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A clear mask, complete with a protective pellicle, is used in the evaluation of contributions to defects from processing and handling in a given photoprocessing step per se.
English (United States)
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Defect Analyses Using a Clear Mask With a Pellicle
A clear mask, complete with a protective pellicle, is used in the evaluation of
contributions to defects from processing and handling in a given photoprocessing
step per se.
A standard process is used to apply, expose, and develop photoresist on a
bare, clean semiconductor wafer. Following development, any small islands of
photoresist remaining on the wafer are a result of particles in or on the
photoresist or particles on the mask surface normally coated with an opaque film,
e.g., chromium, etched into a circuit pattern image. Such islands of photoresist
(defects) may be counted visually or by any of several automated instruments
available in the commercial market.
By making defect counts repeatedly in a single photo-process sector and
using more than one clear mask, contributions to defect count made by the
handling and processing steps (as opposed to the mask per se) are assessed. If
mask cleaning and pellicle mounting make significant contributions, there is a
significant difference in the associated defect counts.
Utilizing standard mask glass and pellicle material for the clear mask allows
standard exposure in the usual exposure unit without having to be concerned
with possible effects of deviation from normal processing when assessing defect
contribution. For instance, exposure without any mask in the exposure unit could
possibly lead to a change in radiant energy reaching the photoresist and change