Adhesion and Diffusion Barrier Properties of Ta Films Fabricated by Auxiliary Plasma Assisted Bias Sputtering

Abstract

The formation of an adhesion/barrier layer and a seed layer by sputtering techniques followed by electroplating has been one of the most widely used methods for filling through-Si vias (TSVs) for three-dimensional packaging. In this research, the adhesion and diffusion barrier properties of Ta films deposited by auxiliary plasma assisted bias sputtering were investigated. As substrate power increased, the deposition rate and sheet resistance of the film decreased while the surface roughness and degree of crystallinity increased owing to the bombardment of energetic ions on the growing film. The strength of adhesion between the Cu/Ta film and the SiO2/Si substrate was quantitatively measured by a topple test and a 180 peel test. The highest adhesion strength was obtained when the thickness of the Ta film was within 20–40 nm, which was about two times higher than that in the case without a Ta adhesion layer. The application of a substrate power of over 0.51W/cm2 caused 20–40% enhancement of the strength of adhesion between the Cu/Ta film and the SiO2/Si substrate. The enhancement of adhesion strength was attributed to intermixing in the interface region, the increase in surface roughness, and the removal of contaminants by the bombardment of energetic ions. The improved barrier property of the Ta film against Cu diffusion could be obtained by applying an appropriate substrate power during the deposition of Ta films.