Wafer Acceptance Criteria (WAC) are the set of measurable thresholds that a semiconductor wafer must pass at various stages of fabrication — to be accepted for the next process step or for final shipment to the customer.

What Are Wafer Acceptance Criteria?

• Definition: Quantitative pass/fail limits on critical parameters.
• Parameters Tested:
• Defect Density: Max defects per cm² (inspected by KLA tools).
• Film Thickness: Uniformity within $pm$ specification (measured by ellipsometry).
• Critical Dimension (CD): Line width within tolerance (SEM measurements).
• Electrical: Sheet resistance, threshold voltage ($V_t$), leakage current.
• Disposition: Pass (ship), Fail (scrap), Hold (review by engineer).

Why It Matters

• Yield Protection: Catching bad wafers early prevents wasting downstream processing costs.
• Customer SLA: Contractual obligations for defect levels (e.g., < 0.1 defects/cm²).
• Continuous Improvement: Trending WAC data drives process optimization and equipment maintenance.

Wafer Acceptance Criteria are the quality gates of semiconductor manufacturing — ensuring every wafer meets the exacting standards required for reliable chips.