Biomedical Engineering Reference
In-Depth Information
(a)
(b)
1
µ
m
1
µ
m
Cl
2
RIE
O
2
RIE
(c)
(d)
HF etch
1
µ
m
1
µ
m
FIGURE 12.11
Outline of the templating procedures for fabricating antireflective silicon pillar arrays by using spin-
coated, non-close-packed, monolayer colloidal crystal as template. Adapted from Ref.
105
.
12.3.1.2 Dry-Etched Single-Crystalline Silicon
Moth-Eye Antireflection Coatings
To fabricate periodic arrays of moth-eye pillars
with high aspect ratio, a versatile dry-etching-
based templating nanofabrication technology
has been developed
[105, 109]
. The outline of
the templating procedures for patterning moth-
eye pillar arrays on single-crystalline silicon
substrates is shown in
Figure 12.11
. The spin-
coating technique
[99]
is first used to gener-
ate non-close-packed colloidal monolayers of
hexagonally ordered silica particles on silicon
wafers (
Figure 12.11
a). These particles are then
used as etching masks during a chlorine-RIE
process (5 mTorr pressure, 20 sccm chlorine flow
rate, and 80 W) or a SF
6
-RIE process (40 mTorr
pressure, 26 sccm SF
6
, 5 sccm O
2
, and 25 W).
Because the etching rate of silica is much lower
than that of silicon under above-RIE conditions
[112]
, silica particles protect silicon immediately
underneath them from being etched, resulting
in the formation of pillar arrays directly on the
silicon surface (
Figure 12.11
b). Once the silicon
pillars are deep enough, the templating silica
spheres can be removed by dissolving in a 2%
hydrofluoric-acid aqueous solution.