Biomedical Engineering Reference
In-Depth Information
12.3.1.1 Wet-Etched Single-Crystalline Silicon
Moth-Eye Antireflection Coatings
by the size of the templating silica spheres, can
be formed
[129]
. These circular nanoholes can
then be used as etching masks during a KOH
anisotropic etching process to create wafer-scale
inverted pyramidal arrays (
Figure 12.10
b) on
the wafer surface
[101]
.
The specular optical reflectivity of the repli-
cated pyramidal arrays is evaluated using visi-
ble-near-IR reflectivity measurement at normal
incidence.
Figure 12.10
c shows the measured
specular reflection spectra from a polished (1 0
0) silicon wafer and an inverted pyramidal array
with 360-nm pits. The flat silicon substrate
exhibits high reflectance (>35%) for visible and
near-infrared wavelengths, whereas the tem-
plated gratings show reduced reflectance of
∼
10% for long wavelengths (>600 nm). The
reflectance is further reduced to
∼
2% for
The first approach to fabricate nanostructured
ARCs on sc-Si wafers is similar to the conven-
tional anisotropic etching processes used in
standard crystalline-silicon solar-cell produc-
tion. A schematic illustration of the fabrica-
tion procedures is shown in
Figure 12.9
[102]
.
Non-close-packed colloidal monolayers on
(1 0 0) silicon wafers are first assembled by
the spin-coating technology
[98, 99]
. The non-
close-packed silica particles function as shadow
masks during an electron-beam evaporation
process for depositing a 30-nm-thick chromium
layer. After lifting off the templating silica par-
ticles, a periodic array of nanoholes (
Figure
12.10
a), the diameter of which is determined
Silica in monomer
EB-evaporate Cr
Remove silica
Spin coat; UV-cure
RIE
Wet etch; Cr etch
FIGURE 12.9
Schematic illustration of the templating nanofabrication procedures for creating inverted pyramidal grat-
ings on single-crystalline (1 0 0) silicon wafers. Adapted with permission from
Chem Mater
19
(2007), 4551-4556. Copyright
2007, American Chemical Society.
