Plasma-Processed Biomimetic Nanoand Micro-Structures - Biomimetic Architectures by Plasma Processing - page 96

Figure 3.4 EDX spectra of the RIE grass. The relative intensities are high

for fluorine indicating a fluorine predominant compound.
Reprinted with permission from Ref. [10]. Copyright 2005
American Chemical Society.

The second step is DRIE which is also known as Bosch process.
The DRIE process is a time-multiplexed etching process which
alternates etching (sulfur hexafluoride, SF gas) and polymerisation

6

(octofluorocyclobutane, C gas) steps in order to microfabricate

silicon microstructures with high aspect ratio [15]. Not only the
plasma etching parameters such as the balance between etch and
passivation periods, plasma density, chamber pressure, bias power,
and plasma power, but also other parameters such as pattern
density (i.e., the silicon area exposed to plasma) have critical roles in
achieving appropriate silicon structures.
In the DRIE etching step, the silicon surface underneath RIE grass
has much lower etch rate compared to the silicon exposed to the
RF plasma because the RIE grass works as an etch mask. After the
DRIE etching process, silicon nanotips are nicely formed as shown in
Fig. 3.3. As shown in this figure, the etching selectivity between RIE
grass and silicon is greater than 25

F

4 8

µ

m, high enough to microfabricate

silicon nanotips.
The RIE grass looks like short, approximately quadrilateral,
cross-sectional stumps with a concave top (Fig. 3.5, left). Depending
on the process time, these growth sites may vary in their side di-