FOCUSED ION-BEAM LINE-PROFILES - A STUDY OF SOME FACTORS AFFECTING BEAM BROADENING

The current-density profile of a focused ion beam (FIB) has a central peak accompanied by broader ''wings'' that, while unimportant in litho graphic applications, can lead to unwanted effects during an implantat ion operation. The origin of the wings, and hence the best way to mini mize them, is not clear and needs further study. We have measured the line profiles of several of the ions available in our FIB machine as a function of a number of variables, under ultrahigh vacuum (UHV) condi tions. No effects are observed from changes in emission current or del iberate defocusing of the objective lens. There are some changes with beam aperture and/or current, but the biggest differences seem to be a ssociated with a change of source type and hence, possibly, with a cha nge in the source/extractor configuration or in the alloy and the emis sion process. The wing amplitudes are appreciably lower than many prev iously observed, and their profiles, at least for the lighter ions stu died (Be++, Be+, and B+), are Gaussian rather than exponential. It see ms possible that our UHV conditions may have eliminated a scattering m echanism responsible for the larger, exponential wings previously obse rved. The corresponding beam and rectangle-edge profiles have been cal culated. (C) 1995 American Vacuum Society.