Abstract
Short-pulse extreme ultraviolet (EUV) of a free-electron laser (FEL) is a prime candidate as a next-generation EUV lithography light source. However, the physical events and chemical reactions in resist materials, induced by the short-pulse EUV, have not yet been elucidated. In this study, the morphological and chemical changes in poly(methyl methacrylate) (PMMA) induced by picosecond-pulsed EUV were investigated using an X-ray laser (XRL) as a touchstone for next-generation EUV-FEL lithography. The XRL is suitable for the evaluation of resist materials in next-generation EUV-FEL lithography because of its short pulse width (7 ps) and high intensity (approximately 200 nJ/pulse at a maximum). The sensitivity of PMMA upon exposure to a 7 ps XRL pulse was enhanced by approximately 50 times in comparison with using conventional EUV sources, which have a typical pulse width of the order of nanoseconds. X-ray photoelectron spectroscopy revealed the decomposition of both the main and side chains of PMMA after XRL irradiation. These changes only occurred for relatively high doses of EUV irradiation at picosecond timescales. Thus, the results suggest the importance of a specific resist design for next-generation EUV-FEL lithography.
Highlights
The X-ray laser (XRL) is suitable for the evaluation of resist materials in next-generation extreme ultraviolet (EUV)-free-electron laser (FEL) lithography because of its short pulse width (7 ps) and high intensity
Next-generation EUV-FEL lithography will follow the conventional EUV lithography (EUVL) process, that is, EUV irradiation forms a latent image through radiation-induced chemical reactions and, subsequently, development forms real features
It is worth investigating whether conventional resist materials and processes can apply to EUV-FEL lithography
Summary
The morphological and chemical changes in poly(methyl methacrylate) (PMMA) induced by picosecond-pulsed EUV were investigated using an X-ray laser (XRL) as a touchstone for next-generation EUV-FEL lithography. The XRL is suitable for the evaluation of resist materials in next-generation EUV-FEL lithography because of its short pulse width (7 ps) and high intensity (approximately 200 nJ/pulse at a maximum). The sensitivity of PMMA upon exposure to a 7 ps XRL pulse was enhanced by approximately 50 times in comparison with using conventional EUV sources, which have a typical pulse width of the order of nanoseconds.
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