Precursor-based designs of nano-structures and their processing for Co(W) alloy films as a single layered barrier/liner layer in future Cu-interconnect

Abstract

The drive to continuously downscale Cu interconnects in ultra-large-scale integrated (ULSI) devices requires strategic improvements in materials and their design processes. For example, development of thinner single-layer barrier/liner materials is desired, because Cu line widths approaching the mean free path greatly increase RC signal delays. We designed Co films with the addition of W [Co(W)] for use as a single-layer barrier/liner material using principles from surface engineering and metallurgy. Dupre's equation was used to evaluate the adhesion of metals to Cu, which suggested Co as the main component of our proposed single-layer barrier/liner material. Metallurgical analysis suggested that the addition of W would lead to nanostructural improvements and increased barrier performance in Co films. The Co–W phase diagram suggested that W would segregate at grain boundaries, thereby improving barrier performance due to grain-boundary stuffing. Amidinato, metallocene, and carbonyl Co and W precursors were evaluated in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes for the formation of Co(W) films. Oxygen and halogen inclusions were undesirable, because they were predicted to increase the resistivity and cause deviation from the Co–W binary system. To reduce the prevalence of grain boundaries through formation of an amorphous structure, sequential feeding of Co and W precursors in an ALD process was developed for each set of precursors. Oxygen-free Co(W) CVD and ALD processes were achieved using amidinato and metallocene precursors, both of which led to stuffed grain-boundary structures. ALD-Co(W) films exhibited amorphous structures with sufficient barrier performance and low resistivity, which was consistent with our material and process design.