BEFORCE: a pathway to unravel metal oxide resist (MOR) reactions upon EUV exposure, bake, and environment

Metal oxide resists (MORs) have shown excellent performance in EUV lithography, offering high resolution, low line-edge roughness, and low EUV dose sensitivity. These attributes make them strong candidates for advanced patterning solutions. While the basic molecular mechanisms of Sn-based MORs are relatively well understood, environmental factors—such as the presence of moisture and other gases—have been found to influence reactions, leading to variations in critical dimension (CD) stability. Researching these phenomena is challenging because EUV exposures occur in vacuum environments, while conventional measurement techniques like Fourier Transform Infrared (FTIR) spectroscopy are typically conducted on off-line tools. This offline process can introduce variability due to uncontrolled environmental factors, such as atmospheric moisture and time delays. To enable a more detailed investigation of MOR reactions under controlled conditions, imec has developed the BEFORCE* tool. Built on an existing system that already includes EUV exposure and Residual Gas Analysis (RGA) capabilities, the BEFORCE tool integrates FTIR spectroscopy and hotplate units, allowing for post-exposure bake under different gas atmospheres and varying levels of humidity. Additionally, the system employs transfer arms to move MOR samples between units under controlled environments, such as vacuum or dry nitrogen. In this paper, we will clarify the chemical changes in model MORs induced by EUV exposure, baking, and environmental conditions. The high signal-to-noise ratio of the FTIR measurements enables precise quantification of processes such as ligand removal and the presence of water. Moreover, measurements conducted within the BEFORCE tool's controlled environment were found to be significantly more stable than those taken with off-line FTIR, which are susceptible to delays and environmental variability. * BEFORCE: Bake and Exposure system with FTIR and Outgas measurement for Resist evaluation in Controlled Environment