Factors affecting surface roughness and coercivity of Ni ₈₀Fe ₂₀ thin films

This article reports the effects of dc sputter power, film thickness and rf substrate bias on surface roughness and magnetic properties of Ni ₈₀Fe ₂₀ thin films sputtered on Si (100) substrates for their application in magnetic tunneling junctions. The surface roughness of Ni ₈₀Fe ₂₀ thin films varied from 0.197 nm to 0.376 nm when dc sputter power was changed from 50 to 250 W. The optimum value was achieved with 200 W dc sputter power. Film thickness dependence study shows that the surface roughness of Ni ₈₀Fe ₂₀ thin films changes from 0.164 nm to 0.264 nm, with a minimum at film thickness of 8 nm. The small magnitude of change was attributed to a 20 W rf substrate bias that was applied during the thickness studies. We varied the substrate rf bias from 0-20 W, with fixed 200 W dc power and 8 nm film thickness. A dramatic change of surface roughness of Ni ₈₀Fe ₂₀ film from 0.984 nm (without rf bias) to 0.197 nm (with 20 W rf bias) on Si was achieved. The coercivity of the Ni ₈₀Fe ₂₀ thin films changes in a similar way as surface roughness. We conclude that the surface roughness of Ni ₈₀Fe ₂₀ thin films can be well controlled by applying a rf substrate bias during the deposition.