Oxidized ALD-deposited Titanium Nitride Films as a Low-temperature Alternative for Enhancing the Wettability of Through-Silicon Vias (TSVs)

Abstract

In this paper we report on a new technique to attain superhydrophilicity in high aspect ratio through-silicon vias (TSVs) for void-free and uniform copper electroplating. Atomic Layer Deposition (ALD) is used to deposit a conformal layer of TiN on the surface of a silicon substrate and onto the sidewalls of vias etched in this substrate. A superhydrophilic film is obtained by oxidizing the TiN in oxygen plasma and by exposing the oxidized TiN to UV light. This results in a decrease of the contact angle to 5° and even lower. Next, the superhydrophilic material is integrated in a process flowchart for high aspect ratio TSVs. For the electrical characterization cross-Kelvin structures were fabricated and connected on both sides of the wafer by a bottom-up copper electroplating technique. The obtained TSVs exhibit a low average resistance of 50 mO, which is very suitable for RF signal transmission. The low thermal budget of the ALD process and the solely dry technology employed to achieve the superhydrophilicity, make the developed process suitable for integration in via-last flowchart schemes for advanced 3D interconnects.