| Summary: | 碩士 === 國立交通大學 === 材料科學與工程系 === 90 === The purpose of this thesis is to establish Cu electropolishing technology for the back-end multi-layer interconnects, including the production of copper wires by electropolishing process, the planarization of step-height for Cu electroplating layers and the pattern effects on Cu electropolishing. The main issue for the requirement of planarization and reliability is the development of the electropolishing electrolyte and the optimum of operation parameters.
In tradition, electropolishing is the important technology of surface treatment. It can dissolve metallic film uniformly and produce a smooth and bright surface. In electropolishing processes, the composition of an electropolishing and operation parameters are the key points affecting the capability of the planarization. The challenge for electropolishing being a technology of globe planarization in sub-micron copper interconnects is how to develop an effective electropolishing electrolyte and proper additives.
In sub-micron semiconductor interconnects, chemical-mechanical polishing (CMP) is one candidate technology for global planarization. However, mechanic stress, waste stream, scratches, and post-CMP clean are critical problems in CMP applications.
Therefore, we could utilize the electropolishing technology to improve the performance for CMP of electroplated copper. For example, in the typical two-steps Cu-CMP processes, we can employ electropolishing technology as the first-step CMP to eliminate scratches produced by CMP slurry and then improve the planarization capability of CMP. In this study, citric acid was added into the electrolyte as additives in order to further improve the planarization efficiency of Cu electropolishing. With the few additives producing a diffusion gradient on the step-height surface of Cu films, those local acidities and conductivities at the recess and protrusion between inside and outside of the trenches will change. Furthermore, the capability of step-height reduction on Cu electropolishing will improve. Besides,
The polyethylene glycol (PEG) was also employed to suppress the pitting resulting from the production of Oxygen bubbles at highly operation voltages on Cu electropolishing; then a smooth and bright surface of Cu films would be accomplished due to the better wetting ability of PEG.
In the future, we could furthermore integrate copper electropolishing with non-barrier low-dielectric materials (non-barrier low-k materials) to replace CMP processes. Since uniformly dissolved copper film is intrinsic characteristic of electropolishing, the problems of removal selectivity between copper film and barrier film, oxide erosion, and post-CMP clean could be disappeared naturally. As we mentioned above, the throughput will become higher.
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