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.
Extreme ultraviolet lithography ͑EUVL͒ requires the vacuum environment for exposing the resist. The contamination in the vacuum environment decreases the reflectivity of the reflective mask and that of the imaging optics. The photoinduced outgassing from the resist becomes the contamination in the vacuum environment. Therefore, the outgassing detection investigation is very important. The outgassing from the chemically amplified ͑CA͒ resists EUV001 for EUVL, EUV006N for EUVL, UV5 for KrF lithography and the nonchemically amplified resists OEBR2000 and ZEP520 for electron beam lithography were investigated. Based on the photoinduced reactions of the resist, the fragment ions species that were measured by the quadrupole mass spectrometer were identified. It is found that the amount of the photoinduced outgassing such as hydrocarbons from the DQN resist and annealing-type CA positive-tone resist is small.
Extreme ultraviolet focus sensor design optimizationa)We have developed a three-aspherical mirror system which is capable of replicating in a large exposure area ͑30 mmϫ28 mm͒. This system consists of the synchronized scanning mechanism of a mask and a wafer, the alignment optics between a mask and a wafer, the focus detector of a wafer position, and the load-lock chamber for exchanging wafers. The aspherical mirrors have a figure error of 0.58 nm and a surface roughness of 0.3 nm. To obtain a high efficiency mirror, a couple of mirrors were coated with a graded d spacing Mo/Si multilayer. The peak reflectivity is 65% at the wavelength of 13.5 nm. The wavelength matching of each mirror spans 0.45 nm. The mirrors were aligned with a Fizeau-type phase shift interferometer, and a final wave front error of less than 3 nm was achieved. Exposure experiments carried out at NewSUBARU synchrotron facility and a diffraction limited resolution of 56 nm was obtained in an exposure-field size of 10 mmϫ2 mm in static exposure. Furthermore, fine patterns in an area of 10 mmϫ5.2 mm were obtained using the mask and wafer synchronized scanning stages. These results revealed that this system can be applied to fabricate large scale integrated devices.
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