Theoretical estimation of photo-absorption of resist molecules in the EUV and VUV region

Extreme ultraviolet lithography (EUVL) and vacuum ultraviolet lithography (VUVL) at a wavelength of 13 nm and 157 nm, respectively, are promising candidates for the fabrication of patterns with feature sizes of 100 nm and below. One of the most important parameters in the design of photoresist materials is the absorption coefficient of a polymer because, if the polymer is not transparent enough, the resist pattern deteriorates. Thus, as the starting point of our theoretical study on ELJV and VUV resist polymers, we have performed an estimation of photo-absorption in these wavelength regions. The absorption coefficients of about 150 polymers were calculated using the mass absorption coefficients of Henke et al. (1993). It is found that the inclusion of fluorine atoms in a polymer significantly increases the absorption, whereas the inclusion of aromatic rings reduces it. In addition, polymers containing silicon atoms are generally more transparent than those consisting of C, H, and O (and N) atoms.