LAYERS 9 – Advancing Contact Resistance Control in High Density Packaging
As advanced packaging technologies move toward higher interconnect densities and finer critical dimensions, maintaining stable and low contact resistance has become a key requirement for ensuring electrical performance and yield. To support this need, Evatec and Fraunhofer IZM ASSID have developed a highly sensitive Kelvin resistor test vehicle designed to accurately measure seed layer contact resistance in vias as small as 2.0 micrometers.
The test structures use an Al/Ti/Cu metallization scheme and incorporate via diameters from 2.0 to 20.0 micrometers. A 5 micrometer PBO passivation layer mimics the organic load characteristic of wafer level packaging environments, enabling realistic evaluation of seed layer processing conditions. The improved “Generation 2” design features a dual layer via architecture: a small via etched in SiO₂ surrounded by a larger via patterned in PBO. This approach enables precise formation of very small contact areas while overcoming photolithography limitations observed in earlier designs.
The Kelvin resistors are fabricated using Evatec’s HEXAGON Indexer platform, which includes degas, ICP sputter etch, and Ti/Cu seed layer deposition. Aluminum pasting is used to stabilize chamber conditions by gettering volatile contaminants and reducing oxide related issues. A 25 wafer test lot processed at 55 wafers per hour demonstrated stable contact resistance for 10 and 20 micrometer vias, while smaller structures showed sensitivity to chamber contamination during continuous production. For example, 2.0 micrometer vias increased from 36.5 mΩ to 44 mΩ across the lot, revealing a 20 percent rise.
These results confirm that the new Kelvin resistor structures are effective diagnostic tools for benchmarking PVD seed layer processes and establishing robust process windows for high density packaging. Their high sensitivity makes them particularly valuable for optimizing chamber conditioning strategies and maintaining performance at high throughput. Future work will focus on refining aluminum pasting frequency to ensure stable results at even higher productivity levels.
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