Medical Applications of Micro-Electro-Mechanical Systems (MEMS) Technology - Biomaterials Science: An Integrated Clinical and Engineering Approach - page 53

Laser Micromachining
Lasers can generate an intense amount of energy in very short pulses of light
and direct that energy onto a selected region of material for micromachin-
ing [9]. Among the many types of lasers now in use for micromachining are
CO 2 , YAG, and excimer. Each has its own unique properties and capabilities
suited to particular applications. Factors that determine the type of laser to
use for a particular application include laser wavelength, energy, power, and
temporal and spatial modes; material type; feature sizes and tolerances; pro-
cessing speed; and cost. The action of CO 2 and Nd:YAG lasers is essentially a
thermal process, in which focusing optics are used to direct a predetermined
energy/power density to a well-defined location on the work piece to melt or
vaporize the material. Another mechanism, which is nonthermal and referred
to as photoablation, is the exposure of organic materials to ultraviolet radia-
tion generated from excimer, harmonic YAG, or other UV sources. Similar to
microEDM, laser micromachining can produce features on the order of tens of
microns, but it is a serial process and therefore slow. Figure 3.20 is a photo of
some very small holes made in a medical catheter using laser micromachining.
Focused Ion Beam Micromachining
Another versatile tool for performing micromachining is the focused ion
beam (FIB) [9]. The accelerating voltages are adjustable from few keV to sev-
eral hundred keV. The spot sizes can be focused down to below 25 nm, mak-
ing it capable of producing extremely small structures. The user can input a
3-D CAD solid model of desired etching topology; the computer-controlled
stage with sub-micron positional accuracy allows very precise registration
of sample. In addition to material removal, the FIB can also be used to per-
form ion-induced deposition, lithography, implantation doping, mask repair,
device repair, and device diagnostics. Many of these tools can also be outfit-
ted with a secondary column for mass analysis of particles removed from the
substrate using uSIMS.
FIGuRE 3.20
Very small holes made in a medical catheter using laser micromachining.