Defect Inspection
Brightfield, darkfield, and e-beam inspection for finding killer defects
Optical Inspection
Optical Inspection
Defect inspection finds particles, pattern defects, and process anomalies that could kill dies:
- Brightfield inspection: Illuminates the wafer and compares the image of each die to its neighbors (die-to-die comparison). Differences = potential defects. High throughput but limited by optical resolution (~30 nm sensitivity).
- Darkfield inspection: Detects light scattered by defects against a dark background. Higher sensitivity to small particles than brightfield. Used for unpatterned and patterned wafer inspection.
- E-beam inspection: Scans with a focused electron beam for ultimate resolution (<10 nm). Can detect electrical defects (voltage contrast) invisible to optical tools. Very slow — used for development and focused areas, not full-wafer production inspection.
After inspection finds defect locations, a Review SEM takes high-resolution images of individual defects for classification — determining what type of defect it is and its root cause.
Key Concept: ML for Defect Classification
Automatically classifying defects from SEM review images is a major ML application in fabs. CNNs can classify defects into dozens of categories (particle, scratch, bridging, missing pattern, etc.) faster and more consistently than human operators.
Inspection Vendors and Tool Lineup
Inspection Vendors and Tool Lineup
Defect inspection is a more concentrated market than litho or etch. Three vendors dominate, each with a clear specialty:
| Vendor | Notable tools | Strength |
|---|---|---|
| KLA | 2900-series broadband plasma (BBP), Voyager DUV brightfield, eDR-7100 e-beam review | Pattern wafer inspection, broad coverage from logic to memory |
| Applied Materials | UVision (DUV optical), VeritySEM (CD-SEM), SEMVision (e-beam review) | Strong in CD-SEM and e-beam review |
| Hitachi High-Tech | CG6300/CG5000 CD-SEM, GT2000 inspection | Reference CD-SEM platforms |
How inspection tools work together
- Inspection (KLA 2900 / AMAT UVision) scans the wafer for defects → outputs a defect coordinate file
- Review SEM (Hitachi CG, AMAT SEMVision) revisits each coordinate at 1–5 nm resolution and captures a SEM image
- Automatic Defect Classification (ADC) labels each image (particle, scratch, missing pattern, bridge…) — modern fabs use CNN-based classifiers
- Yield management system (KLA Klarity, PDF Solutions, in-house) correlates defects to test wafer maps and assigns root-cause to tools, recipes, or lots
Key Concept: Wafer Inspection Cost
A single advanced BBP inspection tool costs $30–60 million and a fab may need 10+ of them. Inspection equipment alone runs into the hundreds of millions of dollars — but at $10–20 k per wafer of finished value, even a 1% yield rescue pays it back fast.
Knowledge Check
Knowledge Check
1 / 2What is the advantage of e-beam inspection over optical inspection?