Cu Deposition on AAO Substrate for Interposer Applications

Abstract

In recent days, the demand for high-performance devices has increased in the semiconductor industry. These devices require integrated circuits to test out their performance. For this purpose, interposer with both vertical and horizontal copper circuits which offers advanced connections is used. Interposer consists of a substrate material and metal circuits. Common substrate materials for the interposer are silicon and glass. Whereas anodized aluminum oxide (AAO) has less current leakage than silicon substrate, which results in no need for the insulation, and has a vertically self-aligned nanopore structure though wet etching process, which enables high density holes with less cost. AAO was proposed as a substrate material for interposer.AAO substrate was fabricated using 0.3M oxalic acid solution, followed by fabricating through-hole of AAO. For the interconnection, copper layer was deposited on the surface and hole of AAO substrate by electroless and electrochemical techniques sequentially. Sol-gel catalyst was adopted followed by heat treatment, instead of Sn/Pd catalyzation, to increase the adhesion property and breakdown voltage. Fabricated AAO is a circle shape with 4.8 cm diameter and average pore size is about 98 nm. Cu electroless deposition was performed on AAO with and without through-holes. Thin Cu layer was deposited without voids. The adhesion was measured by SCRATCH TESTER PRO, J&L Tech, Korea, showing first crack around 1.5 N to 2 N. Pulse electrodeposition with surfactant was used to fill the trough-hole of AAO substrate for through-AAO interconnects. The more details will be presented. Figure 1