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Porous Anodic Aluminum Oxide Interposer: Process Integration, Fabrication, Characterization, and Evaluation


Interposer technology is a key technology for microelectronic industry to miniaturize devices, reduce signal/response latency, lower power consumption, increase signal bandwidth, and reduce overall cost. This work is proposing porous anodic aluminum oxide (AAO) as interposer material taking advantage of its material properties and unique vertical self-aligned nanoporous structure. AAO/Al was first introduced as working substrate to create metallized through AAO vias, however, several process issues were observed and occurred during the manufacturing phase. New set of fabrication process directly on AAO was integrated and introduced to drill through vias, metallize vias, and deposite re-distribution layers (RDL) to form final structures. The proposed fabrication process of AAO interposer is less complicated than that of Si interposer and via/pitch dimension can possibly be manipulated smaller than that in glass interposer. Test and characterization started by chemical durability test of AAO film in solutions showing the weakness of as-fabricated AAO, coefficient of thermal expansion (CTE) showed comparable result to glass. SEM, optical microscope, and X-Ray images were taken to inspect dielectric deposition, through via, and metallization conditions showing good coating and etching results. DC measurements was done with 4-point kelvin setup to test daisy chain from 25 nodes to 400 nodes, no open circuit failure was found while total resistance versus numbers of via showed linearity. RF performance was measured by probing coplanar waveguide on AAO and solenoid inductors embedded in AAO. Results showed comparable values to that in glass interposer which suggested AAO could potentially be interposer material with reasonable performance.

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