Biomedical Engineering Reference
In-Depth Information
frequently be characterized for the exact mask feature and depth to obtain
desirable results. DRIE is a commonly used process technology for the imple-
mentation of MEMS and microfluidic devices for medical applications.
Deep Reactive Ion Etching of Glass
Glass substrates can also be etched deep into the material with high-aspect
ratios. This is a much newer process technology and it has been gaining in
popularity in MEMS fabrication [32]. Figure 3.13 shows a structure fabricated
into fused silica using this technology. The typical etch rates for high-aspect-
ratio glass etching range between 250 and 500 nm per minute. Depending
on the depth of the photoresist, metal or a polysilicon can be used as a mask.
This deep, high-aspect-ratio etching technology can be used to make MEMS
and microfluidic devices from glass materials, which obviously has consid-
erable utility in medical applications.
LIGA
Another popular high-aspect-ratio micromachining technology is called
LIGA, which is a German acronym for “Lithographie, Galvanoformung,
Abformung” [33]. This is primarily a non-silicon based technology and
requires the use of synchrotron generated X-ray radiation. The basic process,
outlined in Figure 3.14, starts with the cast of an X-ray radiation sensitive
Polymethylmethacrylate (PMMA) onto a suitable substrate. A special X-ray
mask is used for the selective exposure of the PMMA layer using X-rays. The
PMMA is then developed and will be defined with extremely smooth and
120 um
125 um
FIGuRE 3.13
SEM of deep, high-aspect-ratio trenches etched into fused silica using a plasma etch technology.
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