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Reticles
and Photomasks are key elements in the manufacture of integrated circuits,
displays, disks, optical networking components, biochips and many other
applications. Reticles and photomasks are high precision quartz plates that
contain microscopic images of electronic digitized patterns. Enabling the
microlithography processes employed in these many applications, reticles and
photomasks are used to print critical patterns onto wafers or other
substrates in the fabrication of devices.
Photomasks
are an integral component in the lithographic process of semiconductor
manufacturing. High-purity quartz or glass plates containing precision
images of integrated circuits (or chips), photomasks are used as masters by
chipmakers, and other industries, to optically transfer these images onto
semiconductor wafers. Current advanced lithographic tools, such as deepUV
steppers, project light through a photomask and a high aperture lens. The
intensity of the light casts an image of the device's design--the pattern on
the photomask--onto a silicon wafer coated with a light sensitive material
called photoresist. Using negative photoresist the unexposed, or masked,
portion of this material is then removed so it can either be etched to form
channels or be deposited with other materials. (The process is reversed
using positive photoresist.)
Chips are manufactured
layer by layer, so these selective deposition/removal steps are repeated
until circuit is built. The current generation of semiconductors has 25 or
more layers, each requiring an unique photomask.
Why is a photomask more
than a mere stencil that maps out the chip's design for projecting onto
wafers? Because the physical constraints of current lightsources and
shrinking design rules driven by the (nearly insatiable) demand for more
powerful, faster, lighter and cheaper devices, have rendered the photomask a
critical and enabling technology in optical lithography.
Photomasks, requiring
sophisticated manufacturing techniques and complex mathematical algorithms
to design, are at the forefront of the microminiaturization of chips,
enabling more functionality to be embedded within a smaller area. This trend
in making devices as powerful and as small as possible facilitates the
proliferation of handheld and other portable electronic applications.
Although photomasks have always been a necessary component in the chipmaking
process, today they are a true enabler of semiconductor technology.
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