Nn. Matsuzawa et al., Theoretical calculation of photoabsorption of various polymers in an extreme ultraviolet region, JPN J A P 1, 38(12B), 1999, pp. 7109-7113
We have calculated the linear absorption coefficients of various resist pol
ymers using the mass absorption coefficients at 13 nm and the density obtai
ned from the graph-theoretical treatment derived by Bicerano. The values in
dicate that the transmittance at 13 nm of conventional resists used in 193-
nm, 248-nm and 365-nm lithography is about 30% when the thickness is 3000 A
ngstrom and 60-70% when it is 1000 Angstrom. This shows that conventional r
esists are suitable for an EUVL (extreme ultraviolet lithography) thin-laye
r resist (TLR) process using a hard-mask layer, but their large photoabsorp
tion makes them unsuitable for a single-layer resist (SLR) process. To desi
gn polymers that are suitable for an SLR process, we further calculated the
absorption of about 150 polymers. The results suggest that the introductio
n of aromatic groups into a polymer not only reduces the absorption at 13 n
m but also increases the etching resistance.