generates friction (static) and risks scratching coatings—critical for EUV lenses (costing $100k+). Follow with a dry anti-static wipe to blot excess solvent.

  • Equipment Interfaces (USB Ports, Sensor Connectors):

    Use mini anti-static wipes wrapped around a non-metallic probe to clean narrow interfaces. Wipe in a twisting motion to cover all connector pins—ensures no ESD buildup (which causes signal interference) and removes dust that blocks data/ power transfer.

4. Post-Use Practices: Maintain Cleanroom Integrity

Class 100 compliance extends beyond cleaning—proper post-wipe handling prevents recontamination:
  • Dispose of Wipes Immediately:

    Place used anti-static wipes in sealed, Class 100-approved waste bags (labeled “ESD-Safe Waste”) immediately after use. Do not leave wipes on workbenches or tool surfaces—they shed particles over time and can reintroduce contaminants.

  • Validate Post-Clean Conditions:

    After cleaning, use a portable particle counter to verify surface particle counts (≤1 particle ≥0.1μm per ft²) and an ESD field meter to check surface charge (≤50 V). Log results in the cleanroom’s maintenance record—critical for audit compliance (e.g., SEMI S2).

  • Store Wipes Properly:

    Keep unused anti-static wipes in temperature- and humidity-controlled cabinets (20–24°C, 30–50% RH). Extreme conditions degrade anti-static coatings or cause wipes to dry out—rendering them ineffective for Class 100 tasks.