Development of compact electron undulating ring

Recently, since synchrotron radiation (SR) as a source for X-ray lithography is considered to be one of the most promising techniques for pattern printing of future's very large scale integrated circuits (VLSI), compact electron storage rings which can be used for industrial purposes have been developed. SR is superior to conventional sources from a viewpoint of short wavelength, small divergence and high intensity, but it has difficulty in large-area exposure because of the vertical small angular spread. The electron undulating method first presented at the Electrotechnical Laboratory can expand the vertical exposed area by making use vertical undulating motion of the stored beam around the horizontal design orbit with a steering magnet. We have examined the source characteristics of the compact electron undulating ring by applying this method. As a result, the SR power density more than 175 mW/mrad is required to expose a 50 mm x 50 mm stepfield in less than 2 s with a 4∼7 m long beamline and the estimation indicates that a beam size with a σx and a σz both less than 1 mm is fully acceptable for a 250 nm resolution. In order to design the ring system in which all of the beam ports can be used for the vertical wide area exposure of SR, we have shown that optimization of a vertical betatron oscillation number and of a location of a steering magnet is needed. Finally, regarding beam instability which enlarges a beam size, we described that suppressions of ion trapping and longitudinal coupled-bunch instability are important for SR lithography. (author)