semiconductor metrology

**Semiconductor Metrology** — the science of measuring and inspecting features on semiconductor wafers to ensure process control and yield. **Key Measurements** - **CD (Critical Dimension)**: Feature width measured by CD-SEM (scanning electron microscope). Sub-nm precision required at advanced nodes - **Overlay**: Alignment between successive lithography layers. Must be < 2nm at leading edge - **Film Thickness**: Measured by ellipsometry or XRR (X-ray reflectometry). Angstrom-level precision - **Defect Inspection**: Brightfield/darkfield optical inspection or e-beam inspection to find killer defects **Major Tools** - **KLA**: Dominant in inspection and metrology (80%+ market share) - **ASML (YieldStar)**: Overlay and CD metrology - **Hitachi High-Tech**: CD-SEM - **Onto Innovation**: Film metrology **In-Line vs Off-Line** - In-line: Measure during production (sampling strategy) - Off-line: Detailed analysis of problem wafers **Metrology** is the eyes of the fab — without precise measurement, process control is impossible. The industry saying: "You can't improve what you can't measure."