Plasma Ion Sources for High Resolution Primary Ion Beams
Milling speeds with a gallium focused ion beam (FIB) are often much too slow for many sample preparation and surface engineering applications. Also, engineered devices must generally be tolerant of high gallium concentrations being implanted in the near-surface region. These are major restrictions when fabricating micro-mechanical devices that require nanometer-scale precision across dimensions of several hundred micrometers. Furthermore, elemental secondary ion mass spectrometric imaging (SIMS-Imaging) has been limited to a lateral resolution of 200nm when using an oxygen focused ion beam for high sensitivity surface analysis. Many applications in material science and biology could benefit from an ability to image trace level surface chemistry with <20nm resolution.
Example applications include, sub-cellular imaging of trace metals in the brain for neurodegenerative disease studies, analysis of trace element segregation in metal alloys and studying isotope distributions in meteorites and interplanetary dust particles. At Oregon Physics, we have developed the HyperionTM inductively coupled plasma ion source that is now capable of generating smaller Xe+ probe diameters than the liquid metal ion source (LMIS, Ga+) FIB at beam currents in excess of 20nA. When operated with oxygen, this ion source exhibits imaging resolution, source lifetime and current stability, that are significantly better than provided by a duoplasmatron. FIB and SIMS data will be presented from this new ion source technology. The operating principles of the inductively coupled plasma source, the properties of the ion beam(s) being created and the projected future for this technology will also be described