FFKM vs FKM seals for semiconductor equipment
FKM (fluoroelastomer) and FFKM (perfluoroelastomer) O-rings often fit the same groove, but they behave very differently in a process chamber. FFKM is fully fluorinated and is used where heat, plasma radicals or aggressive chemistry shorten FKM life; it also costs much more, so the choice should follow the seal location and process.
This guide uses only values published by the FFKM manufacturers. Check the current compound data sheet for your process before ordering.
Where each material is usually used
| Location | Typical choice | Why |
|---|---|---|
| Chamber lid, gas inlet, window and slit-valve seals in plasma tools | FFKM plasma grade | Exposure to fluorine and oxygen plasma radicals and high temperature |
| Seals in the direct path of UV light (UV cure, strip) | FFKM UV grade, for example Kalrez 8705 | DuPont designs 8705 for high-energy UV and oxygen radicals |
| Heat-traced foreline and exhaust seals | FFKM, confirmed with the manufacturer | DuPont lists these as a location to assess with its engineers |
| General vacuum and gas-line fittings at moderate temperature, away from plasma | FKM | Lower cost where the compound limits are not reached |
Seal locations from the DuPont Kalrez plasma selector guide. A final choice depends on the exact chemistry, temperature and duty.
Published FFKM temperature ranges
| Manufacturer | Grade | Published temperature | Manufacturer description |
|---|---|---|---|
| DuPont | Kalrez 9100 | 300 °C maximum service | PECVD, ALD, HDPCVD, conductor etch |
| DuPont | Kalrez 9600 | 315 °C maximum service | High-purity, high-temperature PECVD/PEALD |
| Greene Tweed | Chemraz 657 | −18 °C to 280 °C, excursions to 300 °C | Dry wafer processing, plasma resistance |
| Greene Tweed | Chemraz XPE | 280 °C maximum service | O2 and CF4 plasma resistance |
| Precision Polymer Engineering | Perlast G67P | −15 °C to +275 °C | High purity |
| Precision Polymer Engineering | Perlast G7HA | −15 °C to +310 °C | High temperature, plasma resistant |
Each manufacturer uses its own test method; DuPont notes its values are typical and not for specification. Do not compare limits across brands as if they were measured the same way.
When FFKM is worth the cost
- The seal temperature is above the FKM compound limit.
- The seal sees plasma radicals, ozone, ammonia or water vapour that erode or swell FKM.
- Particles, outgassing or metal content from the seal matter to the process.
- A seal change means tool downtime that costs more than the seal.
Groove and fitting notes
- An FFKM ring in the same AS568 size usually fits an FKM groove, but Parker notes perfluoroelastomers may need groove adjustments; check squeeze and fill.
- Plasma grades differ in hardness (for example Kalrez 9100 at 70 Shore A and 9300 at 77 Shore A), which changes sealing force.
- Use the squeeze and fill calculator in the AS568 guide to check the groove.
What to send for an FFKM recommendation
- Tool and process step (for example PECVD, oxide etch, ash/strip).
- Seal location, static or dynamic, and temperature.
- Gases or chemicals, and plasma type.
- Current seal part number or compound and the failure you see (erosion, cracking, sticking, particles).
Frequently asked questions
Is FFKM always better than FKM?
No. FFKM resists higher temperatures and harsher chemistry, but it costs more and grades differ in hardness and purity. Where FKM stays within its compound limits and sees no plasma, FKM is usually the practical choice.
Which FFKM grade should I use in oxide etch?
The DuPont Kalrez plasma selector guide suggests Kalrez 9300 for dielectric (oxide) etch. Other manufacturers publish their own recommendations; validate any grade in your process.
Can I put an FFKM O-ring in an FKM groove?
Often yes for size, but Parker notes perfluoroelastomers may need groove adjustments. Check squeeze and gland fill before switching.
Does MST make FFKM seals?
No. MST is a distributor and technical sourcing partner. Seals are made by the manufacturers named on the quote.
Ask an engineer
Send the process step, seal location, temperature and chemistry. MST, as distributor and technical sourcing partner, replies with candidate compounds from the manufacturers, price and lead time. Kalrez is a trademark of DuPont, Chemraz of Greene Tweed and Perlast of Precision Polymer Engineering; all trademarks belong to their owners. MST is a distributor and technical sourcing partner, not the manufacturer, and does not claim to be an authorized distributor of these brands.
Ask an engineerRelated pages
Sources
- DuPont Kalrez semiconductor plasma product selector guide (KZE-A40111-00-A0422)
- Greene Tweed, Chemraz FFKM overview
- Precision Polymer Engineering, high temperature elastomers (Perlast grade table)
- Parker O-Ring Handbook ORD 5700
Values are taken from the manufacturer documents above, checked 2026-10-23. Specifications can change; confirm against the current datasheet before ordering. MST is a distributor; products are made by the manufacturers named.