Vacuum cleaning of amorphous carbon using hydrogen plasma for EUV lithography

EUV lithography has a promising application, but carbon contamination limits its efficiency and service lifetime. The key issue is how to remove carbon contaminations efficiently and non-destructively on EUV optics. Plasma cleaning technology has been proven to clean carbon effectively. However, the surface reaction mechanism underlying plasma cleaning of carbon contamination remains incompletely understood. To analyze the mechanism of carbon removal via plasma treatment, we first experimentally investigated the effects of different macro conditions (RF power and pressure) on plasma cleaning of carbon contamination. Subsequently, the chemical properties, along with the surface roughness and morphology of the substrates were analyzed, utilizing Raman spectroscopy, XPS, contact angle measurements and AFM. The effectiveness of plasma in removing amorphous carbon, restoring surface character, and inducing changes in surface morphology and roughness was revealed. These findings provide important clues for realizing in-situ non-destructive cleaning of EUV optics.