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Broadband Characterization of Copper Roughness by Comparing Striplines Fabricated on VLP and RTF Copper

This paper presents a method for broadband characterization of copper roughness factor on stripline interconnects. The characterization relies on S-parameter measurements of striplines fabricated with smooth (VLP) and rough (RTF) copper finishing on otherwise identical stack-ups. The VLP and RTF interconnects are each characterized from two-line measurements; then the R, L, G, C parameters for each are extracted under the same Tanδ condition, which yields the copper roughness factor for the RTF interconnects accurately characterized up to 40 GHz. The characterization allows a straightforward comparison against the predictions of standard copper roughness models such as Hammerstad, Huray, and Groiss. The experimental characterization shows excellent correlation to the Hammerstad model, and good correlation to the Huray and Groiss models for the studied interconnects.