Characteristics of focused beam spots using negative ion beams from a compact surface plasma source and merits for new applications

The characteristics of H- beams from a compact Penning-type surface plasma source have been studied with the goal of evaluating their merits for improved focused ion beam (FIB) systems. As a proof-of-the principles experiment to demonstrate the beam quality a simple, prototype source was developed without any special cooling arrangement of the electrodes. The source is operated in a pulsed mode with a maximum duty factor of 1%; and the operation can be extended to the de mode by using water cooling. The beam brightness is estimated to be similar to 0.5x10(5) A cm(2) sr(-1) at a beam energy of 7 kV, and the energy spread of the beam for angular beam intensity of similar to 40 mA/sr is less than or equal to 3 eV. The beam at an energy of 7 keV has been focused by a lens with a magnification factor of M similar to 0.1, and the spot size is determined by scanning a Si knife edge over the beam as well as by poly(methylmethacrylate) resist exposures. A focused spot, with diameter of similar to 6 mu m and current density of similar to 10 mA/cm(2), has been achieved. The dependence of the spot characteristics with the beam intensity from the source has been studied. The results suggest that a submicron size spot with a current density of similar to 1 A/cm(2) can be generated using these beams for M similar to 0.01. The source, with its simple, robust technology, seems an attractive choice for FIB applications. (C) 1998 American Vacuum Society.