Low Cost, High Density Interposers in Aluminum Oxide Films

In this paper, anodic aluminum oxide (AAO) is introduced as a potential new material for making interposers, and a low cost process for building high density interposers is demonstrated. Hard anodic process was used to create thick anodic aluminum oxide (AAO) films containing high density vertical nanopores on aluminum substrates. Silicon dioxide (SiO2) deposition by plasma enhanced chemical vapor deposition (PECVD) was performed to form a hard mask against deep etching by a hydroxide based solution. Wet hydroxide etch produced nearly vertical openings in the AAO due to the highly anisotropic nature of the AAO material. Vias were metallized by bottom-up copper electroplating directly from the aluminum substrate, which acted as both a structural material and a seed layer for electroplating. After via plating, the top surface was polished to reach submicron surface roughness; the bottom surface was polished after etching away the aluminum carrier substrate to produce a final AAO interposer. This interposer benefits from high density vertical vias, low cost, and ease of manufacture.