Development of EUV resists in supercritical CO 2 solutions using CO 2 compatible salts (CCS): results from a two-level full factorial design of experiments (DOE)

Abstract

Direct development of EUV resists in homogeneous carbon dioxide (CO2) solutions containing CO2 compatible salts (CCS) has been demonstrated. These CCS complexes have been designed and prepared such that the anion and/or the cation of the salt contains at least one CO2-soluble portion. In the described method, standard positive tone EUV resists are processed in supercritical CO2 containing less than 20 mM CCS, at pressures ranging from 3500 to 5500 psi, 35 to 65 C with cycle times as short as 1 minute to give reverse image development. Substantial reduction in image collapse and LER/LWR has been observed; large aspect ratios approaching 10 have been measured in dense line/space features, and dense lines with 3 sigma LWR values that are 30% smaller than comparable TMAH developed samples have been observed. This paper will describe results from a two level full factorial design of experiments (DOE) using four factors. Two experimental samples were processed at each point, along with four center point runs to give a total of 36 experimental samples. An additional seven supplemental runs were also prepared. Responses measured for the DOE include half height resist thickness, resist height, contrast, iso/dense bias, aspect ratio of collapse, line edge roughness, and line profile. Details of how the responses were measured will be presented in the paper. Effects of individual factors on each response, along with the significant interactions between factors will be reported. An optimized parameter space will be selected and additional follow-up experiments will be described.