Improving Copper Nucleation on Liner Materials

Abstract

The damascene process for fabrication of interconnects requires a copper seed conductive layer on top of a liner material, which acts as a copper diffusion barrier. Copper metal is electrochemically deposited from solutions containing additives onto the conductive seed layer, for void-free bottom up fill. However, as interconnect dimensions continue to decrease, copper damascene faces significant challenges1. As such, alternative metallization approaches are under development. These include electrodeposition of copper directly onto liner materials such as ruthenium2,3 or cobalt4-6. Direct plate onto liner materials pose new challenges that must be overcome prior to implementation. For example, ruthenium and cobalt are easily oxidized upon exposure to air7. This native oxide film inhibits nucleation, resulting in heterogeneous growth of copper islands8. The literature shows that oxide removal improves nucleation at ruthenium and that copper can successfully be deposited onto cobalt using additives6. While there are some insights on how to achieve nucleation of copper onto resistive substrates, this must be improved prior to commercialization. We present methods for pretreatment of ruthenium in order to reduce the native oxide, allowing for more uniform deposition of the copper films (as shown by Fig. 1). Upon addition of our additives, early film coalescence and uniform deposition of copper is achieved, resulting in void-free bottom up filling. These findings will be presented and discussed.Fig. 1. Nucleation of copper onto (a) as received compared to (b) pretreated ruthenium substrate plated from a typical copper electrolyte containing no additives.