Defect Inspection

Defect Inspection — detecting and classifying nanoscale defects on wafers during fabrication to maintain yield, the critical feedback loop that keeps a semiconductor fab running.

Types of Defects

• Particles: Foreign material on wafer surface (from equipment, chemicals, air)
• Pattern defects: Missing features, bridging (shorts), broken lines (opens)
• Scratches: From CMP or wafer handling
• Film defects: Pinholes, thickness variations, voids in metal fill
• Crystal defects: Stacking faults, dislocations (from thermal stress)

Inspection Technologies

• Optical (Brightfield/Darkfield): Scan wafer with focused light, detect scattered/reflected signal anomalies. KLA 39xx series. Catches particles >20nm
• E-beam inspection: Scan with electron beam for highest resolution. Slower but catches sub-10nm defects. Voltage contrast detects buried opens/shorts
• Scatterometry: Measure diffraction from periodic patterns to detect dimensional variations

Inspection Flow

1. Inline inspection after critical process steps (litho, etch, CMP)
2. Defect detected → coordinates recorded in defect map
3. Defect review: High-resolution SEM images of flagged defects
4. Classification: Systematic (process issue) vs random (particle)
5. Root cause analysis → process correction

KLA Corporation dominates the inspection market (~80% share). Their tools are essential — no advanced fab operates without them.

Defect inspection is the immune system of a semiconductor fab — it detects problems before they affect millions of chips.