Wafer inspection systems scan silicon wafers for surface defects—particles, scratches, and pattern anomalies—and produce a defect map: a spatial record of where each anomaly sits on the wafer surface. Metrology systems measure physical dimensions: the width of etched lines (called critical dimension, or CD), layer thickness, film stress, and overlay—the alignment between successive patterned layers. Both types of tool feed their output data directly into the fab's process control system.
The two families use different calibration artifacts and traceability paths. An inspection tool is validated against reference wafers with certified particle or scratch standards. CD and overlay metrology tools span several optical methods—including ellipsometry and scatterometry, which have distinct calibration approaches—and dimensional reference standards certified by a national metrology institute or the original equipment manufacturer (OEM). The category table further below identifies what to ask about for each type. Regardless of type, the output is only valid when the tool has been calibrated against a traceable reference. At advanced process nodes, even a sub-nanometre systematic offset can fall outside the process window; at mature nodes the tolerance is wider, but offsets can still reach tens of nanometres. Either way, an uncalibrated tool produces measurements that cannot be relied on.
Calibration means verifying that the tool's measurements agree, within a defined tolerance, with measurements made on a certified reference artifact. The tool's measurement output is then traceable: you can follow a documented chain from the tool's reading back to a recognised physical standard, as required by ISO/IEC 17025.
Calibration is not a one-time event. Tools drift. Laser sources age, optics accumulate contamination, and mechanical stages develop small positional errors. Production fabs calibrate metrology tools on defined schedules and track measurement drift over time using statistical process control (SPC) charts or long-term monitoring data. That longitudinal record is as important as the calibration certificate itself.
Calibration and service records are not the same thing
A preventive maintenance log confirms that a technician cleaned optics, replaced consumables, or tested subsystems. It does not confirm that the tool's measurement output was compared against a traceable reference. Ask for both, and treat them as separate documents.
What documentation to request before the lot goes live
Before you publish a wafer inspection or metrology lot, ask the consignor for the following. Record what was provided, what was declined, and what was confirmed unavailable. That disclosure protects you and helps bidders price the lot correctly.
- Calibration certificates: the most recent certificate and at least two prior ones, showing dates, the reference artifacts used, the measured values against specification, and the certifying body or OEM service centre.
- GR&R records and long-term drift data: gauge repeatability and reproducibility (GR&R) records confirm short-term measurement precision; SPC charts or long-term monitoring data show whether the tool's output drifted over time. Ask for both—a single GR&R report is not a substitute for a longitudinal drift record.
- Reference wafer traceability documents: the certificates for any reference wafers used in calibration, including the certifying body, the certified dimension values, and their uncertainties.
- Qualification records: the tool's most recent process qualification report, sometimes called a process of record (POR) document—a formal record confirming the tool was accepted for production use at a specific process step—including the process node and wafer size.
- Service history relevant to measurement performance: records of laser replacement, optical alignment, stage re-levelling, or software updates that affected measurement output.
- Last known measurement performance summary: a summary printout of key performance metrics—sensitivity, repeatability, capture rate—against specification at the time the tool was last in production.
Share this checklist with registered bidders
Include items 1 through 4 above in the lot information pack you send to registered bidders before the sale opens. If you cannot produce calibration certificates and a POR document, state that clearly so buyers can plan for full re-qualification when forming their bids. The pre-purchase screening checklist at /resources/inspection-checklist—which covers wafer metrology and inspection tools by category—gives bidders a structured framework they can work through alongside the lot description.
How missing documentation affects value and bid strategy
The table below gives a practical framework for how documentation completeness maps to the buyer's qualification burden. Use it to inform your lot description and reserve-setting conversation with the consignor.
Documentation completeness and buyer re-qualification burden| Documentation available | Buyer's qualification burden | Effect on perceived value |
|---|
| Full calibration certificates, drift logs, reference wafer traceability, qualification report | Abbreviated re-qualification or direct process integration, depending on buyer's process node | Highest: buyer can plan integration cost with reasonable confidence |
| Calibration certificates only (no drift logs or qualification report) | Buyer must run GR&R study and confirm stability before use in production | Moderate: one known cost item, but uncertainty about drift history |
| Service history only (no calibration certificates) | Full metrology re-qualification required; reference wafers must be sourced or certified | Reduced: buyers factor in re-qualification cost and risk of specification failure |
| No documentation of any kind | Full re-qualification plus potential OEM re-certification; timeline is open-ended | Lowest: often priced as a parts source or speculative lot unless the tool is rare |
Re-qualification is not a trivial line item. It involves OEM or third-party metrology engineers, reference artifact procurement or certification, engineering time, and lost production capacity during the qualification period. Buyers who understand this will discount accordingly. The auctioneer who discloses the documentation gap explicitly—rather than leaving it for the buyer to discover after the gavel falls—avoids post-sale disputes and builds credibility with the technical buyer community.
What to include in the lot description
A wafer metrology lot description should state the tool type (inspection or metrology), the measurement parameter (CD, overlay, defect inspection, film thickness, or other), the OEM and model, the process node or wafer size the tool was qualified to, and an explicit statement of which documentation is available. Do not describe documentation as 'available on request' without confirming it has been reviewed and is in hand. Buyers at this level know the difference.
If calibration certificates are present, state the date of the most recent certificate and whether it was issued by the OEM or a third-party metrology service. If reference wafer traceability is confirmed, name the certifying body. These specifics signal to a technical buyer that the lot has been handled carefully, and they justify a higher opening bid.
Used wafer inspection and metrology tools span several distinct measurement disciplines. The documentation requirements are consistent across all of them, but the specific calibration artifacts and performance metrics differ by tool type. The notes below identify what to ask about for each category. EasiMachines is independent and not sponsored by any manufacturer; trademarks belong to their respective owners.
Common tool categories and key calibration documentation points| Tool category | Primary measurement | Key calibration artifact or reference to request | Key performance metric to verify |
|---|
| Brightfield / darkfield wafer inspection | Surface defect location and classification | Reference wafer with certified particle or scratch standards | Detection sensitivity (minimum defect size at stated capture rate) and false-positive rate |
| CD-SEM (critical dimension scanning electron microscope) | Feature width at nanometre scale | Certified CD reference wafer or linewidth standard | Measurement repeatability (3-sigma), linearity across feature size range |
| Optical CD — ellipsometry | Film thickness and CD by optical modelling | OEM-certified or national-metrology-institute-traceable optical thickness reference wafers | Repeatability and accuracy against certified reference values; wavelength calibration records |
| Optical CD — scatterometry | CD and profile reconstruction by optical modelling | Hardware subsystems (detector linearity, wavelength, illumination intensity) are calibrated using physical references—ask for those records alongside the OEM model library version, cross-tool matching records, and SEM cross-section validation data |
Applying this at the lot level
Before the lot goes live, review the documentation against the checklist at /resources/inspection-checklist, note any gaps explicitly in the lot description, and set the reserve in conversation with the consignor to reflect the buyer's likely re-qualification cost. If calibration documentation is incomplete or absent, make that the first sentence of the lot description—not a footnote. Technical buyers read quickly, and a clear statement of documentation status earns more trust than qualified language that leaves them to guess.
If you are comparing multiple consignment lots of similar tools, the compare tool on EasiMachines lets you place listings side by side so documentation completeness can be assessed across lots in one view.
For lots where documentation is strong, the valuation tool at /valuation can provide a directional price range. It is not a certified appraisal. When evidence is thin—which is precisely the case for poorly documented lots—the tool will decline to return a figure rather than produce a misleading estimate.
If you are looking for buyers in this category, the semiconductor manufacturing equipment industry hub connects you with the relevant buyer community. For lots where no suitable bidder appears in the current sale, a Wanted request at /wanted/post?industry=semiconductor-manufacturing-equipment allows relevant buyers and sellers to find each other directly.
Frequently asked questions
Can a buyer re-calibrate a used wafer metrology tool themselves, or does it have to go back to the OEM?
It depends on the tool and the buyer's process requirements. Many tools can be re-calibrated by qualified third-party metrology service providers using OEM-approved procedures and certified reference artifacts. Some advanced CD-SEMs require OEM involvement because proprietary calibration routines are not accessible through all third-party channels, but this varies by platform and OEM; several third-party providers do hold authorised access for specific models. Buyers should verify service options for the exact model before assuming OEM-only access. Ask the consignor whether the tool's service history was OEM-direct or third-party, and confirm that the relevant service provider is still active and holds the required toolsets.
What is a reference wafer, and how does a buyer confirm it is still valid?
A reference wafer is a silicon wafer with precisely characterised features—particle size, film thickness, linewidth, or other parameters—certified by a national metrology institute or an OEM calibration laboratory. Its validity is time-limited: the certified values carry a stated uncertainty, and the wafer itself can degrade through handling or contamination. A buyer should ask for the reference wafer's original certificate, its storage and handling log, and whether it has been re-certified recently. An expired or undocumented reference wafer cannot support a traceable calibration claim.
Does the process node the tool was originally qualified to matter when re-selling it?
Yes, significantly. A tool qualified for a mature process node—for example, for 200 mm wafers at relaxed feature sizes—may not have the sensitivity or resolution to meet specifications at a tighter node, regardless of its calibration status. Buyers targeting advanced nodes will apply a heavier discount or pass entirely. State the original qualification node and wafer size in the lot description so bidders can assess fit before the auction opens.
How should an auctioneer handle a consignor who claims documents exist but cannot produce them before the sale?
Set a clear deadline for document delivery before the lot is published. If the deadline passes without documentation, describe the lot as one for which calibration documentation was not available for review prior to publication, and advise buyers to contact the seller directly to verify availability before bidding. Do not carry a verbal assurance into a written lot description. Post-sale disputes over undisclosed calibration status are difficult to resolve and damage repeat business with technical buyers.
