Semiconductor circuit board
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Seals for Semiconductor Manufacturing 

Seals for semiconductor manufacturing involve critical choices related to the material used. And this is not surprising, given the high stakes of semiconductor fabrication, where a single contamination event or seal failure can compromise an entire wafer batch, costing hundreds of thousands of dollars in yield loss.

While seals are small and often overlooked in semiconductor manufacturing, they are exposed to some of the most aggressive conditions imaginable in any industrial environment. However, selecting the right material means not only a reliable seal but also improved equipment uptime, yield, and process integrity.

The Hostile Environment of Semiconductor Manufacturing

There are several factors that contribute to the extremely hostile environment that semiconductor manufacturing seals must be able to withstand. Seals in semiconductor equipment are regularly exposed to acids, bases, solvents, amine-based strippers, and chlorinated gases, depending on the process step. 

There is also exposure to plasma: fluorine and oxygen plasmas, commonly used in dry etch and resist stripping, are among the most chemically reactive environments currently known. In addition, plasma exposure will rapidly degrade traditional elastomers that lack full fluorination.

Another challenge lies in extreme temperatures and vacuum pressures. Processes such as CVD (Chemical Vapor Deposition) and LPCVD nitride deposition both demand good thermal stability under sustained high temperatures. Also, many chambers operate under vacuum conditions where outgassing becomes a critical failure mode for the seal material used.

There are also UHP (Ultra-high purity) requirements. In short, any ionic contamination, particulate generation, or elevated TOC (Total Organic Carbon) introduced by a seal can corrupt the process chemistry or inadvertently dope the wafer. This has serious repercussions for semiconductor manufacturing processes and quality.

Seals for Semiconductors: Application-Specific Demands

No single material or seal geometry will work for every process step, so requirements vary significantly by application. 

CVD and LPCVD demand thermal stability and vacuum-compatible materials with minimal outgassing. On the other hand, dry and wet etch processes will require a material that is plasma-resistant and compatible with fluorine-based gases and corrosive media. 

CMP is especially interesting as it presents a dual challenge: exposure to an abrasive slurry and high-pH chemistry. This necessitates seals with strong abrasion and chemical resistance. Also consider track and lithography equipment that prioritizes solvent resistance, as photoresist developers and solvents readily degrade standard elastomers. Finally, resist stripping adds yet another layer of complexity, requiring seals that can withstand aggressive strip chemistries and sustained ozone exposure.

ProcessPrimary Sealing ChallengeKey Material Requirements
CVD / LPCVDHigh-temperature vacuum operationThermal stability, vacuum compatibility, minimal outgassing
Dry & Wet EtchHighly aggressive etch chemistriesPlasma resistance, compatibility with fluorine-based gases, and acid/base media
CMPAbrasive, alkaline slurry exposureAbrasion resistance, high-pH chemical resistance
Track & LithographyPhotoresist solvent and developer exposureBroad solvent resistance, dimensional stability
Resist StrippingOzone and aggressive strip chemistry exposureExceptional chemical resistance, ozone resistance

Material Solutions: Engineering Polymers With Superior Performance

The primary candidate materials for semiconductor manufacturing sealing solutions are polymers selected for their ability to meet the overlapping requirements just described. The engineering polymers discussed are well-adapted to the challenges related to semiconductor manufacturing environments. 

FFKM (Perfluoroelastomer)

FFKM is considered the top choice for O-rings in semiconductor manufacturing. It is able to deliver the sealing force and resilience of rubber, but with the chemical compatibility of PTFE. It offers a wide operating temperature, approximately -15°F to 620°F. In addition, there are various grades available for  UHP applications that have been optimized for minimal extractable ion content, low metallic contamination, and enhanced O₂/F₂ plasma resistance. FFKM is suitable for static and limited dynamic applications across CVD, CMP, etch, lithography, and stripping processes.

PTFE (Polytetrafluoroethylene)

PTFE is known for its extremely low coefficient of friction, self-lubrication, exceptional chemical compatibility, and high purity. It also performs extremely well in high-temperature, corrosive environments that degrade other material options. Note that PTFE is often the material of choice for highly effective spring-energized seals and reliable encapsulated O-ring jackets.

PEEK (Polyether Ether Ketone)

Like PTFE, PEEK offers good wear resistance and moderate friction properties. It also offers low outgassing, good plasma resistance, and excellent dimensional stability at elevated service temperatures (which can prove crucial). Because of these properties, PEEK is a strong candidate for labyrinth seals and spring-energized seal lips in dynamic semiconductor applications.

Supporting Materials: PI, PCTFE, and PAI (Torlon)

There are some additional supporting materials, namely:

  • Polyimide (PI): known for its low outgassing, excellent cryogenic performance, and high purity
  • PCTFE: offers improved strength and hardness over PTFE while retaining excellent chemical inertness
  • PAI (Torlon): ideal where high pressure, cryogenic temperatures, and corrosive media are all part of the operating environment; known for excellent wear resistance and self-lubrication

Choosing the Right Material

ProcessRecommended MaterialsRationale
CVD / LPCVDFFKM, PEEK, PI (Polyimide)High thermal stability, low outgassing, vacuum-compatible; FFKM grades available for water vapor and ammonia processes
Dry & Wet EtchFFKM, PTFE, PCTFESuperior plasma resistance and broad chemical inertness, including fluorine-based gas compatibility; minimal particle generation
CMP (Chemical Mechanical Polishing)FFKM, PAI (Torlon), PEEKAbrasion-resistant with strong resistance to high-pH slurry chemistry; PAI offers excellent wear resistance and self-lubrication
Track & LithographyFFKM, PTFE, PCTFEBroad solvent resistance; chemically inert to photoresist solvents and developers that attack standard elastomers
Resist StrippingFFKM, PTFEOutstanding ozone resistance and broad chemical compatibility; FFKM specifically rated for ozone and aggressive strip process chemistry

Material selection for semiconductor sealing applications must be matched carefully to the demands of each individual process. For CVD and LPCVD, FFKM, PEEK, and polyimide (PI) are the leading candidates, as all three offer the thermal stability and low outgassing required for sustained high-temperature vacuum operation. Specialized FFKM grades are also available that are formulated specifically for processes involving water vapor and ammonia.

In dry and wet etch environments, FFKM, PTFE, and PCTFE are the materials of choice, owing to their broad chemical inertness and resistance to fluorine-based plasmas and corrosive etch chemistries. Minimal particle generation is a critical secondary requirement in these applications, and all three materials perform well in this regard. For CMP, the combination of abrasive slurry and high-pH chemistry narrows the field to FFKM, PAI (Torlon), and PEEK, with PAI offering a particular advantage due to its exceptional wear resistance and self-lubricating properties.

Track and lithography equipment demands seals that can withstand the photoresist solvents and developers that rapidly degrade conventional elastomers, making FFKM, PTFE, and PCTFE the preferred options given their broad solvent resistance and dimensional stability. Resist stripping represents perhaps the most chemically aggressive environment of all, with ozone exposure compounding an already demanding chemical profile. Here, FFKM and PTFE are the primary recommendations, with select FFKM grades formulated specifically for ozone-intensive strip process chemistry.

Conclusion

In semiconductor manufacturing applications, the seal material selection has an incredible impact on process reliability, contamination control, and total cost of ownership. And there is no universal, one-size-fits-all solution to choosing a seal material. Engineers must look for the optimal combination of material properties to be matched to each process step’s specific chemical, thermal, and purity demands and there are engineering polymers available that are ideal for different applications.

 Advanced EMC is your partner when it comes to semiconductor sealing solutions. With over 100 years of combined experience, Advanced EMC has access to UHP-grade FFKM along with a full range of engineered polymer seal type. The Advanced EMC Sealing Solutions Team is ready to identify and supply the right sealing solution for any semiconductor application, whether standard or custom-designed. Contact Advanced EMC today for a consultation or to request a quote.

O-Rings in Spaceflight | Advanced EMC Technologies
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Designing Seals for Space Environments

Seals for space environments face a myriad of challenges. Space is one of the most unforgiving operating environments ever encountered by engineers. Seals that would be considered routine in terrestrial applications become mission-critical in space, where a single leak can mean the loss of a spacecraft, a payload, or a crew. This blog post examines the major sealing challenges presented by the space environment, along with the solutions best equipped to address them (including PTFE and PEEK seals).

Seals for Space Environments: Design Challenges

From extreme cryogenic temperatures to atomic oxygen, there are a host of factors to consider when engineering a sealing solution for space environments.

Extreme Temperature Ranges

Seals for space environments experience enormous thermal swings ranging from cryogenic temperatures in shadowed regions or propellant lines (as low as -450°F) to the intense heat experienced during atmospheric re-entry or sun-facing surfaces (+750°F). This poses a serious problem as most elastomers become brittle and crack at cryogenic temperatures, while at high temperatures they can experience hardening, outgassing, and loss of elasticity. These extremes add an extra layer of difficulty when designing effective, reliable seals or space environments. 

Spring-energized PTFE seals are an excellent solution here. The spring core maintains a highly consistent sealing force across the full thermal range, regardless of jacket expansion or contraction. For the most extreme high-temperature applications, a spring-energized Kalrez FFKM jacket will good superior heat resistance while still retaining the same self-energizing benefits for high-temperature sealing, but is not suitable for re-entry surfaces.

Vacuum and Outgassing

In hard vacuum conditions, most traditional seal materials are going to release trapped gases and plasticizers (outgassing). This leads to the potential for contaminated optics, sensors, and electronics, which can lead to catastrophic failure in many space applications. The seak materials used must possess a very low vapor pressure and minimal volatile content. To complicate things further, standard lubricants used to aid seal installation or reduce friction often evaporate entirely in a vacuum.

Both virgin PTFE and space-grade FFKM compounds are certified to NASA’s ASTM E595 outgassing standard. These materials are the preferred choices for vacuum applications as they offer exceptionally low vapor pressure and minimal volatile content. Spring-energized designs using these jackets also eliminate the need for installation lubricants, thus entirely removing another potential source of outgassing.

Radiation Exposure

In space, equipment is exposed to cosmic rays, solar particle events, and trapped radiation belt particles. These factors can quicly degrade the polymer chains in elastomers and plastics, causing major problems that include embrittlement, increased porosity, and loss of sealing performance over time. This potential for failure is especially severe in high-radiation orbits (e.g., near the Van Allen belts or at Jupiter).

PTFE offers improved radiation resistance compared to most elastomers, though prolonged exposure to high doses can still lead to material degradation. And PEEK can provide good performance for missions involving prolonged exposure to high doses of radiation.

Long Mission Life with No Maintenance

Unlike terrestrial seals that can be replaced, those used in space must often function for 10–30 years without any servicing. The lack of maintenance leads to a demand for near-zero wear and highly predictable aging behavior, both of which can be very difficult to validate on the ground. 

Spring-energized PTFE or PEEK seals have been found ideal for long-life missions, as the spring continuously compensates for material creep that would cause conventional elastomeric seals to lose contact stress over time. In addition, PTFE and PEEK seals also have extremely low friction, self-lubrication, and little to no stick-slip behavior. 

Mechanical Loads and Vibration

Launch seals will be exposed to incredibly intense acoustic and mechanical vibration, along with powerful shock loads and extreme acceleration. Seals for space environments must survive such a violent dynamic environment before even reaching the operating environment that was the primary target for the seals’ operating environment.

Spring-energized seals with glass-filled PTFE or PEEK jackets resist rolling, extrusion, and dislodgement under shock and vibration loading, and do so far better than convential O-ring designs.

Atomic Oxygen at LEO (Low Earth Orbit)

In LEO, the residual atomic oxygen in the upper atmosphere is highly reactive. It posseses the potential to aggressively erode many polymers (e.g., silicones, polyurethanes, etc.) resulting in the problematic thinning of seal cross-sections and the fast degradation of polymer surface properties.

PEEK offers significantly better resistance to atomic oxygen than many common polymers, though protective coatings may still be required for long-duration LEO exposure. PEEK’s dense aromatic backbone is significantly more resistant to atomic oxygen erosion than materials such as silicone, polyurethane, or virgin PTFE.

Micrometeorite and Debris Impact

Consider naturally occurring meteoroid particles that travel at extremely high speeds, and human-made orbital debris (often fragments from rocket bodies, collision ejecta, defunct satellites, and even paint flakes). Small particle impacts due to these types of debris can score or nick sealing surfaces, creating leak paths that are impossible to detect or repair once on orbit, and there are plenty of them in space. 

In the case of micrometeorite and debris impact, material selection helps, but system-level redundancy and shielding are critical. Carbon-filled PTFE or PEEK sealing solutions offer good surface hardness against glancing impacts and are best paired with a redundant dual spring-energized seal configuration with a monitored inter-seal cavity. 

Lubrication and Friction in Vacuum

Many seals rely on a thin fluid film to achieve low friction and reduced wear. However, in vacuum environments, conventional lubricants evaporate, which then leads to serious problems with stick-slip behavior and accelerated wear on dynamic seals (e.g., rotating joints on robotic arms or docking mechanisms).

PTFE’s inherently low coefficient of friction eliminates the need for additional lubrication in vacuum conditions.  In addition, carbon-filled or MoS₂-filled PTFE variants offer even lower friction for dynamic sealing applications. PEEK, including filled PEEK, also offers a very low coefficient of friction and self-lubrication, although not quite on the order of PTFE.

Material Selection Constraints

The combination of the above factors inevitably narrows the list of acceptable materials drastically. Traditional sealing material choices such as nitrile rubber are often ruled out, pushing engineers toward high-performance engineering polymers such as PTFE or Viton, as well as spring-energized polymer seals.

Spring-energized seals with PTFE or PEEK jackets (with filled grades selected to target specific performance gaps) represent the most versatile and broadly applicable solution across all space sealing challenges.

Summary of Seals for Space Design Challenges

Below is a summary of some of the key issues related to seals in space, along with some suggested solutions.

ChallengeKey issueSuggested solution(s)
Extreme temperaturesElastomers crack at cryogenic temps or degrade at high heatSpring-energized PTFE seals; Kalrez FFKM jacket for high-heat applications
Vacuum & outgassingMaterials release gases that contaminate optics and sensorsVirgin PTFE or space-grade FFKM (NASA ASTM E595 certified)
Radiation exposurePolymer chain degradation, embrittlement, increased porosityPTFE (moderate doses); PEEK (high-dose / long-duration missions)
Long mission lifeNo maintenance possible; seals must last 10–30 yearsSpring-energized PTFE or PEEK, pring continuously compensates for material creep
Vibration & shockIntense launch loads can dislodge or extrude sealsGlass-filled PTFE or PEEK spring-energized seals
Atomic oxygen (LEO)Reactive oxygen aggressively erodes many polymersPEEK, dense aromatic backbone resists erosion; protective coatings for long durations
Micrometeorite impactDebris scoring creates irreparable leak paths on orbitCarbon-filled PTFE or PEEK + redundant dual spring-energized seal with monitored inter-seal cavity
Vacuum lubricationConventional lubricants evaporate in vacuum, causing wearPTFE (self-lubricating); carbon- or MoS₂-filled PTFE variants for dynamic seals

Conclusion

Each challenge outlined in this blog post is demanding on its own. When combined, they eliminate most conventional sealing solutions entirely. What consistently emerges from these challenges is a short list of solutions built around spring-energized seal architectures and/or high-performance PTFE and PEEK. Together, they offer the broadest combination of thermal stability, radiation tolerance, and mechanical robustness available today.

If you are tasked with designing seals for space environments, contact Advanced EMC today.