Page 29 - Chip Scale Review_May June_2023-digital

Figure 7: Three different defects for after-etch
inspection of the Cu seed layer. The three images
on the left are from using CF inspection, while
the three images on the right are corresponding
images captured with a BF color camera at higher
magnification.
For residual Cu seed, if the residual Cu
Figure 5: Organic defects after dry-film resist development inspection. All four images show defects at the seed extends to 30% or more into the space
same site but with different illuminations, as indicated in the panels. between the Cu trace lines, it is considered
to be a critical defect.
Figure 7 shows three different defects
for after-etch inspection of the Cu seed
layer. The three images on the left are from
using CF inspection, while the three images
on the right are corresponding images
captured with a BF color camera at higher
magnification. The two top images, (a-1)
and (a-2), show a short circuit defect that
could be easily detected with either CF or
BF illumination. For the two images in the
middle, (b-1) and (b-2), the defect was very
clear in CF, but was not seen in BF. This is
because the top flat surface of the Cu trace
line only reflects light to the detector, making
the area bright, while the reflection is very
weak from Cu in the sloped area or from the
thin and rough surface of the Cu residue.
The CF technology image (c-1) clearly shows
an open circuit, while an open circuit is
not obvious in the corresponding BF color
image (c-2). This is because the surface of
Cu trace lines tend to become very rough
and grainy after the etching process, making
any brightness variation of the Cu line
significant. In addition, any dark regions of
the Cu lines can be easily mistaken for open
circuits. Because the CF image is insensitive
to the rough or grainy surface of metal, it is
Figure 6: Inorganic defects after dry-film resist development inspection. All four images show defects at the the most robust inspection technology for the
same site but with different illuminations, as indicated in the panels. after-etch inspection of Cu.

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