Supercritical resist drying for isolated nanoline formation

Supercritical resist drying enables the formation of fine resist patterns with a nanometer-scale resolution. Fine isolated and dense lines of resist collapse when dried by conventional methods after development, thereby lowering the useful resolution of resist patterns. For nanolines, the collapse is due to the swelling of the resist that results from development and rinsing. To prevent collapse, the cause of the swelling must be removed from the resist before drying. The use of supercritical fluid is the most suitable way to do that because such fluid has a diffusion coefficient as large as that of a gas. Supercritical resist drying with carbon dioxide prevents the collapse of isolated lines and enables the formation of nanolines with a width of about 7 nm and a high aspect ratio of over 10 in the case of the negative tone resist of hydrogen silsesquioxane and 100 kV electron beams.