Electroless Ru/Cu Deposition Without Pd Activation for the Formation of Continuous Cu Seed Layers in High-Aspect-Ratio Via-Holes

Abstract

As the aspect ratio of via-holes is increased, the difficulty in forming a conformal seed layer with sputtered Cu also increases, especially at the side-walls of the holes. Electroless deposition is a cost-effective, non-vacuum process; however, it requires the noble metal, Pd, during the activation process. In this study, we investigated the deposition of a continuous Cu lining in via-holes with an aspect ratio of 11 (5 mu m-width and 55 mu m-depth) using electrolessly deposited Ru as an activator instead of Pd on a Ta diffusion barrier layer. The electroless Ru deposition was successfully developed without an activation process. This was accomplished by increasing the hydrophilicity of the surface of the Ta barrier layer. The formed Ru layer can be utilized for the diffusion barrier as well as the activator. The bilayer barrier (Ru/Ta) may enhance the total diffusion barrier properties, allowing a reduction in the thickness of the Ta barrier layer while maintaining the same properties.