Evaluation of vacancies in positive-tone non-chemically and chemically amplified EUV / EB resists: relationship between free-volume and LER

EUV, X-ray and EB mainly induce ionization in resist materials and its energy deposition process is different from ArF exposure. Linear energy transfer (LET) effect for resist sensitivity is very important issue from the viewpoint of radiation induced chemical reactions for high-volume nanofabrication. Therefore the knowledgebase of radiation chemistry is required for understanding the resist performances for EUV lithography. In order to acquire the knowledge of resist materials for EUV / EB lithography from a viewpoint of the free-volume, the positron annihilation lifetime spectroscopy was carried out using positron probe microanalyzer (PPMA) installed at AIST. The size of free-volume can be evaluated from the lifetime of ortho-Positronium (o-Ps). The lifetime and intensity of o-Ps in EB-exposed positive-tone non-chemically amplified (non-CA, ZEP) and CA (UV-III) EUV / EB resists were observed. Moreover, to evaluate the relationship between line edge roughness (LER) and free-volume, EB lithography was carried out, and then sensitivities (E0 and Esize) and LER were measured. For both non-CA and CA resist materials, the changes of free-volume due to evaporation of outgas, polarity change or chain scission would hardly influence on their LER and resolution.