The Role of PFAS in Semiconductor Manufacturing

Overview of PFAS

Per- and polyfluorinated alkyl substances—widely known as PFAS—are a family of around 15,000 synthetic chemicals that were developed in the 1940s and 1950s by manufacturing giants 3M and DuPont. In the decades following their introduction to the market, PFAS became popular in essential consumer goods ranging from apparel and upholstery to cookware and food packaging. This is due to their beneficial properties such as being waterproof, stain-repellant, grease-resistant, and more. 

PFAS Usage In Electronics

PFAS have also been widely adopted in electronics manufacturing, and can be found in such things as electronic cables, computer parts, electrical insulation, medical devices, seals and gaskets, tubing, and more. As a result, PFAS can be detected in a variety of electronics goods, including:  

• PCBAs
• PCB Laminates
• Computer Hard Drives
• Semiconductors
• PTFE Tapes

Recommended Reading: Where are PFAS in your electronics supply chain?

Why PFAS Are Suddenly Getting a Bad Rap

Research conducted over the last quarter-century, combined with nearly 80 years of experience with the compounds, has demonstrated that PFAS are dangerous. Many of these chemicals are bioaccumulative, toxic to humans and animals, and capable of persisting in the environment for decades or even centuries. As the evidence against PFAS has continued to mount, a growing public consensus has emerged: PFAS and their usage need to be substantially curtailed in order to protect the health of human beings and wildlife. 

PFAS: A Necessary Evil? 

But while the public’s awareness of the sectors incorporating the so-called “forever chemicals” into their products is growing rapidly, one field is often left out of discussions around PFAS and the imperative to discontinue their use: semiconductor manufacturing. 

PFAS have long played an essential role in chipmaking and the intricacies of the semiconductor manufacturing process. The chemicals are crucial to several specific aspects of fabrication, are a key component in packaging materials, and have a range of important applications in semiconductor manufacturing equipment and facility infrastructure. Without access to PFAS, semiconductor manufacturers would risk falling short of current production levels. Further, their ability to continue fabricating the highest-quality, most cutting-edge chips could be severely compromised. 

Put differently, PFAS have in some ways become a necessary evil in the vitally important semiconductor industry. In the years to come, governments, regulatory agencies, and the public at large are going to have to grapple with a deeply complicated question: How do you restrict the use of PFAS by a sector that needs the compounds to manufacture what is arguably the most critical technological hardware of our time? 

How do you restrict the use of PFAS by a sector that needs the compounds to manufacture what is arguably the most critical technological hardware of our time? 

PFAS in Semiconductor Manufacturing 

Semiconductor firms have taken a few meaningful steps in recent years to jettison some of the more notorious PFAS from their cleanrooms, fabs, and packaging facilities. They’ve successfully phased out the use of PFOA, and are continuing the process of removing other long-chain PFAS from chip manufacturing. The sector does still, however, rely heavily on short-chain PFAS. These are versions of the chemicals with shorter carbon backbones, typically consisting of seven carbons or fewer in each molecule.

The Industry Shift to Short-Chain PFAS

The semiconductor industry’s decision to transition to short-chain versions of PFAS was not made in a vacuum. Myriad industries are replacing “legacy PFAS”—as the long-chain compounds are now known—with their shorter-chain successors. This is largely based on the logic that shorter carbon backbones will lead to shorter half-lives and lower bioaccumulation, therefore reducing the presence of these chemicals in our environment and attenuating their toxic effects on human beings and wildlife. Up to this point, however, no substantive evidence has emerged unequivocally demonstrating that short-chain PFAS are any less harmful than their predecessors. 

At this time, short-chain PFAS remain utterly essential to the industry. SEMI, one of the leading industry associations for chipmakers and other companies in the microprocessor ecosystem, recently put out a statement on the role PFAS play in semiconductor manufacturing. The trade group explained that the controversial chemical family is used throughout “semiconductor production, semiconductor manufacturing equipment, the full semiconductor industry supply chain, and in technology in general.” The statement went on to flatly assert that semiconductor chips and similar devices “cannot be produced without PFAS being available at multiple points in the supply chain.”

The trade group explained that the controversial chemical family is used throughout “semiconductor production, semiconductor manufacturing equipment, the full semiconductor industry supply chain, and in technology in general.

PFAS in the Photolithography Process 

The photolithography process is a vital stage of semiconductor manufacturing. During this step, a photoresist is applied to a silicon wafer, and then complex geometric patterns on a mask are transferred onto the wafer using ultraviolet (UV) light (which interacts with the photoresist). PFAS are often used in the photoresist to help enhance the material’s adhesion, durability, and thermal stability. 

The chemical compounds are especially important to the formulation of photoresists for deep UV (DUV) lithography, a process critical to manufacturing the industry’s leading-edge nodes. As noted by the Semiconductor PFAS Consortium, a group of industry stakeholders focused on developing a comprehensive strategy for addressing PFAS use, fabs are utilizing PFAS in this capacity to harness “critical characteristics such as surface coat uniformity, complete resist removal with low defectivity, improved line edge roughness and reduced line collapse.”

PFAS are also used as surfactants in the rinsing solutions used to remove the photoresist from the wafer. In this capacity, the chemicals can help reduce surface tension and prevent pattern collapse. 

PFAS are also used as surfactants in the rinsing solutions used to remove the photoresist from the wafer. In this capacity, the chemicals can help reduce surface tension and prevent pattern collapse. 

PFAS in Packaging Materials

In addition to their role in chip fabrication, PFAS are also valuable substances in back-end manufacturing stages like packaging. The substances’ thermal and chemical stability, low surface energy, low moisture absorption, and low dielectric constant—which is preferable in order to minimize electrical power loss—are all useful properties for the materials involved in the complex, delicate packaging process. 

Packaging substrates need to fulfill a slew of crucial specifications to meet the necessary mechanical, thermal, and electrical functions of a semiconductor. These include many of the characteristics outlined above—such as thermal and chemical stability, low moisture absorption, and a low dielectric constant—as well as nonflammability. PFAS possess all of these properties, making them essential to the formulation of substrate materials. Fluorinated polymers (a type of PFAS) are also used in the manufacturing of the substrate core in order to give it a low coefficient of thermal expansion (CTE) and thus help the packaging maintain stability and form across a wide range of temperature exposures. 

PFAS have also proven to be highly effective chemicals for packaging adhesive formulations. During die attach, for example, a powerful adhesive is required to mount or attach the silicon chips to the package substrates and frames. Because many semiconductors are utilized in mechanical environments characterized by extreme heat, these adhesives need to possess a high heat transfer coefficient, low CTE, and resilience to the thermal fatigue that often sets in with cyclical fluctuations in temperature. Fluorinated polymers fulfill all of these requirements. According to the National Academy of Engineering, the polymers are “ideal for enabling a high heat-transfer co­efficient, low CTE, and resistance to thermal fatigue.”

PFAS have also proven to be highly effective chemicals for packaging adhesive formulations.

PFAS in Semiconductor Manufacturing Equipment, Lubrication, and Infrastructure 

PFAS are critical to the sophisticated, highly specialized manufacturing equipment that are used in chip fabrication. The compounds’ resistance to chemical reactions—a property known as chemical inertness—as well as several of the other characteristics outlined above make them valuable materials in the manufacturing of equipment components like pipes, containers, and gaskets. 

A range of PFAS are also incorporated into the lubricants that are applied to semiconductor fabrication and processing equipment. In order for manufacturers to meet the high yields required for economic viability, these lubricants need to be exceptionally effective, maintaining a high level of performance amid the extreme physical environments and array of aggressive chemicals that characterize fabrication facilities. 

The environment in the clean rooms where semiconductor manufacturing takes place is a chemical war zone. The space is replete with corrosive, caustic substances like sulfuric acid, hydrogen peroxide, and tetramethylammonium hydroxide, reactive gas radicals like ionized chlorine and fluorine gas, and a number of pyrophoric gases capable of spontaneously igniting under the right temperature conditions. Equipment lubricants need to be formulated to resist all the potential reactions to these chemicals, as well as possess the general resilience critical to consistently performing across a wide spectrum of chemistries and temperatures. PFAS like perfluoropolyether (PFPE), polychlorotrifluoroethylene (PCTFE), and polytetrafluoroethylene (PTFE) can give lubricants the thermal stability, chemical inertness, and resistance to degradation that are necessary to functioning seamlessly under such extreme conditions. 

PFAS like perfluoropolyether (PFPE), polychlorotrifluoroethylene (PCTFE), and polytetrafluoroethylene (PTFE) can give lubricants the thermal stability, chemical inertness, and resistance to degradation that are necessary to functioning seamlessly under such extreme conditions. 

Finally, this uncanny stability also makes PFAS an important substance in fabrication facility infrastructure. The chemicals are frequently used in water distribution systems and the highly specialized tanks, seals, and valves that assure high purity levels during the manufacturing process. 

The Evolving State of PFAS Regulations Worldwide

While PFAS continue to serve an irreplaceable function in semiconductor manufacturing—industry trade group SEMI posits that there are currently hundreds if not thousands of specific use-cases—the breadth of PFAS regulations restricting use of the compounds is growing swiftly. In the European Union, the Stockholm Convention on Persistent Organic Pollutants (POPs) imposes restrictions on several PFAS, including perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). The EU’s Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH) regulation, meanwhile, includes a number of PFAS on its Substances of Very High Concern (SVHC) Candidate List. 

The U.S. hasn’t been as aggressive as its European counterparts in implementing significant PFAS regulations. (Though the EPA has started adopting a more proactive, assertive strategy to limit use of the substances and hold corporations accountable for PFAS contamination.) But because of this highly deliberative—some might say slow-footed—approach to reigning in these toxic chemicals at the federal level, U.S. states have been taking PFAS regulation into their own hands. 

California, Maine, Minnesota, and Washington have all passed legislation banning the chemicals in specific consumer products, and a growing raft of states have established drinking water standards that include maximum contaminant levels (MCLs) for key PFAS. In all, 34 U.S. states have introduced some form of legislation aimed at restricting the chemicals, enforcing transparency of their use, or allocating funds for research, testing, and remediation efforts. 

The Semiconductor Industry’s Response to Expanding PFAS Regulations

The full sweep of this swelling landscape of PFAS regulations is not lost on the semiconductor industry. If the public-facing statements, research papers, and other materials published by trade groups like SEMI and the Semiconductor Industry Association (SIA) over the past few years are any indication, chip firms are determined to communicate the criticality of PFAS to what is arguably the fulcrum of modern technology. “In the semiconductor industry, policymakers should proceed carefully in placing restrictions on the uses of fluorinated chemicals,” SIA Vice President of Government Affairs David Isaacs wrote in a 2023 post arguing for essential use of PFAS within the industry. “Given the critical role of semiconductors in our economy and national security, it is important to avoid policies that unduly restrict current semiconductor operations or future innovation.”

If the public-facing statements, research papers, and other materials published by trade groups like SEMI and the Semiconductor Industry Association (SIA) over the past few years are any indication, chip firms are determined to communicate the criticality of PFAS to what is arguably the fulcrum of modern technology.

In response to a proposal made by the EPA in 2023 to revoke low volume exemptions (LVEs) for PFAS, SEMI assumed an even more forceful, dire tone. The organization submitted a comment to the agency arguing that such a restrictive stance could trigger a devastating fallout within domestic semiconductor manufacturing. “The semiconductor industry uses PFAS in critical applications with a lack of viable alternatives,” the group asserted, and revoking LVEs could ultimately “result in the shutdown of all domestic semiconductor operations.”

And that’s just a modest sample of the vigorous industry pushback against the expanding regulatory actions and negative public sentiment concretizing around PFAS. The practical urgency behind statements like these could hardly be clearer: these chemicals have become all but inextricable from the burgeoning chip industry. Manufacturing firms and the associations that represent them are unifying around a complicated but consequential message: while PFAS may pose certain dangers to human health and the environment, the compounds are not simply a categorically evil family of man-made chemicals that need to be expunged en masse. Contemporary society’s relationship to PFAS are more layered and enmeshed than that, and the heart of that complexity can arguably be found within semiconductor manufacturing. 

It also bears underscoring that the role PFAS play in the semiconductor industry is meaningfully different from other sectors. Other industries under scrutiny for their use of the compounds may sacrifice some of the durability and utility of their foundational products by stripping out the chemicals from their formulations, but most of their goods are only enhanced by PFAS. In chip manufacturing, conversely, short-chain PFAS are an essential, constitutive part of the process. And in the words of SEMI, potential restrictions like the revocation of LVEs would be “catastrophic” to the chipmaking ecosystem in America. 

In chip manufacturing, conversely, short-chain PFAS are an essential, constitutive part of the process.