INDIA IMP vFinal DR 17/6/08 09:17 Page 38
Semiconductor India
Fabrication of electrodes
for micro squid
Magnetic nano structures, self assembled or
lithographically made, are of great
technological importance for small scale
devices like dense magnetic memory.
However, the properties of material depend
on individual feature, magnetic anisotropy
of the material and the exact geometry of
the features. Among the recent developed
techniques for local magnetic measurements
of bulk samples or to measure the magnetic
response of a single magnetic nano particle,
scanning squid microscopy is the most
suitable in terms of spatial resolution and
sensitivity. To develop such a technique one
initially requires fabrication of special nano
structures, namely two Josephson Junctions
(JJ) in parallel. Large features of these
Figure 2-An SF-100 ELITE Maskless Lithography System junctions have been fabricated using the
maskless lithography system whereas small
area. The light reflects off of the Smart computer controlled actuation of the filter. features of nm size are incorporated using
Filter assembly to provide the optical All of the energy from the mercury arc focused ion beam (FIB). Fabricating large
pattern. After passing through additional lamp is then projected onto the substrate, features using FIB is not recommended as it
optical components, the pattern is facilitating exposure of the substrate. The takes a long time and energy.
projected onto the substrate. The SF-100 length of time that the filter is removed
includes an alignment fixture for from the light path is a user provided setting We first design and fabricate the initial
mounting of the substrate. This allows the in the software. pattern using maskless lithography system
substrate to be moved in three dimensions, of dimension of the order of 60 micron and
providing alignment in two, co-planar Using this system, a number of different then use the focused ion beam to get nano
dimensions and the capability to produce devices have been easily fabricated. The size features. The maskless lithography
three dimensional structures by aligning the flexibility of the system allows the user to system helps us to get a sample ready for
substrate in a third dimension perpendicular easily change over to different materials, the nano-patterning very precisely and
to the two co-planar dimensions. An substrates and masks. Examples of rapidly accurately. Examples of these devices are
inline camera is used for feature registration prototyped devices are given below. shown below in Figure 3.
and inspection of the exposed substrate
pattern.
A UV filter shutter is included in the light
path to provide for image to substrate
alignment. This filter is normally located in
the optical path allowing for viewing of the
image on the substrate. By filtering all UV
energy, the substrate can be aligned to the
projected image without exposing the
substrate. After the substrate has been
placed in the appropriate position, the filter Figure 3-Examples of MicroSquid Devices Fabricated Using FIB and Maskless
is removed from the light path through Photolithography
38 www.semiconductor-india.com | Summer 2008
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