Electron-Induced Reactions in Solid Carbon Dioxide: Lithography and Methane Formation under High-Energy Irradiation

Ice-assisted electron-beam lithography (iEBL) utilizes cryogenic ice layers as resists for micro/nanofabrication. Water ice, the most widely used positive-tone resist, exhibits a high critical dose that limits lithographic efficiency. Here, we investigate solid carbon dioxide (CO₂) as a potential alternative. Lithographic characterization via SEM shows that solid CO₂ has a critical dose an order of magnitude lower than that of water ice. To investigate electron-induced chemical pathways, mixed cryogenic CO₂/H₂O ices were irradiated with a 10 MeV linear electron beam. Volatile products were monitored in situ using quadrupole mass spectrometry. Hydrogen and methane were detected as reaction products, with methane formation strongly dependent on the repetition frequency. These results establish CO₂ as a promising resist material and provide mechanistic insight into electron-stimulated decomposition in iEBL.