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We report here results from the first two steps, namely ALoT
bonding and LT wafer thinning.
Figure 6 shows an ALoT-bonded LT-glass wafer. Due to
imperfect cleaning, voids are seen inside the wafer as well as
near the edge. The edge voids would cause delamination during
thinning, so careful trimming was applied to make sure these
are removed. When necessary, the trimming wheel performed
linear, “surgical” actions to ensure the edge voids were removed.
Disco model DFG8640 was used to grind the LT. The equipment
configuration schematic is shown in Figure 7. The equipment has
multiple stages that can be configured to do coarse grinding, fine
grinding and CMP, all on the same tool. Our experiment only used
two grinding steps (Z1 and Z2 in the picture).

Figure 7: DISCO wafer grinding/polishing tool configured to perform coarse
grinding, fine grinding and CMP, all on the same tool. SOURCE: DISCO website.

Figure 8: After grinding LT to a thickness of 15µm, the LT wafer is largely intact,
with minor chipping at the 9:30 position near the edge.

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