Advanced Anodic Aluminum Oxide Interposer Fabrication and 3D Embedded Inductors

Porous Anodic Aluminum Oxide (PAAO, AAO) is a promising material for electronic devices because of its thermal stability, low electrical loss, mechanical hardness, and low cost. In this paper, an advanced fabrication technology was carried out making AAO an interposer material. This technology featured fabricating through AAO vias, fully metallizing through vias, and finally building daisy chains and different types of embedded inductors directly on 100 μm bare AAO membrane without the support of aluminum foil. This fabrication technology took advantage of the special characteristic of nanopores to create vertical through vias in AAO membrane by wet chemical etch which means no semiconductor fabrication tool was needed to drill vias. The via dimension could be reduced to 10 μm in diameter and 30 μm in pitch easily. It is believed that if photolithography mask is well designed to compensate over-etch and if wet etchant concentration is accurately controlled, via with even smaller diameter will be highly achievable following the same process. Metallization of through vias did not need to bond AAO membrane to any carrier substrate, however, desirable solid filling of vias was still successfully accomplished instead of conformal electroplating in most of the glass interposer technologies. Redistribution layer (RDL) on both side of AAO membrane was finally formed by semi-additive process (SAP) to complete the manufacturing of daisy chain and embedded inductors. This advanced fabrication technology, compares to previous work, can be used to get even higher via density and, at the same time, create various passive devices on the same AAO membrane.