Optical column design with liquid metal ion sources

We have applied the results of our studies of fundamental properties of liquid metal ion (LMI) sources to the design of an optical system which exploits their unique characteristics. A gun with a beam current regulating system, a three‐element asymmetric electrostatic lens, and an einzel lens were incorporated into an optical column with a six‐pole electrostatic stigmator and post‐lens deflection. A design consideration with LMI sources is that material sputtered from apertures near the source can ’’poison’’ it, leading to source instability and short life. This problem can be avoided by large source‐lens spacing, but we have chosen to place the source close enough to the lens aperture that virtually no ion current strikes it, resulting in stable operation. While close source‐lens aperture spacing normally requires an undesirably low (∠5 kV) voltage on the source to achieve the conditions for ion emission, we have overcome the problem by surrounding the source with a grid (similar to a Wehnelt) maintained...