Case Studies
Photoactivated Reductive Defluorination Destruction of Fluorochemicals in Semiconductor Manufacturing Waste
Authors: Suzanne Witt, Ph.D., Sarah Meyer
Enspired Solutions Inc.
- Enspired Solutions’® photoactivated reductive defluorination (PRD) technology successfully destroyed fluoropolymers in a popular top antireflective coating (TARC) product, Aquatar, used in semiconductor manufacturing
- Rapid fluoride ion release was observed in a solution of Aquatar diluted 10,000x, indicating efficient destruction of fluoropolymers in solution
- Based on data collected, a treatment train scenario was developed for the 10,000x diluted TARC waste stream using Enspired Solutions’ PFASigator®. Destruction costs were estimated at ~$0.01/L of diluted TARC waste or ~$0.70/L of concentrated TARC waste.
Semiconductors are used heavily in everyday life, from consumer electronics to transportation and communication, and annual sales are in the hundreds of billions of dollars. In semiconductor manufacturing, per- and polyfluoroalkyl substances (PFAS) are present in a variety of essential processing chemicals. Photoacid generators, fluorinated polyimides, poly(benzoxazole)s, antireflection coatings, topcoats, embedded barrier layers, fluorinated surfactants, and materials for nanoimprint lithography all contain some form of PFAS. Due to increasing regulations, the semiconductor industry has formed an international Semiconductor PFAS Consortium aimed at addressing the use of PFAS in manufacturing, including pollution prevention to reduce its use and control releases.
In this case study, the ability to destroy fluoropolymers present in a popular top antireflective coating (TARC) product, Aquatar, using photoactivated reductive defluorination (PRD) was investigated. During the semiconductor manufacturing process, TARC waste is generated in low volumes (average ~ 500 L/day) at a 10x dilution in spin bowl waste, and at much higher volumes (average ~30,000 L/day) at a 10,000x dilution in downstream process wastes. The higher volume, more dilute waste stream containing TARC was the focus of this project.
Enspired Solutions®’ patented PRD process efficiently breaks the carbon-fluorine bonds of PFAS, destroying the molecules and resulting in the release of fluoride ion. PFAS destruction by PRD is under atmospheric temperature and pressure, highly efficient, and amenable to a wide range of environmental conditions and water types. PRD is activated by adding liquid reagents that act to sequester PFAS in a reactive cage to a wastewater solution (Figure 1). Upon exposure to ultraviolet light, solvated electrons that have sufficient energy to defluorinate PFAS are generated in solution, resulting in free fluoride ions, non-toxic carbon compounds, and water. Therefore, fluoride ion can be measured during the reaction in real-time to monitor reaction progress.
In this case study, a solution of Aquatar diluted 10,000x was subjected to PRD and the release of fluoride ion was measured. Rapid fluoride ion release was observed, indicating efficient destruction of the fluoropolymers present in Aquatar (Figure 2). Estimated total organic fluorine in 10,000x diluted Aquatar is 1,125 ppb, and fluoride release at a relatively low PRD UV dose reached 720 ppb, or approximately 64% defluorination. These preliminary results indicate that higher degrees of defluorination may be achieved by increasing the UV dose.
Based on the data collected in this case study, a treatment train scenario was developed for the 10,000x diluted TARC waste stream (Figure 3). The treatment train combines preconcentration (e.g. foam fractionation) with PRD PFAS destruction using Enspired Solutions’ commercial-scale equipment, the PFASigator®. Cost estimates for PFAS destruction for this treatment train are ~$0.01/L of wastewater or ~$0.70/L of the PFAS concentrate. Cost for foam fractionation is not included. We conclude that Enspired Solutions’ PRD technology is an energy efficient and cost-effective approach for on-site TARC waste management in semiconductor manufacturing.