With the most advanced generation of IC and the integration of Copper and fragile ultra low-k (ULK) materials in Cu interconnects, the constraints on Cu chemical mechanical polishing process (CMP) have become critical. There has been a great effort made to develop processes at lower pressure with improved topography, to reduce sheet resistance (Rs) variations, to meet the stringent designs rules and compatibility with lithography budget for depth of focus (DOF). CMP is a balanced process, relying on the chemical interaction of the slurry with polishing substrate and mechanical down force applied to the substrate. The classical slurry approach at lower pressures results in slow polish rates. Therefore, the industry has to introduce more complex slurry systems, harder to stabilize, to achieve a total planarization after Cu clear with dishing and erosion values below 20nm. A new approach is electrochemical mechanical polishing (Ecmp) that allows achieving these performances at a much reduced pressure while using an electrolyte which is simpler in its conception. It uses an applied electric potential instead of an oxidizer as the driving force to oxidize metal copper to copper ions. In a second step, copper ions react with the agents present in the electrolyte to be complexed or create a passivation layer that can be removed at a very low pressure (0.3psi) with a polishing pad. Previous Ecmp approaches have not provided polishing of copper all the way to the barrier to fully utilize the advantage of topography gains [1]. The Ecmp approach presented here replaces copper (bulk and clearing steps) processing of conventional CMP, providing polishing direct to the barrier. In this work, we demonstrate the capability of Ecmp to meet the 45nm and 32nm technology node requirements in terms of topography behavior, the related electrical spread, lithography DOF budget and ULK compatibility.
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