Pattern Formation Method for Misalignment Measurement in Stepping Exposure Process

Pattern Formation Method for Misalignment Measurement in Stepping
Exposure Process

        Disclosed is a pattern formation method for overlay
measurements to accurately measure stitching overlay misalignment
for photolithographic exposures on the same layer.

   In conventional misalignment measurements, first a larger
square shape is formed on the initial layer, and a smaller square
shape is formed on a subsequent layer as shown in Fig. 1.  The
difference in position of the subsequent pattern from the center of
the first pattern indicates the overlay misalignment.  The amount of
vertical misalignment of the subsequent pattern to the first pattern
is given by (A-B)/2, in Fig. 1.  The amount of horizontal
misalignment can be found in a similar manner.  The conventional
method does not work though for misalignment measurements between
exposures on the same level because only the smaller square shape
remains after both shapes are exposed and developed.

   Our disclosed pattern, which can be used to measure the
misalignment between exposures on the same level, is shown in Fig. 2.
The pattern shown in Fig. 2 is formed by exposing the two patterns,
labeled "A" and "B" shown in Fig. 3 where pattern "A" is exposed
prior to "B".  The method of calculating the misalignment from
exposure "A" to "B" is shown in Fig. 2.  To understand the disclosed
misalignment method, in Fig. 3 note that the inner square is defined
by exposure "A" and the outer shape is defined by expos...