Emission and emittance measurements of electron beams generated from Cu and diamond photocathodes A unique approach to photocathode operation is described in this article. We utilize a relatively large bandgap CsBr photocathode material that under normal conditions would not photoemit with radiation energy less than the bandgap plus the work function. However, the material can be activated by proper UV illumination to obtain photoemission at wavelengths as long as 532 nm. Photoyields as high as several hundred nA/ mW and current densities greater than 100 A / cm 2 have been routinely obtained with lifetimes (50% degradation) well in excess of 200 h at 257 nm. The performance of the photocathode meeting all the requirements for a multi-electron-beam pattern generator will be presented.
A prototype raster multibeam optics is evaluated for 45 nm mask pilot lithography. A laser beam is split into 32 beamlets, which are modulated acousto-optically then focused onto a photocathode. This generates 32 electron beams which are scanned and focused on a writing surface. Photocathode photoyield and lifetime exceed 200 nA/mW and 100 h per spot, respectively. Photoyield recovers to within 1% after 1 min fully extinguished. The size of the laser spot is 300 nm, full width half maximum (FWHM) and the size of the corresponding electron beam spots is 50 nm (FWHM) at the writing plane. In the first demonstration of multiple electron beam lithography, 200 nm line/space arrays and 100 nm isolated lines were printed with an interim four-beam datapath. Preliminary experiments and a theoretical evaluation indicate that resist outgassing does not significantly reduce photocathode performance. An improved electron-optical column has also been designed, with a 35 nm pixel pitch, and a placement accuracy of <0.8 nm over a 120 μm field of view at the cathode and the scan field of 410×10 μm at the writing plane.
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