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Electrical Demonstration of TSV Interconnects and Multilevel Metallization for 3D Si Interposer Applications
Keywords: 3D Si Interposer, TSV, Multi-level Metal
Within the emerging area of 3D integration technologies, passive 3D Si interposers enable novel packaging solutions with reduced size and increased functionality. For Si interposer applications, through-silicon via (TSV) and large area multi-level metallization (MLM) electrical performance are critical, as these affect power consumption, input impedance and other important electrical parameters. This paper will report the electrical test results for TSV interconnect and MLM structures used for an advanced Si interposer application. TSV interconnects were formed using a vias-last approach – with TSVs etched from the backside, and the first level of front-side metal acting as the etch stop layer. Following the DRIE Si etch and subsequent TSV passivation, a critical DRIE bottom-clear etch was performed to remove the passivation layer from the bottom of the TSV, while resulting in minimal erosion of the passivation layer on the TSV sidewall. Bottom-clear process time and pressure were varied, and these changes were correlated to electrical test results. TSV interconnect electrical properties, including resistance, isolation, and yield, were measured. An equivalent circuit model was developed and used to calculate TSV chain yields. For TSV contact chains up to 540 vias in length, 100% yield has been achieved. The TSV resistance was less than 50mOhm. TSV interconnect compatibility with subsequent thermal treatments (solder reflow cycles) was investigated by measuring shifts in electrical performance as a result of the treatments. MLM contact chains have been fabricated using a self-aligned, dual-damascene metallization process. Metal and dielectric thicknesses were varied, and the effect of a cap layer was investigated. For metal and dielectric thicknesses up to 2µm, contact resistances of 4mOhm have been demonstrated, and 100% yield has been achieved for MLM contact chain sizes up to 26400 vias.
Erik Vick, Research Engineer
RTI International
Durham, NC

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