Scanning ion microscopy with low energy lithium ions

• We use an ion source based on photoionization of laser-cooled lithium atoms.
• The ion source makes possible a low energy (500 eV to 5 keV) scanning ion microscope.
• Low energy is preferred for ion microscopy with backscattered ions.
• We use the microscope to image a thin resist used in nano-imprint lithography.

Using an ion source based on photoionization of laser-cooled lithium atoms, we have developed a scanning ion microscope with probe sizes of a few tens of nanometers and beam energies from 500 eV to 5 keV. These beam energies are much lower than the typical operating energies of the helium ion microscope or gallium focused ion beam systems. We demonstrate how low energy can be advantageous in ion microscopy when detecting backscattered ions, due to a decreased interaction volume and the potential for surface sensitive composition analysis. As an example application that demonstrates these advantages, we non-destructively image the removal of a thin residual resist layer during plasma etching in a nano-imprint lithography process.