Study on the adhesion strength of CVD-Cu films with ALD-Co(W) underlayers made using amidinato precursors

We investigated the adhesion strength of Cu films grown using chemical vapor deposition (CVD) on a Co(W) layer, which was grown using atomic layer deposition (ALD), for Cu interconnect applications in ultra-large scale integration (ULSI). Co(W) forms an effective barrier to the diffusion of Cu and forms an adhesion layer in a single barrier. Amidinato precursors were used in the deposition of Co and W, which contain neither O nor F, and yielded high-purity Co(W) films. Furthermore, the use of an amidinato Cu precursor was also found to be important in enabling Cu deposition without interfacial contamination. The W content of the Co(W) layer was optimized to 14 at% via an evaluation of the diffusion barrier properties, the electrical conductivity, and the adhesion strength with the Cu layer. A CVD-Cu/ALD-Co(W) stack was formed using amidinato precursors for the growth of both films, and was found to exhibit favorable properties compared with a conventional PVD-Cu/PVD-Ta/TaN stack. It was also favorable to a PVD-Cu/PVD-Ru/TaN stack in terms of the diffusion barrier properties and electrical conductivity, with a similar adhesion strength for Cu. For these reasons, our Co(W) films have potential applications in reliable and high-performance Cu interconnects in next-generation ULSI.