Semiconductor on glass photocathodes as high-performance sources for parallel electron beam lithography

The throughput of electron beam lithography has historically been limited by electron-electron interactions that cause blurring at high currents. We present a system configuration for maskless parallel electron beam lithography using a new multiple primary source technology that, by employing widely spaced beams, significantly reduces this problem. The proposed source technology, a negative electron affinity (NEA) photocathode, allows us to generate an array of high brightness, low energy spread, independently modulated beams over a large area. In order to assess the effects of electron-electron interactions in this system, Monte Carlo simulations have been performed. The results of these calculations indicate that this configuration enjoys significant advantages over existing maskless systems. By restricting the area of emission for the individual beamlets to submicron dimensions, the blurring due to statistical electron-electron interactions can be significantly reduced for a given current at the wafer. For example, at 50 kV a total current of more than 2.5 mu A can be obtained with less than 10 nm beam blurring. Preliminary experimental results suggest that high brightness emission can be maintained from a NEA photocathode in a demountable vacuum system. (C) 1996 American Vacuum Society.