Chemical-mechanical planarization of Cu and Ta

As device dimensions continue to shrink, multilevel (>8) interconnects are required to efficiently implement complex logic device designs in a single silicon chip. When the number of metal interconnect levels increases, the available depth-of-focus budget of lithographic tools imposes stringent planarity requirements that can only be met currently by chemical-mechanical planarization (CMP). Improved speed and performance are extracted from such devices by switching to copper from Al/Cu as the interconnect metal and to lower dielectric constant inner layers. Use of copper also requires the simultaneous introduction of diffusion-barrier/adhesion-promotion layers of tantalum or TaN. This paper reviews some of the recent advances in the fundamental understanding of the interplay between the mechanical and chemical components of the material-removal process during CMP of copper and tantalum films. The emphasis will be on the role of different process variables in slurries containing silica or alumina abrasives in hydrogen peroxide/glycine solutions.