CNST Researchers Develop Novel Optics to Accelerate Ions

CNST researchers Adam Steele, Brenton Knuffman, and Jabez McClelland, together with Jon Orloff of FEI Co., have invented an innovative way to extract and accelerate ions generated in a spatially distributed ion source. The NIST-invented magneto-optical trap ion source (MOTIS), a high-brightness, low-emittance source makes use of the very cold temperatures of laser cooled atoms to generate a highly collimated beam of ions that is ideally suited for creating a focused ion beam with nanoscale probe size. In order to make the best possible use of these ions, it is often desirable to accelerate them to a high energy, up to 30 keV or more. With conventional ion optics, it is very difficult to do this without creating "crossover" in the beam – a region of very high current density that leads to strong Coulomb interactions in the beam and loss of resolution. To circumvent this obstacle, the researchers developed an ion optical system that makes use of a pair of extraction plates in combination with a long resistive tube that allows the ions to be accelerated gradually with minimal lensing. This preserves the collimation of the beam and avoids crossover. So far, this invention has been implemented and works exactly as expected with both a chromium ion source and a lithium ion source. Work is ongoing to create focused ion beam systems with these sources, with the first scanning-focused-ion-beam images emerging in recent weeks. Applications for these focused ion beams include new forms of microscopy, new circuit edit processes for next-node semiconductor manufacturing, and new nanoscale fabrication processes. This research was performed under a CRADA with FEI Co., of Hillsboro, OR, and a U.S. Patent application has been filed for the invention.