Effects of He on Cu film formation by rf sputtering

Abstract Cu films have been deposited at room temperature by the rf sputtering using a gas mixture of Ar and He in order to investigate the effects of He gas on film formation by sputtering. The plasma diagnosis was performed as a preliminary experiment by the single probe method and the optical emission spectroscopoy analysis for the He+Ar sputtering plasma. From the results, it was found that the electron density increased by mixing He gas with the sputtering Ar gas, suggesting that Ar + ions increased. This indicates that Ar + ions are effectively generated by collision with He m atoms in neutral excited metastable states with high energies through the Penning ionization process, so that the deposition rate of Cu films increased. For Cu films deposited using the He+Ar gas, the preferential growth of a (111) plane was observed. The film surface of Cu films deposited using the He+Ar gas were smoother than those deposited using the pure Ar gas. The films deposited using the He+Ar were conductive even at thickness less than 5nm and have lower resistivities than thoes deposited using the pure Ar gas. These results suggest that the migration of Cu atoms on film surfaces is enhanced by an increase in an amount of Ar + ions which bombard the Cu film surface.