Nanotechnology-Enabled Sensors

Substrate with a
PMMA layer
Lift-off
4.9 Nanolithography and Nano-Patterning 195
Fig. 4.47 Electron beam lithography and lift-off process for making Au patterns.
Focused Ion Beam (FIB)
E-beam writing and
development
Au deposition
FIB systems generally employ a highly focused beam of ions, such as
Ga + (as gallium can be used to easily produce a liquid metal ion source),
which is raster scanned over the sample surface in a similar manner to an
electron beam in a scanning electron microscope. 87 However, it differs
from an electron microscope in that the FIB is destructive to the specimen.
Atoms on the sample surface are sputtered as the high-energy ions impinge
on the sample. Furthermore, gallium atoms from the ion beam are also implanted
into the top few nanometers of the sample surface.
As can be seen in Fig. 4.48, the primary Ga + ion beam strikes the sample
surface. In doing so, a small amount of the material is sputtered and
leaves the surface. These can be either neutral atoms (n 0 ) or secondary ions
(i + ). Just as in sputtering, the incident ion beam also produces secondary
electrons (e - ). Additionally, these secondary electrons, or sputtered ions,
may also be collected by the detectors which convert the signal to an image
of the surface.