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Figure 2: Cross-section workflow comparisons.
Cu-pillar microbumps in a 3D electrons. The laser quality allows imaging sectioned microbump void superimposed
package of some structures right after laser polishing. upon the virtual plan-view XRM slice that
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A laserFIB workflow for imaging Ga beam polishing provides the highest- guided the laser cuts. The void is indicated by
25µm-diameter Cu-pillar microbumps quality surfaces for imaging, removing the a red arrow. The microbump containing the
buried almost one millimeter deep in a shallow LAZ and laser-induced periodic void is circled in the XRM image. The large-
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3D stacked-die package is detailed in surface structures (LIPSS) to enable imaging area ablation volume was 0.9 x 0.9 x 1.0mm ,
Figure 3a-h: a) registration of 3D XRM intermetallic compounds and other features. and the cumulative laserFIB process time
virtual cross-sections to SEM images via the The combined speed and accuracy of the to cross-section the void in the microbump
system’s software for precise laser pattern laserFIB has been demonstrated on a 3D was less than one hour, following the
placement [10]; b) bulk laser ablation of a package test vehicle for 14nm node silicon workflow described in Figure 3. Both large-
large region; c) fine laser polishing; d-e) technology. The test vehicle has 50µm pitch area laser ablation and laser fine polishing
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imaging after the laser polish; f) Ga FIB Cu-pillar microbumps sandwiched beneath were completed in 29 minutes. The Ga FIB
polishing of a 300µm-wide local area; g) a 725µm thick top die and a 50µm thick polishing was done over a 110µm-wide area
imaging 25µm diameter microbumps using bottom die. Using 1µm voxel resolution, 3D that included the affected microbump and
high-resolution secondary-electrons; and XRM scans were done at a region of interest. progressed until reaching the void. This step
h) imaging the same using backscattered Figure 4 shows a SEM image of the cross- took 22 minutes. Therefore, the 5µm void
Figure 3: Steps for correlated 3D XRM and laserFIB analysis of deeply buried microbumps in a 3D package.
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