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PFOS

A successful voluntary approach

PFOS (perfluorooctane sulfonates) is a substance that was used in very small quantities in the manufacture of semiconductor devices. The industry had carefully managed and used PFOS in tightly contained systems in the semiconductor manufacturing process, to yield de minimis emissions. Since the first environmental concerns with the PFOS substance noted in the 1990s, the European semiconductor industry, proactively and together with its chemical suppliers, had been working at reducing PFOS use in applications and trying to find alternatives wherever technologically possible.

In May 2017, the World Semiconductor Council (WSC), an international forum that brings together industry leaders from China, Chinese Taipei, Europe, Japan, Korea, and the United States to address issues of global concern to the semiconductor industry announced that participating companies have successfully eliminated the remaining critical uses of PFOS in semiconductor manufacturing processes.

Global semiconductor PFOS elimination

WSC Milestones in global semiconductor PFOS elimination

Path to elimination

Following a voluntary agreement reached through the WSC in 2006, the use of PFOS-containing materials ended were phased out for non-critical uses. This industry-wide agreement reflects the semiconductor industry’s continued proactive approach to its use of PFOS as well as its concerns about the environmental and human health impact related to the use of such chemicals. In addition, the industry has worked on identifying substitutes for PFOS in critical uses for which no other materials were available and to eliminate solvent wastes from critical uses.

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 firefighting 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. An amendment to the UN's Stockholm Convention on Persistent Organic Pollutants (POPS) also exempted these semiconductor uses.

In 2011, ESIA and the WSC announced that the industry had successfully eliminated all non-essential uses of PFOS and identified substitutes for most other uses, although continued use of very small quantities of PFOS remains critical in a few remaining processes. The remaining uses of PFOS are limited and highly controlled, and emissions of PFOS by the global semiconductor industry have been reduced to approximately 6kg/year. This global agreement is a good example of how industry wide sustainability is valued not just in Europe. For a report on the progress which the global semiconductor industry has achieved with PFOS consult the 2011 WSC Joint Statement and annexes.

The elimination of the remaining critical uses of PFOS in May 2017 in semiconductor manufacturing processes is a major environmental management achievement for the worldwide semiconductor industry that has been working on managing and substituting PFOS. Even though the semiconductor industry was only a minor user of the substance, companies proactively took steps to address their uses of the material through a voluntary agreement. This effort was the result of years of work by all companies in identifying appropriate substitutes and significant investments in development, process qualification, and process modifications. Here, you can consult the WSC announcing the Successful Completion of the PFOS Elimination Agreement.

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How the industry took a proactive approach to its PFOS usage?

In May 2006, the global semiconductor industry agreed, through the WSC, 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 its use of PFOS and the concerns about environmental and human health impacts related to PFOS. Under the agreement, members of the WSC, 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 of non-critical uses for PFOS by specific dates. In addition, the industry had worked to identify substitutes for PFOS in critical uses for which no other materials had then been available, and to destroy solvent wastes from critical uses. The successful phase-out of PFOS in critical use cases was announced in May 2017 by the WSC.

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“Substitution” of substances: What does it entail for the industry?

Despite significant R&D efforts in recent years, there are currently no replacement substances for certain chemicals in specific use cases, which provide critical functionality & equal performance required at given technology nodes (levels). First, an invention is required before a substitution of a certain chemical can occur. Any potential substitution of alternatives for a certain chemical in critical usage is a complex multi-stage process. ‘Substitution’ first requires an invention from the suppliers for alternatives that is free of said chemical, 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 & approvals, and final replacement is not a simple process. It is often vastly different across technologies and, generally, takes considerable time to be executed. It is often necessary for the semiconductor industry to continue using certain chemicals until adequate substitutes have been discovered and proven to work in full-scale manufacturing. It is for these reasons that proposed timetables for ending certain chemical usage in critical use cases is often not appropriate for the industry.

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