Monolithic multichannel secondary electron detector for distributed axis electron beam lithography and inspection

Abstract

The attractiveness of electron beam systems would be greatly enhanced if the throughput could be improved. One approach, described previously by the authors employs a uniform axial magnetic field to focus thousands of electron beams simultaneously [D. S. Pickard, J. Vac. Sci. Technol. B 21, 2709 (2003); T. R. Groves and R. A. Kendall, ibid., 16, 3168 (1998)]. The beamlets never combine to form a common crossover, thereby avoiding the throughput limitations due to space charge blurring. With this approach, one challenge was to fashion a detection scheme that maintains a tight beamlet packing density (250 μm pitch) while minimizing cross-talk between adjacent secondary electron signals, either by crossing trajectories or within the detector. A pin-diode-based detector was investigated as a potential component of the multielement detection scheme for the authors' system. The detector features a two-dimensional array of elements on high resistivity float-zone silicon. The detector attributes that were attractive to their application include modest internal amplification (>5000 at 25 kV), fast response time (measured at <10 ns), ability to be made compact and with dense packed electrodes (<250 μm), low electrode capacitance (<1 pF), and ability for (complementary metal-oxide semiconductor) circuitry to be integrated directly onto the detector array so that low noise amplification of each signal can be performed. This detector requires a retarding field for the primary beam, which accelerates the secondary electrons to energies sufficient to excite a large number of internal secondaries. © 2007 American Vacuum Society.