The effects of substrate plasma etching on the performance of thin metal films

In very thin Group 11 metal films (i.e., copper, silver, and gold), with thicknesses of the same order of magnitude or smaller than the electron mean free path, the morphology of the film surface can affect the physical properties of the film. To investigate the effects of etching a substrate with a low-pressure argon plasma (as a surface “pre-treatment”) using a custom-built plasma etcher, we grew a set of Group 11 metal films in a custom-built electron-beam deposition system at room temperature on both treated and untreated c-cut Al2O3 substrates. We compared the properties expected to be most affected by surface morphology (i.e., roughness, conductivity, surface free energy, and adhesion) for each film. Although the surface free energy of the metal films was not affected by plasma etching the substrate, the surface morphology (roughness and conductivity) was affected.