Design of Amorphous Diffusion Barriers for Cu Metallization Open Access

[摘要] The incorporation of Cu interconnects into the manufacturing of integrated circuits has accompanied several modifications to the fabrication process and the associated material systems. The new fabrication process involves the development of dual damascene process, while the new materials systems include development of diffusion barrier materials. The latter imposes a critical challenge as Cu is a fast diffuser in Si and the adjacent dielectric layers, and results in device deterioration and failure. Technology development has been driven mainly by continuous feature size scaling, thus the developed barrier will be required to perform satisfactorily at the continuously reduced thicknesses. The conventional barriers used for Cu interconnects are TaNx based films which require the deposition of an additional Cu seed layer prior to filling of the interconnects by electrochemical deposition. In the face of reducing feature size and barrier thickness, there has been great interest in developing diffusion barriers that are amenable to direct electrodeposition of Cu without the need for a seed layer. However, there is a need for a suitable guide for selecting material systems suitable for diffusion barrier applications. In this thesis, a systematic approach is adopted to select an amorphous, low resistivity diffusion barrier material with the possibility of direct electrodeposition of Cu. After comprehensive consideration of possible alloys, the Ta-Rh system is selected as the candidate barrier. Thermodynamic calculations are performed to select the most stable amorphous composition in the system. The predictions made based on the thermodynamic calculation are verified by detailed structural characterizations. The performance of the selected TaRhx alloy as a diffusion barrier is evaluated by metallurgical and electrical characterizations. The metallurgical characterizations are performed by in-situ and ex-situ heating experiments on Si/diffusion barrier/Cu stacks. The common issues associated with in-situ transmission electron microscopy heating of Cu metallization stacks are identified and addressed. The electrical characterizations are performed by monitoring the capacitance-voltage characteristics of metal oxide semiconductor capacitors after bias temperature stress testing. For comparison, TaNx barriers are deposited and tested as diffusion barriers using a similar methodology. The reliability of the developed barrier system is compared with the current industry solution, i.e. TaNx.

[发布机构] University of Alberta

[效力级别] Tantalum