Evolution of hillocks in Bi thin films and their removal upon nanoscale mechanical polishing

Bismuth thin films were grown on oxidized Si substrates by electron beam evaporation. The films showed clear tendency to form hillocks inducing large surface roughness. The evolution of hillocks with film thickness and deposition rate was studied. In order to improve the surface quality of the Bi films a nanoscale mechanical polishing was performed. Upon polishing, hillocks-free Bi thin films were obtained without influencing the crystalline structure and the resistivity of the films. The achieved film surface quality allows to prepare high quality Bi Hall probes with an active area down to the nm2 range promising for advanced device performance.

► Smooth Bi films were prepared using mechanical polishing. ► With increasing the film thickness larger hillocks were formed. ► With increasing the film thickness the surface roughness increases too. ► Higher deposition rate results in a smoother film surface.