PFAS in semiconductor photolithography: a mass balance model

Per- and poly-fluoroalkyl substances (PFAS) have come under increased scrutiny because all members of this class of compounds exhibit very high environmental persistence (vP), and some exhibit toxicity (T) and/or bioaccumulation (B) potential. Because of these attributes, PFAS chemicals are being scrutinized by regulatory authorities for restrictions on use and releases to the environment. At the same time, PFAS are crucial components of many process materials used in semiconductor photolithography, to the extent that manufacture of advanced chips is currently not possible without them. While PFAS uses are crucial, the amounts used in these key applications are small relative to global PFAS production and use, a fact that may not be generally known. The purpose of this paper is to provide a quantitative assessment of the amount of PFAS used in semiconductor photolithography, and to present a mass balance model for the disposition of these materials into the different waste streams. This model allows identification of key areas for prioritized action, including the need for targeted research and development.