Sensitivity and Contrast Characterization of PMMA 950K Resist Under 30 keV Focused Ga⁺ Ion Beam Exposure

In this study, the key lithographic performance of PMMA 950K resist was evaluated by exposure to a 30 keV focused gallium (Ga⁺) ion beam. The sensitivity and contrast of PMMA 950K were directly compared with those of electron exposure under identical development conditions. It was found that the sensitivity of PMMA 950K to Ga⁺ ions for 50 nm films reaches a value of about 0.4 μC/cm², which is more than 250 times higher than its sensitivity to electron exposure. A method for evaluating the resist contrast during ion exposure is proposed in this work, taking into account the highly non-uniform dose distribution across the resist depth; it yielded a contrast value of γ = 2.6, which is consistent with the result obtained with electron exposure (γ = 2.8). In addition, a pronounced dependence of the resist sensitivity on the resist thickness was found: with an increase in thickness from 10 nm to 60 nm the sensitivity decreases by an order of magnitude. The obtained results form a reliable methodological basis for characterizing the behavior of polymer resists under ion irradiation and provide valuable recommendations for optimizing lithography with a focused beam of Ga⁺ ions when creating nanostructures for microelectronics, photonics, and quantum technologies.