A Path Toward Non-Destructive 3D Metrology for Through-Silicon Vias

As integrated circuit designs are pushed to tighter dimensions, chip real-estate is becoming of increasing value. Much like the growth of a developing city, a common modern approach is to grow the circuits upwards, building one layer on top of another. In this 3D stacking approach, the common issue lies in how to connect the multiple layers, for which direct connections through the silicon substrates have been found to produce the smallest footprint. These through-silicon vias (TSVs) are currently the subject of heavy research and development (R&D) investigation and their efficiencies are, in part, directly related to the occurrence or absence of voids within the metal structures. 3D x-ray microscopy (XRM) has recently been pushed to unprecedented resolution levels and may fit the inspection needs of the TSV R&D community. Using a unique projection-based micro-CT imaging geometry, entire packages may be inspected with as high as 1 μm resolution. This technique delivers non-destructive metrology of the metal fills as well as the post-etch regions in 3D, without the need for physical cutting or sectioning. By employing x-ray optics, resolution as high as 50 nm is now routinely achievable, allowing the detection of far sub-micron voids within the post-metallization TSV structures. These results may be further analyzed for void sizes and void volume fractions per via. Post-etch samples are also well-visualized using this technique, which allows high-resolution inspection of the side walls as well as measurement of the critical dimensions using the same system as for the post-metallization structures.