Sub-system
Modern process control depends on measuring features far below the wavelength of visible light, thousands of times a day, without damaging the wafer. That measurement is what turns a process from a recipe into something controllable — and it is the reason yields improve at all.
In one sentence
Metrology measures dimensions, film thickness and material properties on a wafer during fabrication; inspection finds defects; wafer test electrically probes each die before it is packaged.
The measurements are indirect. Features are far smaller than optical wavelengths, so systems illuminate the wafer and infer dimensions from how light scatters, using a model of the structure. Electron microscopy gives direct images but is slower and cannot be used on every wafer. Practical control combines fast indirect measurement everywhere with slow direct measurement on samples.
Inspection is a different job: not measuring a known structure but finding an unexpected particle or pattern defect anywhere on the wafer. Doing that at production rates, at the sensitivity required, is why inspection systems are among the most expensive tools in a fab after lithography.
Measurement exists to correct the process. Overlay data adjusts the next exposure's alignment; thickness data trims deposition time; defect maps trace back to the tool that produced them. A fab without dense, fast measurement cannot find the source of a yield loss, and yield learning is what makes a node profitable.
Each die is probed on the wafer with fine needles to check basic function before it is cut and packaged. This matters enormously in multi-die packaging, where assembling one bad die ruins the good ones attached to it — so known-good-die testing is a prerequisite for chiplet-based construction.
More layers, tighter tolerances and three-dimensional structures each add measurement steps, and multi-die packaging adds test steps that did not previously exist. Metrology and test intensity per wafer has risen through successive nodes, which is why this segment grows faster than wafer starts.
Technology dependencies are solved by engineering; supply dependencies are solved by building something, which takes years.
Wafer test needs a card of fine contacts matched to a specific die layout, custom per product and a real lead-time item.
Test interface hardwareProbing pads reaches only what the design exposes. Without scan chains and built-in self-test the coverage at wafer level is poor however capable the tester is.
Physical designWafer probe runs the same class of instrument used at final test, and its cost per second is what makes test time a design constraint this early in the flow.
Final testOther pages in this map that name Metrology and test as something they cannot do without.
What each company supplies at this step, and — where a public figure exists — its share of this specific market — with what that share measures, the period it covers and who published it. Some rows also show the company’s own reported revenue for the segment covering this step, which is a different thing: it says how much this business matters to that company, not how much of the market it holds. Not a ranking and not a recommendation.
Leading supplier of wafer inspection and process control systems.
Wafer Inspection segment — 48.8% of KLA’s reported revenue ($6.6B)FY2026 · company filings · not a market share
Supplies metrology and inspection for wafer and advanced packaging processes.
Supplies dimensional and materials metrology for process control.
Supplies probe cards and test systems used in wafer-level electrical test.
Supplies electron-beam inspection and in-line metrology alongside the process tools that create the defects.
Supplies optical inspection and metrology, increasingly on the packaging and bumping steps.
Supplies actinic mask inspection, which catches a defect once rather than on every wafer printed with it.
Supplies the electron-beam metrology line it acquired, next to the testers it is better known for.
Whether measurement intensity per wafer keeps rising with structural complexity.
Whether packaging inspection becomes as demanding as front-end wafer inspection.
Whether electron-beam inspection throughput improves enough to widen its use.
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