What this application demands
Semiconductor process and metrology equipment imposes requirements that are closer to a cleanroom consumable than to an optical component. Particle cleanliness, outgassing, dimensional stability and flatness are often what the tool engineer worries about; the transmission curve may already be fixed by the process wavelength and simply has to be held repeatably from lot to lot.
UV transmission is the other defining requirement. As process wavelengths move deeper into the ultraviolet, the choice of substrate narrows sharply — ordinary borosilicate stops transmitting where the process needs to work, and only UV-grade fused silica or sapphire will do. Flatness matters in metrology because the reference surface defines the measurement, not just the image.
Specifications we recommend
| Component | Typical specification | Why |
|---|---|---|
| Viewport and process windows | UV-grade fused silica, low OH, tight thickness tolerance | Transmits the process wavelength without solarisation or absorption losses |
| Carrier and support wafers | Borosilicate or display glass, TTV below 3 µm | Flatness controls the uniformity of the process above it |
| Metrology reference plates | Polished fused silica, flatness to λ/10, verified interferometrically | The reference surface defines the accuracy of the instrument |
| Inspection optics | Broadband AR coatings on glass and quartz | High transmission for defect review without adding ghost images |
Failure modes we design against
Particle contamination arriving with the optic is the most common cause of a rejected part in this sector, which is why we clean and pack to a protocol rather than as a final step. Surface haze and water marks show up immediately in dark-field inspection and are prevented by controlled rinsing and drying rather than by additional polishing.
Mechanical stability is the second concern. Where a window is clamped into a tool and cycled thermally, small thickness or flatness variation translates directly into optical variation. Holding thickness tolerance tightly at the start is cheaper than compensating for it in the tool.
Frequently asked questions
Can you supply UV-grade material for deep-UV windows?
Yes — UV-grade fused silica with low OH content is the standard route, with sapphire where hardness or mid-IR transmission also matters.
Is wafer-level flatness achievable on coated parts?
Coating adds a small figure contribution. We measure wavefront or flatness after deposition, which is the number that governs performance in the tool.