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Focused Ion Beams

Sub-micrometer Spot Size and High Current Density

FIB system
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 LMIS results.

Ion Graph
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.


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