Metrology or inspection
Metrology Measures; Inspection Hunts for Defects
Metrology measures things that are supposed to be there: how wide a line is, how thick a film is, how well one layer lines up with the one below. Inspection looks for things that are not supposed to be there: particles, scratches, bridges between lines, missing features. Metrology produces numbers that tune the process. Inspection produces defect maps that drive yield work.
Both use optical and electron-beam imaging, and both run after nearly every other step. A defect caught early costs one wafer; the same defect found at wafer sort, after hundreds more steps, costs the whole lot that shared its cause. See Wafer Sort Test.
Where it runs
Every Patterning Loop Has Measurement Points
Not every wafer is measured at every step. Fabs sample a few sites on a few wafers per lot, and raise the sampling during a new process ramp or after an excursion. Lithography gets the closest watch because a bad exposure can still be stripped and redone, which is impossible once the pattern is etched. The software that turns these measurements into tool adjustments is covered on Process Control.
Metrology types
Each Quantity Has Its Own Measurement Method
| Type | Technique | Measures |
|---|---|---|
| Critical dimension (CD) | CD-SEM: a scanning electron microscope that images lines from above | Line and space width, line edge roughness |
| Optical CD (OCD) | Scatterometry: models light scattered from a test pattern | CD, sidewall angle and depth, fast and non-destructive |
| Overlay | Image-based or diffraction-based marks, measured after exposure | Alignment of each layer to the one below; tight for multi-patterning and EUV |
| Film thickness | Ellipsometry and reflectometry | Thickness and optical constants of dielectric and metal films |
| X-ray | X-ray fluorescence, reflectometry and small-angle scattering | Composition and buried structure of very thin films |
| 3D structure | Atomic force microscopy, TEM cross-section after FIB milling | Shape of fins, nanosheets and 3D NAND channels |
Inspection types
Optical Inspection Is Fast; E-Beam Sees More
| Type | Technique | Finds |
|---|---|---|
| Brightfield optical | Broadband plasma or DUV light imaged directly | Pattern defects, bridges, missing features; the leading-edge workhorse |
| Darkfield optical | Off-axis light; only scattered light reaches the sensor | Particles and scratches on unpatterned and post-CMP surfaces, at high speed |
| E-beam inspection | Electron beam, including voltage contrast for electrical defects | The smallest and buried defects; slow, so used on samples and hot spots |
| Defect review | SEM revisits defects found by the inspectors | Classifies each defect and its likely cause |
| Mask inspection | DUV inspection, and actinic inspection at 13.5 nm for EUV masks | Mask defects that would print on every wafer |
| Macro and edge | Whole-wafer and bevel imaging | Gross defects, edge chips and edge contamination |
Tool makers
KLA Holds About Three Quarters of the Market
| Maker | Home | Position |
|---|---|---|
| KLA | United States | About 74% of the market in 2025; optical and e-beam inspection, overlay, film and CD metrology, reticle inspection |
| Applied Materials | United States | About 10%; e-beam inspection and SEMVision defect review, CD-SEM |
| Hitachi High-Tech | Japan | CD-SEM leader alongside KLA; defect review |
| ASML | Netherlands | YieldStar diffraction overlay metrology and HMI e-beam inspection, tied to its scanners |
| Onto Innovation | United States | Film, OCD and packaging metrology and inspection |
| Nova | Israel | Optical and X-ray dimensional and materials metrology |
| Lasertec | Japan | Sole supplier of actinic EUV mask inspection; ACTIS A200HiT released October 2025 |
| Zeiss | Germany | AIMS EUV mask review, which emulates the scanner image |
| Thermo Fisher Scientific | United States | TEM and FIB tools for cross-section analysis |
| Skyverse, RSIC (Jingce) | China | Domestic optical inspection and film metrology, mainly at mature nodes |
KLA's share is far larger than any other front-end equipment maker's share of its category. A fab ramping a new node has no second source for its most sensitive inspection tools, and a fab making EUV masks has none for actinic inspection. Tool detail is on Metrology and Inspection Equipment, and packaging-level inspection on Packaging Inspection and Metrology.
Rising intensity
Each Node Adds More Measurement Than Process
Each new node adds measurement steps faster than it adds process steps. The market more than doubled from 2020 to 2025, faster than wafer fab equipment as a whole.
- Gate-all-around nanosheets: TSMC N2, Intel 18A and Samsung SF2 hide the critical features inside the stack, so they need X-ray, OCD and e-beam measurements a top-down image cannot give.
- High-NA EUV: ASML's EXE:5200 prints finer features with a smaller depth of focus, tightening overlay and CD budgets. Lasertec is developing an actinic inspector for High-NA masks.
- Backside power and bonding: Intel PowerVia and TSMC Super Power Rail align a backside layer to the front through a thinned wafer; hybrid bonding needs overlay between two wafers.
- Chiplets: each die in a multi-die AI package must be known good, which pushes inspection into packaging lines.
Record
Page Record
- Covers
- Metrology versus inspection, measurement points, metrology and inspection types, tool makers and rising process control intensity
- Sources
- Equipment market report cited by 24/7 Wall St (market size and shares, May 2026); Lasertec product release (ACTIS A200HiT, October 2025, via Semi-Connect); company product pages for KLA, Applied, Hitachi High-Tech, ASML, Onto, Nova, Zeiss and Thermo Fisher
- Last verified
- October 2026