Using the NIST-invented magneto-optical trap ion source (MOTIS), CNST researchers recently took a significant step toward the goal of creating a more versatile ion source for use in focused ion beams. Focused ion beams (FIBs) are widely used in nanoscale fabrication and imaging. Ions focused to nanometer dimensions with energies up to 30 kV can be scanned across a surface, removing or adding material through bombardment and beam-induced chemistry, or imaging via the generation of secondary electrons. While commercial FIB tools have been available for several decades, these generally use only gallium ions. Expanding the available ion species beyond gallium would create a suite of focused ion beam tools with a wide range of new nanofabrication and imaging possibilities. As described in the November 2010 issue of the Journal of Vacuum Science and Technology B,* the researchers demonstrated a focal spot size of 200 nm using a focused chromium ion beam, and were able for the first time to acquire a clear secondary electron image, in this case of a microchannel plate surface containing a regular array of 10 µm-diameter holes. These early results are a significant step in an ongoing research project carried out under a CRADA with FEI Company to develop new sources of ions for high resolution imaging and fabrication. Future work will attempt to improve the focused chromium beam system to attain the theoretical limit of a few-nanometer focus, as well as develop sources of both lighter and heavier ions, such as Li, Cs, and Er, based on the MOTIS principle. If these ions can be focused to the nanometer scale, light ions could image without damaging the sample, heavy ions could efficiently remove material by sputtering, and specific ionic species could be exploited for their chemical, material or conductive properties to realize new ways to perform localized chemistry, deposit high purity nanoscale conductors, or implant dopants.
*Focused Chromium Ion Beam, A. V. Steele, B. Knuffman, J. J. McClelland, and J. Orloff, Journal of Vacuum Science and Technology B 28, C6F1 (2010). [NIST Publication Database Entry] [Journal Web Site]