edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 25 NO. 4 14 surface structure and film roughness.[13,14] Figure 3b demonstrates that with additional laser passes over the same pad, the film thickness increases and results in additional surface structure that causes the film to appear dark under direct illumination. When deposited on transparent material, such as glass, the copper films appear bright when observed through the glass due to the strong adhesion on the glass substrate. A FIB cross-section examination of the copper deposition morphology is shown in Fig. 4. This copper deposition was grown on a 250 nm silicon oxide (SiO2)/p-doped silicon substrate by spotting the CW laser for 60 seconds at 600 mW. This image has a bright FIB platinum protective capping layer on top of the copper deposition, supported by the silicon oxide and silicon substrate. This copper deposition shows there are two distinct growth regions: a center region with well-defined copper grain structure and two outside edge boundary regions with a porous structure. The copper grain structure in the center corresponds to the location of the direct laser energy exposure, the growth on the boundaries is due to the substrate heat transfer at the surface. The deposition rate under these conditions can be approximated to be greater than 25 µm3/s. The deposition shows the roughness of the copper is similar to previously published literature results. This has been widely attributed to the introduction or presence of water in the deposition chamber. In addition to surface roughness, the presence of water also is reported (a) Fig. 3 A scanning electron microscope (SEM) image showing the complex grain structure and surface roughness of the copper line. Fig. 4 A FIB cross section and SEM image showing the complex grain structure and surface roughness of the copper deposition. Fig. 5 An SEM image showing the interface of the copper deposition on silicon oxide thin film. (b)
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