Study on resist sensitivities for nano-scale imaging using water window X-ray microscopy

The sensitivities of deep-UV resist TDUR-P722 (Tokyo Ohka Kogyo Co., Ltd.) and two types of electron beam (EB) resists ZEP520A and ZEP7000 (ZEON Co.) to soft X-rays in the water window region (284-532eV) were investigated for the nano-scale imaging of the contact X-ray microscopy. At the periphery of the water window, there are absorption edges of main constituent elements of the resist materials, namely carbon and oxygen. It was found that the sensitivities varied widely along the range of X-ray energies used, which correlated with the X-ray absorption of the resists. Moreover for the first time, it was confirmed that K- and L-edge absorptions have a strong influence on the resist sensitivity. Among these resists, ZEP7000 had the highest sensitivity. It was suggested that water window X-ray imaging with nano-scale resolution would be possible with about 1/500 of the fluence, which has the same units (mJ/cm² or J/cm²) as that of so-called dose/sensitivity in the field of resist research, compared with the previously reported method of using polymethylmethacrylate (PMMA). The details of the reaction mechanisms of the resists will be published elsewhere.