Atomistic Modeling of Focused Ion Beam Processing
Kallol Das (University of Illinois), Jonathan Freund (University of Illinois at Urba), Harley Johnson (University of Illinois)
From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium A
Mon 9:00 - 10:30
CIT 165
Focused ion beam (FIB) processing is widely used for nanostructuring of semiconductor materials for a variety of applications. Beams of 30keV Ga ions are focused to spot sizes as small as 5-10nm, and used to remove material with very high precision. Building on our previous studies of low energy ion irradiation of surfaces over long time scales, we consider here the problem of FIB processing of free-standing semiconductor films. Using a fast parallel molecular dynamics method, combined with statistical and continuum interpretation of unit-process events, we simulate FIB hole drilling in silicon films of varying thickness, with beams of varying ion flux. We establish film thickness and beam flux conditions in which through thickness hole drilling is possible. Furthermore, we show that counter to intuition, material is removed not by a sputtering process, in which kinetic energy is used to break individual atomic bonds, but by a process of boiling and evaporation that occurs when the incident energy flux is sufficiently large compared to the rate of heat transfer away from the process zone.