Theoretical calculation of photoabsorption of various polymers in an extreme ultraviolet region

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.