Semiconductor
by Daniel Mays Daniel Mays No Comments

Meeting SEMI Standards for Seal Purity, Outgassing, and Chemical Resistance

Semiconductor fabrication facilities are among the most demanding environments for seal materials on the planet because a single contamination event can scrap a wafer batch worth hundreds of thousands of dollars. And every polymer, lubricant, and elastomeric material contains residual volatiles. SEMI standards deal with how to take these residual volatiles into account when designing components, such as seals, for wafer fabrication environments. The purpose of this blog post is to discuss what SEMI standards actually require and how engineers select bearings to meet them.

The SEMI Standards Landscape

SEMI standards serve as the common language of the global semiconductor supply chain. For example, SEMI standards define fitness for use by establishing minimum thresholds (e.g., outgassing limits, contamination levels, chemical compatibility requirements) that a component must meet to be considered safe for use in semiconductor manufacturing environments. These standards also protect the wafer from contamination that can destroy device yield and make suppliers accountable. 

By referencing a SEMI standard in a procurement specification, a fabrication engineer can require documented, third-party-verifiable compliance rather than relying on a supplier’s marketing claims. These standards also enable global interoperability: tools, chemicals, and components built to SEMI standards can move across fabrications and geographies without extensive re-qualification. This serves as a major economic benefit in a highly globalized industry.

SEMI F-Series (Facilities and Materials)

The SEMI F-series serves as the most relevant category for seals. Standards like SEMI F57 govern polymeric components and wetted surface materials used in UHP (ultra-high purity) gas distribution systems, covering surface finish requirements, material qualification, and cleanliness protocols. SEMI F2 addresses test methods for metallic contamination on wetted surfaces. These are the specs a seal or bearing supplier is most likely to be asked to demonstrate compliance with.

SEMI C-Series (Chemicals)

The SEMI C-Series of standards defines purity grades and acceptable contamination levels for process chemicals such as acids, solvents, and oxidizers. While these standards primarily govern the chemicals themselves, they are also critically important for material selection. If your seal is sitting in a bath governed by a C-series chemical specification, that specification indirectly defines the chemical resistance your seal must demonstrate. Engineers selecting materials for wetted components need to understand what chemical grade they are designing for.

SEMI S2 (Safety Guidelines for Semiconductor Manufacturing Equipment)

S2 is a broad equipment safety standard with direct implications for materials selection. It addresses chemical containment, materials of construction for chemical-wetted components, ventilation requirements, and labeling. It’s often the standard a tool OEM must satisfy as a condition of fab entry, making it a gateway document that touches bearing and seal design.

Purity: Metallic Contamination and Ionic Cleanliness

When it comes to cleanliness in fabrication environments, the core concern when it comes to contamination is the presence of trace metals (Fe, Na, K, Ca) as killer defects in semiconductor devices. Both dynamic seals are going to shed particles, and this includes wear debris, surface oxides, and manufacturing residues. Among the key material considerations are the use of PTFE bearings and seals, while other options include ceramic bearings (Si₃N₄, ZrO₂) as the go-to for ultra-pure applications and surface treatments (e.g., electropolishing, passivation, and their limits).

Outgassing: The Invisible Contamination Problem

Through outgassing, volatile organic compounds (VOCs) deposit on wafer surfaces and disrupt lithography, deposition, and etch processes. Two standards commonly apply: SEMI F10 and NASA ASTM E595, serving as the benchmarks engineers reference. And there are two key metrics that matter: ML (Total Mass Loss) and CVCM (Collected Volatile Condensable Materials). The general targets used by engineers are TML < 1.0% and CVCM < 0.1%. And remember that a material can pass TML and fail CVCM. Bearings and seals must comply with both. However, CVCM is the one that matters most because it captures what actually re-deposits on a cooler surface.

In seal assemblies, the vast majority of problems come from lubricants and greases (silicone-based greases are particularly problematic in vacuum) and adhesives, polymer cage materials, and elastomeric seals. This includes nylon and acetal bearing cages and standard elastomeric seals with curative that can volatize under heat and vacuum. To avoid these issues, industry best practice is to use …

  • PFPE-based dry film lubricants
  • PTFE lip seals (which are known for their high purity and self-lubrication)
  • Perfluoroelastomers (FFKM)

Bake-Out Procedures

As already discussed, every polymer, lubricant, and elastomeric material contains residual volatiles that may include trapped solvents from manufacturing, absorbed moisture, unreacted monomers, and plasticizer fractions. At room temperature, these substances release slowly over weeks or months. Elevated temperature, however, drives that same process in hours, forcing the material to shed its residual volatiles before it is ever installed. This process is known as bake-out and must be accomplished for a material to be safe to use in a high-purity environment.

Chemical Resistance: Surviving the Process Chemistry

The process chemistry involved with semiconductor manufacturers includes chemicals such as HF, H₂SO₄, HCl, H₂O₂, IPA, NMP, ozone, and aggressive plasma environments. And although a material may be listed as chemically resistant on a data sheet, that does not account for critical variables such as concentration, temperature, and exposure time. Swell, extraction, and stress cracking are the failure modes that tables consistently miss.

The material compatibility hierarchy for seals is:

  • FFKM (Kalrez®, Perlast®): broadest chemical resistance, low extractables
  • PTFE: excellent passive resistance but poor dynamic sealing performance
  • EPDM / FKM (Viton®): acceptable in some applications, disqualified in others (HF is a hard no for FKM)

Conclusion

SEMI compliance is not just a checklist, but rather a systems-level engineering discipline. Material selection, outgassing qualification, and chemical resistance validation must work together to result in a fully SEMI-compliant seal. Engineers who treat these as a system rather than separate line items build better products. If you are looking for a SEMI-compliant sealing solution, contact the engineers at Advanced EMC today.

by Daniel Mays Daniel Mays No Comments

Hydrogen Embrittlement and Seal Permeation

What Every Engineer Needs to Know

The hydrogen economy is scaling fast, with global demand for hydrogen expected to double between 2021 and 2030 (Statista). And the growing demand for fuel cells, electrolyzers, pipelines, and green energy storage is all driving demand for hydrogen-compatible hardware.

Here is the problem engineers are facing: hydrogen is uniquely aggressive. It is the smallest molecule in existence, and it attacks both metallic components and elastomeric seals through. That is why it is dangerous for engineers to treat hydrogen as a typical gas and attempt to reuse designs from natural gas or nitrogen service.  Doing so is just setting up a system for premature and potentially catastrophic failure.

Given the importance of the topic, the blog post focuses on hydrogen embrittlement and seal permeation, including the causes and industry best practices for addressing their effects in a hydrogen sealing solution.

Hydrogen Embrittlement in Metal Seals

At metal surfaces, H₂ dissociates into atomic hydrogen at metal surfaces. This atomic hydrogen then diffuses into the metal’s crystal lattice, where it accumulates at grain boundaries, dislocations, and stress concentrations.

While the metal’s yield strength remains unchanged, its ductility and fracture toughness decrease. The metal part can then fail without warning at stresses far below what a standard tensile test would suggest is safe. This phenomenon is particularly dangerous. 

The metals most susceptible to hydrogen embrittlement are high-strength steels above ~1,000 MPa; BCC crystal structures (ferritic and martensitic steels); and hardened fasteners like Grade 12.9, which are notorious. On the other hand, the more resistant metals include austenitic stainless steels (304L, 316L) and nickel-based alloys, as their FCC crystal structure resists hydrogen diffusion more effectively.

One of the best practices for addressing hydrogen embrittlement in metal seals is to use materials with reduced strength levels where conditions allow. For example, steel with an ultimate tensile strength of 800 MPa often outperforms 1,400 MPa steel when it is used in H₂ service. And for wetted components, engineers often opt for austenitic stainless steel. 

Another approach is to control hydrogen-generating manufacturing processes (acid pickling, electroplating) per ASTM A143. Parts can also be baked at about ~190°C within hours of processing to drive out the absorbed hydrogen.

Finally, minimizing stress concentrations on metal seals is another effective approach. The impact of these stress concentrations is significantly greater in hydrogen service.

Seal Permeation and Rapid Gas Decompression with Elastomeric Seals

Elastomeric seals can also be sensitive to hydrogen, but through a different mechanism. Because of their small atoms, hydrogen dissolves into and diffuses through elastomeric seal materials at rates far exceeding other common gases. The permeation is made worse in the presence of elevated pressure and temperature, where a seal can become fully saturated with hydrogen.

When system pressure drops during shutdown or a relief event, dissolved hydrogen tries to exit the elastomer faster than it can diffuse out of the surface, a process known as  RGD (Rapid Gas Decompression). The result is the elastomeric seals experiencing internal nucleation, blistering, and explosive tearing from the inside out. In short, a seal that survives thousands of cycles can be destroyed by a single fast depressurization event.

The most direct way to mitigate the effects of elastomeric seal permeation is to use a material that effectively resists it. Several options are summarized below.

  • FFKM (Kalrez, Perlast) — Excellent: Best all-around performance in H₂ service; highest cost
  • PTFE (spring-energized seals) — Good: Very low permeation rate; requires a different design approach than standard elastomeric seals
  • EPDM — Good: Surprisingly strong RGD resistance; widely used in fuel cell systems
  • FKM (Viton) — Moderate: Adequate at lower pressures but evaluate carefully for high-pressure cycling applications
  • NBR / Silicone — Avoid: High hydrogen permeability; not suitable for H₂ service

Other best practices include controlling the decompression rate by utilizing engineered bleed-down or staged depressurization. In addition, face seals instead of radial seals tend to work better in high-pressure applications. Backup rings are another tool to use, limiting extrusion and preferving the seal geometry. Finally, design the seals in compliance with NORSOK M-710 or ISO 23936-2. Keep in mind that data sheets alone are not sufficient for high-pressure hydrogen duty

Conclusion

Neither hydrogen embrittlement nor seal permeation is a mystery as both are well-characterized and manageable. The engineers who will struggle are those who reach for familiar materials and assume the physics is the same. Here at Advanced EMC, we encourage engineers to know the mechanisms behind these failure modes related to hydrogen service, then select deliberately and test accordingly. And Advanced EMC is here to help you every step of the way. Contact one of our seal solution experts today to explore what your options are and put industry best practices to use.