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PFOS
PFOS (Perfluorooctane/ octyl Sulfonates) is a substance used in very small quantities in the manufacture of semiconductor devices.
The manufacture of advanced semiconductor devices is not currently possible without the use of PFOS in ‘critical applications’ such as photoresists and antireflective coatings. PFOS is a process chemical; it does not remain in the final product – the semiconductor device. The industry carefully manages and uses PFOS in tightly contained systems in the semiconductor manufacturing process, to yield de minimis emissions. Since the first environmental concerns with the PFOS substance were noted in 1990s, the European semiconductor industry, proactively together with our chemical suppliers, has been working at reducing PFOS use in applications and trying to find alternatives wherever technologically possible.
Unfortunately for society and the environment it is likely that most of the actual PFOS emissions and distribution in the global environment are caused by the presence of large quantities of PFOS in historical applications over many years, many with very high environmental and end user exposure potential such as carpets, fabrics and textiles, paper treatment and fire fighting foams. The EU’s Scientific Committee on Health and Environmental Risks (“SCHER”) issued a report which reviewed the UK/RPA risk reduction strategy for PFOS in March 2005 which concluded that: “the contribution of the confirmed on-going industrial/professional uses to the overall risks for the environment and for the general public are probably negligible with regard to the sectors photographic industry, semiconductor industry and aviation industry.” This report also notes that “Emissions from ongoing uses in the photographic, semiconductor and aviation industry amount to 64 kg, i.e. less than 0.3% of the emissions caused by the former uses.”
In 2006, the European Union adopted a Marketing and Use Directive (2006/122/EC) that bans the use of PFOS. The directive exempts photoresists and ARCs used in photolithography from these restrictions imposed. Currently other regions and international bodies are reviewing and considering regulatory measures on PFOS.
questions
Why is PFOS required for critical applications in semiconductor manufacturing?
How is the industry taking a proactive approach to its PFOS usage?
What does "substitution" mean?
Why is PFOS required for critical applications in semiconductor manufacturing?
Photolithography is one of the most important processes in semiconductor manufacturing, as it plays the critical process in defining the level of sophistication and performance of devices.The most critical need in photolithography is to be able to develop increasingly smaller features on the surface of a silicon wafer.
Small circuit feature development currently requires the use of chemicals which contain certain fully fluorinated materials in these photo-acid generators (PAGs) and anti-reflective coatings (ARCs). As circuit development gets ever smaller the properties of small amounts of specialty materials becomes more important. The most common fluorinated material which has demonstrated the properties required has been perfluorooctane sulfonate (PFOS). PFOS play a critical role in photoresists and antireflective coatings (ARCs) used in semiconductor manufacturing. Photoacid generators (PAGs) increase the sensitivity of the photoresist to allow etching images smaller than wavelength of light. Anti-reflective coatings (ARCs) prevent blurred images caused by surface reflections.
How is the industry taking a proactive approach to its PFOS usage?
The global semiconductor industry through the world semiconductor council (WSC) in May 2006 agreed to curtail the use of PFOS-based chemicals where they are not critical to the manufacturing process. This industry-wide agreement reflects the semiconductor industry’s continued proactive approach to our use of PFOS and the concerns about environmental and human health impacts related to PFOS. Under the agreement, members of the World Semiconductor Council, which comprises the trade associations representing the semiconductor industries of the world’s leading semiconductor-producing countries and SEMI (material suppliers) have committed to the phase out non-critical uses for PFOS by specific dates. In addition the industry will work to identify substitutes for PFOS in critical uses for which no other materials are presently available and to destroy solvent wastes from critical uses.
What does "substitution" mean?
Despite significant R&D in recent years, currently there are no replacement substances for these specific uses of PFOS, which provide the critical functionality and equal performance required at these technology nodes (levels). An invention is first required before a substitution of PFOS can occur. Any potential substitution of PFOS free alternatives in critical usage is a multi-stage and complex process. ‘Substitution’ requires first an invention for PFOS free alternatives from the suppliers, a significant lead-time for stringent material qualification, and then subsequent integration and verification of technical performance in company technologies. Only after these aspects have been proven successful can the actual act of final replacement, be attempted in volume manufacturing. There are no ‘drop in’ replacements for these applications and the process of technology implementation, test and approvals and final replacement is not a simple process is different across technologies and will take time. The semiconductor industry needs to continue using PFOS until adequate substitutes have been discovered and proved to work in full scale manufacturing. It is for these reasons that a proposed timetable for ending PFOS usage in critical use is not appropriate for the industry.