A Look at Perfluorooctyl Sulfonates in High-End Lithography for the Semiconductor Industry
Tario, Nancy
(University of Minnesota, Duluth)
Background
Perfluorooctyl Sulfonate (PFOS) is a chemical required by the semiconductor industry for formulation of resists and anti-reflective coatings in high-end lithography. Although there is currently no known health risk associated with its use, it is a known persistent bioaccumulative toxin (PBT). According to the Environmental Protection Agency (EPA), studies have found PFOS in very small quantities in the blood of the general human population and in wildlife. This indicates that exposure to the chemicals is widespread. Recent testing raised concerns about potential for systemic toxicity of PFOS and the long term potential for adverse effects in people and wildlife.
The EPA believes that Minnesota Mining and Manufacturing Company (3M) is the only manufacturer of these chemicals. 3M, who had essentially phased out PFOS chemical production, has continued to produce it as the result of a joint agreement between the EPA and the semiconductor industry. The agreement gives permission for controlled use in lithography applications (Federal Register, 2000).
3M, however, had been involved in some studies that indicated that fluorocarbons may be hazardous to human health and the environment. Toxicology studies show that PFOS is absorbed orally and distributes primarily in the serum and liver. PFOS can also be formed as a metabolite of other perfluorinated sulfonates, but it does not appear to be further metabolized. Elimination from the body is very slow. Serum PFOS levels in three retired male 3M chemical workers followed for 5 ‘/ years showed an average elimination half life of 1,428 days (about 4 years). PFOS showed moderate acute oral toxicity with a rat LDso of 251 mg/kg and a 1 hour LC 50 of 5.2 mg/L in rats was reported. Adverse signs of toxicity observed in rat studies included increases in liver enzymes, hepatic vacuolization and hepatocellular hypertrophy, gastrointestinal effects, hematological abnormalities, weight loss, convulsions and death (Olson, 1999).
And although the U.S. semiconductor industry is the world leader in finding alternatives to hazardous chemicals and pollutant emissions, the Semiconductor Industrial Association and photoresist suppliers succeeded in retaining the use of Perfluorooctyl Sulfonates (PFOS) and Perfluoroalkyl Sulfonates (PFAS) in photoresists and anb-reflective coatings. These materials are considered essential to the future of semiconductor manufacturing in the United States. Both PFOS and PFAS were reviewed by the EPA under the Toxic Substances Control Act (TSCA) for potential banning through a Significant New Use Rule (SNUR). The semiconductor industry worked with the EPA to demonstrate that it can control the use of these materials and their proper disposal (SIA, 2002).
Understandably, manufacturers of semiconductor wafers would like to know if they should be concerned about employee generated lawsuits in regard to PFOS (Sawicki, 2002). IBM is being sued by 128 employees in regard to chemical exposure. In Scotland, 70 women are suing another U. S. company, the National Semiconductor Corporation, claiming exposure to cancer-causing chemicals (Schmit, J., USA Today). It is unclear whether any of the IBM or National Semiconductor lawsuits concern this material.
Purpose Statement
It is uncertain as to what extent PFOS is a concern to the general population and the environment. It is not known if it is a threat to human existence, a hazard to only those in the semiconductor industry, or if it is simply a benign substance that just happens to accumulate in the bodies of humans and animals. It is not known why the substance is found in every blood sample tested, including children and people who have never worked with the material. Should we consider the toxic effect of PFOS on lab animals to be a red flag? Several years back it was reported that overcooked bacon caused cancer based on studies using laboratory rats. It was later reported that the amount of bacon the rats were force-fed would have been equivalent to a human eating many pounds of it a day. How well do the lab studies relate to human bioaccumulation of PFOS? Are we becoming complacent as a result of these studies and ignoring real threats? Are we dealing with a chronic health situation like the asbestos disaster? Is this a job for Erin Brockovich?
Or are we being too conservative – turning every substance into a poison? Over 500 years ago Paracelsus (1493-1541) stated that AII substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy.” Is the sky really falling, Chicken Little, or was it merely an acorn falling from a tree?
These are the questions that need to be answered. The primary purpose of this paper, then, will be to review available information regarding the use of PFOS in the semiconductor industry and to report objectively the opinions held by the various concerned industrial, environmental and governmental parties.
A secondary objective will be to determine if there are currently any lawsuits against employers in regard to PFOS exposure in the workplace. This was not ascertained in the initial research for this proposal.
References
Federal RegisterNol. 65, No. 202NVednesday, October 18, 2000, Proposed Rules.
Olsen, G. W., Burris, J. M., Mandel, J. H., Zobel, L.R. Serum perfluorooctane sulfonate and hepatic and lipid clinical chemistry tests in fluorochemical production employees. J. Occup. Env. Med. (1999, in press).
Sawicki, D., Telephone conversation regarding perfluorooctyl sulfonate in the semiconductor industry. November 2, 2002.
Http://www.semichips.org. Semiconductor Industry Association Issues: Environmental Safety and Health. October 2002.