Types of Contact Masks
There are several types of contact lithography masks.
The standard binary intensity amplitude mask defines dark and light areas where light is blocked or transmitted, respectively. The dark areas are patterned films consisting of chromium or other metal.
The light coupling mask has a corrugated dielectric surface. Each protrusion acts as a localized waveguide. Light is transmitted primarily through the protrusions as a result of this localized guiding effect. Since less contact area is needed, there is less potential for defects.
A hybrid nanoimprint-contact mask utilizes both contact imaging and mechanical imprinting, and has been proposed to optimize imaging of both large and small features simultaneously by eliminating imprint residual layer issues.
Contact masks have traditionally been fairly large (>100 mm), but it is possible that alignment tolerances may require smaller mask sizes to allow stepping between exposures.
As in nanoimprint lithography, the mask needs to have roughly the same feature size as the desired image. Contact masks can be formed directly from other contact masks, or by direct writing (e.g., electron beam lithography).
Read more about this topic: Contact Lithography
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