Safer and effective alternatives to perfluoroalkyl-based surfactants in etching solutions for the semiconductor industry
By Rashmi Sharma, Shreyas Shelke, Mohammad Bagheri Kashani, Gregory Morose, Christopher Christuk, and Ramaswamy Nagarajan
J. Clean. Prod.
June 26, 2023
DOI: 10.1016/j.jclepro.2023.137879
Surfactants based on poly and perfluoroalkyl substances (PFAS) such as Fluoroalkyl sulfonamide, fluoroalkyl sulfonyl amino propane sulfonic acid, and potassium perfluorooctane sulfonate surfactants are widely used in etching solutions in the semiconductor industry to improve the wetting characteristics of the etchant and substrates.
Their excellent stability in strongly acidic, alkaline, and oxidizing etching solutions such as Tetramethyl ammonium hydroxide (TMAH), perchloric acid/ceric ammonium nitrate aqueous solution (chrome), ammonium hydrogen fluoride solution, or buffered oxide etchant (BOE) and a mixture of phosphoric, acetic, and nitric acid etchant (PAN), has warranted their continuous use as a surfactant.
The toxicity and extremely high persistence of PFAS necessitate their replacement with less toxic and effective alternative surfactants.
A generic methodology is described for the identification of safer alternative surfactants and the experimental validation of properties to facilitate the drop-in replacement of these safer surfactants in etching solutions for the semiconductor industry. Hydrophilic-Lipophilic Balance (HLB) values, critical micelle concentration (CMC), compatibility, and wetting characteristics of etchants were analyzed on substrates relevant to the semiconductor industry.
Biobased BG10 alternative surfactant outperformed PFAS surfactant in improving the wetting characteristics of the TMAH etchant on substrates of interest as evidenced by the significantly lower contact angle. The wetting characteristics of the PAN and BOE etchants containing BG10 and CG50 surfactants were comparable to PFAS surfactants.
Toxicity comparisons indicated that these alternatives are far less hazardous to human health than PFAS. These safer alternatives have been tested successfully by over 100 semiconductor companies. These companies have provided positive feedback with no reported deleterious effects on the final products. This successful approach opens new possibilities for the replacement of PFAS in numerous other applications where PFAS is commonly used as a surfactant. Using this methodology, alkyl polyglucosides with trade names BG10 and CG50 and polyoxyethylene surfactants of Brij35 and BrijS100 were identified as alternatives to PFAS surfactants.
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