How to Evaluate a Diamond Wafer Beyond Its Diameter

A wafer announcement tells you the diameter that a process can reach. It rarely tells you how much of that area meets a device’s requirements. The first question is therefore how the material was produced, followed by how its usable region was measured.

Identify the route before comparing diameters

Route	How it is made	Size context	What to inspect
Homoepitaxial single-crystal plate	Grown on a diamond single-crystal seed	Common plates are in the millimeter-to-centimeter range; larger-scale work exists	Seed-related defects, extended defects, and usable-area limits
Heteroepitaxial wafer	Grown on a non-diamond template such as Ir/YSZ/Si	A two-inch research wafer has been reported	Dislocations, stress, and thickness uniformity
Mosaic wafer	Several single-crystal seeds are arranged for co-growth	Depends on the number and layout of seeds	Joint regions, local stress, and orientation mismatch

“Millimeter-to-centimeter” describes commonly encountered homoepitaxial plates, not a technical ceiling. Orbray and Element Six report a reproducible process for three-inch wafer-scale single-crystal diamond. Routes and defects must be evaluated separately; a diameter does not determine a usable area.

Turn nominal size into usable area

Nominal size describes the outside shape. Usable area is the portion meeting stated acceptance limits after edge exclusion, defect mapping, processing-damage assessment, and thickness checks. The same wafer can yield different usable areas under different device layouts or acceptance thresholds.

Ask how the edge exclusion is defined, which defect classes count as failures, whether maps cover the entire wafer, and how the passing area is calculated. Request the data behind the percentage, not just a headline yield.

Check the measurements that matter to the application

Dimension	Request from the supplier
Orientation and miscut	Target crystal plane, tolerance, and measurement method, especially for epitaxy
Crystal defects	Whole-wafer map of dislocations, cracks, and inclusions, with definitions and detection limits
Stress and birefringence	Spatially resolved images, especially for large or heteroepitaxial material
Surface	Roughness, polishing condition, and subsurface-damage assessment
Geometry	Center and mapped thickness, minimum and maximum, total thickness variation (TTV), sampling grid, edge exclusion, and bow/warp in a stated measurement state
Function	Thermal, optical, electrical, or quantum tests under application-relevant conditions

Friel and coauthors’ published study addresses both surface and bulk crystalline quality. A mirror finish cannot stand in for defect and subsurface-condition data.

What did the Orbray/Element Six announcement actually claim?

The company announcement, checked on 2026-10-06, makes four distinct claims:

• a reproducible process has been established for three-inch WSC diamond;
• four-inch substrates are under development;
• two-inch wafers for epitaxial applications are nearing finalisation;
• two-inch material for thermal bonding is being prepared for volume production at Element Six’s Gresham CVD facility.

These are meaningful manufacturing milestones. They are not interchangeable with published figures for passing area, defect density, yield, lot statistics, or actual shipment volume; the announcement does not provide those figures. “Under development” must not be rewritten as “in production.”

A supplier inquiry you can use

1. State the intended application: heat spreading, epitaxy, electronic device, or quantum device.
2. Ask for the growth route: homoepitaxy, heteroepitaxy, or mosaic growth.
3. Specify nominal dimensions, thickness tolerance, orientation, miscut, and their measurement methods.
4. Request the thickness map and its grid, minimum/maximum, TTV, bow/warp, and edge exclusion.
5. Request whole-wafer defect and stress/birefringence maps, detection methods, and passing-area thresholds.
6. Request surface and subsurface-damage reports. Distinguish one best specimen from a whole-wafer distribution and from multi-lot data.
7. Confirm that the surface and geometry are suitable for the next cutting, bonding, or epitaxy step.

For a thermal application, continue with interface thermal resistance. For material classification and structure, see diamond material grades and single-crystal versus polycrystalline CVD diamond.

Is the largest diameter the usable diameter? No. Usable area exists only after the acceptance limits and inspection coverage have been defined.

Does a shiny surface establish crystal quality? No. Surface appearance, polish damage, internal defects, and stress are different measurements.