(375b) Electric Current-Induced Nanoscale Surface Roughness Reduction in Conducting Thin Films

Thin film surface roughness is responsible for various materials reliability problems in nanoelectronics and nanofabrication technologies, which requires the development of surface roughness reduction strategies. For example, in present and next-generation electronic technologies, with feature scales on the order of 10 nm, there is a great need for nanoscale surface roughness reduction, since even atomic-scale roughness can lead to significant reduction of the electrical and thermal conductivity of copper thin films.

Toward this end, in this presentation, we report a modeling and simulation study that has established the electrical surface treatment of conducting thin films as a viable physical processing strategy for surface roughness reduction. We have developed a continuum model of surface morphological evolution that accounts for the residual stress in the deposited conductor film, surface diffusional anisotropy and film texture, the film’s wetting of the layer that is deposited on, and surface electromigration. Supported by linear stability theory, self-consistent dynamical simulations based on the model demonstrate that the action over several hours of a sufficiently strong and properly directed electric field on a conducting thin film can reduce its nanoscale surface roughness and lead to a smooth planar film surface. The modeling predictions are in good agreement with experimental measurements on copper thin films deposited on silicon nitride layers. Moreover, through systematic linear stability analyses and dynamic simulation protocols, we have examined in detail the effects of film texture and applied electric field direction and optimized the electrical surface treatment by minimizing the electric current density required for film surface smoothening. We have found that the critical electric field strength requirement for surface roughness reduction on {110}, {100}, and {111} copper film surfaces exhibits a very strong dependence on the applied electric field direction, i.e., the electric field alignment with respect to the principal residual stress directions in the film and the fast surface diffusion direction.