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We have calculated the linear absorption coefficients of various resist polymers using the mass absorption coefficients at 13 nm and the density obtained from the graph-theoretical treatment derived by Bicerano. The values indicate 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 Å and 60–70% when it is 1000 Å. This shows that conventional resists are suitable for an EUVL (extreme ultraviolet lithography) thin-layer resist (TLR) process using a hard-mask layer, but their large photoabsorption makes them unsuitable for a single-layer resist (SLR) process. To design polymers that are suitable for an SLR process, we further calculated the absorption of about 150 polymers. The results suggest that the introduction of aromatic groups into a polymer not only reduces the absorption at 13 nm but also increases the etching resistance.

To use a TMAH (tetramethylanmonium hydroxide aqueous solution) developer with a resist based on adamantylmethacrylates, we proposed a cleavable adamantyl ester by protonic acid. We found that a 2-methyl-2-adamantyl ester was cleavable by protonic acid and poly(2MAdMA) (2-methyl-2-adamantylmethacrylate) worked as a chemically amplified resist with good sensitivity. We achieved high resolution by improving the adhesion.The 2MAdMA-MAA (methacrylic acid) resist achieved 0.165 pm L/S with 3.0 mJ/cm2 in ArF evaluation using a dilute TMAH developer. We could use a 2.38% TMAH developer by introducing 2MAdMA to the strongly polar acid labile protect group, OCMA (3-oxocyclohecylmethacrylate) or MLMA (mevalonic lactone methacrylate), which had good adhesion. We obtained fine patterns below 0.20µm at below 10 mJ/cm2 in ArF evaluation with 2.38%TMAH developer. We achieved a minimum resolution with 0.15 pm L/S patterns and a D.O.FE of 0.6 pm at 0.18 pm L/S patterns using a 2MAdMA-MLMA resist.

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