Focused Ion Beams
Sub-micrometer Spot Size and High Current Density
Focused ion beam (FIB) system|
Focused ion beam (FIB) systems using a compact plasma source are
being developed at FMT. The figure below shows the ion beam test stand facility.
Currently available FIB technology with high resolution (<1micrometer beam size) primarily
uses the liquid metal ion source (LMIS), a high brightness, stable, field emission ion
source. This technology has made a signifcant impact on industries, particularly
semiconductor manufacturing industries. These FIBs, using LMIS, are characterized by
beam sizes in the 5-500 nm range with target current densities J ~ 10A/cm2.
Unresolved issues include a relatively broad ion energy distribution (5 eV FWHM) and the
inability to produce inert ion species such as Ar, reactive ion species such as O and light
species such as H.
The FIB system being developed at FMT is competitive optically with a LMIS and produces
ions from the gas phase, including species unobtainable from a LMIS. Experiments with H-
ions indicate a brightness of 105 A sr-1 cm-2, angular beam intensity > 40 mA sr-1 and
an energy distribution with FWHM of ~ 2 eV. It is estimated that a spot size of < 100 nm,
with target current density of > 1 A/cm2, can be achieved using a modest magnification of
about 0.01. A comparison of focused beam parameters from different sources is shown below.
Note that the results for our plasma source SPS with M = 0.01 are quite comparable to the
|click for larger image|
Formation of negative ion beams with a low charge-up voltage of the striking surface
allows the landing of the probe beam on targets with a much higher degree of positional
accuracy than in the case of conventional positive ions. Applications of practical very
high-resolution (~ 2.5 nm) H- ion beams include new avenues of research in ion beam
microscopy as well as in nucleation-site control for producing microcrystals. Extracting
other ion species from this source and adapting the beams to a suitable optical column
will capture a wide arena of applications in microelectronics, materials science and biology.