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| LIGA etches 3-D patterns that are electroplated to form master molds for microdevices. |
X-ray photolithography will be a primary tool for the production of micromachines with nanosized features. The technique starts with a sharply focused beam of electrons that "write" a desired pattern onto a recording medium called a resist. Various steps involving microplating, chemical etching, or vapor deposition can then be used to convert the resist into a stencil-like mask. X-rays are used to transfer the mask's pattern onto a target material.
To make a 2-D object like a computer chip, a semiconductor blank is coated
with a special light-sensitive polymer, the resist, and x-rays are shone
on it through the mask. Surface areas of the resist not shadowed by the
mask are degraded by the light and washed away; these exposed areas can
be doped with other materials to make a series of thin layers.
To make a 3-D device, the mask is bathed in high-energy, or "hard,"
x-rays, which carve patterns deep into the resist. A metal is then electroplated
into the open space to produce either a master mold that can be used for
injection molding or a structure with 3-D heights and lateral dimensions.
This is the form of lithography called LIGA.
"Two properties essential for a LIGA x-ray beam are high flux and a high degree of collimation," says Keith Jackson, who manages Berkeley Lab's LIGA programs.
And these are the signature properties of the x-ray beams at Berkeley Lab's Advanced Light Source (ALS), making this synchrotron radiation facility ideal for LIGA research and development.
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