Appeal No. 1996-2284
Application No. 08/228,889
illuminating said fiducial marks and projecting images thereof
through said lens,
a pair of folding mirrors secured to said lens and
positioned to receive and reflect said images, a detector
associated with each said mirror and positioned to receive
said reflected images, said detectors being in planes which
are reflections by said mirrors of said image plane, and
a feedback system operatively associating said detectors
with said alignment means,
whereby misalignment caused by environmental changes in
said lens can be detected and corrected.
5. A method of correcting misalignments in lithographic
systems resulting from environmental effects upon the lens of
the system, said method including
projecting fiducial marks from a reticle through the
system lens, said fiducial marks being on opposite sides of
said reticle,
intercepting the images of said fiducial marks with
folding mirrors after they have passed through said lens, said
mirrors directing each said image to a detector positioned in
the image plane of said lens as said image plane is reflected
by said mirrors,
using said detectors to determine whether said images are
in alignment, and, if not in alignment, using alignment means
operatively associated with said detectors to move said
reticle into alignment.
The references, rejections, and level of skill in the art
The examiner relies on the following references:
Mitome et al. (Mitome) 4,901,109 Feb. 13,
1990
Sakamoto et al. (Sakamoto) 4,999,669 Mar. 12,
5
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