Nanoscratching-induced plastic deformation mechanism and tribology behavior of Cu/Ta bilayer and multilayer by a molecular dynamics study

Abstract

Molecular dynamics simulations are adopted to study the deformation mechanism and friction and wear properties of Cu/Ta bilayer and multilayer during a nanoscratching process. The results indicate that in bilayer the Cu/Ta interface adsorbs and blocks dislocation propagation, while the Ta/Cu interface acts as an emission source of dislocations. In multilayers (particularly for thickness δ = 25 Å), the dislocation could overleap the hard Ta layer and then nucleate in the next Cu layer although the friction shear is still in the first Cu layer, indicating the deformation transition of plasticity-elasticity-plasticity across Cu/Ta/Cu layers due to stress transfer. The increase in monolayer thickness facilitates dislocation propagation and deformation recovery, as well as surface removal quantified by wear volume. Severer plastic deformation and surface removal occur in Cu layer while higher friction appears in Ta layer. The preferred accumulation of worn Ta atoms in the left front, up to 80% in δ = 45 Å multilayer and 60% in others, is observed and attributed to the nonsymmetrical slip directions. The differences in plastic deformation and tribological property indicate a critical thickness of about 25 Å used to guide the ultraprecise manufacture of Cu interconnections in microdevices or semiconductor industry.