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.