manufacturing entails the formation of various
wafers. These patterns define the structure of and interconnection
between the different components and features of the integrated circuit.
The patterns are formed on wafers using patterning tools known as
masks and reticles. Below are some key points about masks and
is defined as a tool that contains patterns which can be transferred to
an entire wafer or another mask in just a single exposure.
is defined as a tool that contains a pattern image that needs to be
stepped and repeated in order to expose the entire wafer or mask.
- Reticles have
two major applications: 1) printing of images directly onto wafers in
equipment known as step-and-repeat aligners; and 2) printing of images
onto masks which, in turn, transfer the images onto wafers.
patterns on a reticle are usually 2X to 20X the size of the patterns on
the substrate. However, some reticle patterns are 1X the substrate
equipment used for printing patterns on substrates that are smaller than
the patterns on the reticles is also referred to as a 'reduction
stepper', while one that's used for printing equal-size patterns is
known as a 1X stepper.
of a mask or
reticle can either be positive or negative. A positive mask or
reticle has background areas (or fields) that are clear or transparent,
which is why a positive mask or reticle is also known a
mask or reticle has fields that are opaque, which is why a negative mask
or reticle is also known a
are many ways by which a pattern may be transferred to a wafer using a
mask, a reticle, or a combination of both. Regardless of the pattern
transfer process, everything starts with a set of pattern data that are
converted into an actual pattern by a
pattern generators include: 1) plotters; 2) optical pattern generators;
and 3) electron beam pattern generators.
patterns generated by the pattern generators are formed on either a mask
or reticle. For example, plotter-generated patterns can be
photo-reduced and formed on 10X emulsion reticle, while optically
generated patterns can be formed on 5-20X hard-surface reticles.
E-beam generated patterns can be formed on a 5-10X reticle, a 1X
reticle, a 1X hard surface mask, or even directly to the wafer.
patterns formed on a reticle can be transferred directly onto the wafer,
or they may first go to a mask which is the one that transfers the
patterns to the wafer. Patterns on masks generally get transferred
to the wafer directly.
Silicon Processing for the Vlsi Era: Process Technology
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