Comparison of Copper and Cobalt Surface Reactivity for Advanced Interconnects

The constant shrinking of critical dimensions in logic manufacturing is driving a change in integration of interconnects. While copper has been the material of choice for the past few decades, it is currently facing a serious challenge from other materials like cobalt. The focus of this paper is three-fold. First, we compare the reactivity of both materials in different media. Next, we confirm that kinetics of native oxide formation when exposed to atmosphere is an order of magnitude slower for copper than for cobalt and that, in the case of cobalt, the presence of an oxide is not avoidable in the industry conditions. And finally, we investigated the compatibility of plating solutions manufactured by aveni for cobalt and copper deposition. Both solutions reveal that, not only do they etch the native oxide of a cobalt seed, but they also preserve the integrity of the underlying metallic cobalt layer. This is highlighted by the fact that no oxide is detected at the interface between the deposited metal and the seed after deposition. We therefore provide evidence of the compatibility of aveni plating solution with a wide array of integrations for next generation interconnects such as copper extension with direct-on-cobalt integration or full cobalt integration.