Biomedical Engineering Reference
In-Depth Information
FIGURE 4.4
Anisotropic dry etching: (a) cryogenic etching; and (b) alternate etching and deposition.
is often called the Bosch process. The etch cycle consists of two steps: etching and deposition. In the
etching step, silicon is removed by SF 6 . The etching step lasts from 5 to 15 s, in which the etch front
advances from 25 to 60 nm in silicon. In the deposition step, supply gas is switched to C 4 F 8 . A film of
fluorocarbon polymer of about 10 nm is deposited on the trench wall. In the next cycle, the polymer
film at the bottom surface is removed by ion bombardment, while the film at sidewalls is intact and
protects the sidewalls from etching. In this way, the etch front advances into the substrate at rates
ranging from 1.5 to 4
m
m/min ( Fig. 4.4 (b)).
4.1.2.3 Bulk micromachined microchannels and nanochannels
Microchannels are the key components of a micromixer. This section illustrates the fabrication of
microchannels in bulk silicon and glass using the techniques discussed in the previous sections. Both
isotropic and anisotropic etching can be used to fabricate microchannels in bulk materials. Avariety of
cross-sectional channel shapes can be achieved by combining different micromachining techniques
discussed previously.
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