Microstructure evolution analysis in Co/Cu layers during the annealing process

Abstract

By means of molecular dynamics simulation, this article investigates the annealing process of a Co/Cu two-layer structure used for giant magnetoresistance applications. The many-body, tight-binding potential method is used to model the interatomic force which acts between the atoms, and the Langevin technique is incorporated into the motion equation such that the thermal control layer is maintained at a constant equilibrium temperature. The issues considered within this article include the annealing Cu surface roughness and Co/Cu interfacial roughness, the annealing morphology, the annealing microstructure, a comparison of Co and Cu migration abilities, and the extent of Co and Cu interdiffusion. The results of the present study indicate that the annealing temperature required to cause Co atom migration is greater than that which is required for Cu atoms. Consequently, once the annealing temperature exceeds a certain threshold value, a significant change in the Cu surface roughness will be observed before there is any obvious change in the Co/Cu interfacial roughness. It is also noted that the Cu film microstructure adopts a disordered state earlier in the annealing process when the annealing temperature is higher. Finally, it is determined that Co/Cu interdiffusion occurs at elevated annealing temperatures. The degree of interdiffusion becomes more pronounced as the annealing temperature increases, and in extreme cases, it is observed that Co atoms may diffuse to such an extent that they even appear on the Cu film surface.