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in Figure 1). Figure 4 shows example After-development inspection: dry
images of vias with ABF residue. resist film
The left three images are those using To create circuit patterns on each
Clearfind® illumination, while the right build-up layer of the IC substrate, a dry-
three images are corresponding images film resist is laminated and developed
but with BF color illuminations at on a Cu seed layer, as shown in process
higher magnification. steps 14 and 15 in Figure 1. Any process
For examples (a-1) and (a-2) shown excursion during development will lead
in Figure 4, the residue is detectable to poor circuit patterning. Figure 5 shows
using either CF or BF technology. For an image of an organic defect after dry-
the CF image examples of (b-1) and (c- film resist development. All four images
1), residual ABF inside the vias is easily show defects at the same site but with
detectable because secondary photons different illuminations. The BF image does
from the residual ABF are brighter than not show any defects, while the DF and
the rest of the Cu, which does not emit Clearfind images do. It should be noted
®
secondary photons. However, in the case that not all the defects found with DF are
of the corresponding BF images of (b- seen in the CF image. This is because DF
2) and (c-2), the area of residue in the illumination is sensitive to scattering from
image can be easily confused with the various particles, while CF illumination is
via bottom. This is because the surface sensitive to organic defects only. The DF
of the bottom of the via is rough Cu— image shows vias because of a difference
and because of the grainy structure of in scattered light intensity, while CF cannot
the Cu, this image is very similar to identify the difference between vias and the
images of ABF residue. These example Cu seed layer because neither of these emits
Figure 4: Images of vias with ABF residue. The left images clearly demonstrate that the new secondary photons, causing both regions to
three images are those using CF illumination, while the illumination technology is more robust appear dark. Therefore, the best illumination
right three images are corresponding images, but with for leftover ABF residue in vias. technique to find defects after dry-film
BF color illuminations at higher magnification. resist development is to use both DF and CF
illumination simultaneously, as shown on
the bottom right of Figure 5.
Figure 6 shows another defect example
after dry-film resist development. All four
images show defects at the same site but
with different illuminations. In this case,
Clearfind technology images do not
®
indicate defects. This is an indication that
these defects are either metallic or inorganic
dielectrics. Considering the stage in the
process flow in which these defects are
identified, it is very likely that these are
metallic defects. The BF image indicates
some defects, but with relatively low
contrast, while the DF image clearly shows
all defects. As we have seen, CF illumination
is very effective in finding organic defects,
and we believe a combination of it and
DF illumination together offers the best
illumination tool for the inspection of dry-
film resist after development.

After-etch inspection: Cu seed
After the dry-film resist is developed, the
substrate goes through Cu plating to form
Cu trace lines for the circuit, and then the
dry-film resist is removed by stripping. At
this stage, all Cu trace lines are connected
E-Tec Interconnect AG, Mr. Pablo Rodriguez, Lengnau Switzerland by a Cu seed layer that needs to be etched
Phone : +41 32 654 15 50, E-mail: p.rodriguez@e-tec.com to complete circuits as designed. During the
process, under-etching may cause shorts,
while over-etching may cause open circuits.

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