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Overview of Pellicles
 Introduction |
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The pellicle is used primarily for two purposes
- to increase die yield and reduce overall p handling, i.e.
cleaning and inspection. It is a thin film stretched on a frame
used to protect a photomask from particle contamination. Today,
the pellicle has become an integral component in the manufacturing
process for most IC manufacturers and high-resolution projection
photolithography systems used in the manufacturing of thin film
magnetic reading heads, LCD flat panels, micro electromechanical
system (MEMS), etc. |
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| The
Use of a Pellicle |
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During the printing process the image of any particle
on the pellicle film will be out of focus on the wafer plane
and therefore has only a blurry shadow which has a minimal effect
on the photomask's image on a wafer. Without pellicle protection,
a photomask can easily get a particle on its surface and form
a distorted image on the wafer, creating a defect on a chip.
Before a time when pellicle was used, a photomask would require
daily cleaning and inspection. Consequently, the photomask would
easily become contaminated from environment or damaged from
cleaning process, resulting in a low die yield and high replacement
cost.
The use of a pellicle in an optical projection system is illustrated
below.
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Figure 1: The Use of a Pellicle
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Once a pellicle is properly attached
on the photomask, the surface that is covered by the pellicle
is free from future outside particle contamination. The original
quality of the photomask can therefore be preserved. Now only
a brief inspection of the pellicle film and photomask surface
is required to insure the quality of the photomask. |
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